Risks of vegetarian diets

A New Study Suggests Vegetarians and Vegans Are at Higher Risk of Stroke. But Don’t Reach for That Steak Just Yet

Vegetarians and vegans are likely to be concerned by the results of a new study with a surprising finding: those following meat-free diets, which are typically associated with better cardiovascular health, may actually have a higher risk of stroke than those who eat meat.

But it’s too soon to run out and order a steak. The paper, published in the BMJ, found only a small increase in the risk of stroke, while confirming findings in other studies that vegetarians and vegans may have a lower risk of heart disease than meat-eaters.

“It’s important to emphasize that we’ve looked at two outcomes here,” says study co-author Tammy Tong, a nutritional epidemiologist in the University of Oxford’s Nuffield Department of Population Health. “The lower risk of heart disease does seem to outweigh the higher risk of stroke.”

Plus, both effects were fairly small. Based on their data, the researchers estimate that vegetarian diets—compared to those that include meat—are associated with 10 fewer cases of heart disease per 1,000 people over 10 years, and three more strokes in the same population.

To reach that finding, Tong and her colleagues collected dietary, health and demographic data from about 48,000 U.K. adults without a history of heart problems, about 24,400 of whom ate meat and 7,500 of whom ate fish but not meat. The remaining people were either vegetarians or vegans, who were grouped together for the purposes of the study. The researchers monitored these individuals for about 18 years, asking them to complete another detailed dietary survey toward the end of the study.

Over the nearly two decades of follow-up, about 2,800 people developed heart disease and about 1,100 had a stroke. Approximately 96% of people who began the study eating meat still did by the second dietary questionnaire, while 73% of vegetarians were still following a vegetarian or vegan diet.

After adjusting for factors like lifestyle and demographic characteristics, the researchers found a 20% higher rate of stroke among people who either began or ended the study as vegetarians compared to meat eaters. However, there was a 13% lower rate of heart disease among vegetarians (and fish eaters) compared to those who eat meat.

Since “stroke is a much rarer event than heart disease,” the lower risk of heart disease may actually be the more impactful finding, Tong says.

The results about stroke may be surprising, given the years of research that have encouraged people to limit consumption of meat, particularly red and processed varieties. A recent flurry of studies, for example, found heart-health benefits associated with plant-based diets—and health risks associated with those heavy in meat.

But Tong’s isn’t the first study to find an uptick in stroke rates among vegetarians and vegans. Some prior research suggests that the same low cholesterol levels that protect people from heart disease may put them at greater risk of having a stroke. Other papers posit that nutritional deficiencies common among those who don’t eat meat—like low levels of vitamin B12, vitamin D, amino acids and fatty acids—could put them at risk, Tong says.

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Still, Tong emphasizes that no one should drastically change their habits based on the results of one observational study using self-reported dietary information, which by nature can only uncover trends, not prove cause and effect. The researchers also didn’t ask why people were following certain diets, so it’s possible—even though the researchers tried to adjust for influencing factors—that some people with health issues or family histories of medical problems were following vegetarian diets for those reasons. Overall, more studies are needed, Tong says.

In other words: The research probably isn’t cause for a celebratory hamburger.

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Write to Jamie Ducharme at [email protected]

Brown University

The key to any healthy diet is to choose a wide variety of foods, and to consume enough calories to meet your energy needs. It is important for vegetarians to pay attention to these five categories in particular.

Protein is found in both plant foods and animal foods. Vegetarians should be aware that while there are plenty of plant-based protein options, many of these foods contain less protein per serving compared to animal foods. Therefore, combining one or more protein sources at a meal is helpful. Adequate intake with a wide variety of foods from all food groups should fulfill your protein needs. Good sources of protein include lentils, beans, tofu, soybeans (edamame), soy products (veggie burgers, “chik’n” strips, etc), textured vegetable protein (TVP), low-fat dairy products, nuts, seeds, tempeh, and eggs.

The AND recommends that adults 19 to 50-years-old consume at least 1000mg of calcium per day — the equivalent of 3 cups of milk or yogurt. Vegetarians can meet their calcium needs if they consume adequate amounts of low-fat and fat-free dairy products such as milk, yogurt, and cheese. Calcium is also found in many plant foods including dark, leafy greens (e.g. spinach, kale, mustard, collard and turnip greens, and bok choy), broccoli, beans, dried figs, and sunflower seeds, as well as in calcium-fortified cereals, cereal bars and some fortified juices.

Vegans (people who don’t eat any animal products) must strive to meet their daily calcium requirements by regularly including these plant sources of calcium in their diets. Many soy milk products are fortified with calcium, but be sure to check the label for this. Although almond milk may also be calcium-fortified, it is lower in protein so soy milk may be a better alternative to dairy.

Calcium is best absorbed by the body when it comes from food, so it’s best to include calcium-rich foods in your diet on a regular basis. If these foods are not part of your typical diet, then you may consider a calcium supplement. Look for one that has 500 mg calcium or more per serving AND contains vitamin D. It’s important to take this supplement with a meal, rather than on an empty stomach. Calcium supplements are available at the pharmacy in Health Services.

Vitamin D
Vitamin D helps your body absorb and use calcium. There are few foods that are naturally high in vitamin D, though. Therefore, dairy products in the US are fortified with vitamin D. Many soy milk products are also fortified with vitamin D. Your body can make its own vitamin D, but only when the skin is exposed to adequate sunlight (but that can have its own risks). A person only needs about 10 minutes of sunlight exposure for an adequate dose of vitamin D; then it’s important to apply sunscreen. People who do not consume dairy products and who do not receive direct exposure to sunlight regularly should consider taking supplemental vitamin D. The recommended intake of Vitamin D for college students is 600 international units (IU) per day. Despite research suggesting that higher intakes of vitamin D may be protective against a variety of diseases, intakes above 2000 IU per day can result in vitamin D toxicity. Both multivitamin supplements and calcium supplements with vitamin D are available at the pharmacy in Health Services

Iron-fortified breads and cereals, dark green vegetables (e.g. spinach and broccoli), dried fruits, prune juice, blackstrap molasses, pumpkin seeds, sesame seeds, and soybean nuts are good plant sources of iron. Consuming foods high in vitamin C, such as citrus fruits or juices, tomatoes, and green peppers helps your body absorb iron from these plant sources. Cooking food in iron pots and pans will also add to your iron intake.

Vitamin B-12
Vitamin B-12 is produced in animals and by bacteria in the soil. Vegetarians who consume dairy products and/or eggs usually get enough B-12 since it is found in these foods. Vegans, however, should add vitamin B-12 fortified soy milk to their diets. Regularly taking a broad-spectrum multivitamin and mineral supplement (available at the pharmacy in Health Services) will also supply the necessary amount of B-12.

The Potential Health Risks of a Vegetarian Diet

If you’re considering a vegetarian or vegan diet, you’ve got plenty of company. Five percent of Americans now consider themselves vegetarians and are enjoying the various health benefits that stem from a plant-based diet, a recent Gallup poll found. “The advantages include a lower risk of high cholesterol, heart disease, high blood pressure, metabolic syndrome, and type 2 diabetes,” says Ann Kulze, MD, a nutrition and wellness expert and author of the Eat Right for Life book series.

Although the benefits are real, becoming a vegetarian is not a lifestyle choice to make lightly. If not done properly, it can lead to some very real risks to your health. That’s why it’s important to consider vegetarian diet safety before taking the leap.

Finding Balance in a Plant-Based Diet: The Benefits

Eating a nutritionally sound plant-based diet has many benefits. You’ll be eating lots more fruits and vegetables and getting more healthful food components like fiber, vitamins, minerals, and important micronutrients. By eliminating meat, you’ll be cutting out a significant source of harmful saturated fat and cholesterol.

“Every individual’s diet is different. However, a well-balanced vegetarian diet may be higher in complex carbohydrates and certain nutrients like magnesium, folic acid, vitamin C, vitamin E, and phytonutrients,” says Allison Massey, RD, of Mercy Medical Center in Baltimore. “The result is lower rates of heart disease, diabetes, and certain types of cancer.”

Massey adds that a vegetarian or vegan diet can have benefits that go beyond nutrition. “Switching to a vegetarian/vegan diet can be budget-saving,” she says. “Animal proteins like chicken, fish, and beef are much more expensive than vegetable-based proteins like beans, quinoa, nuts, seeds, and tofu products. You may notice a decrease in the grocery bill if you shop wisely.”

Knowing the Risks of a Vegetarian Diet

The problems associated with a plant-based diet can come from not shopping wisely and not knowing how to compensate for nutrients missed from animal products. “If you do not have a plan in place for getting the nutrients found in animal sources through vegetarian sources, you can come up short on protein, B12, calcium, vitamin D, and others,” says Lona Sandon, RD, an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center in Dallas. “Many of these nutrients can be found in vegetarian sources. To get them requires a wide variety of food choices and some planning. Don’t just stop eating meat: You need to find an alternative source of nutrients.”

Steps to Enhance Vegetarian Diet Safety

Dr. Kulze recommends the following steps to ensure sound nutrition and minimize the risks of a vegetarian diet:

  • Be especially vigilant to avoid refined carbohydrates and sugars from processed foods, as you will already be eating more carbs overall.
  • As a safety net, take a multivitamin that contains 100 percent of the daily value (DV) for B12 and at least 70 percent of the DV for zinc. For children and women of child-bearing age, be sure it also contains 100 percent of the DV for iron.
  • Take an algae-based DHA supplement or a high-quality (molecularly distilled) fish oil supplement and be sure to consume plentiful amounts of plant-based forms of omega-3 fats, such as whole soy foods, chia seeds, hemp seeds, flaxseeds, canola oil, dark leafy greens, wheat germ, and walnuts.
  • To get the protein you need, eat beans, whole soy foods, quinoa, nuts, and seeds regularly.
  • If pregnant, nursing, or managing a chronic disease, always check with your health care provider before taking any supplements.
  • Eat large quantities of fresh or frozen fruits and veggies, especially nonstarchy veggies, to take advantage of their appetite-controlling volume.

A vegetarian diet can be great for your health as long as you compensate for the important nutrients you’ll give up in animal products.

TELL US: Do you eat a vegetarian diet?

More and more women are vegging out…of their minds. New research suggests that along with shedding pounds, slashing cancer risk, and boosting life expectancy, vegetarianism could come with lesser-known side effects: Panic attacks. OCD. Depression. WH investigates the puzzling blow of going meatless—and how to stay plant-based without going mental.

Her symptoms were sudden and severe. Drew Ramsey’s 35-year-old patient had always been fit and active, but her energy had flatlined. When she did manage to drag herself to the gym, it didn’t help. She felt anxious and was often on the verge of tears for no reason, even when she was with friends. Worst of all were her panic attacks, a rare occurrence in the past but now so common that she was afraid of losing her job because she had trouble getting out of bed, and she’d become terrified of taking the New York City subway.

Ramsey, a Columbia University professor and psychiatrist with 14 years of experience, wanted to put her on medication. His patient demurred. She was so conscious of what she put in her body, she’d even given up meat a year ago, having heard about all the health benefits of vegetarianism. So Ramsey prescribed something else: grass-fed steak.

It may sound like an episode of House, but Ramsey had a hunch. He’d seen a dramatic link between mood and food before (he even researched it for his forthcoming book Eat Complete), and guessed that his patient’s well-intentioned meat-free diet was the very thing causing her mental deterioration. Sure enough, six weeks after adding animal protein back onto her plate, her energy rebounded and her panic attacks dropped by 75 percent.

Her case is far from unique. “I hear from vegetarians every day; they have this terrible depression and anxiety, and they don’t understand why,” says Lierre Keith, author of The Vegetarian Myth. “People think they’re eating a beautiful, righteous diet, but they don’t realize there’s a potential dark side.”

It’s true that many of America’s estimated 8 million vegetarians are drawn to the diet’s promise of a healthier weight, heart, and planet. They pass on beef, poultry, and pork, unaware that a growing body of research suggests a link between going meatless and an elevated risk for serious mental disorders.

(Hit the reset button—and burn fat like crazy with The Body Clock Diet!)

Garden State

Paleo aside, it’s been decades since meat eating has been considered truly healthy. Practically every day, it seems, a new study emerges showing that vegetarian diets are the key to everything from shedding pounds to beating cancer. One group of California researchers even found evidence that ditching meat can tack more than three years onto your lifespan.

The plant-based love has gone well beyond medical opinion—it’s become part of a cultural shift. Some 29 million U.S. adults now take part in Meatless Monday. Amazon alone has more than 7,000 vegan cookbooks in its inventory (60 of those are best sellers). Open Table has scores of “top restaurants for vegetarians” lists, highlighting star chefs experimenting with zero-meat meals. Even chains like Wendy’s and White Castle are grilling up veggie burgers.

“I hear from vegetarians every day; they have this terrible depression and anxiety, and they don’t understand why.”

It’s tough to argue with the science—and with a movement that’s been endorsed by everyone from Gandhi to Beyonce. And it’s natural to assume that peak mental health and a perpetually blissed-out attitude are just two more side effects of the glowing vegetarian lifestyle.

So it was startling last year when Australian researchers revealed that vegetarians reported being less optimistic about the future than meat eaters. What’s more, they were 18 percent more likely to report depression and 28 percent more likely to suffer panic attacks and anxiety. A separate German study backs this up, finding that vegetarians were 15 percent more prone to depressive conditions and twice as likely to suffer anxiety disorders.

Even the pros find the stats confounding in a chicken-or-egg way. “We don’t know if a vegetarian diet causes depression and anxiety, or if people who are predisposed to those mental conditions gravitate toward vegetarianism,” says Emily Deans, M.D., a Boston psychiatrist who studies the link between food and mood.

Most likely, says Deans, there’s truth to both theories. People with anxious, obsessive, or neurotic tendencies might be more inclined to micromanage their plates (in one study, vegetarians had triple the risk of developing an eating disorder compared with meat lovers). Yet experts all agree that, regardless of where you rank on a scale of 1 to OCD, what you swallow plays a major role in what happens in your head.

“Food is a factor in mental health,” says Ramsey. “We should be talking about it. You can’t just make a sweeping change to your diet and expect it won’t have any effect on you mentally.”

These “healthy” foods are actually bad for you:

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Risky Nutrition

Quick: Name some “brain foods.” Well, there’s avocado. Olive oil. Nuts. Red meat? Not so much. Yet anthropological evidence shows that, long before we could choose to subsist on cashew cheese and tofu, animal flesh provided the energy-dense calories necessary to fuel evolving cerebellums. Without meat, we’d never have matured beyond the mental capacity of herbivores like gorillas.

Today, stronger brains are still powered by beef—or at least, by many of the nutrients commonly found in animal proteins. At the top of the list are B vitamins, which your noggin needs to pump out neurotransmitters such as glutamate; low levels of it have been linked to depression, anxiety, and OCD (sound familiar?). Similarly, meager levels of zinc and iron, two nutrients far more prevalent in meats than veggies, may manifest as moodiness—or worse. “I’ve had vegetarians come in thinking they’re having panic attacks when it’s really an iron deficiency,” says Deans. Without iron to help blood shuttle oxygen around, the brain gets less O2, leaving it sluggish and more prone to misfiring. Then there’s tryptophan, an essential amino acid found almost exclusively in poultry. Your body can’t make it on its own and needs it to produce serotonin, a hormone that acts as the brain’s natural antidepressant.

“Today, stronger brains are still powered by beef—or at least, by many of the nutrients commonly found in animal proteins.”

Some vegetarians inadvertently dig themselves in deeper by filling up on white bread, rice, and pasta; sugar-laden cereals; and cookies. This so-called carbitarian diet is free of meat but rich in problems, says internist Vincent Pedre, M.D., author of Happy Gut. “The resulting seesaw of blood sugar and hormone levels may lead to even more irritability, depression, and anxiety.”

Meat in the Middle

Of course, plenty of vegetarians never experience so much as a single mental-health hiccup, and savvy ones are able to eat around the aforementioned nutritional deficiencies (see “Eat Your Feelings,” page 143). Clearly, it’s possible to adjust to, even thrive on, a meat-free existence.

But quitting meat shouldn’t be done cold turkey, cautions Deans. Consult a nutritionist or doctor beforehand, especially if you’re susceptible to mood disorders or have a family history of them. Then cut down gradually. “Start using meat as a garnish in a dish rather than as the main attraction,” suggests Diana Rice, R.D., a dietitian in New York City. Other healthy ways to lean in to veggie-based eating: Scale back to just one meaty meal per day; nix meat only on weekends or certain weekdays; or practice flexitarianism—the term for when you eat meat only on occasion, or don’t do meat but still eat dairy, eggs, and fish.

As you go, keep tabs on how you feel, physically and mentally. “Everyone responds to going vegetarian differently,” says Rice. “Some feel amazing right away, some may feel the same, and some realize they’re better off with a little bit of animal protein in their diets after all.”

Isabel Smith, 27, was one of the latter. Just like Drew Ramsey’s patient, she was active and energetic and thought a vegetarian diet was the perfect complement to her health-conscious lifestyle. But after a few weeks sans meat, she found herself uncharacteristically weepy. “I was tired and frustrated and got upset more easily, especially over things that wouldn’t normally bother me,” she says. “I would find myself sad for no reason.” Shortly after she started eating meat again, she noticed an uptick in her mood.

The twist? Smith is a registered dietitian. One who now understands personally what she studies professionally: Not everyone is cut out for a life without meat. For many people, it’s crucial to realize that the emphasis in food writer Michael Pollan’s oft-quoted advice to eat “mostly plants” shouldn’t always be on the second word.

Learn which meat substitutes are our favorite and get other healthy-eating tips in the December issue of Women’s Health, on newsstands now.

  • Good Food’s great vegan meat taste test

It was just a few months ago that experts were declaring the end of meat. Earlier this year, consultancy firm AT Kearney predicted that by 2040, animal products will have become so socially and environmentally unacceptable that most “meat” eaten across the globe will come in the form of plant-based or lab-grown substitutes. The anti-meat movement has certainly gained momentum in recent years, with vegetarians and vegans set to make up one quarter of the UK population by 2025, according to analysis by Sainsbury’s.

But a major study released this week just might put the brakes on the rapidly accelerating plant-based trend. According to Oxford University research, published in the British Medical Journal, vegetarians and vegans have a 20 per cent higher risk of stroke than those who regularly tuck into a plate of bacon and sausages. The authors of the study, which tracked almost 50,000 Britons for 18 years, said this might be because vegies did not have enough cholesterol in their blood.

The study found vegetarians and vegans have a 20 per cent higher risk of stroke than those who regularly tuck into a plate of bacon and sausages. Photo: William Meppem

The finding flies in the face of much conventional wisdom, which says that vegetarianism is a healthy alternative to a carnivorous lifestyle. We are forever being hectored about the need – apparently for health and environmental reasons – to cut back on red meat altogether.

But nutritionists say the increased risk of stroke is just one of the many health risks that any would-be vegetarian should be made aware of before they take the plunge.

Helen Bond, a registered dietitian, says the large-scale Oxford study should be taken seriously, although she notes that the increased risk of 20 per cent is actually “quite small” once the sample size is taken into account (it equates to three more cases of stroke per 1,000 people over 10 years). She says that those who cut out meat entirely don’t always understand the full health implications of their lifestyle choice: “I think people shouldn’t just embark on a vegan diet because it’s on trend, and they’re following some Instagram guru. They should delve deeper and understand that there are nutrient shortfalls.”

Last week, nutritionist Emma Derbyshire told the BMJ that vegans may find themselves deficient in choline, a crucial nutrient for brain health commonly found in eggs, milk and beef that influences memory, mood and muscle control. With planning, the British Dietetic Association said, it was possible for vegans to reach requisite levels, but not everyone who avoids meat plans carefully enough.

Vegan diets can be devoid of vitamin B12 and vitamin D, which can be found in eggs. Photo: William Meppem. Styling by Hannah Meppem

Such diets, Bond adds, are usually devoid of vitamin B12, which is found only in animal products. Without it, you run a greater risk of becoming fatigued and your immune system can be weakened, although she says “full-blown B12 deficiency is not very common in today’s society”. More concerning is getting enough vitamin D, the so-called “sunshine vitamin”, which is important for our bones, teeth and immune system, and can be difficult to include in your diet if you are vegetarian, and very difficult if you are vegan. “Vitamin D-rich foods are mainly oily fish, eggs and things like that,” Bond says. “There is some in mushrooms, but sadly very few foods.”

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Bond thinks the UK is gradually moving towards a vegetarian way of life, pointing to Public Health England’s latest Eatwell Guide, which stressed the health benefits of plant-based foods; according to research published at the end of last year, one in eight Britons is now vegan or vegetarian, while a fifth of the population describes themselves as “flexitarian”. But it doesn’t have to be that way: as countless studies have suggested, she thinks the biggest health benefits actually come from a Mediterranean-style diet, which combines lots of vegetables with modest amounts of (mostly white) meat, plus pulses and oily fish, which are rich in omega-3 fats and help to reduce our blood pressure.

Ian Marber, a nutritionist, adds that vegetarians and vegans might miss out on some of their essential amino acids, a source of protein. A lack of protein can mean weight loss; skin, hair, and nail problems; and increased risk of bone fractures.

Although it is usually vegans whose culinary choices make headlines, he thinks they are usually better prepared than vegetarians, with a steady supply of vitamin supplements lining their cupboards. “I find that vegans tend to be quite motivated and do it quite well – they are aware that they need omega-3 fats, for example. Vegetarianism tends not to be done with the same attention to detail.” Previously, his clutch of vegan clients “knew what they were doing”; now that meat-free numbers have swelled, he finds himself more frequently doling out advice on how to stay healthy and plant-based at the same time.

Many newly signed-up vegans have also noted cognitive effects – known as “brain fog” – and there’s plenty of science to back that up, according to Sophie Medlin, a lecturer in nutrition and dietetics at King’s College London. “Anyone following a plant-based diet is likely to have suboptimal levels of vitamin B12 and an essential fatty acid called DHA ,” she says. “These are vital for the health of our neurons or brain cells. When we are deficient, we suffer symptoms such as brain fog, short-term memory loss, changes in mood, difficulty sleeping, agitation, and anxiety.”

It’s not all bad news for the plant lovers, though. As well as showing an increased risk of stroke, the Oxford study also found that vegetarians had a 22 per cent lower risk of heart disease compared to meat eaters. Experts said the difference might be because vegetarians have lower weights and blood pressures than meat eaters, and thus are less likely to have diabetes. Previous studies have shown that those who avoid red meat see a reduced risk of bowel cancer.

“In the battle between meat eaters and non-meat eaters, everyone’s looking for one answer,” says Ian Marber. “If we can only declare that one’s better than the other. But it’s not better, it’s just different.”

The Daily Telegraph

What are the risks of following a vegetarian diet?

Vegetarian diets can be extremely healthy:

  • lots of vegetables, whole grains and legumes
  • low fat
  • high fiber
  • healthy vegetable oils

With all those benefits, how could a vegetarian diet be risky? It all depends on balance.
Some people think being vegetarian just means not eating meat. They eat a highly processed diet, full of snack foods, soft drinks and convenience foods. It’s entirely possible to be a vegetarian and never touch a vegetable. Leaving pepperoni off a pizza may technically be vegetarian, but it isn’t necessarily healthy. Swapping soy burgers for beef burgers is technically vegetarian, but it isn’t necessarily healthier if you eat soy burgers, French fries and soda pop for lunch everyday.
Another risk for vegetarians is lack of certain nutrients found primarily in animal foods, especially meat. Protein is usually the first thing vegetarians think about. Our highest quality sources for protein are animal foods: meats, poultry, fish, eggs, milk, yogurt and cheese. While plant foods have some protein, it’s not as high quality or as concentrated. For example, 2 TB of peanut butter has almost as much protein as 1 oz of cooked chicken breast meat. The peanut butter is almost 200 calories, while the chicken is around 50. And the quality of that peanut butter protein isn’t quite as good for human needs.
Iron is another nutrient of concern. We get lots of iron from meat, especially red meats like beef, pork, bison and lamb. Dairy foods, which vegetarians can eat, are not good iron sources; eggs are a fair source. So cutting out meat means getting more iron from plant sources. Leafy green vegetables and whole grains have significant iron, but if you’re a vegetarian who doesn’t eat vegetables or whole grains, your iron sources will be more limited.
One possible benefit of a vegetarian diet is the emphasis on healthy fats from vegetable oils. But if your vegetarian diet is heavy on cheese, sour cream and cream cheese you could end up eating a high saturated fat diet. That’s easy to do if you depend on pizza, burritos, bagels and soy burgers every day.

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Vegetarianism and veganism are a broad terms that encompasses a diverse and heterogeneous range of dietary practices that avoid flesh foods. This food practice has been known for many centuries and, in last years, demand for vegetarian food have increased notably. Reasons for choosing a vegetarian diet include potential health benefits, economic status, religious and sociopolitical, ecological, ethical, environmental, etc, and many studies have shown health benefits associated with vegetarian diets. This article presents some characteristics related to the consumption of food of plant origin and its repercussion on the body and health of the adolescent.

Key words

vegetarianism, veganism, adolescence, nutrition


Vegetarianism is a broad term that encompasses a diverse and heterogeneous range of dietary practices that avoid flesh foods (meat, poultry, seafood) and their products, while vegetarian diet is defined as a “diet consisting wholly of vegetables, fruits, grains, nuts, and sometimes egg or dairy products” . This food practice has been known for many centuries and, in last years, the number of consumers following a vegetarian diet and the demand for vegetarian food have increased notably in many countries .

According to the American Dietetic Association the vegetarian diet can be classified into three main types: 1) strict vegetarianism: excludes all kinds of animal food; 2) lactovegetarianism: in addition to vegetables includes milk and dairy products; 3) ovolactovegetarianism: in addition to vegetable includes milk, dairy products and eggs .

Reasons for choosing a vegetarian diet are varied and include potential health benefits, economic status, religious and sociopolitical, ecological, ethical, and environmental issues related to allocation of resources and animal rights . The decision to use a vegetarian diet for health reasons might be strongly influenced by public perceptions of the health advantages, and clinical and epidemiological research studies have shown health benefits associated with vegetarian diets . The types and composition of vegetarian diets also are varied and have important implications for the growth and development of adolescents.

Adolescence is widely recognized as the stage of development that occurs between childhood and adulthood and is characterized across cultures and species by the onset of puberty as well as unique neurobiological, social, and cognitive development . It is a time to explore new roles and lifestyles, establish independence, and expres a unique identity. Interest in alternative lifestyles and diets, including vegetarianism, is a growing phenomenon in this age group. Furthermore, during adolescence, both males and females have a heightened sensitivity about their appearance and often experience pressure to conform to a cultural ideal, resulting in body dissatisfaction and experimentation with various weight loss methods . Adolescents may adopt eating patterns, such as vegetarianism, as a way to establish an identity, expres values, and assert control over their lives .

Nutritional needs during adolescence are influenced by the onset of puberty with associated increased growth rate and changes in body composition and organ systems. The recommended dietary energy requirements in adolescents are defined to maintain health, promote optimal growth and maturation, and support a desirable level of physical activity .

Vegetarian diets can meet nutrient needs for growth and development when they are carefully planned with attention. In general vegetarian diets are rich in fibre, iron, folic acid, magnesium, vitamins C and E, n-6 polyunsaturated fatty acid, carotenoids, flavonoids, other phytochemicals and antioxidants. However, these diets are low in calories, total fat, n-3 PUFA, calcium, iodine, zinc, vitamins B12 and D .

While there is a range of health benefits associated with a vegetarian diet, there are potential risks as well. If vegetarian diets are not well-planned, there may be an increased potential for specific nutrient deficiencies . In addition to potential nutrient deficiencies, there is concern about the consistente pattern associating vegetarianism and disordered eating behaviors in adolescents .

With a good planning and careful attention, vegetarian can include in their diets all essential nutrientes . In general, it has been observed that vegetarians had lower risks of obesity, hypertension, cardiovascular diseases, diabetes, arthritis, cancers (especially colon and prostate cancer) and fatal ischemic heart disease, thanks to protective substances found in fruits, vegetables, legumes, seaweed, seeds, whole grains, vegetable oils and other plant-based foods .


Daily energy needs during adolescence vary according to sex and pubertal spurt, and can be easily obtained with any type of diet. Until the age of 14 years 2500 calories are sufficient for both sexes. However, boys over 15 years require 3000 calories while 2300 calories are sufficient for girls. It is important to note that a diet with a high fiber content may provide a sense of fullness before an adequate amount energy is ingested, and vegetarian diets that contain less than 15% of calories from fat can adversely impact on growth and development of children and adolescentes .


Protein is necessary for growth, imune function and tissue repair and its quality is determined by amino acid composition. The difference between proteins of plant and animal origin is the concentration of essential amino acids, and protein needs of vegetarians are met when the diet includes a variety of plant foods and caloric intake is adequate . Animal foods are considered complete or high-quality proteins because they contain all nine essential amino acids while plant-based foods are usually deficient in one or more of the essential amino acids. The deficit of one plant food can be overcome by combining it with a complementary plant food that provides adequate amounts of the limited essential amino acid. Vegetarians should consume a wide variety of vegetables to obtain all the daily necessary amino acids . The daily requirement for protein is 1.0 g/kg for individuals aged 10 and 14 years, while adolescents older than 14 years require 0.8 /kg . The major plant food sources of protein are beans, lentils, cereals, nuts and seed, and each variety has diferent composition of essential amino acids and digestibility.

Omega-3 fatty acids

Fats should represent 35% of the daily caloric intake for the adolescent. Vegetarian diets generally are rich in omega-6 fatty acids, but marginal in omega-3 fatty acids, unless the diet includes fish, eggs, or generous amounts of algae. Omega-3 fatty acids, which include eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), or their precursor alpha-linolenic acid (ALA), are important for cardiovascular health and eye and brain development . Vegetarians have lower blood levels of EPA and DHA than nonvegetarians .

Vegetarians can improve their n-3 nutritional status by regularly consuming good sources of ALA (flaxseeds, walnuts, chia seeds and their oils) and limiting intake of sources of linoleic acid (corn and sunflower oils). To enhance the conversion of ALA to EPA and DHA, vegetarians should be advised to ensure their diet contains sufficient proteins, pyridoxine, biotin, calcium, copper, magnesium, and zinc .


Up to 13 years of age adolescents need 8 mg/day of iron, and this concentration increases to 12 mg for boys and 15 mg for girls age 14 to 18 years . Potential consequences of iron deficiency include growth retardation, behavioral problems, impaired cognitive and motor development, and deficient immune response. Concerns about iron nutrition for vegetarian are related to the differences between heme and nonheme iron. Heme iron is more readily absorbed than nonheme iron and the absorption of nonheme iron is reduced greatly by some dietary components, whereas heme iron is little affected. Tannins and polyphenols present in coffee and tea form iron-tannate complexes that greatly reduce nonheme iron absorption while phytate of legumes, nuts, seeds, whole grains, and soy protein also bind with nonheme iron to form insoluble complexes and reduce its absorption .

Some strategies used to increase iron absorption include supplementation with ascorbic acid and avoidance of large intakes of tannin-containing teas. Thus the bioavailability of iron in a vegetarian diet can be enhanced by consuming ascorbic acid during a meal containing iron. Other organic acids in fruits and vegetables (citric, malic, lactic and tartaric acids), as well as carotenes andretinol, also enhance non-haem iron absorption . Good plant sources of iron include legumes, dried fruits, soy, green leafy vegetables, bulgur, blackstrap molasses, and wheat germ. The widespread fortification of enriched breads, cereals, and pasta products has helped increase iron intake for adolescents.


Zinc is found in foods of both animal and plant origin and its recommendations are 8 mg/day for adolescent aged 10 to 13 years, while for adolescent females and males aged 14 to 18 years are 9 mg/day and 11 mg/day, respectively . Good plant sources of zinc include whole grains, legumes, wheat germ, and nuts. Cereals are the primary source of zinc for adolescents that consume vegetarian diets without milk. Zinc deficiency can be associated with growth impairment and an increased risk of infections, particularly diarrhea and pneumonia .

Sulphuramino acids, cysteine-containing peptides, hydroxy acids (present in fruits) and other organic acids present in fermented food may all increase zinc absorption. As with iron, procedures that activate the endogenous phytases present in cereals and pulses, like milling, sprouting, soaking, and sour-dough leavening, increase the bioavailability of zinc .

Phytates found in larger quantities in vegetarian diets bind zinc and reduce its bioavailability. Certain food preparation techniques, such as the soaking of sprouting beans, grains, and seeds, as well as leavening breads, can reduce binding of zinc by phytates and increase zinc bioavailability .


Calcium is an essential mineral during growth when bone mass is expanding. Maintenance of adequate calcium intake is important throughout life to ensure peak bone mass accumulation, especially during periods of growth. Adolescent with stronger bones may experience fewer fractures and may be more resistant to the development of osteoporosis in later life . The optimal daily dietary allowance of calcium for adolescents is 1300 mg for those 10 to 18 years for skeletal growth; for losses in urine, sweat, and endogenous secretion; and to adjust for average calcium absorption efficiency . Dairy products have been positively associated with bone health because of their calcium content. Low calcium intake leads to increased bone remodeling and increased risk of hip fracture. Milk is the most economical source of many limiting nutrients, especially calcium, potassium, and magnesium .

Several plant foods, particularly leafy vegetables pulses, nuts, kale, mustard greens, broccoli, bok choy, contain good quantities of calcium, however the bioavailability of this mineral is inversely proportional to the amounts of oxalate and phytate in the diet . Calcium intake may need to be increased to overcome the effects of other dietary constituents that decrease calcium absorption (oxalate and phytate) or increase excretion (salt and protein). The diminished intake of animal protein by vegetarians may help their net calcium balance by decreasing urinary calcium loss. Animal protein, with sulfur-containing amino acids, produces an increased acid load and decreases renal tubular calcium reabsorption. Most of the calcium needs of adolescent that consume lactovegetarian or lacto-ovovegetarian diets can be met by low-fat milk and dairy products .

Vitamin D:

Occurs naturally in animal products such as liver, fatty ocean fish and egg yolks and may be lacking in vegetarian diets. Normal levels of vitamin D metabolites are necessary for adequate intestinal calcium, phosphate absorption, and bone formation. Vitamin D availability is a function of sunlight exposure and dietary intake and maintenance of normal serum vitamin D concentrations requires exposure to the sun on hands, arms, and face for 10 to 15 minutes/day for fair-skinned. In addition to sun exposure a dietary intake of 600 IU generally is recommended . Vegetarians that do not consume milk are at risk for vitamin D. A dietary alternative is soy milk or breakfast cereal fortified with calcium and vitamin D. For those that can’t get adequate sun exposure vitamin D supplementation needs to be considered .

Vitamin B12

Vitamin B12 is necessary for cell division, blood formation, and nervous system maintenance. Vitamin B12 deficiency can produce abnormal neurologic and psychiatric symptoms that include ataxia, psychoses, paresthesia, disorientation, dementia, mood and motor disturbances, and difficulty with concentration . In addition individuals may experience too apathy and macrocytic anemia. Because vitamin B12 deficiency develops slowly, the vitamin status of vegetarians should be monitored regularly. Vitamin B12 (cobalamin) is only found in foods from animal sources (meat, fish, eggs, and dairy products) . The RDA for cobalamin is 1.8 mcg for 9 to 13 years and 2.4 mcg for 14 to 18 years . Sometimes, lacto-ovovegetarians and lactovegetarians can consume sufficient amounts of vitamin B12 from eggs, and milk products. Nonanimal sources of vitamin B12 include cereals, breads, nutritional yeast, and some fortified soy products. Because a high folic acid intake can hide the symptoms of B12 deficiency, neurologic symptoms may occur before detection . Vegan and other vegetarians whose diet does not contain adequate vitamin B12 should consume a regular and reliable source of the vitamin, either in fortified foods or an oral B12 supplement. Commonly used B12-fortified foods include certain brands of nutritional yeasts, most ready-to-eat cereals, many meat analogs, and some milk alternatives. Vegetarian diets are usually high in folic acid intake, which could mask B12 deficiency anemia but still leave children at risk for neurological commitment .


Vegetarians often have high dietary fiber intake and this can to promote normal laxation and possibly reduces the risk of developing certain diseases in adulthood. However, a diet with a great quantity of fiber can compromise dietary energy intake and reduce the bioavailability of minerals such as iron, calcium, and zinc due the presence of oxalates and phytates. A small loss of energy, primarily as fat, and protein may occur with a high intake of dietary fiber. Daily fecal energy loss is estimated to increase by 1 percent for every 6-gram increase in dietary fiber . For adolescents aged 10 to 13 years the recommended fiber intake ranges from 26 to 31 g/day. This amount of dietary fiber should not have an adverse effect on mineral bioavailability, provided the dietary mineral intake is adequate. Intake of fiber that exceeds the recommendation is unlikely to decrease mineral bioavailability in vegetarian that consume a balanced diet from a variety of foods. Food processing, such as sprouting and fermentation, is known to degrade phytates, thereby enhancing the bioavailability of iron, zinc, and calcium .


According to the American Academy of Nutrition and Dietetics vegetarian diets, when well thought out, are appropriate for adolescentes . A detailed dietary history, with specific attention to the variety of foods supplied (especially in cases of strict vegan or other restrictive diets), needs to be taken and appropriate advice given . Besides that na appropriate education of the family and follow-up over time are essential.

A vegetarian diet could be used as a ‘‘socially acceptable’’ method to restrict intake and control weight has raised questions regarding the role of such a diet in the development or maintenance of disordered eating patterns or clinical eating disorders . Because eating behaviors developed during adolescence can have health implications and influences on future chronic disease risk adolescents that follow a vegetarian diet as a means of weight management should be monitored closely for evidence of an eating disorder.

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Vegans and vegetarians may have higher stroke risk

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People who eat vegan and vegetarian diets have a lower risk of heart disease and a higher risk of stroke, a major study suggests.

They had 10 fewer cases of heart disease and three more strokes per 1,000 people compared with the meat-eaters.

The research, published in the British Medical Journal, looked at 48,000 people for up to 18 years.

However, it cannot prove whether the effect is down to their diet or some other aspect of their lifestyle.

Diet experts said, whatever people’s dietary choice, eating a wide range of foods was best for their health.

What does this study add?

It analyses data from the EPIC-Oxford study, a major long-term research project looking at diet and health.

Half of participants, recruited between 1993 and 2001, were meat-eaters, just over 16,000 vegetarian or vegan, with 7,500 who described themselves as pescatarian (fish-eating).

They were asked about their diets, when they joined the study and again in 2010. Medical history, smoking and physical activity were taken into account,

Altogether, there were 2,820 cases of coronary heart disease (CHD) and 1,072 cases of stroke – including 300 haemorrhagic strokes, which happen when a weakened blood vessel bursts and bleeds into the brain.

The pescatarians were found to have a 13% lower risk of CHD than the meat-eaters, while the vegetarians and vegans had a 22% lower risk.

But those on plant-based diets had a 20% higher risk of stroke. The researchers suggested this could be linked to low vitamin B12 levels but said more studies were needed to investigate the connection.

It is also possible that the association may have nothing to do with people’s diets and may just reflect other differences in the lives of people who do not eat meat.

Media playback is unsupported on your device Media captionIs there such a thing as vegan junk food?

So does it show vegan and vegetarian diets are unhealthy?

Dr Frankie Phillips, from the British Dietetic Association, says not – because this was an observational study.

“They looked at what people ate and followed them for years, so it’s an association, not cause-and-effect,” she says.

“The message, for everyone, is it makes sense to have a well-planned diet, and to eat a wide variety of foods.

Image copyright Getty Images Image caption A varied diet is the key, not “meat and potatoes every night”

“Meat-eaters don’t necessarily have a varied diet, because they might live on meat and potatoes for dinner every night and not have any vegetables.”

Has what people eat changed since this study started?

Researchers did go back to participants in 2010 to ask them again about their diets.

But Dr Phillips says vegan and vegetarian diets will have changed.

“This is data that’s been collected from a couple of decades ago,” she says.

“It might well be that the typical vegetarian diet today looks very different to a vegetarian or vegan diet from 20 or 30 years ago.

“The range of vegetarian and vegan convenience foods has escalated massively. It’s a lot more mainstream.”

And we know more about the health risks linked to eating too much processed and red meat, which has been linked to an increased risk of bowel cancer..

So what should go on my plate?

Image copyright Getty Images

The NHS’s the Eatwell Guide sets out the balance of foods you need, whatever kind of diet you eat:

  • Eat at least five portions of fruit and vegetables a day
  • Base meals around higher-fibre starchy foods such as potatoes, bread, rice or pasta
  • Don’t forget protein – from lean meat, fish, seafood, pulses, tofu or unsalted nuts
  • Include dairy or dairy alternatives
  • Foods high in fat, sugars or salt should be eaten less often and in small amounts

But people on vegan and vegetarian diets also need to take particular care to consume enough of some specific nutrients.

For example, people who eat meat, dairy and fish usually have enough vitamin B12, needed for healthy blood and nervous systems.

However, vegans can become deficient, though B12 is also present in foods such as fortified breakfast cereals and yeast extract spreads.

Iron is also less easily absorbed from plant-based foods, so those who choose not to eat meat need to ensure they include foods such as wholemeal bread and flour, dried fruits and pulses.

And there was a call last month for vegans to be aware of the need to ensure they were consuming enough of another nutrient, called choline, important for brain health.

Research Checks interrogate newly published studies and how they’re reported in the media. The analysis is undertaken by one or more academics not involved with the study, and reviewed by another, to make sure it’s accurate.

A UK study finding vegetarianism is associated with a higher risk of stroke than a meat-eating diet has made headlines around the world.

The study, published in the British Medical Journal last week, found people who followed vegetarian or vegan diets had a 20% higher risk of having a stroke compared to those who ate meat.

But if you’re a vegetarian, there’s no need to panic. And if you’re a meat eater, these results don’t suggest you should eat more meat.

While we don’t fully understand why these results occurred, it’s important to note the study only showed an association between a vegetarian diet and increased stroke risk – not direct cause and effect.

Read more: Clearing up confusion between correlation and causation

What the study did and found

The researchers looked at 48,188 men and women living in Oxford, following what they ate, and whether they had heart disease or a stroke, over 18 years. The researchers grouped the participants according to their diets: meat eaters, fish eaters (pescatarians) and vegetarians (including vegans).

While vegan diets are quite different to vegetarian diets, the investigators combined these two groups as there were very small numbers of vegans in the study.

In their analysis, the researchers accounted for variables which are known risk factors for heart disease and stroke, including education level, smoking status, alcohol consumption, and physical activity.

Read more: Is vegetarianism healthier? We asked five experts

They found vegetarians had a 22% lower risk of heart disease than meat eaters. This is equivalent to ten fewer cases of heart disease per 1,000 vegetarians than in meat eaters over ten years.

Yet the vegetarians had a 20% higher rate of stroke, equivalent to three more strokes per 1,000 vegetarians compared to the meat eaters over ten years.

The decrease in heart disease risk seemed to be linked to lower body mass index (BMI), cholesterol levels, incidence of diabetes, and blood pressure. These benefits are all known to be associated with a healthy vegetarian diet, and are protective factors against heart disease.

This study showed fish eaters (who did not consume meat) had a 13% lower risk of heart disease, but no significant increase in the rate of stroke when compared to meat eaters.

As with any study, there are strengths and weaknesses

The main strength of this study is that it closely followed a very large group of people over a long period of time.

The major weakness is that being an observational study, the researchers were not able to determine a cause and effect relationship.

So this study is not showing us vegetarian diets lead to increased risk of stroke; it simply tells us vegetarians have an increased risk of stroke. This means the association may be linked to other factors, aside from diet, which may be related to the lifestyle of a vegetarian.

The study’s authors suggest a difference in vitamin B12 levels between the vegetarian and meat-eating groups may have contributed to the results. From .com

And while vegetarian and vegan diets may be seen as generally healthier, vegetarians still may be eating processed and ultra-processed foods. These foods can contain high levels of added salt, trans fat and saturated fats. This study did not report on the whole dietary pattern – just the major food groups.

Another major weakness of this study is that vegans and vegetarians were grouped together. Vegetarian and vegan diets can vary considerably in nutrient levels.

So why would the vegetarian group have a higher stroke risk?

These kind of observational studies are unable to provide what scientists call “a mechanism” – that is, a biological explanation as to why this association may exist.

But researchers will sometimes offer a potential biological explanation. In this case, they suggest the differences in nutrient intakes between the different diets may go some way to explaining the increased risk of stroke in the vegetarian group.

They cite a number of Japanese studies which have shown links between a very low intake of animal products and an increased risk of stroke.

Read more: Eat your vegetables – studies show plant-based diets are good for immunity

One nutrient they mention is vitamin B12, as it’s found only in animal products (meat, fish, dairy products and eggs). Vegan sources are limited, though some mushroom varieties and fermented beans may contain vitamin B12.

Vitamin B12 deficiency can lead to anaemia and neurological issues, including numbness and tingling, and cognitive difficulties.

The authors suggest a lack of vitamin B12 may be linked to the increased risk of stroke among the vegetarian group. This deficiency could be present in vegetarians, and even more pronounced in vegans.

But this is largely speculative, and any associations between a low intake of animal products and an increased risk of stroke remain to be founded in a strong body of evidence. More research is needed before any recommendations are made.

What does this mean for vegetarians and vegans?

Vegetarians and vegans shouldn’t see this study as a reason to change their diets. This is the only study to date to have shown an increased risk of stroke with vegetarian or vegan diets.

Further, this study has shown overall greater benefits are gained by being vegetarian or vegan in its association with reduced risk of heart disease.

Meanwhile, other studies have shown meat eaters – particularly people who eat large amounts of red and processed meats – have higher risk of certain cancers.

Read more: Are there any health implications for raising your child as a vegetarian, vegan or pescatarian?

Whether you’re an omnivore, pescatarian, vegetarian or vegan, it’s important to consider the quality of your diet. Focus on eating whole foods, and including lots of vegetables, fruits, cereals and grains.

It’s equally important to minimise the intake of processed foods high in added sugars, salt, saturated and trans fats. Diets high in these sorts of foods have well-established links to increased risk of heart disease and stroke. –Evangeline Mantzioris

Blind peer review

The analysis presents a fair and balanced assessment of the study, accurately pointing out that no meaningful recommendations can be drawn from the results. This is particularly so since the majority of the data was collected via self-reported questionnaires, which reduces the reliability of the results.

While in many cases the media has reported an increased stroke risk in vegetarians, total stroke risk was not actually statistically different between the groups. The researchers looked at two types of stroke: ischaemic stroke (where a blood vessel supplying blood to the brain is obstructed) and haemorrhagic stroke (where a blood vessel leaks or breaks).

A statistically significant increased risk in the vegetarian group was only seen in haemorrhagic stroke – and even there it’s marginal. Statistically, and in total numbers of people affected, the reduced heart disease risk in the vegetarian group is more convincing. –Andrew Carey

Becoming a vegetarian

Updated: October 23, 2018Published: October, 2009

People become vegetarians for many reasons, including health, religious convictions, concerns about animal welfare or the use of antibiotics and hormones in livestock, or a desire to eat in a way that avoids excessive use of environmental resources. Some people follow a largely vegetarian diet because they can’t afford to eat meat. Becoming a vegetarian has become more appealing and accessible, thanks to the year-round availability of fresh produce, more vegetarian dining options, and the growing culinary influence of cultures with largely plant-based diets.

Approximately six to eight million adults in the United States eat no meat, fish, or poultry, according to a Harris Interactive poll commissioned by the Vegetarian Resource Group, a nonprofit organization that disseminates information about vegetarianism. Several million more have eliminated red meat but still eat chicken or fish. About two million have become vegans, forgoing not only animal flesh but also animal-based products such as milk, cheese, eggs, and gelatin.

Traditionally, research into vegetarianism focused mainly on potential nutritional deficiencies, but in recent years, the pendulum has swung the other way, and studies are confirming the health benefits of meat-free eating. Nowadays, plant-based eating is recognized as not only nutritionally sufficient but also as a way to reduce the risk for many chronic illnesses. According to the American Dietetic Association, “appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases.”

“Appropriately planned” is the operative term. Unless you follow recommended guidelines on nutrition, fat consumption, and weight control, becoming a vegetarian won’t necessarily be good for you. A diet of soda, cheese pizza, and candy, after all, is technically “vegetarian.” For health, it’s important to make sure that you eat a wide variety of fruits, vegetables, and whole grains. It’s also vital to replace saturated and trans fats with good fats, such as those found in nuts, olive oil, and canola oil. And always keep in mind that if you eat too many calories, even from nutritious, low-fat, plant-based foods, you’ll gain weight. So it’s also important to practice portion control, read food labels, and engage in regular physical activity.

You can get many of the health benefits of being vegetarian without going all the way. For example, a Mediterranean eating pattern — known to be associated with longer life and reduced risk of several chronic illnesses — features an emphasis on plant foods with a sparing use of meat. Even if you don’t want to become a complete vegetarian, you can steer your diet in that direction with a few simple substitutions, such as plant-based sources of protein — beans or tofu, for example — or fish instead of meat a couple of times a week.

Only you can decide whether a vegetarian diet is right for you. If better health is your goal, here are some things to consider.

Varieties of vegetarians

Strictly speaking, vegetarians are people who don’t eat meat, poultry, or seafood. But people with many different dietary patterns call themselves vegetarians, including the following:

Vegans (total vegetarians): Do not eat meat, poultry, fish, or any products derived from animals, including eggs, dairy products, and gelatin.

Lacto-ovo vegetarians: Do not eat meat, poultry, or fish, but do eat eggs and dairy products.

Lacto vegetarians: Eat no meat, poultry, fish, or eggs, but do consume dairy products.

Ovo vegetarians: Eat no meat, poultry, fish, or dairy products, but do eat eggs.

Partial vegetarians: Avoid meat but may eat fish (pesco-vegetarian, pescatarian) or poultry (pollo-vegetarian).

Can becoming a vegetarian protect you against major diseases?

Maybe. Compared with meat eaters, vegetarians tend to consume less saturated fat and cholesterol and more vitamins C and E, dietary fiber, folic acid, potassium, magnesium, and phytochemicals (plant chemicals), such as carotenoids and flavonoids. As a result, they’re likely to have lower total and LDL (bad) cholesterol, lower blood pressure, and lower body mass index (BMI), all of which are associated with longevity and a reduced risk for many chronic diseases.

But there still aren’t enough data to say exactly how a vegetarian diet influences long-term health. It’s difficult to tease out the influence of vegetarianism from other practices that vegetarians are more likely to follow, such as not smoking, not drinking excessively, and getting adequate exercise. But here’s what some of the research has shown so far:

Heart disease. There’s some evidence that vegetarians have a lower risk for cardiac events (such as a heart attack) and death from cardiac causes. In one of the largest studies — a combined analysis of data from five prospective studies involving more than 76,000 participants published several years ago — vegetarians were, on average, 25% less likely to die of heart disease. This result confirmed earlier findings from studies comparing vegetarian and nonvegetarian Seventh-day Adventists (members of this religious group avoid caffeine and don’t drink or smoke; about 40% are vegetarians). In another study involving 65,000 people in the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford), researchers found a 19% lower risk of death from heart disease among vegetarians. However, there were few deaths in either group, so the observed differences may have been due to chance.

For heart protection, it’s best to choose high-fiber whole grains and legumes, which are digested slowly and have a low glycemic index — that is, they help keep blood sugar levels steady. Soluble fiber also helps reduce cholesterol levels. Refined carbohydrates and starches like potatoes, white rice, and white-flour products cause a rapid rise in blood sugar, which increases the risk of heart attack and diabetes (a risk factor for heart disease).

Nuts are also heart-protective. They have a low glycemic index and contain many antioxidants, vegetable protein, fiber, minerals, and healthy fatty acids. The downside: nuts pack a lot of calories, so restrict your daily intake to a small handful (about an ounce). The upside: because of their fat content, even a small amount of nuts can satisfy the appetite.

Walnuts, in particular, are a rich source of omega-3 fatty acids, which have many health benefits. Even so, fish are the best source of omega-3s, and it’s not clear whether plant-derived omega-3s are an adequate substitute for fish in the diet. One study suggests that omega-3s from walnuts and fish both work to lower heart disease risk, but by different routes. Walnut omega-3s (alpha-linolenic acid, or ALA) help reduce total cholesterol and LDL (bad) cholesterol, while omega-3s from fish (eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA) lower triglycerides and raise HDL (good) cholesterol levels.

Cancer. Hundreds of studies suggest that eating lots of fruits and vegetables can reduce the risk of developing certain cancers, and there’s evidence that vegetarians have a lower incidence of cancer than nonvegetarians do. But the differences aren’t large. A vegetarian diet can make it easier to get the recommended minimum of five daily servings of fruits and vegetables, but a purely vegetarian diet is not necessarily better than a plant-based diet that also includes fish or poultry. For example, in a pooled analysis of data from the Oxford Vegetarian Study and EPIC-Oxford, fish-eaters had a lower risk of certain cancers than vegetarians.

If you stop eating red meat (whether or not you become a vegetarian), you’ll eliminate a risk factor for colon cancer. It’s not clear whether avoiding all animal products reduces the risk further. Vegetarians usually have lower levels of potentially carcinogenic substances in their colons, but studies comparing cancer rates in vegetarians and nonvegetarians have shown inconsistent results.

Type 2 diabetes. Research suggests that a predominantly plant-based diet can reduce the risk for type 2 diabetes. In studies of Seventh-day Adventists, vegetarians’ risk of developing diabetes was half that of nonvegetarians, even after taking BMI into account. The Harvard-based Women’s Health Study found a similar correlation between eating red meat (especially processed meats, such as bacon and hot dogs) and diabetes risk, after adjusting for BMI, total calorie intake, and exercise.

What about bone health?

Some women are reluctant to try a vegetarian diet — especially one that doesn’t include calcium-rich dairy products — because they’re concerned about osteoporosis. Lacto-ovo vegetarians (see “Varieties of vegetarians”) consume at least as much calcium as meat-eaters, but vegans typically consume less. In the EPIC-Oxford study, 75% of vegans got less than the recommended daily amount of calcium, and vegans in general had a relatively high rate of fractures. But vegans who consumed at least 525 milligrams of calcium per day were not especially vulnerable to fractures.

Certain vegetables can supply calcium, including bok choy, broccoli, Chinese cabbage, collards, and kale. (Spinach and Swiss chard, which also contain calcium, are not such good choices, because along with the calcium they have oxalates, which make it harder for the body to absorb calcium.) Moreover, the high potassium and magnesium content of fruits and vegetables reduces blood acidity, lowering the urinary excretion of calcium.

People who follow a vegetarian diet and especially a vegan diet may be at risk of getting insufficient vitamin D and vitamin K, both needed for bone health. Although green leafy vegetables contain some vitamin K, vegans may also need to rely on fortified foods, including some types of soy milk, rice milk, organic orange juice, and breakfast cereals. They may also want to consider taking a vitamin D supplement.

Selected resources

Becoming a vegetarian requires planning and knowledge of plant-based nutrition. Here are some resources that can help:

American Dietetic Association

The Vegetarian Resource Group

Vegetarian Society of the United Kingdom

What about the health risks of being vegetarian?

Concerns about vegetarian diets have focused mainly on the following nutrients:

Protein. Research shows that lacto-ovo vegetarians generally get the recommended daily amount of protein, which is easily obtained from dairy products and eggs. (Women need about 0.4 grams of protein per pound of body weight per day. Because the protein in vegetables is somewhat different from animal protein, vegans may need 0.45 grams of protein per pound of body weight per day.) There are many plant sources that can help vegans meet their protein needs, including peas, beans, lentils, chickpeas, seeds, nuts, soy products, and whole grains (for example, wheat, oats, barley, and brown rice). Vegetarians used to be told that they had to combine “complementary” plant proteins (rice with beans, for example) at every meal to get all the amino acids contained in meat protein. Now, health experts say that such rigid planning is unnecessary. According to the American Dietetic Association, eating a wide variety of protein sources every day is sufficient.

Vitamin B12. Vitamin B12 is found only in animal products, but those products include dairy foods and eggs, so most vegetarians get all they need. If you avoid animal products altogether, you should eat foods fortified with vitamin B12 (certain soy and rice beverages and breakfast cereals) or take a vitamin B12 supplement to avoid a deficiency, which can cause neurological problems and pernicious anemia.

Iron. Studies show that in Western countries, vegetarians tend to get the same amount of iron as meat eaters. But the iron in meat (especially red meat) is more readily absorbed than the kind found in plant foods, known as non-heme iron. The absorption of non-heme iron is enhanced by vitamin C and other acids found in fruits and vegetables, but it may be inhibited by the phytic acid in whole grains, beans, lentils, seeds, and nuts.

Zinc. Phytic acid in whole grains, seeds, beans, and legumes also reduces zinc absorption, but vegetarians in Western countries do not appear to be zinc-deficient.

Omega-3 fatty acids. Diets that include no fish or eggs are low in EPA and DHA. Our bodies can convert ALA in plant foods to EPA and DHA, but not very efficiently. Vegans can get DHA from algae supplements, which increase blood levels of DHA as well as EPA (by a process called retroversion). DHA-fortified breakfast bars and soy milk are also available. Official dietary guidelines recommend 1.10 grams per day of ALA for women, but vegetarians who consume little or no EPA and DHA should probably get more than that. Good ALA sources include flaxseed, walnuts, canola oil, and soy.

For more on eating for optimum health, buy the Harvard Special Health Report Healthy Eating: A guide to the new nutrition.

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