About all

Is fiber important: Fiber | The Nutrition Source

Fiber | The Nutrition Source

Fiber is a type of carbohydrate that the body can’t digest. Though most carbohydrates are broken down into sugar molecules called glucose, fiber cannot be broken down into sugar molecules, and instead it passes through the body undigested. Fiber helps regulate the body’s use of sugars, helping to keep hunger and blood sugar in check.

Children and adults need at least 25 to 35 grams of fiber per day for good health, but most Americans get only about 15 grams a day. Great sources are whole grains, whole fruits and vegetables, legumes, and nuts.

Types of Fiber

Fiber comes in two varieties, both beneficial to health:

Soluble fiber, which dissolves in water, can help lower glucose levels as well as help lower blood cholesterol. Foods with soluble fiber include oatmeal, chia seeds, nuts, beans, lentils, apples, and blueberries.

Insoluble fiber, which does not dissolve in water, can help food move through your digestive system, promoting regularity and helping prevent constipation. Foods with insoluble fibers include whole wheat products (especially wheat bran), quinoa, brown rice, legumes, leafy greens like kale, almonds, walnuts, seeds, and fruits with edible skins like pears and apples.

Fiber and Disease

Fiber appears to lower the risk of developing various conditions, including heart disease, diabetes, diverticular disease, and constipation. Fiber’s beneficial role in the gut microbiome may produce anti-inflammatory effects that alleviate the chronic inflammation associated with these conditions. [2]

Heart disease

Soluble fiber attracts water in the gut, forming a gel, which can slow digestion. This may help prevent blood glucose surges after eating and reduce hunger. Control of blood glucose and weight is important because these are risk factors for diabetes, a condition which doubles the risk of developing heart disease.

Soluble fiber may also lower blood cholesterol by interfering with bile acid production. Cholesterol is used to make bile acids in the liver. Soluble fiber binds to bile acids in the gut and excretes them from the body. Because of this reduced amount of available bile acids, the liver will pull cholesterol from the blood to make new bile acids, thereby lowering blood cholesterol. [3] A meta-analysis of 67 controlled trials found a modest benefit of dietary soluble fiber in lowering total and LDL cholesterol. [4]

Epidemiological studies find that a high intake of dietary fiber is associated with a lower risk of heart disease and deaths from cardiovascular disease. [5-7] In large cohorts of male and female health professionals, researchers found that higher intakes of cereal fibers were associated with a lower risk of heart disease and heart attacks. [8,9] Keep in mind that cereal fiber doesn’t necessarily refer to the aisle of boxed breakfast cereals in your local supermarket. “Cereals” in these studies referred to the seeds of minimally refined whole grains that include the germ, bran, and endosperm. Examples are steel-cut oats, quinoa, brown rice, millet, barley, and buckwheat.

A higher fiber intake has also been linked to a lower risk of metabolic syndrome, a combination of factors that increases the risk of developing heart disease and diabetes: high blood pressure, high insulin levels, excess weight (especially around the belly), high triglyceride levels, and low HDL (good) cholesterol. [10,11]

Type 2 diabetes

Diets low in fiber, especially insoluble types, may increase the risk of type 2 diabetes (T2DM). Large cohort studies of women found that a diet low in fiber (especially lacking cereal fibers) but containing foods with a high glycemic index (causing blood glucose surges) increased the risk of developing T2DM. [12,13] Other large cohorts of male and female health professionals have found that high-fiber whole grains (brown rice, rye, oats, wheat bran) are most strongly associated with lower diabetes risk. [14,15] Fibers from fruits and vegetables do not appear to have as strong an association. [16]

Read about what you can do to help prevent type 2 diabetes.

Breast cancer

A prospective cohort study of more than 90,000 premenopausal women found that a higher fiber intake as well as eating fiber during adolescence reduced breast cancer risk. When comparing the highest to lowest intakes of fiber, there was a 25% reduced risk of breast cancer. [32] This protection of dietary fiber on breast cancer risk was also found in a later meta-analysis of 17 prospective cohort studies when comparing highest to lowest fiber intakes. It was found protective from both premenopausal and postmenopausal breast cancers. [33]

A high-fiber diet was also associated with a lower risk of benign breast disease, a risk factor in adolescents for the later development of breast cancer. [34]

Colorectal cancer

Earlier epidemiological studies show mixed results on the association of fiber and colorectal cancer (CRC). [27]

One reason may be due to differing effects of fiber on specific subtypes of CRC. When accounting for this, fiber was found to be protective with certain subtypes. [28] A meta-analysis of prospective cohort studies found fibers from fruits, vegetables, and legumes to offer some protection from CRC, but cereal fibers showed a stronger association with CRC prevention. [29] Other later meta-analyses have also found significant associations between a high-fiber diet and lower risk of CRC. [30,31]


Constipation is generally defined as having three or fewer bowel movements a week, difficulty or pain passing bowel movements, or small hard “pebbly” stool. Occasional bouts of constipation are common, but chronic constipation that does not resolve can lower quality of life and lead to symptoms of bloating, cramping, and even nausea. Chronic constipation increases the risk of diverticular disease and hemorrhoids.

Lifestyle behaviors that help relieve constipation include eating more fiber from fruits, vegetables, and whole grains; drinking more water; and regular exercise. There are various reasons why fiber reduces constipation. Some types of soluble fiber bind to water, creating a gel that helps to soften and bulk stool. Insoluble fibers mildly irritate the intestinal lining, which stimulates the secretion of water and mucus to encourage movement of stool. [26] Certain fibers act as prebiotics, or food for gut bacteria, which ferments fibers into short chain fatty acids and increases water in the intestines to produce softer, easier-to-pass stools. [26]

Because of the differing actions of various fiber types with constipation, a range of high-fiber foods from whole grains, fruits, legumes, and vegetables is recommended. It is suggested to increase fiber intake gradually, because a sudden significant increase in dietary fiber can cause bloating and cramping. Drinking more fluids while eating more fiber can also help lessen these side effects.

Diverticular disease

Diverticulosis is a condition in which small “pouches” called diverticula develop in the lower intestine. It is one of the most common disorders of the colon in the Western world, with the highest rates in the U. S. and Europe. [17] The risk of developing diverticulosis increases with age (more than half of people over age 60 have diverticula) and is usually silent, not causing noticeable symptoms unless the pouches tear or become inflamed, leading to diverticulitis. Diverticulitis can cause persistent abdominal pain (usually in the lower left side), nausea, vomiting, and fever. Treatment is typically a brief period of no food, drinking liquids only, and antibiotic medications. In severe cases where an abscess or perforation may develop, surgery may be needed. However, most people who develop diverticulosis will not develop diverticulitis, with more recent studies estimating only 5% progressing to diverticulitis. [18]

Research shows that a Westernized diet low in fiber and high in red meat and ultra-processed refined foods is a major contributor. [19-21] An eating pattern such as this can lead to constipation, which over time weakens the colon muscles while increasing pressure when trying to defecate; small pouches can form within these weak spots. It can also lead to an increase in harmful intestinal bacteria, causing inflammation and further increasing the risk of diverticular disease. [17,20]

Large cohort studies show a protective effect of fiber on diverticular disease, particularly fibers from fruits, cereal grains, and vegetables. [22,23] A cohort of more than 43,000 men from the Health Professionals Follow-up Study found a protective effect of dietary fiber from diverticulitis, especially cellulose, a type of insoluble fiber. [24] Cellulose is found in the skins of fruits, leafy vegetables, root vegetables, legumes, and wheat bran. A Nurses’ Health Study following more than 50,000 women found that those with the highest fiber intakes (25 or more grams daily) had a 13% lower risk of diverticulitis than those who ate the least (less than 18 grams daily). [2] The protective effect came especially from fibers from cereal grains and whole fruits, but not fruit juices.

Other factors that increase the risk of diverticular disease are increasing age, smoking, lack of exercise, use of certain medications (NSAIDs, steroids, aspirin, opioids), family history, and history of irritable bowel syndrome. [18]

Should I avoid nuts and seeds with diverticulosis?

If you have diverticulosis, chances are you’ve heard that maybe you should avoid certain foods with small hard-to-digest particles: nuts, seeds, popcorn, corn, and fruits and vegetables with seeds like raspberries, strawberries, cucumber, or tomatoes. The reasoning is that these small undigested food particles might become trapped in the diverticular pouches and become inflamed from bacterial infection, causing the uncomfortable condition called diverticulitis. People who have experienced intense symptoms of diverticulitis often change their diets to avoid these foods in hopes of preventing a recurrence. However, evidence has shown this practice to be more of an urban legend than helping to reduce recurrences, and can deter people from eating foods that may actually help their condition in the future.

Although the role of diet with diverticular disease has long been debated, a high-fiber intake with a focus on whole grains, fruits, and vegetables has been found to have a strong association with decreased risk of diverticular disease and diverticulitis. [18] When it comes to nuts and popcorn, research following more than 47,000 men from the Health Professionals Follow-up Study actually found a lower risk of diverticulitis when eating these foods. [25] Including these foods also did not increase the risk of developing new diverticulosis or diverticular complications.


Bottom Line

There are many types of dietary fibers that come from a range of plant foods. It’s important to not hyperfocus on a particular fiber because of its specific proposed action, as each type offers some level of health benefit. Therefore, eating a wide variety of plant foods like fruits, vegetables, whole grains, legumes, nuts, and seeds to reach the fiber recommendation of 25-35 grams daily best ensures reaping those benefits.

Some tips for increasing fiber intake:

  • Eat whole fruits instead of drinking fruit juices.
  • Replace white rice, bread, and pasta with minimally processed brown rice and other whole grains like barley, millet, amaranth, farro, and
  • Add high-fiber foods to current meals: 1-2 tablespoons of almonds, ground flaxseeds, or chia seeds to cereals; diced vegetables to casseroles, stir-fried dishes, and soups.
  • For breakfast, choose cereals that have a whole grain as their first ingredient. Another tip is to look on the Nutrition Facts label and choose cereals with 20% or higher of the Daily Value (DV) for fiber.
  • Snack on crunchy raw vegetables or a handful of almonds instead of chips and crackers.
  • Substitute beans or legumes for meat two to three times a week in chili and soups.
  • If it is difficult to eat enough fiber through food, a fiber supplement such as psyllium or methylcellulose powders or wafers can be used. They can help bulk and soften stool so it is easier to pass. However, fiber supplements are not intended to completely replace high-fiber foods.


  1. Institute of Medicine 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. https://doi.org/10.17226/10490.
  2. Ma W, Nguyen LH, Song M, Jovani M, Liu PH, Cao Y, Tam I, Wu K, Giovannucci EL, Strate LL, Chan AT. Intake of dietary fiber, fruits, and vegetables, and risk of diverticulitis. The American journal of gastroenterology. 2019 Sep;114(9):1531. *Disclosure: Andrew T. Chan receives consulting fees from Janssen, Pfizer Inc., and Bayer Pharma AG for work unrelated to the topic of this manuscript.
  3. Jesch ED, Carr TP. Food ingredients that inhibit cholesterol absorption. Preventive nutrition and food science. 2017 Jun;22(2):67.
  4. Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. The American journal of clinical nutrition. 1999 Jan 1;69(1):30-42.
  5. Pereira MA, O’Reilly E, Augustsson K, Fraser GE, Goldbourt U, Heitmann BL, Hallmans G, Knekt P, Liu S, Pietinen P, Spiegelman D. Dietary fiber and risk of coronary heart disease: a pooled analysis of cohort studies. Archives of internal medicine. 2004 Feb 23;164(4):370-6.
  6. Acosta S, Johansson A, Drake I. Diet and lifestyle factors and risk of atherosclerotic cardiovascular disease—a prospective cohort study. Nutrients. 2021 Nov;13(11):3822.
  7. Yang Y, Zhao LG, Wu QJ, Ma X, Xiang YB. Association between dietary fiber and lower risk of all-cause mortality: a meta-analysis of cohort studies. American journal of epidemiology. 2015 Jan 15;181(2):83-91.
  8. Rimm EB, Ascherio A, Giovannucci E, Spiegelman D, Stampfer MJ, Willett WC. Vegetable, fruit, and cereal fiber intake and risk of coronary heart disease among men. JAMA. 1996 Feb 14;275(6):447-51.
  9. AlEssa HB, Cohen R, Malik VS, Adebamowo SN, Rimm EB, Manson JE, Willett WC, Hu FB. Carbohydrate quality and quantity and risk of coronary heart disease among US women and men. The American journal of clinical nutrition. 2018 Feb 1;107(2):257-67.
  10. McKeown NM, Meigs JB, Liu S, Wilson PW, Jacques PF. Whole-grain intake is favorably associated with metabolic risk factors for type 2 diabetes and cardiovascular disease in the Framingham Offspring Study. The American journal of clinical nutrition. 2002 Aug 1;76(2):390-8.
  11. McKeown NM, Meigs JB, Liu S, Saltzman E, Wilson PW, Jacques PF. Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort. Diabetes care. 2004 Feb 1;27(2):538-46.
  12. Schulze MB, Liu S, Rimm EB, Manson JE, Willett WC, Hu FB. Glycemic index, glycemic load, and dietary fiber intake and incidence of type 2 diabetes in younger and middle-aged women. The American journal of clinical nutrition. 2004 Aug 1;80(2):348-56.
  13. Krishnan S, Rosenberg L, Singer M, Hu FB, Djoussé L, Cupples LA, Palmer JR. Glycemic index, glycemic load, and cereal fiber intake and risk of type 2 diabetes in US black women. Archives of Internal Medicine. 2007 Nov 26;167(21):2304-9.
  14. Hu Y, Ding M, Sampson L, Willett WC, Manson JE, Wang M, Rosner B, Hu FB, Sun Q. Intake of whole grain foods and risk of type 2 diabetes: results from three prospective cohort studies. BMJ. 2020 Jul 8;370.*Author disclosure: FBH reports grants from California Walnut Commission, personal fees from Metagenics, personal fees from Standard Process, and personal fees from Diet Quality Photo Navigation, outside the submitted work.
  15. Kyrø C, Tjønneland A, Overvad K, Olsen A, Landberg R. Higher whole-grain intake is associated with lower risk of type 2 diabetes among middle-aged men and women: the Danish Diet, Cancer, and Health Cohort. The Journal of nutrition. 2018 Sep 1;148(9):1434-44.
  16. Weickert MO, Pfeiffer AF. Impact of dietary fiber consumption on insulin resistance and the prevention of type 2 diabetes. The Journal of nutrition. 2018 Jan 1;148(1):7-12.
  17. Boynton W, Floch M. New strategies for the management of diverticular disease: insights for the clinician. Therapeutic Advances in Gastroenterology. 2013 May;6(3):205-13.
  18. Hawkins AT, Wise PE, Chan T, Lee JT, Mullaney TG, Wood V, Eglinton T, Frizelle F, Khan A, Hall J, Ilyas MM. Diverticulitis–An Update from the Age Old Paradigm. Current problems in surgery. 2020 Oct;57(10):100862.
  19. Strate LL, Keeley BR, Cao Y, Wu K, Giovannucci EL, Chan AT. Western dietary pattern increases, and prudent dietary pattern decreases, risk of incident diverticulitis in a prospective cohort study. Gastroenterology. 2017 Apr 1;152(5):1023-30.
  20. Cao Y, Strate LL, Keeley BR, Tam I, Wu K, Giovannucci EL, Chan AT. Meat intake and risk of diverticulitis among men. Gut. 2018 Mar 1;67(3):466-72. *Disclosure: ATC previously served as a consultant for Bayer Healthcare, Aralaz Pharmaceuticals and Pfizer Inc. for work unrelated to the topic of this manuscript.
  21. Carabotti M, Falangone F, Cuomo R, Annibale B. Role of Dietary Habits in the Prevention of Diverticular Disease Complications: A Systematic Review. Nutrients. 2021 Apr;13(4):1288.
  22. Crowe FL, Balkwill A, Cairns BJ, Appleby PN, Green J, Reeves GK, Key TJ, Beral V. Source of dietary fibre and diverticular disease incidence: a prospective study of UK women. Gut. 2014 Sep 1;63(9):1450-6.
  23. Mahmood MW, Abraham-Nordling M, Håkansson N, Wolk A, Hjern F. High intake of dietary fibre from fruit and vegetables reduces the risk of hospitalisation for diverticular disease. European journal of nutrition. 2019 Sep;58(6):2393-400.
  24. Aldoori WH, Giovannucci EL, Rockett HR, Sampson L, Rimm EB, Willett WC. A prospective study of dietary fiber types and symptomatic diverticular disease in men. The Journal of nutrition. 1998 Apr 1;128(4):714-9.
  25. Strate LL, Liu YL, Syngal S, Aldoori WH, Giovannucci EL. Nut, corn, and popcorn consumption and the incidence of diverticular disease. JAMA. 2008 Aug 27;300(8):907-14.
  26. Bellini M, Tonarelli S, Barracca F, Rettura F, Pancetti A, Ceccarelli L, Ricchiuti A, Costa F, de Bortoli N, Marchi S, Rossi A. Chronic Constipation: Is a Nutritional Approach Reasonable?. Nutrients. 2021 Oct;13(10):3386.
  27. Fuchs CS, Giovannucci EL, Colditz GA, Hunter DJ, Stampfer MJ, Rosner B, Speizer FE, Willett WC. Dietary fiber and the risk of colorectal cancer and adenoma in women. New England Journal of Medicine. 1999 Jan 21;340(3):169-76.
  28. Hidaka A, Harrison TA, Cao Y, Sakoda LC, Barfield R, Giannakis M, Song M, Phipps AI, Figueiredo JC, Zaidi SH, Toland AE. Intake of dietary fruit, vegetables, and fiber and risk of colorectal cancer according to molecular subtypes: A pooled analysis of 9 studies. Cancer research. 2020 Oct 15;80(20):4578-90.
  29. Oh H, Kim H, Lee DH, Lee A, Giovannucci EL, Kang SS, Keum N. Different dietary fibre sources and risks of colorectal cancer and adenoma: a dose–response meta-analysis of prospective studies. British Journal of Nutrition. 2019 Sep;122(6):605-15.
  30. Nucci D, Fatigoni C, Salvatori T, Nardi M, Realdon S, Gianfredi V. Association between dietary fibre intake and colorectal adenoma: A systematic review and meta-analysis. International journal of environmental research and public health. 2021 Jan;18(8):4168.
  31. Zhang XF, Wang XK, Tang YJ, Guan XX, Guo Y, Fan JM, Cui LL. Association of whole grains intake and the risk of digestive tract cancer: a systematic review and meta-analysis. Nutrition journal. 2020 Dec;19(1):1-4.
  32. Farvid MS, Eliassen AH, Cho E, Liao X, Chen WY, Willett WC. Dietary fiber intake in young adults and breast cancer risk. Pediatrics. 2016 Mar 1;137(3).
  33. Farvid MS, Spence ND, Holmes MD, Barnett JB. Fiber consumption and breast cancer incidence: A systematic review and meta-analysis of prospective studies. Cancer. 2020 Jul 1;126(13):3061-75.
  34. Berkey CS, Tamimi RM, Willett WC, Rosner B, Hickey M, Toriola AT, Frazier AL, Colditz GA. Adolescent alcohol, nuts, and fiber: Combined effects on benign breast disease risk in young women. NPJ breast cancer. 2020 Nov 23;6(1):1-5.

Last reviewed April 2022

Terms of Use

The contents of this website are for educational purposes and are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The Nutrition Source does not recommend or endorse any products.

Why Is Fiber Good for You? The Crunchy Truth

Some types of fiber may benefit your health, including your gut microbiome, blood sugar, and the walls of your colon.

Fiber is one of the main reasons whole plant foods are good for you.

Growing evidence shows that adequate fiber intake may benefit your digestion and reduce your risk of chronic disease.

Many of these benefits are mediated by your gut microbiota — the millions of bacteria that live in your digestive system.

However, not all fiber is created equal. Different types have different health effects.

This article explains the evidence-based health benefits of fiber.

What is fiber?

Put simply, dietary fiber is a non-digestible carbohydrate found in foods.

It’s split into two broad categories based on its water solubility:

  1. Soluble fiber: dissolves in water and can be metabolized by the “good” bacteria in the gut
  2. Insoluble fiber: does not dissolve in water

Perhaps a more helpful way to categorize fiber is as fermentable versus non-fermentable, which refers to whether friendly gut bacteria can use it or not.

It’s important to keep in mind that there are many different types of fiber. Some of them have important health benefits, while others are mostly useless.

There is also a lot of overlap between soluble and insoluble fibers. Some insoluble fibers can be digested by the good bacteria in the intestine, and most foods contain both soluble and insoluble fibers.

Health authorities recommend that men and women eat 38 and 25 grams of fiber per day, respectively.


Non-digestible carbohydrates are collectively known as fiber. They are most often categorized as soluble or insoluble.

Fiber feeds “good” gut bacteria

The bacteria that live in the human body outnumber the body’s cells 10 to 1. Bacteria live on the skin, in the mouth, and in the nose, but the great majority live in the gut, primarily the large intestine (1).

Five hundred to 1,000 different species of bacteria live in the intestine, totaling about 38 trillion cells. These gut bacteria are also known as the gut flora (2, 3).

This is not a bad thing. In fact, there is a mutually beneficial relationship between you and some of the bacteria that live in your digestive system.

You provide food, shelter, and a safe habitat for the bacteria. In return, they take care of some things that the human body cannot do on its own.

Of the many different kinds of bacteria, some are crucial for various aspects of your health, including weight, blood sugar control, immune function, and even brain function (4, 5, 6, 7, 8).

You may wonder what this has to do with fiber. Just like any other organism, bacteria need to eat to get energy to survive and function.

The problem is that most carbs, proteins, and fats are absorbed into the bloodstream before they make it to the large intestine, leaving little for the gut flora.

This is where fiber comes in. Human cells don’t have the enzymes to digest fiber, so it reaches the large intestine relatively unchanged.

However, intestinal bacteria do have the enzymes to digest many of these fibers.

This is the most important reason that (some) dietary fibers are essential for health. They feed the “good” bacteria in the intestine, functioning as prebiotics (9).

In this way, they promote the growth of “good” gut bacteria, which can have various positive effects on health (10).

The friendly bacteria produce nutrients for the body, including short-chain fatty acids such as acetate, propionate, and butyrate, of which butyrate appears to be the most important (11).

These short-chain fatty acids can feed the cells in the colon, leading to reduced gut inflammation and improvements in digestive disorders such as irritable bowel syndrome, Crohn’s disease, and ulcerative colitis (12, 13, 14).

When the bacteria ferment the fiber, they also produce gases. This is why high fiber diets can cause flatulence and stomach discomfort in some people. These side effects usually go away with time as your body adjusts.


Consuming adequate amounts of soluble, fermentable fiber is very important for optimal health because it optimizes the function of the friendly bacteria in your gut.

Some types of fiber can help you lose weight

Certain types of fiber can help you lose weight by reducing your appetite.

In fact, some studies show that increasing dietary fiber can cause weight loss by automatically reducing calorie intake (15, 16).

Fiber can soak up water in the intestine, slowing the absorption of nutrients and increasing feelings of fullness (17).

However, this depends on the type of fiber. Some types have no effect on weight, while certain soluble fibers can have a significant effect (18, 19, 20, 21).

A good example of an effective fiber supplement for weight loss is glucomannan.


Some types of fiber can cause weight loss by increasing feelings of fullness, leading to a reduced calorie intake.

Fiber can reduce blood sugar spikes after a high carb meal

High fiber foods tend to have a lower glycemic index than refined carb sources, which have been stripped of most of their fiber.

However, scientists believe that only high viscosity, soluble fibers have this property (22).

Including these viscous, soluble fibers in your carb-containing meals may cause smaller spikes in blood sugar (23).

This is important, especially if you’re following a high carb diet. In this case, the fiber can reduce the likelihood of the carbs raising your blood sugar to harmful levels.

That said, if you have blood sugar issues, you should consider reducing your carb intake — especially your intake of low fiber, refined carbs such as white flour and added sugar.


Foods that contain viscous fiber have a lower glycemic index and cause smaller spikes in blood sugar than foods that are low in fiber.

Fiber can reduce cholesterol, but the effect isn’t huge

Viscous, soluble fiber can also reduce your cholesterol levels.

However, the effect isn’t nearly as impressive as you might expect.

A review of 67 controlled studies found that consuming 2–10 grams of soluble fiber per day reduced total cholesterol by only 1.7 mg/dl and LDL (bad) cholesterol by 2.2 mg/dl, on average (24).

But this also depends on the viscosity of the fiber. Some studies have found impressive reductions in cholesterol with increased fiber intake (25, 26).

Whether this has any meaningful effects in the long term is unknown, although many observational studies show that people who eat more fiber have a lower risk of heart disease (27).


Some types of fiber can reduce cholesterol levels. However, most studies show that the effect isn’t very large, on average.

What about fiber and constipation?

One of the main benefits of increasing fiber intake is reduced constipation.

Fiber is believed to help absorb water, increase the bulk of stool, and speed up the movement of stool through the intestine. However, the evidence is fairly conflicting (28, 29).

Some studies show that increasing fiber can improve symptoms of constipation, but other studies show that removing fiber improves constipation. The effects depend on the type of fiber.

In one study in 63 individuals with chronic constipation, going on a low fiber diet fixed their problem. The individuals who remained on a high fiber diet saw no improvement (30).

In general, fiber that increases the water content of your stool has a laxative effect, while fiber that adds to the dry mass of stool without increasing its water content may have a constipating effect.

Soluble fibers that form a gel in the digestive tract and are not fermented by gut bacteria are often effective. A good example of a gel-forming fiber is psyllium (22).

Other types of fiber, such as sorbitol, have a laxative effect by drawing water into the colon. Prunes are a good source of sorbitol (31, 32).

Choosing the right type of fiber may help your constipation, but taking the wrong supplements can do the opposite.

For this reason, you should consult a healthcare professional before taking fiber supplements for constipation.


The laxative effects of fiber differ. Some fibers reduce constipation, but others increase constipation. This appears to depend on the individual and the type of fiber.

Fiber might reduce the risk of colorectal cancer

Colorectal cancer is the third leading cause of cancer deaths in the world (33).

Many studies have linked a high intake of fiber-rich foods with a reduced risk of colon cancer (34).

However, whole, high fiber foods like fruits, vegetables, and whole grains contain various other healthy nutrients and antioxidants that may affect cancer risk.

Therefore, it’s difficult to isolate the effects of fiber from other factors in healthy, whole-food diets. To date, no strong evidence proves that fiber has cancer-preventive effects (35).

Yet, since fiber may help keep the colon wall healthy, many scientists believe that fiber plays an important role (36).


Studies have associated a high fiber intake with a reduced risk of colon cancer. However, correlation doesn’t equal causation. To date, no studies have confirmed that fiber has direct benefits for cancer prevention.

The bottom line

Dietary fiber has various health benefits.

Not only does it feed your gut bacteria, but fermentable fiber also forms short-chain fatty acids, which nourish your colon wall.

Additionally, viscous, soluble fiber may reduce your appetite, lower your cholesterol levels, and decrease the rise in blood sugar after high carb meals.

If you’re aiming for a healthy lifestyle, try to get a variety of fiber types from whole fruits, vegetables, and grains.

Fiber: why is it needed, what is useful and what products contain


© Dose Juice/Unsplash


Julia Tsiruleva

October 04, 2021

We try to take into account the amount of proteins, fats and carbohydrates in order to fully eat. But we often forget about another important element – fiber. RBC Style understands how much dietary fiber and why the body needs it.

  1. How fiber works
  2. How much fiber does the body need
  3. How to choose products
  4. Which foods are rich in fiber
  5. How to lose weight with fiber
  6. Daily diet

Fiber is a dietary fiber that does not provide us with energy and is not digested by the body, so food and beverage manufacturers do not include fiber when they list a food’s nutritional information. Why fiber should not be forgotten and what is its use?

How fiber works

Advertising on RBC www.adv.rbc.ru

Fiber fibers are processed by beneficial intestinal microflora and support the stable functioning of the digestive system. Fiber reduces the feeling of hunger, and this helps not to overeat and control weight. Soluble dietary fiber regulates blood sugar and cholesterol levels, while insoluble fiber cleanses the body and removes toxins. And this is only part of the beneficial properties of fiber.

In February 2019, Harvard Medical School published the results of 250 studies [1] that confirm the protective function of dietary fiber. Approximately 30 grams of fiber per day reduces the risk of heart disease, heart attacks, strokes, type 2 diabetes and colon cancer by 16-24%.

According to the US National Library of Medicine, eating fiber-rich foods reduces mortality from infectious and respiratory diseases from 24 to 56% in men, and from 34 to 59% in women [2].

Fiber is extremely important for intestinal microflora

© Maddi Bazzocco/Unsplash

How much fiber the body needs

The more, the better, according to experts [3]. American scientists indicate [4] that women and men under 50 need 25 and 38 grams of fiber per day, and after 50 – 21 and 30 grams, respectively. That’s roughly equal to a cup of lentils, a bowl of boiled beans or buttered broccoli, two pears, a large bowl of tomato and cucumber salad, a serving of vegetable soup, and a handful of prunes.

Nutritionists in the UK add [5] that children aged 2 to 5 need 15 grams of fiber per day, 5 to 11 years 20 grams and 11 to 16 years 25 grams. The average teenager needs to eat 2-3 vegetables a day-these can be cucumbers, tomatoes or carrots, the same amount of fruits (for example, bananas, kiwi, pears, apples), 1-2 toasts of whole-grain bread, a portion of vegetable soup, a plate of baked eggplants or boiled broccoli, a portion of whole cereals (buckwheat, rice), a cup of dry fuel . Experts advise offering children and teenagers plenty of raw vegetables and fruits, so vegetable and fruit salads and vegetable juices can be added above the minimum daily allowance or instead of hot meals.

Fiber can be offered to children in the form of raw vegetables

© Foodism360/Unsplash

How to choose foods

Experts recommend natural, high-fiber foods. For example, 6 or more grams of fiber is optimal for cereal and muesli, 3 or more for bread and crackers, and 4 or more for pasta. It’s important to make sure whole grains have at least 1 gram of fiber per 10 grams of carbs. The best ratio would be 1:5. Nutritionists emphasize that the words “multigrain” or “12 grains” in the name do not mean anything by themselves – you need to check the list of ingredients.

Which foods are rich in fiber

First of all, eat as many natural plant foods as possible. Fresh fruits and nuts are often more expensive than regular sweets, and making inexpensive cereals, beans, and lentils isn’t always easy, but it can help you eat a balanced diet.

Experts consider leaders in fiber content [6]:

  1. Wheat bran — 43.6 grams of fiber per 100 grams of product.
  2. Chia seeds – 34.4 gr.
  3. Dried fruits (figs, apricots, dried apricots) – 18 gr.
  4. Almonds – 12.5 gr.
  5. Buckwheat – 11.3 gr.
  6. Dark chocolate – 10.9 gr.
  7. Oats (oatmeal) – 10.6 gr.
  8. Artichokes – 8.6 gr.
  9. Peas – 8.3 gr.
  10. Barley, oat and barley groats – 8.0 gr.
  11. Lentils and chickpeas – 7.9 gr.
  12. Raspberry, gooseberry, blackberry – 6.5 gr.
  13. Beans – 6.4 gr.

How to Lose Weight with Fiber

Soluble fiber helps fight belly fat [7], one of the most dangerous types of obesity according to experts. An additional 10g of vegetable fibers in the daily diet reduces the risk of gaining excess weight by 3.7% [8].

Fiber keeps the gut microflora healthy, reduces the production of hormones [9] that cause hunger and slows down the movement of food in the intestines, helping to prevent overeating.

As with most weight loss methods, a fiber-rich diet alone is not enough to lose weight and maintain results. It is also necessary to take into account the general state of health [10], the usual diet, sleep quality and physical activity.

To add fiber to your daily diet, you need to eat as many natural plant foods as possible. Fresh fruits and nuts are often more expensive than regular sweets, and making inexpensive cereals, beans, and lentils isn’t always easy, but it can help you eat a balanced diet.

If you decide to lose weight with fiber, then you should pay attention to:

  • raw and cooked vegetables;
  • whole grain flakes, muesli;
  • oatmeal;
  • soups with vegetables, beans or beans;
  • Vegetarian stews with various varieties of beans and vegetables;
  • salads with seeds, berries and cereals.

In addition, nutritionists advise snacking on broccoli, carrots, beans or cauliflower, seasoned with hummus or fresh salsa, and adding nuts, berries and fruits to simple sugar-free yogurts.

How to determine the approximate amount of fiber in a serving [11]:

© Table: fiber content in foods

Daily diet

The UK National Health Service gives an example of a diet rich in fiber (approximately 32.5 grams of fiber per day) [12].


Two whole grain toast, banana and a glass of fruit juice – 9.4 grams of fiber.


Jacket baked potatoes, 200 grams of beans in tomato sauce without salt and sugar and an apple – 13.6 grams of fiber.


Vegetable curry with tomato sauce, onion and spices, whole grain rice, low-calorie fruit yogurt – 6.5 grams of fiber. Since yogurt can contain a lot of sugar, you need to check its composition.


A handful of nuts without sugar and salt – 3 grams of fibre.

© Foodism360/Unsplash

Things to remember:

  • the body will take time to get used to a large amount of fiber, so it is worth increasing its share in the diet gradually;

  • need to drink more water to help digestion;

  • fiber in raw vegetables can irritate sensitive stomachs and intestines;

  • Before changing your diet, you should consult your doctor, especially if you have health problems.

What fiber is for and how it affects health


© Shutterstock


Natalia Germanovich

May 20, 2021

Understanding why eating fiber that cannot be digested, how it affects the microbiome, and why it is necessary to avoid its excess in the body

The American Association of Microbiologists has published a study, the results of which show that increasing the fiber in the diet changes the composition of bacteria in the intestine. Experts believe that this will help to learn more about how diet affects the body and why the diet should be enriched with cereals, nuts, legumes, fruits and vegetables [1].

At the moment, according to US research, only 1 in 20 US residents consumes the required amount of fiber daily. Lack of dietary fiber can adversely affect health, reduce immunity and lead to obesity [2].

The material was checked and commented by Zinaida Medvedeva, Executive Director of ANO Healthy Nutrition

Advertising on RBC www. adv.rbc.ru

What is fiber

Fiber is a general term that applies to any type of soluble or insoluble fiber that is not digested. Despite the fact that the body does not use these substances as fuel, they have a strong impact on health [3].

There are two types of dietary fiber:

  • Soluble, that is, those that can be dissolved in water. They help lower blood glucose and cholesterol levels. Foods that contain these substances: oatmeal, nuts, beans, lentils, apples, blueberries.
  • Insoluble, which do not dissolve in water. They help food pass through the intestines. Such substances are found, for example, in whole grain bread, brown rice, legumes, carrots, cucumbers and tomatoes.

In addition, dietary fiber helps the body maintain a healthy weight. High fiber foods tend to be lower in calories. In addition, the presence of fiber can slow down the digestive processes in the stomach. As a result, a person experiences a feeling of satiety longer [4].

According to the recommendations of the European Food Safety Authority, an adequate dose of fiber is 25 g per day [5].

© Shutterstock

American doctors believe that the daily norm for women is 21–25 g (approximately 5–6 apples) and 30–38 g for men (7–8 apples) [6]. However, much depends on the age and health of the person.

Research on adequate fiber intake for children is limited and somewhat inconsistent.

How Fiber Affects the Microbiome

UC Irvine conducted a small study with 26 participants. For the first week, they all followed their normal diet, after which they were tested. In the second week, they switched to a high-fiber diet, eating approximately 40 g of dietary fiber per day. In the third week, the subjects increased their fiber intake to 50 g. After analyzing the changes in the microbiome, the scientists found that with the new diet, the composition of the gut bacteria of the subjects changed by about 8%. Due to the small number of respondents, this result should be considered preliminary, but now there is reason to believe that due to a change in diet, more organisms that break down dietary fiber may appear in the gastrointestinal tract. They are able to adapt to a healthy diet and better process foods that are low in fat, but rich in vitamins and can strengthen the immune system [7].

In 2018, the American Journal of Clinical Nutrition published a meta-analysis of 64 studies involving more than 2,000 people. According to these data, the presence in the diet of the required amount of fiber led to a greater diversity of the microbiome compared to placebo control groups [8].

How to increase your fiber intake

You don’t need to radically change your diet. The fact is that a sharp transition to a diet rich in dietary fiber can cause unpleasant side effects. For example, bloating and flatulence.

Excessive fiber intake (more than 70 g per day) can lead to cramping, loss of appetite, nutritional deficiencies, vitamins and minerals (especially calcium, magnesium and zinc because fiber can limit their absorption). Another possible adverse effect is an increased risk of intestinal obstruction [9].

© Shutterstock

That’s why it’s best to introduce new foods into your diet gradually, while remembering to drink plenty of water. Then the change in diet will be painless.

One of the leaders in the amount of dietary fiber per 100 g is chia seeds. Due to the high proportions (34.4 g), this product is recommended to be soaked in advance and consumed in small quantities [10].

What foods are high in fiber

Fiber is found in cereals (the less processed, the more fiber), as well as in nuts, fruits and vegetables.

Fiber content of products:

  • Almonds: 13.3 g
  • Dark chocolate: 10.9g
  • Sunflower seeds: 10.3 g
  • Bran: 10.1 g
  • Peas: 8.3 g
  • Lentils: 7.3 g
  • Chickpeas: 7g
  • Beans: 6.8 g
  • Avocado: 6.7 g
  • Raspberry: 6.5 g

Zinaida Medvedeva, Executive Director of ANO Healthy Nutrition

According to the Lancet magazine, Russians consume much less fiber than they should. However, we are not far behind other developed countries. It all depends on the region, climatic and cultural characteristics.

Whole grains, one of the sources of fiber, are the most deficient foods in Russian diets, according to a large-scale study of major dietary mistakes published in the European Journal of Epidemiology. A low intake of fruits, nuts and seeds rich in dietary fiber was also recorded.

The main issue of the fiber diet is the state of the microbiome. It began to be studied relatively recently, but it is already clear that the influence of intestinal bacteria on the general condition of a person is enormous. Some even call the microbiome the second brain, as it is directly connected to the brain and affects our psychological and emotional state.

© Shutterstock

Increasing your fiber intake looks like a simple, cheap, and effective solution to multiple health problems at once. If you increase your intake of vegetables/fruits/legumes (fresh, frozen, pickled) to the recommended 660 grams per day, you will already get enough fiber.