Average carbs in a day

Are Carbs Standing in the Way of Your Weight Loss?

There’s no question that obesity is a major problem in the United States, with about two-thirds of all adults weighing more than they should. In recent years, carbohydrates have shouldered much of the blame for our struggles with weight loss and eating a healthy diet.

The reality, however, is that a low carb diet is not the only factor when it comes to weight loss. Americans are eating about as many carbohydrates as the government recommends — the problem is the type of carbs we’re choosing.

Although the recommended daily allowance of carbohydrates is around 130 grams, that’s the absolute minimum amount that is recommended for brain function. In 2010, the government suggested that Americans get about 45 to 65 percent of their calories from carbohydrates. For a 2,000-calories-a-day diet, that’s about 275 grams of carbohydrates, which is right in line with what most people are eating.

“Americans are not eating too many carbohydrates. This is a fact and not my opinion,” says Mary Hartley, RD, director of nutrition for www.caloriecount.com. “An analysis of the most recent data from the National Health and Nutrition Examination Survey showed the average carbohydrate intake to be about 50 percent of total calories. The Acceptable Macronutrient Density Range for carbohydrates is 45 to 65 percent of total calories.”

However, though the amounts of carbohydrates for a healthy diet are about right, the kinds of carbohydrates are wrong.

Are You Eating the Right Carbohydrates?

Americans should be eating more unprocessed complex carbohydrates, such as fruits, vegetables, and whole grains, and less refined carbohydrates, such as packaged crackers, cookies, cereals, and breads.

These refined carbohydrates are certainly part of the reason that Americans have trouble with weight loss and a healthy diet. “My thoughts are that people eat too many calories and too much sugar, period,” Hartley says. “An upper limit of 10 percent of total calories should come from added sugar. On a 2,000-calories-a-day diet, that’s 50 grams (1 gram of carbohydrate is equal to 4 calories). To put it in perspective, a 12-ounce can of soda has 27 grams, and that’s not to mention the added sugar in yogurt, cereals, energy bars, syrups, salad dressing, and other sources.”

While eating the wrong carbohydrates is part of the problem, it’s not the only stumbling block to weight loss. “The issue is that we consume too many calories for the amount of activity (calories burned) we expend each day, and the quality of those calories is not very good,” says Timothy S. Harlan, MD, medical director of the Tulane University Medical Group in New Orleans and author of Just Tell Me What to Eat.

To put it another way, adds Dr. Harlan, Americans are just eating too much to promote weight loss and a healthy diet, plain and simple. “The most recent and reliable data puts the average calorie availability in the United States at around 3,700 calories per day,” he says. “This is a lot considering that the average American female needs about 1,500 calories and males need 2,000 calories per day.”

Weight-Loss Help From Complex Carbs

Considering all this, the answer to weight loss may not necessarily be a low carb diet. Instead, it might be to eat the correct type of carbohydrates — complex carbohydrates rather than refined carbohydrates.

“Of an average intake of 250 grams of carbohydrates on a 2,000-calorie-a-day diet, at least 125 grams should come from whole grains, such as foods made from whole-wheat flour (bread, cereal, pasta), bulgur (tabouli), oatmeal, brown rice, whole corn meal (tortillas), popcorn, barley, and the novelty grains such as amaranth and millet,” Hartley says. “However, this intake amount can vary per person.”

And when it comes to carbs and weight loss, one critical factor is to choose carbohydrate sources with plenty of fiber. Hartley adds that, “the recommendation is to eat at least 14 grams of dietary fiber for every 1,000 calories consumed. You’ll find dietary fiber in whole grains and also in fresh fruit and vegetables — in peels, seeds, stalks, leaves, roots, and pulp; in dried fruit, dried beans, and legumes; and in all seeds.”

TUESDAY, Sept. 24, 2019 (HealthDay News) — Decades into the obesity epidemic, Americans are still eating far too much sugar, starch and saturated fat, a new report claims.

Since 1999, Americans have cut down a bit on “low-quality” carbs, like heavily processed grains and snack foods with added sugar. But that amounts to only a 3% drop overall, the researchers found.

And Americans have made little headway in boosting their intake of “high-quality” carbohydrates — like beans, fiber-rich whole grains, fruit and vegetables other than potatoes: Consumption rose by only 1% between 1999 and 2016.

Meanwhile, total fat intake rose by the same amount, but half was from saturated fat — which comes mainly from meat and full-fat dairy products. Americans today typically get 12% of their daily calories from saturated fat, the study found. That’s above the 10% recommended limit.

The study cannot answer any “why” questions, according to senior researcher Dr. Fang Fang Zhang, an associate professor at Tufts University Friedman School of Nutrition Science and Policy, in Boston.

But Americans’ reliance on processed foods and take-out is a likely culprit.

“Our study shows that Americans are eating a lot of low-quality carbohydrates from refined grains and added sugars — 42 percent ,” Zhang said.

“That’s a lot of calories without many nutrients,” she added. “It’s reasonable to say that’s partially related to convenience foods.”

The findings, reported in the Sept. 24 issue of the Journal of the American Medical Association, are based on a long-running government nutrition survey. Between 1999 and 2016, nearly 44,000 Americans were interviewed about their eating habits.

Over those years, Zhang’s team found, people reduced their total carb intake from an average of 52.5% of daily calories, to 50.5%. At the same time, protein and fat intake inched up.

But there was not much improvement in the national appetite for healthy carbs. And consumption of plant proteins — like nuts and beans — barely budged, from about 5.4% of calories, to 5.8%, the findings showed.

On balance, Americans still seem to love their meat and potatoes.

Chapter 2 Shifts Needed To Align With Healthy Eating Patterns

Current Eating Patterns in the United States

The typical eating patterns currently consumed by many in the United States do not align with the Dietary Guidelines. As shown in Figure 2-1, when compared to the Healthy U.S.-Style Pattern:

  • About three-fourths of the population has an eating pattern that is low in vegetables, fruits, dairy, and oils.
  • More than half of the population is meeting or exceeding total grain and total protein foods recommendations, but, as discussed later in the chapter, are not meeting the recommendations for the subgroups within each of these food groups.
  • Most Americans exceed the recommendations for added sugars, saturated fats, and sodium.

In addition, the eating patterns of many are too high in calories. Calorie intake over time, in comparison to calorie needs, is best evaluated by measuring body weight status. The high percentage of the population that is overweight or obese suggests that many in the United States overconsume calories. As documented in the Introduction, Table I-1, more than two-thirds of all adults and nearly one-third of all children and youth in the United States are either overweight or obese.

Figure 2-1. Dietary Intakes Compared to Recommendations. Percent of the U.S. Population Ages 1 Year and Older Who Are Below, At, or Above Each Dietary Goal or Limit

Read text description of Figure 2-1

Figure 2-1 is a bar graph indicating the percentage of the U.S. population ages 1 year and older with intakes below the recommendation or above the limit for different food groups and dietary components.

Vegetables: 87% have intakes below the goal;
Fruit: 75% have intakes below the goal;
Total Grains: 44% have intakes below the goal;
Dairy: 86% have intakes below the goal;
Protein Foods: 42% have intakes below the goal;
Oils: 72% have intakes below the goal;
Added sugars: 70% have intakes above the limit;
Saturated fats: 71% have intakes above the limit;
Sodium: 89% have intakes above the limit.

Note: The center (0) line is the goal or limit. For most, those represented by the orange sections of the bars, shifting toward the center line will improve their eating pattern.

Data Sources: What We Eat in America, NHANES 2007-2010 for average intakes by age-sex group. Healthy U.S.-Style Food Patterns, which vary based on age, sex, and activity level, for recommended intakes and limits.

Current eating patterns can be moved toward healthier eating patterns by making shifts in food choices over time. Making these shifts can help support a healthy body weight, meet nutrient needs, and lessen the risk for chronic disease.

The following sections highlight average intakes of the food groups and other dietary components for age-sex groups and show that, in some cases, individuals are close to meeting recommendations, but in others, more substantial change is needed. They also provide examples of foods commonly consumed. Understanding what current intakes are and how food groups and other dietary components are consumed can help inform shifts that are needed to support healthy eating patterns.

In this chapter, intakes of food groups and other dietary components are described in two ways: (1) the total amount consumed from all sources in comparison to recommendations or limits, and (2) the proportion of this intake that comes from different food categories based on the form in which foods are eaten—such as soups, sandwiches, or burritos. The What We Eat in American (WWEIA) Food Categories provide insight into the sources of food group and nutrient intakes and are therefore useful in identifying strategies to improve eating patterns.

Figure 2-2. Empower People To Make Healthy Shifts

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Making changes to eating patterns can be overwhelming. That’s why it’s important to emphasize that every food choice is an opportunity to move toward a healthy eating pattern. Small shifts in food choices—over the course of a week, a day, or even a meal—can make a big difference. Here are some ideas for realistic, small shifts that can help people adopt healthy eating patterns.

  • High Calorie Snacks

    Nutrient-Dense Snacks

  • Fruit Products with Added Sugars


  • Refined


  • Snacks with Added Sugars

    Unsalted Snacks

  • Solid Fats


  • Beverages with Added Sugars

    Added Beverages

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Changing Physical Activity Patterns for a Healthy Lifestyle


Current physical activity: Only 20 percent of adults meet the Physical Activity Guidelines for aerobic and muscle-strengthening activity. Males are more likely to report doing regular physical activity compared to females (24% of males versus 17% of females meet recommendations), and this difference is more pronounced between adolescent boys and girls (30% of males versus 13% of females meet recommendations). Despite evidence that increments of physical activity as short as 10 minutes at a time can be beneficial, about 30 percent of adults report engaging in no leisure time physical activity. Disparities also exist; individuals with lower income and those with lower educational attainment have lower rates of physical activity and are more likely to not engage in leisure time physical activity.

Overall, physical activity associated with work, home, and transportation has declined in recent decades and can be attributed to less active occupations; reduced physical activity for commuting to work, school, or for errands; and increased sedentary behavior often associated with television viewing and other forms of screen time.

Shift physical activity choices: Most individuals would benefit from making shifts to increase the amount of physical activity they engage in each week. Individuals would also benefit from limiting screen time and decreasing the amount of time spent being sedentary.


The What We Eat in America (WWEIA) Food Categories provide an application to analyze foods and beverages as consumed. Each of the food and beverage items that can be reported in WWEIA, National Health and Nutrition Examination Survey, are placed in one of the mutually exclusive food categories. More information about the WWEIA Food Categories is available at http://www.ars.usda.gov/Services/docs.htm?docid=23429. Accessed November 25, 2015.

How Many Carbs Should You Eat In a Day?

Photo: Eric Savage / Getty Images

Culturally, we’ve swung from extreme fat-phobia (when I was growing up in the ’90s, avocados were considered “fattening” and fat-free cookies were the “guilt-free” holy grail) to a fixation on the high-fat, low-carb keto diet. The keto diet was initially introduced as a treatment for drug-resistant epilepsy in the 1920s-and is still used for this purpose today. But now it’s also being touted as a weight-loss diet.

I get a lot of questions about carbohydrates from my nutrition clients: Are they bad? Are they good? Somewhere in the middle? Read on to learn more.

What are carbs?

First, meet the macronutrients: carbs, fats, and protein. The primary purpose of carbs is to give you energy. (FYI: Fat is used for energy, too. But it also protects organs, keeps you warm, and supports hormone production and cell growth. Protein provides structure for your cells and tissues and is used for the function and regulation of numerous body processes.) Most of the carbohydrates you eat are broken down by the digestive system into glucose, which is then used as energy to fuel your cells, tissues, and organs. Carbs can also be stored-so to speak-as fat cells for later use. (That’s why some people practice carb backloading.)

Tons of foods contain carbs. There are more obvious ones like bread, oats, and rice, or sweets like cake, cookies, pastries, candy, and chips. But beans and lentils, fruit and fruit juice, milk and dairy products, and even vegetables like potatoes, peas, and corn have carbs.(All vegetables contain some carbs, but starchy veggies have about 15 grams per serving vs. 5 grams or less for non-starchy veggies.)

Carbs are made up of fiber, starch, and sugar. There are four calories per gram of carbohydrate. You’ll often hear about “simple” carbs and “complex” carbs.

  • Simple carbs are the sugar-both the naturally occurring sugar present in foods and sugar that is added to foods. Some common examples of simple carbs are sugar-sweetened beverages, candy, white flour products, and fruit juice. Many studies have linked a high intake of simple carbs to health issues such as obesity, diabetes, and heart disease. Simple carbs are what you want to cut back on.
  • Complex carbs are generally higher in fiber and digest more slowly. Some common examples are whole grains, beans and legumes, vegetables, and whole fruit. (More on that: The Healthy Woman’s Guide to Eating Carbs-Which Doesn’t Involve Cutting Them)

When you eat carbs, your blood glucose (blood sugar) rises. Consuming foods that contain protein and/or fat at the same time slows the rate at which that breakdown occurs, which helps maintain a more steady blood sugar level rather than causing a sharp spike then crash. Fiber also helps slow that digestive process. That’s why whole foods-which naturally contain a balance of protein, fat, and fiber-are ideal.

What “counts” as a carb serving?

A serving of carbohydrate is equivalent to about 15 grams. These amounts of food each contain around 15 grams of carbs (in addition to their other components):

  • 1/3 to 1/2 cup cooked grain
  • 1 slice bread
  • 1/3 to 1/2 cup cooked pasta
  • 1/3 to 1/2 cup cooked (or 1/4 cup dry) beans, peas, or lentils
  • 1/2 cup cooked potatoes or corn
  • 1/2 of a medium baked potato or sweet potato
  • 1 cup cooked pumpkin or winter squash
  • 3/4 to 1 cup of berries
  • 1/2 of a 9-inch banana
  • 1 small apple or pear
  • 1/4 cup dried fruit
  • 1/2 cup fruit juice
  • Each serving of milk product usually provides about 12 to 15 grams (though strained Greek and Icelandic yogurts often have a smaller amount, around 8 per cup)

How many carbs should you eat per day?

“It depends” is not an exciting answer. But how many carbohydrates you need per day really does have a lot to do with your unique makeup-as well as factors like activity level, whether you have any underlying medical conditions, or are pregnant or breastfeeding. Your needs can also fluctuate. (Here’s everything you should know about carb cycling.)

For one, you may notice that you need different amounts of carbohydrate at different points in your cycle or during certain times of the year. People with seasonal affective disorder (SAD) may gravitate more toward carbohydrate-rich foods in the darker months since levels of the mood-regulating neurotransmitter serotonin take a dip and carb intake plays a role in serotonin production. This need to stabilize serotonin levels is also why you might crave carbs on a tough day or after a breakup.

Different diet plans require different ratios of carbs to fats to protein. The 2015–2020 Dietary Guidelines for Americans recommend consuming 45 to 65 percent of our daily calories as carbohydrate. To give you a ballpark figure, on a 2,000-calorie diet, that’s anywhere from 225 to 325 grams. The recommended minimum amount of carbohydrate per day (according to these guidelines) is 130 grams-about eight or nine 15-gram servings of carbohydrate per day.

As a frame of reference, low-carb diets (such as Atkins or the LCHF diet) generally include anywhere from 20 to 100 grams of carbohydrate per day. The ketogenic diet is a very low-carb diet (~10 percent of total calories coming from carbs) with moderate amounts of protein (~20 percent) and high fat (~70 percent). For someone on a 2,000-calorie diet, that’s only about 20 grams of carbs per day-about the size of a large slice of bread. If that sounds really low, you’re right: It is.

Sometimes I see clients get down on themselves for not being able to stay on the bandwagon with whatever diet is trending. But often your body fights extreme plans because it’s trying to tell you something. Enjoying an eating pattern that feels right for you and allows you to be flexible in the context of real life is something that you’ll actually be able to stick with for the long haul-even as the fads come and go. (See: Why You Should Consider Ditching Restrictive Dieting)

If you want to eat a low-carb diet and track your macronutrients (and if your health-care provider feels it’s safe for you), you can tweak your ratio of carbs to protein to fat until you find what feels sustainable and enjoyable while still allowing you to meet your goals. That said, if you feel yourself starting to overthink it, have a history of disordered eating, or struggle with establishing a healthy balance with food, working with a registered dietitian can help you make changes while ensuring you have the support you need to avoid kicking up dust from past issues or making you feel overwhelmed.

How do you know if you’ve struck the right macronutrient balance?

Consuming too little carbohydrate can make you feel sluggish and mentally tired. You may also find yourself feeling irritable or struggling to “keep it together” emotionally. Some people may also feel really hungry when they’re not eating enough carbohydrates. Because many carb-rich foods are also good sources of fiber, digestive discomfort like constipation is a common issue with inadequate carb intake. (That’s why constipation on the keto diet is a real issue.) Make sure you’re still hitting that daily goal of 25 to 35 grams of fiber and drinking plenty of water to keep things moving.

Consuming too much carbohydrate relative to protein and fat may cause you to feel like you have a hard time staying full, as you burn through meals and snacks quickly, causing a sharp spike in blood glucose, followed by a crash. Over time, constantly riding this “blood sugar roller coaster” could lead to prediabetes or insulin resistance.

No, but really, how many grams of carbs should you have?

As a jumping-off point, I generally recommend having a source of carbs at each of your meals. Whether you get it from grains, legumes, starchy veggies, fruit, or dairy is up to you. To help you stay in balance without overthinking, fill half your lunch or dinner plate with non-starchy veggies, a quarter with protein, and the last quarter with carbohydrate. Spreading your carbs out consistently over the course of the day can also help with keeping your blood sugar stable, which supports continuous energy and balanced mood levels.

Here are some examples of meals and snacks that, when you choose one from each category, provide the minimum 130 grams of carbs. If you need more, of course, listen to what your body is asking for and incorporate additional carbs where it makes sense for you. (Related: How to Lose Weight Without Giving Up Carbs, According to Bob Harper)

Breakfast Ideas

Lunch Ideas

  • Spinach salad with 1/2 cup chickpeas (22 grams), 1 cup cherry tomatoes (5 grams), and 1/2 cup grated carrots (5 grams), with olive oil and vinegar dressing
  • Nut butter sandwich on two slices of whole-grain bread (30 grams) and side of 1 cup baby carrots (7 grams) with salsa
  • 1.5 cups minestrone soup (~30 grams) and a small whole-wheat roll (15 grams)

Dinner Ideas

  • 1 cup whole-wheat or bean-based pasta (32 to 40 grams) with 3 oz cooked chicken and 1 cup broccoli (5 grams)
  • 1 cup vegetarian chili (~30 grams) with 1 cup cauliflower rice (5 grams) or 1/3 cup brown rice (15 grams)
  • 3 oz baked fish with 1/2 cup baked sweet potato (15 grams) and 1 cup cooked greens (5 grams); 1 cup berries (~15 grams) for dessert

Snack Ideas

  • 3 cups air-popped popcorn (~15 grams)
  • 1 small apple (~15 grams) with 1 tablespoon nut butter
  • 2 tablespoons hummus (5 grams) and 1 oz whole-grain crackers (15 grams)

Nearly all Americans fail to eat enough of this actual superfood

When we fret about the deterioration of the American diet, we tend to focus on the excessive amounts of sugar, salt, and calories we’re now eating.

What we don’t talk about: an important ingredient that’s gone missing as we’ve been filling our plates with more chicken and cheese.

Fiber. Only 5 percent of people in the US meet the Institute of Medicine’s recommended daily target of 25 grams for women and 38 grams for men. That amounts to a population-wide deficiency — what nutritionists call the “fiber gap.”

“People are so busy avoiding carbs, they forget that these foods give important dietary components,” said nutritionist Julie Jones, of St. Catherine University.

Fiber is the closest thing we have to a true superfood — or super-nutrient since it’s a part of so many different foods. Eating a fiber-rich diet is associated with better gastrointestinal health and a reduced risk of heart attacks, strokes, high cholesterol, obesity, type 2 diabetes, even some cancers. That’s because fiber is amazingly helpful in many ways: It slows the absorption of glucose — which evens out our blood sugar levels — and also lowers cholesterol and inflammation.

These benefits grow the more fiber people eat. In a recent Lancet review of 185 studies and 58 clinical trials, researchers found that if 1,000 people transitioned from a low-fiber diet (under 15 grams per day) to a high-fiber diet (25 to 29 grams per day), they’d prevent 13 deaths and six cases of heart disease. (Some researchers have described not eating high-fiber carbohydrates as “the opportunity cost” of the ultra low-carb ketogenic diet.)

If fiber were a drug, we’d be all over it. But the average American gets just 16 grams per day — half of what we should be eating.

A big reason for that has to do with what we now eat. Instead of munching on fruits, vegetables, beans, nuts, and seeds, more than half of the calories Americans consume come from ultra-processed foods. On any given day, nearly 40 percent of Americans eat fast food. These prepared and processed meals tend to be low in fiber, or even fiber free. (A cup of cooked oatmeal has 4 grams of fiber and a pear has 6 grams, while a McDonald’s hamburger has one gram and soda has none.)

This pattern of eating is not just leading to weight gain and obesity-related health issues; it’s hurting our gastrointestinal health in ways researchers are only beginning to understand. That’s because fiber’s benefits are a lot more complicated than our prune-peddling moms and grandmothers appreciated.

Fiber doesn’t just help us poop better — it also nourishes our gut microbiome. The science, while still pretty nascent, is fascinating and it points to the fact that the fiber gap may be even more damaging than we’ve realized.

There are many different types of fiber — and they do different things in our guts

To think of fiber as just Metamucil and bran cereal is to do its complexity a disservice.

Fiber (or “fibers,” as the researchers who study it say) is a group of different kinds of plant-based carbohydrates that affect our gastrointestinal tract in myriad ways. The big difference between fiber and other carbs, like starches and sugar, is that we can’t directly digest or absorb it. And some fiber types can only be broken down by the gut microbiome, the ecology of trillions of diverse bacteria lining our intestines and colon.

Scientists have learned over the years that fiber can be soluble (meaning it dissolves in water), viscose (gel-forming), or fermentable (bacteria can metabolize it) — and they’re just beginning to understand how these different fiber types interact with our gastrointestinal tract and affect our health.

Take cellulose, a type of fiber in fruits and vegetables: it’s insoluble and it’s not fermentable. Hemicellulose, found in bran, can’t be dissolved in water and it’s not gel-forming (viscous) but it is fermentable. Psyllium, in Metamucil, is water soluble, gel-forming and less fermentable than other fibers. There’s also another class, known as “functional fiber”: industrially processed but natural fibers (such as inulin or fructan) and synthetic fibers (such as polycarbophil), all of which can be added to foods and supplements.

Understanding this variety is relevant to our health because different fibers have different health effects on our gastrointestinal tract, said William Chey, a professor of gastroenterology and nutrition at the University of Michigan. Gel-forming fibers like psyllium, for example, hold on to water. So if your stool is hard, they can help soften it, Chey said. “If your stool is too loose, the water-absorbing capacity can add form.”

Fermentability is also important, he explained, because it reflects whether the gut microbiome views fiber as a food source or not. Fermentable fibers can exacerbate gas and bloating, so people who experience those symptoms might want to adjust their intake. Researchers have demonstrated that a low FODMAP diet — which limits fermentable foods, including fibers such as fructan — can alleviate irritable bowel syndrome.

“Most doctors and people think all fiber is created equal,” Chey added. “But different types of fiber have different properties in the gut, especially as it pertains to the microbiome.”

Most humans have evolved to eat lots of fiber

The second thing to know about fiber is that humans evolved to eat it — a lot of it. Long before we learned to cook, domesticate animals, and put McDonald’s on every corner, our evolutionary cousins — such as chimps and bonobos — followed frugivore diets, subsisting mainly on fiber-heavy fruits, roots, shoots, nuts, and seeds. There’s also ample evidence that early humans went to great lengths to eat fiber-rich carbohydrates, such as oats and acorns.

Today, studies of Tanzania’s Hadza people, one of the few remaining hunter-gatherer groups on the planet, are a useful model for understanding just how much fiber early humans probably ate. Tribe members consume 100 to 150 fiber grams per day — enough to fill some 50 bowls of Cheerios, and 10 times what Americans take in, as NPR reported. Their daily diet is rich in roughage — tubers, berries, baobab fruits — and the Hadza people don’t eat any ultra-processed foods.

Researchers who study the health effects of fiber, including Jens Walter at the University of Alberta, say the Hadza’s enthusiasm for roughage should remind us of how much the human diet has shifted away from fiber.

“It’s really just within the last 5,000 years, and definitely within the last 100 years, that we basically took all the fiber away,” he said. “The average amount of fiber consumed by now is a small fraction to what we evolved with.” (Caveat: There are human communities — like the Inuit in Greenland — who’ve adapted to survive on meat-heavy diets without many plants, but they’re outliers.)

This change isn’t just attributable to the advent of fiber-free processed and fast foods in advanced economies. More than 10,000 years ago, before agriculture and selective plant breeding, early fruits and vegetables were almost unrecognizable by today’s standards.

Generation after generation of farmers have since bred them to be bigger and tastier — in many cases increasing their sugar content and stripping them of fiber. Milling, meanwhile, cleared the whole-grain fractions out of our bread and bakery products, which were a major fiber source, Walter said. And meat replaced fibrous beans and lentils as the main source of protein in many parts of the world. Researchers are now documenting the health impacts of that change.

Why fiber is good for our gut

Because our intestines can’t directly digest fiber, we’ve long seen fiber as beneficial for relieving constipation by adding bulk to stool and promoting regular bowel movements.

Another commonly touted fiber benefit: It can help us feel full, so we eat less and maybe even lose weight. (There’s some debate about fiber’s effect on satiety and appetite. The most recent systematic reviews of the research suggest fiber’s impact here is surprisingly modest, though others note that many studies have focused on supplements instead of whole foods, which are probably more satiating.)

Still, all this “was before people how much the non-digestible things we eat impact our gut bacteria,” said University of Michigan microbiologist Eric Martens.

Researchers now consider fiber’s role in nourishing our gut microbiome — the ecosystem of microbes in our intestines — to be one of its main health benefits. They don’t yet fully understand why fiber is so good for our gut, but they have some ideas.

Fermentable fibers — which include all soluble fibers and some insoluble fibers — are metabolized or fermented by bacteria in the gastrointestinal tract. That process produces chemicals, including short-chain fatty acids, which are important food sources for our gut bacteria.

They also carry health benefits, Martens said. Short-chain fatty acids have been shown to promote insulin production, so we can better manage the spikes of sugar (or glucose) in our blood, for example, helping to manage type 2 diabetes. In addition, they seem to have anti-inflammatory properties.

“When we don’t consume enough fiber, we are essentially starving our gut microbiome,” said Alberta’s Jens Walter, “which is likely detrimental for a variety of reasons. We also probably lose diversity.”

Andrew Gewirtz of Georgia State University was among the researchers who noticed that mice develop metabolic syndrome — obesity and its associated disorders, such as diabetes and high cholesterol — when they are fed a high-fat diet. But when fiber was added to the high-fat diet, most of that metabolic syndrome went away.

“We realized the fiber is very important for our metabolic parameters,” Gewirtz told Vox. So he decided to compare the microbiomes of mice on a fiber-enriched high-fat diet with mice on a low-fiber high-fat diet, to figure out what they might reveal about why extra fiber seemed to offset the health harms of dietary fat. And he found the two sets of mice wound up having really different microbiomes: Rodents on the low-fiber diet had a marked reduction in the total numbers of bacteria in their gut and a less diverse microbiome compared to the mice on the high-fiber diet.

That lack of diversity might have negative health effects — one of them to do with the mucus layer in the gut. Mucus acts as a protective barrier between us and the outside world. It’s constantly being replenished by secretions from the cells that make up our intestines, and it’s covered with a layer of bacteria, part of our microbiome. Fiber feeds the bacteria on top of the mucus layer as it passes through, helping to keep our microbiomes robust, Gewirtz said.

Another fiber study — again in mice — showed what happens when the bacteria in the digestive tract don’t get any fiber. Researchers, including Martens, found the bacteria begin to eat away at the mucus layer, bringing them into closer contact with the intestinal tissue.

“The hypothesis is if we stop feeding the microbiome , the bacteria will resort more frequently to digesting that mucus barrier as a source of nutrients.”

If bacteria eating up the mucus layer sounds bad, well, it is. The mucus layer keeps pathogens out, and the researchers were able to show that if they introduced a pathogen in the context of a low-fiber diet, it had an easier time getting into the intestine and causing an infection. “The lack of a mucus barrier made the disease get much worse much quicker,” Martens added. “It may irritate the tissue or provoke immune responses,” leaving the mice more vulnerable to disease.

While it’s not yet clear how or whether these findings will translate to people, researchers know that altering the fiber in one’s diet creates changes in the human microbiome.

And for now, this science shows us that we should start thinking about fiber differently, Gewirtz said. The exclusive focus on fiber’s constipation-fighting properties misses the big picture: “It’s just one thing that fiber does” and maybe not as important as fiber’s impact on our microbiome.

Christina Animashaun/Vox

Only five percent of Americans meet the recommended fiber target — and that means most miss out on fiber’s benefits. So how can you eat more fiber? Every researcher I spoke to suggested aiming to get a diversity of fiber from a varied menu of whole foods, instead of relying only on supplements or fiber-enriched processed foods, especially the sugary bars and brownies now being marketed as fiber-delivery tools.

To do that, consider snacking on whole fruits, replacing white bread with whole-grain alternatives, eating potatoes with the skins on, and tossing berries, nuts, and seeds on your yogurt, cereals, or salads, Hannah Holscher, an assistant professor of nutrition at the University of Illinois, suggested. “Lots of small changes can add up.”

If you like smoothies, throw your fruits, veggies, and nuts in a blender. Contrary to the hype about smoothies degrading fiber, some of the researchers I spoke to actually encouraged this approach. “Even baking does not destroy most fibers,” Walter said.

“ natural sources are probably better for both your digestive health and your microbiome. They’re more diverse from the chemical level,” Martens added. “If you can get 25 to 30 grams per day from beans, nuts, vegetables and fruits, and whole grains — that’s a good place to start.”

What a fiber-rich dinner looks like. Andrew Reynolds

Andrew Reynolds, a diabetes and obesity researcher at New Zealand’s University of Otago (and the lead author on that recent Lancet review of fiber’s benefits), laid out what meeting one’s fiber target might look like in a meal plan. He tracked what he ate on a recent day.

Two slices chunky wholegrain toast with apricot jam: 5 grams fiber
Two cups of black coffee: 0 fiber
1 small apple: 2 grams fiber

Red beans and brown rice with salsa verde and hot sauce: 7 grams fiber
Large handful of unsalted peanuts: 2 grams fiber
2 cups tea with low fat milk: 0 fiber
1 carrot, raw: 2 grams fiber
2 small prunes:​ 1.5 grams fiber
Two cups of black coffee: 0 fiber

1 wholemeal Turkish pide bread: 2.5 grams fiber
2 cups of kale and white bean salad with tahini dressing: 8 grams fiber
1/3 eggplant with yoghurt dressing and pomegranate: 2 grams fiber
1 cob of corn: 2 grams fiber
2 lamb meatballs in 1 cup fennel/tomato sauce: 4 grams fiber
1 glass white wine: 0 fiber

Reynolds consumed 38 grams of fiber, the recommended target for adult men. But he also advised that people shouldn’t obsess about meeting fiber targets. “Any increase in fiber is good for you, especially for those on a low-fiber diet.”

For many Americans, upping the fiber intake may be easier said than done. The reasons people aren’t eating fiber look a like like the reasons they’re not following a healthy diet generally. “ a perceived lack of time to prepare meals at home, eating out more, knowledge about how to prepare different high-fiber foods … in a way that tastes good,” Holscher explained.

Some high-fiber foods — like fresh produce and nuts — also cost more than lower-fiber alternatives, such as sweets or soda. And even though grains, beans and lentils come cheap, they’re not always convenient to prepare. So maybe the solution to the fiber gap is making fiber cool, and as cheap and easy to eat as hamburger.

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