3 benefits of fiber

Ms. Terrie is a clinical pharmacy writer based in Haymarket, Virginia.
Daily intake of an adequate amount of dietary fiber is the most common recommendation for the prevention and treatment of constipation and has an important role in the maintenance of normal bowel function.1 Results from various studies have demonstrated that adequate fiber intake has many additional health benefits and may prevent or decrease an individual’s risk of developing coronary disease, stroke, hypertension, diabetes, obesity, and colon cancer.2-5 Increased fiber intake may also lower serum cholesterol levels and be of benefit in gastrointestinal disorders, such as gastroesophageal reflux disease, duodenal ulcer, diverticulitis, and hemorrhoids.2,3 Studies also indicate that adequate intake of soluble fiber may promote better glycemic management for patients with diabetes.3-5 Other health benefits of adequate fiber intake include improved management of irritable bowel syndrome, promotion of weight loss, and restoration of regularity for individuals on low-carbohydrate diets.3-5
Current Recommended Daily Intake of Fiber
An estimated 95% of Americans do not get enough fiber in their diets and fail to meet the recommended daily intake.6 Obtaining dietary fiber through eating fruits, vegetables, whole grains, legumes, and beans is considered the ideal option; however, many individuals may find it difficult to do so through dietary means alone. Therefore, they may elect to take various fiber supplements, also known as bulk-forming laxatives, to meet their daily fiber intake requirement as well as to help maintain normal bowel function and prevent or decrease episodes of constipation. In general, the typical American diet includes an average daily intake of 14 to 15 g of fiber. According to the recommendations of the American Dietetic Association, healthy adults should ideally have a daily intake of 25 to 30 g of dietary fiber, and children older than 2 years should have a daily intake equal to their age plus 5 g.2
According to the National Academy of Sciences Institute of Medicine (IOM), the recommended intake of total fiber for adults 50 years and younger is 38 g for men and 25 g for women. For men and women older than 50 years, the recommended intake of fiber is 30 and 21 g per day, respectively, because of the decreased food consumption common in older individuals. 7 The IOM also recommends that individuals should consume at least 14 g of fiber for every 1000 calories.2,5 The American Heart Association recommends that at least 50% of daily grain intake come from whole-grain food sources.4 Dietary fiber can be divided into 2 basic categories: soluble and insoluble.5,6 Characteristics of these types of fiber are outlined in the Table.5,8

Fiber Supplements
A variety of fiber supplements containing active ingredients, such as wheat dextrin, methylcellulose, psyllium husk, inulin, and calcium polycarbophil, are available. Pharmacists can assist patients in the proper selection of fiber supplements as well as provide the necessary information for using these products appropriately. Fiber supplements come in a variety of dosage formulations, including sugar-free, taste-free, and fruit-flavored versions in the form of shakes, caplets, chewable tablets, capsules, wafers, and dissolvable powders. Many powder formulations can be mixed with 4 to 8 oz of water or noncarbonated beverage or mixed into soft foods, such as applesauce. Some fiber supplements contain vitamins, calcium, and other minerals as well.
The use of certain pharmacologic agents, such as anticonvulsants, antidepressants, and analgesics, may be associated with constipation; therefore, pharmacists are in a pivotal position to identify and inform those patients at risk, encouraging patients to discuss the issue with their physician. Constipation is common among older patients for a variety of reasons, including adverse drug effects, decreased intestinal motility, decreased dietary intake, and dehydration. Fiber supplements are often used to treat or prevent constipation in this population.9
Optimizing Administration of Fiber Products
Patients should be reminded to gradually increase fiber intake over several weeks to avoid or reduce the incidence of adverse effects, such as intestinal flatulence, bloating, diarrhea, and cramping. If possible, patients should also increase water intake, because inadequate fluid intake can reduce the effectiveness of fiber products and may cause intestinal or esophageal obstruction. 1 Many manufacturers of fiber supplements have reminders on the product label that recommend taking fiber supplements with 8 oz of water to avoid choking.1,10-12 Patients with comorbidities that require restricting fluid intake, such as significant renal dysfunction or congestive heart failure,3 or those taking additional agents for other medical conditions, should be advised to discuss these supplements with their primary health care provider before initiating use.
Patients with intestinal ulcerations, stenosis, or disabling adhesions should avoid fiber supplements because of the possibility of fecal impaction or intestinal obstruction.1 Fiber supplements can decrease the absorption of many drugs; thus patients should be advised to avoid ingesting these supplements within 1 to 2 hours of taking other medications and to report any concerns to their physicians.1 The use of fiber supplements should never be a substitute for a fiber-rich diet containing the essential vitamins and minerals necessary for optimal health. It is important to remind patients to try to obtain most of their daily intake of fiber through dietary means. â–

2. Marlett J, McBurney MI, Slavin JL, for the American Dietetic Association. Position of the American Dietetic Association: health implications of dietary fiber. J Am Diet Assoc. 2002;102(7):993-1000.

3. Anderson JW, Baird P, Davis RH Jr, et al. Health benefits of dietary fiber. Nutr Rev. 2009;67(4):188-205.

7. Trumbo P, Schlicker S, Yates AA, Poos M, for the Food and Nutrition Board of the Institute of Medicine, The National Academies. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids. J Am Diet Assoc. 2002;102(11):1621-1630.

9. Bouras EP, Tangalos EG. Chronic constipation in the elderly. Gastroenterol Clin North Am. 2009;38(3):463-480.

10. Metamucil product information. Proctor & Gamble Web site. Available at: www.metamucil.com. Accessed October 29, 2009.

11. Fibercon product information. Wyeth Consumer Healthcare Web site. Available at: www.fibercon.com. Accessed October 29, 2009.

US Pharm. 2006;6:20-28.
Fiber is one of the most misunderstood dietary components. Most people do not know how much fiber should be ingested daily and which foods and supplements offer the best choices for fiber. Pharmacists can provide information and products to help educate and assist their patients in obtaining adequate intake of fiber.
Daily Fiber Recommendations
The average American has a daily fiber intake of only 14 to 15 g. The daily recommendations for fiber intake are higher than this, but they do vary slightly among population groups. For instance, the American Dietetic Association recommends an intake of 20 to 35 g for adults, 25 g daily for girls ages 9 through 18 years and 31 to 38 g for boys ages 9 through 18. 1,2 The American Heart Association recommends 25 to 30 g daily.3 In 1994, the Institute for Cancer Prevention simplified fiber intake guidelines for Americans as the “age + 5” rule.4 For children age 2 years and older, the rule is that children should consume a number of grams of fiber each day that equals their age plus 5 additional grams. Thus, a 7-year-old should consume 12 g of fiber daily for optimal health. This rule should be applied throughout adolescence until the person reaches age 20, when the adult guidelines should be used.
The Definition and Categories of Fiber
At one time, fiber was defined as any part of ingested plants that human enzymatic actions cannot digest, such as cell wall components (e.g., waxes, lignin, pectin, celluloses).5However, during the 1970s, the meaning of “fiber” gradually broadened to encompass and embrace a physiological definition that has greater use for the medical profession.5,6 The expanded definition of fiber now includes ingested materials that are not components of plant cells (e.g., noncellulose plant storage saccharides such as gums, modified celluloses, mucilages, oligosaccharides, and beta-glucans), although they are still resistant to degradation by human enzymes.7
Fibers are most usefully categorized for the medical professional on the basis of their inability to dissolve in water. 8 Fibers that do dissolve in water (e.g., celluloses, pectin, other cell wall components, as well as gums and psyllium) form gels, some of which have one or more health benefits. Found in such foods as wheat, rice, maize, leafy vegetables, peas, beans, and rhubarb, soluble fibers are able to sequester cholesterol and fats, facilitating their elimination. Fibers that do not dissolve in water bind water in the distal colon.9 Their sponge-like effect bulks stools and also binds various materials such as bile acids and carcinogens. Insoluble fibers are found in whole-grain cereals, breads, vegetables, and wheat bran.

Fiber’s Health Benefits

• Normalizing and Regulating Bowel Function: Through its OTC Review, the FDA evaluated fiber products for use in regulating bowel function. Several plant-derived bulk-forming fiber laxatives were found to be safe and effective–such as psyllium, malt soup extract, and bran. Bran and malt soup extract are not often marketed as nonprescription ingredients, but psyllium is widely available in a variety of dosage forms and options. The patient seeking a sugar-free psyllium product may use such products as Metamucil Sugar-Free Powder (3 g of dietary fiber per teaspoonful) or Konsyl Original Powder (6 g of psyllium per teaspoonful). Several non–plant-derived ingredients also were found safe and effective as bulking agents, including methylcellulose (e.g., Citrucel) and polycarbophil (e.g., FiberCon Caplets, Phillips’ FiberCaps, Konsyl Fiber Tablets).
A new fiber ingredient is being marketed in a product known as Fibersure. The product contains inulin-type fructans, chicory-derived carbohydrate polymers characterized by fructosyl– fructose linkages.10 The linkages do not allow digestion in the upper digestive tract. Thus, they are fermented in the colon, increasing the mass and water content of stools. Inulin-type fructans are known as “functional foods” and thus have not been evaluated by the FDA. Fiber supplementation is encouraged by physicians and nurses to treat and prevent constipation.11,12
Little is known about hydrolyzed guar gum, as found in Benefiber. The ingredient has not been approved by the FDA as a nonprescription ingredient but is being marketed as a dietary supplement. The National Academy of Sciences, in its Dietary Reference Intakes for Fiber, states that guar gum has “little effect on fecal bulk or laxation.” 13
• Weaning from Stimulants: The FDA considers seven days to be the safe time limit for use of laxatives without physician consultation. However, stimulant laxatives cause many patients to become habituated to them because of their nonphysiologic and drastic action; some patients might use laxatives for years once they become reliant on them. This practice can lead to changes in the colon that are carcinogenic and may result in death of colonic tissues located in the myenteric plexus. Patients should be urged to replace habitual use of stimulant laxatives with bulking agents. However, abrupt discontinuation in habitual laxative overusers may result in an inability to evacuate the bowels. The colon may not respond normally as a result of years of artificial stimulation. The patient may benefit from a gradual withdrawal. In this method, the pharmacist may recommend short-term stimulant use until the fiber begins to exert its own effect. A combination of a stimulant and fiber (e.g., SennaPrompt) might be useful for a 30-day period to boost colonic function and bridge the transition from stimulant addiction to natural facilitation of bowel movements with fiber. After that period, the goal should be permanent discontinuation of stimulants in favor of fiber intake.
• Lowering Cholesterol: The 1990 Nutrition Labeling and Education Act gave FDA authority to regulate health claims on food labels.14 As a result, manufacturers submitted research attempting to demonstrate the effect of various fibers on health. Two fibers have been proven safe and effective for the claims submitted. Beta-glucan soluble fiber from whole oats met the standard for reduction of risk from coronary heart disease.15,16 Psyllium husk is also able to reduce the risk of coronary heart disease as it contains a soluble fiber similar to beta-glucan. 17,18 Researchers quantified this outcome by determining the effect of psyllium (5 g three times daily) in lowering cholesterol as an adjunct to 10 mg of simvastatin, as compared to doubling the dose of simvastatin to 20 mg.19 They discovered that dietary supplementation with psyllium in patients taking 10 mg of simvastatin was as effective in lowering cholesterol as 20 mg of simvastatin alone. As a result of this research and FDA findings, pharmacists can recommend ingesting psyllium supplements daily to consumers who wish to attain regularity of bowel movements while simultaneously lowering their risk of coronary heart disease.
• Weight Reduction: The popular media has given ample coverage to the epidemic of obesity in America. Almost 100 million Americans are either obese or overweight.20 The figures climb each year, so that the toll of obesity will also continue to rise. Obesity has been linked to such morbid conditions as osteoarthritis in weight-bearing joints, type 2 diabetes, heart disease, cancer, and many other conditions. While hundreds of dietary supplements purported to be obesity cures are launched each year, the rising incidence of the condition attests to their inefficacy. The cure for obesity is actually quite simple. The overweight patient must eat less and exercise more, beginning immediately and continuing over the span of a lifetime.
Stomach distension (feeling full) signals a person to stop eating. It is in this area that fiber can yield lasting benefits through several mechanisms. Fiber is a bulky food, more difficult to digest than fatty foods, fried foods, and candies. Once ingested, fiber enhances satiety and prolongs satiation after a meal through distending the stomach and by prolonging retention of gastric contents.21 The stomach is distended after a fiber-containing meal because it promotes secretion of saliva and of gastric acids, both of which distend the stomach. Ingestion of fiber must be accompanied by water intake, which further serves to distend the stomach during a meal.22 Prolonging gastric retention decreases the absorption rate of nutrients, so that hunger does not return as rapidly.
Fiber also yields dietary benefit through energy displacement or energy dilution. A person who ingests little fiber in an average day usually has a diet of high-energy foods such as fats. However, the bulk that fiber adds to the diet makes it impossible to eat the same quantity of high-energy foods. Research bears this out. If a patient adds 14 g of fiber to the diet, energy intake will be reduced by approximately 10%.22 Further, observational studies of obese people and those who are thin confirm that thin people ingest more fiber and obese people ingest more high-fat foods.
Researchers explored the link between dietary fiber/fat intake and excess weight in young and middle-aged adults.21 They discovered that only 5% of the sample consumed adequate fiber. Further, in women, consumption of a low-fiber, high-fat diet was associated with the highest incidence of obesity when compared to those consuming a high-fiber, low-fat diet.
• Prevention of Colon Cancer: Fiber may help prevent colon cancer. The possible link stems from observational studies in the 1970s demonstrating that natives of Africa consuming high-fiber diets had reduced risk of colorectal carcinoma.23 Studies carried out to explore this link have been contradictory. Some seem to confirm a protective effect, but others show little to no effect.24 There is little risk to fiber consumption. Therefore, with no clearly negative data about fiber, it makes sense to increase fiber intake just in case the positive studies did reveal an actual link. The patient will also experience the ancillary benefits of fiber consumption, such as reduction in cholesterol (with psyllium), prevention of constipation, and reducing risk of hemorrhoids.
Fiber and the Glycemic Index
Fiber is especially beneficial in patients with diabetes. Investigators administered 5.1 g of psyllium as a meal supplement to patients with type 2 diabetes, finding that it reduced the postprandial glucose and insulin concentrations.25 They concluded that psyllium was safe, well tolerated, and improved glycemic control.

Is Taking Fiber Pills the Same as Eating a High-Fiber Diet?

Eating a higher-fiber diet is associated with a lower risk of heart disease, type 2 diabetes, and certain cancers, plus a lower body weight, greater satiety, and improved gut and digestive health. Yet it’s estimated that only about 10% of the population actually meets their daily recommended intake. This has triggered manufacturers to market more fiber-boosted foods, gummies, bars, and supplements than ever. But is reaping the benefits of a high-fiber diet as simple as hitting a daily quota of fiber grams through supplements and fortified products? I dug into the research to see if it really matters where your fiber comes from.

What Is Fiber?

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Fiber is a complex carbohydrate that the body can’t digest, meaning it doesn’t contribute calories or trigger an insulin response like other carbs. Dietary fiber is what gives plants structure (such as the stalk and florets in broccoli, or the peel on an apple). All plant foods such as vegetables, fruits, grains, seeds, and nuts contain some fiber, and most all are good sources. The Adequate Intake (AI) for fiber from the Institute of Medicine is 14g per 1000 calories. Since adults need more than 1000 calories per day, the simplified and more common recommendation is 25g/day for women and 38g/day for men.

What’s the Difference Between Fibers?

In the past, fibers were classified as either “soluble” or “insoluble”, based on their ability to absorb water. But with the increase of fiber-fortified foods and supplements on the market, fibers are now also referred to as dietary or functional, based on where the fiber in a food originates. Here’s a quick look at what the classifications mean and differences.

Soluble fibers: By absorbing water in the GI tract, soluble fibers slow the digestive process and create gels of different viscosities. It’s soluble fibers that research has linked to improvements in glycemic control and lower cholesterol.

Insoluble fibers: While they don’t absorb water, insoluble fibers play a key role in adding bulk to digestive contents. This bulk stimulates the digestive tract to regularly get rid of waste product, which is why most insoluble fibers are associated with preventing or alleviating constipation.

Dietary (intact) fibers: These are fibers that are naturally occurring in food, like the fiber that a pear or brown rice provides. Dietary fiber is made of a variety of different soluble and insoluble fibers.

Functional fibers: These are fibers used in supplements and added to foods during processing. Unlike the dietary fiber makeup in foods, functional fibers usually consist of a single, isolated type of either soluble or insoluble fiber. Foods may contain both dietary and functional fibers if functional ones are added during processing.

Does Where You Get Your Fiber From Really Matter?

Yes, and research suggests that aiming to meet fiber needs—or at least a large portion—through naturally occurring fiber in foods is ideal.

The health recommendation to eat a “higher-fiber diet” isn’t just to encourage people to hit their daily quota of fiber grams, but also to promote improvements in overall eating. When food choices focus on getting fiber, an individual typically consumes fewer calories, chooses foods that have a lower glycemic index, consumes more whole foods like fruits and vegetables (and thus more nutrients), and consumes fewer processed foods. Relying primarily on supplements or fortified foods means missing out on these things. So, while you may be getting plenty of fiber, overall diet quality hasn’t improved. Also, most research looking at health benefits is based on higher dietary or intact fiber intake, so consuming functional fibers doesn’t necessarily guarantee the same outcomes.

Fibers also have different effects based on their solubility. For example, an insoluble fiber like wheat bran helps constipation, but has little to no effect on glycemic response or heart disease; a soluble fiber such as b-glucan lowers cholesterol, but isn’t the most effective when it comes to regularity. Additionally, not all soluble and insoluble fibers are equal in effectiveness. In fact, research has linked only a handful of specific fibers as being effective when it comes to inducing certain health benefits. This means that consuming a supplement or fortified food has little effect if it doesn’t contain a specific type associated with health benefits.

When to Use Fiber-Fortified Foods and Supplements

Even though food should be first, it can be hard to hit daily recommendations, even with a diet full of produce, nuts, seeds, and grains. In this case, it’s not a bad idea to add in some fortified foods or a supplement—particularly if you have a condition like heart disease, pre-diabetes, type 2 diabetes, or a GI issue such as constipation. Because a fortified food or supplement usually only contains one or two types of fiber, the key is finding a product that contains a functional fiber to effectively address issues. To help navigate the grocery and drug store aisles, see the chart below for which fibers are associated with specific health effects, and then look for those on packaging.

Desired Health Effect

Functional Fiber(s) Associated

Alleviate or prevent constipation

Wheat bran (All Bran)

Psyllium* (Metamucil)

Reduce cholesterol levels/heart disease risk

b-glucan (oats & barley)

Psyllium* (Metamucil)

Guar gum

Increased satiety

b-glucan (oats & barley)

Psyllium* (Metamucil)

Improved glycemic control

b-glucan (oats & barley)

Psyllium* (Metamucil)

Guar Gum

Alleviating diarrhea and/or some IBS symptoms

Psyllium* (Metamucil)

Improved gut/microbiota health

In theory, fermentable fibers such as wheat dextrin (Benefiber), inulin (chicory root), guar gum and b-glucan may aid growth of good bacteria, but research has limited documentation that overall gut health is improved due to supplementation of these fermentable fibers.

*Psyllium is from the seed husks of Plantago ovata plant and may also be referred to as ispaghula on labels.

The Power of Fiber

Fiber has long been known to promote good digestive health and regularity, but those are only two of the many benefits fiber offers. Consider that a study published in the American Journal of Clinical Nutrition found that people who ate a high-fiber diet of oats, barley, eggplant, okra, and other vegetables lowered their cholesterol by close to 30 percent after four weeks. In addition to improving digestive health and lowering cholesterol levels, a high-fiber diet can help you reduce the risk of heart disease and diabetes, and keep your weight in check. Here’s a closer look at each benefit.

Fiber and Digestion

As fiber passes through the stomach and intestines, it absorbs water, adding bulk to the stool. This promotes regularity and reduces constipation, says James Anderson, M.D., chair of the National Fiber Council. “Insoluble fiber, found in wheat bran, whole grains, and vegetables, speeds the passage of food through the stomach and intestines,” he says. For more high-fiber foods, read Easy Ways to Add Fiber to Your Diet.

Fiber and Cholesterol

Fiber is undigested starch, says Dr. Anderson, and as such, it traps cholesterol and drags it out of the body through the digestive system. Soluble fiber, found in oat bran, barley, oranges, apples, carrots, and dried beans, turns into a gel during the digestive process and prevents cholesterol, fat, and sugars from being absorbed by the body.

Fiber and Heart Disease

“When it comes to heart health, the importance of fiber in your diet cannot be overstated,” says Kathy Kastan, president of WomenHeart, the National Coalition for Women With Heart Disease.and the coauthor of WomenHeart’s All Heart Family Cookbook.

Several studies have shown that fiber reduces the risk of heart disease. In addition to the above-mentioned cholesterol study in the American Journal of Clinical Nutrition, a study published in the Journal of the American College of Cardiology Foundation that followed 39,876 women for six years found that those who ingested an average of 26.3 grams of fiber daily were at lower risk for developing heart disease or having a heart attack than those who ate less.

Fiber and Diabetes

A high-fiber diet may lower a person’s risk for diabetes. Fiber slows the absorption of sugars, which can reduce glucose levels in the blood and prevent blood sugar spikes, says Dr. Anderson. Results of a study published in the Archives of Internal Medicine suggest that whole-grain fiber (the kind found in some breakfast cereals, breads, and crackers) may be more beneficial in reducing blood sugar than fruits and vegetables.

Fiber and Weight Loss

Fiber expands in the stomach and intestines, which creates a feeling of fullness. This means that after eating a fiber-rich meal, you’ll typically feel fuller longer and may eat less throughout the day. In addition, because soluble fiber turns into a gel in the stomach, it binds to sugars, cholesterol, and fats and carries them, largely unabsorbed, through the digestive tract, says Anderson.

What About Fiber and Colon Cancer?

Can a high-fiber diet help prevent colon cancer? It’s still unknown. Early studies on fiber’s ability to lower the risk of colon cancer were promising, and it seems logical to researchers that fiber may have protective properties against this cancer, but more recent studies have been inconclusive.

Last reviewed: September 23, 2008 | Last updated: September 23, 2008

Increasing Fiber Intake

How do I increase my fiber intake?

Here are some easy ways to increase fiber:

Grains and Cereals

  • As a general rule, include at least one serving of whole grain in every meal.
  • Keep a jar of oat bran or wheat germ handy. Sprinkle over salad, soup, breakfast cereals and yogurt.
  • Use whole-wheat flour when possible in your cooking and baking.
  • Choose whole grain bread. Look on the label for breads with the highest amount of fiber per slice.
  • Choose cereals with at least 5 grams of fiber per serving.
  • Keep whole-wheat crackers on hand for an easy snack.
  • Cook with brown rice instead of white rice. If the switch is hard to make, start by mixing them together.

Legumes and Beans

  • Add kidney beans, garbanzos or other bean varieties to your salads. Each 1/2 cup serving is approximately 7 to 8 grams of fiber.
  • Substitute legumes for meat two to three times per week in chili and soups
  • Experiment with international dishes (such as Indian or Middle Eastern) that use whole grains and legumes as part of the main meal or in salads.

Fruits and Vegetables

  • Eat at least five servings of fruits and vegetables each day. Fresh fruit is slightly higher in fiber than canned. Eat the peel whenever possible — it’s easier than peeling or eating around it.
  • Have fresh fruit for dessert.
  • Eat whole fruits instead of drinking juices. Juices don’t have fiber.
  • Add chopped dried fruits to your cookies, muffins, pancakes or breads before baking. Dried fruits have a higher amount of fiber than the fresh versions. For example, 1 cup of grapes has 1 gram of fiber, but 1 cup of raisins has 7 grams. However, 1 cup of raisins or any other dried fruit has more calories than the fresh fruit variety.
  • Add sliced banana, peach or other fruit to your cereal.
  • Grate carrots on salads.

To find information on fiber supplements, please see Fiber Supplements.

How much fiber do I get from fruits and vegetables?

While all fruits have some fiber, there are some that are higher than others. Here are a few that have 3 to 4 grams of fiber:

  • Apple
  • Orange
  • Tangerine
  • Pear
  • 1 cup blueberries
  • 1 cup strawberries

Raspberries are high in fiber, as one cup has 8 grams.

Here are some vegetable choices that have 3 to 4 grams of fiber:

  • 1/2 cup peas
  • 1/2 cup cauliflower
  • 1 cup carrots
  • 1 medium sweet potato
  • 1/2 cup squash

Why is soluble fiber so important?

Soluble fiber has been shown to reduce total blood cholesterol levels and may improve blood sugar levels in people with diabetes.

The best sources of soluble fiber are oats, dried beans and some fruits and vegetables. Although there is no dietary reference intake for insoluble or soluble fiber, many experts recommend a total dietary fiber intake of 25 to 30 grams per day with about one-fourth — 6 to 8 grams per day — coming from soluble fiber.

Are Foods with High Fiber Really That Good for You?

And many people assume that all foods with high fiber are the same. In fact, some fibers lower cholesterol, some lower blood sugar, and some help with regularity.

Those differences didn’t matter so much when all of our fiber came—intact and unprocessed— from foods with high fiber like whole grains, beans, fruits, and vegetables, since each usually has a mix of fibers.

But now companies are adding isolated fibers—mostly purified powders—to ice creams, yogurts, juices, drinks, and other foods that have always been fiber-free.

What are those fibers good for? It’s not clear that anyone knows.

How much fiber do you need

How much fiber do you need? According to food labels, 25 grams is a day’s worth. That’s right for women 50 and under, but men of the same age need 38 grams, says the National Academy of Sciences. And the targets drop to 21 grams for women and 30 grams for men over 50.

It’s not that people need fiber less as they get older. “The advice is to get 14 grams of fiber per 1,000 calories, and older people need fewer calories,” explains Thomas Wolever, a fiber researcher and professor of nutritional sciences at the University of Toronto.

Most Americans consume half the recommended levels. A typical woman gets about 13 grams of fiber a day, while the average man hovers around 17 grams.

What’s the harm in falling short of the target? Here’s a rundown of some of the links between fiber and health.

Fiber and heart disease

The daily fiber targets “are based on data that fiber prevents cardiovascular disease,” notes Joanne Slavin, a University of Minnesota researcher who served on the National Academy of Sciences Panel on the Definition of Dietary Fiber.

The NAS relied heavily on studies that found a lower risk of heart disease in people who reported eating the most foods with high fiber (about 29 grams a day for men and 23 grams a day for women). In each of those studies, the fiber that seemed to protect the heart came from cereals, breads, and other grains, not from fruits or vegetables.

But it was never absolutely clear that it was the fiber that mattered. Several inconsistencies have always troubled scientists.

What matters about fiber

Fiber or whole grains? It’s hard for researchers to know if it’s the fiber, or something else in whole grains, that matters.

“Whole grains also have phytoestrogens, antioxidants, lignans, vitamins, and minerals, so a lot comes along with the fiber package,” says Slavin.

Soluble or insoluble? The kind of fiber that’s linked to a lower risk of heart disease isn’t the kind that lowers cholesterol.

Although all fruits, vegetables, and grains have both soluble and insoluble fiber, most grains, like wheat, are richer in insoluble fiber, which is not broken down by digestive enzymes or by bacteria in the gut.

In contrast, a few grains (oats and barley, for example) are richer in viscous (gummy) soluble fibers, which the bacteria in the lower intestinal tract can break down.

Fiber and Diabetes

“There’s moderately strong evidence that fiber is linked to a reduced risk of diabetes, and it’s based on whole foods like vegetables, fruits, and whole grains,” says JoAnn Manson, professor of medicine at Harvard Medical School and chief of preventive medicine at Brigham and Women’s Hospital in Boston.

The evidence that fiber prevents diabetes parallels the evidence that it prevents heart disease, as do the inconsistencies.

In two studies—on roughly 65,000 women and 43,000 men—those who reported eating the most fiber from grains (8 grams a day) had about a 30 percent lower risk of diabetes than those who reported eating the least fiber from grains (3 grams a day).

Fiber and GI tract disorders

A few studies have suggested that people who eat more insoluble fiber have a lower risk of diverticular disease, which is caused by small pouches that bulge out through weak spots in the large intestine, sometimes becoming inflamed or infected.

But fiber’s starring role in the GI tract is in the stool department. Insoluble fiber tends to help “laxation” by adding bulk to stool.

“We know that insoluble fibers like wheat bran are good for stool weight and laxation and soluble fibers like pectin aren’t,” explains the University of Minnesota’s Joanne Slavin.

After dozens of studies, researchers have even estimated how much you can expect stool weight to increase for each gram of fiber you eat. (That’s 5.4 grams for wheat- bran fiber, 4.9 grams for fruit and vegetable fiber, 3 grams for isolated cellulose, and 1.3 grams for isolated pectin, in case you were wondering.)

Insoluble fiber from bran helps prevent constipation because it bulks up the stool. “The bran fiber is still there at the end of the GI tract, where it binds water, so it’s going to increase stool weight,” explains Slavin.

In contrast, most soluble fibers, like the pectin in fruits and vegetables, are digested by bacteria in the gut, “so there’s nothing left at the end of the GI tract.”

But it’s not just a question of insoluble vs. soluble. For example, psyllium, the (mostly) soluble fiber in Metamucil, is a laxative. And wheat bran has a bigger impact than cellulose—its purified cousin— even though both are insoluble.

The bottom line on foods with high fiber

  • Whole-grain breads and cereals, which are naturally rich in fiber, are linked to a lower risk of heart disease and diabetes.
  • Foods rich in insoluble fibers, like wheat bran, help prevent constipation and possibly diverticular disease.
  • Isolated oat fiber and soy fiber are insoluble, so they may help keep you regular. Polydextrose may also help, but inulin and maltodextrin don’t seem to.

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