Role of Dietary Fiber in Digestive Health

Dietary Fiber

Sep 28, 2022Imtiaz Hami

Traditionally the Indian population’s diet consisted of surviving on dal/chhole or rajma, roti / unpolished rice. Often people ate parboiled rice and subji and cucumber or salad. Frequently, chutney was also included in the meal.
All over the world it has been found that people who ate whole grains, plenty of fruits and vegetables as per the season, had less health problems, particularly non-communicable diseases like diabetes mellitus and heart disease. Unfortunately, we have changed our dietary habits and with this, more and more people have developed diabetes. Do you know that India is home to the second largest number (77 million) of adults with diabetes worldwide? Initial studies highlighted that there were differences between diets like the ones our older generations consume. Research on why these differences existed revealed that their diets contained something that had been overlooked and that was fiber or what we call dietary fiber.

Dietary fiber (commonly called roughage or bulk) acts like a brush in our gastrointestinal tract, helps to remove the waste and toxins from our bodies and significantly reduces the risk of several health problems ranging from constipation to cancer.

DF are also referred as non-starch polysaccharides (NSP) which are carbohydrate fraction excluding starch and free sugars. Since NSP are not digested hence they do not provide calories whereas starch and free sugars are digested thus provide calories. NSP content of cereals is comparatively low but once the starchy portion in some cereal by-products has been separated away the NSP content is greater. NSP is present in cell wall of the grain and is mostly present in the bran or husk.

Dietary fiber is primarily present in a variety of plant foods in various forms and in varying amounts. DF includes components like cellulose, hemicelluloses, lignin, gums, mucilage, fructo-oligosaccharides, pectin, and other associated minor substances. Each type of fiber differs from each other in its physical form (particle size), water holding capacity and chemical composition. Hence, they have different physiological action(s) on the body. These characteristics are evident in the functional changes that occur during cooking and digestion. Three major mechanisms are believed to be responsible for the benefits of DF, including bulking, viscosity, and fermentation.

In general, DF is divided into two types:

  1. Soluble Dietary fiber (SDF) which dissolves in water
  2. Insoluble Dietary fiber (IDF) which does not dissolve in water
Dietary fiber types

Soluble Dietary fiber (SDF): SDF are soluble in water and form a gel-like material. They include non-cellulosic polysaccharides such as pectin, β-glucans, gums, mucilage, guar gum, gum-Arabic and arabinoxylans. Most of the SDF are fermented in the colon by the bacteria; increase viscosity of the contents in the gut/intestines and exhibit prebiotic effect.

Some of the SDF are fermentable fibers which promote the growth of beneficial bacteria in the intestine. These bacteria in the colon, produce short chain fatty acids (SCFA), which bring favourable changes in the gut thereby they confer numerous beneficial effects and thus improve our health.

The SCFA also play an important role in regulating metabolism, inflammation, and development of disease. They have been found to be anti-inflammatory, antitumorigenic and antimicrobial. They also have a role in maintaining homeostasis (equilibrium) in the gastrointestinal tract and of the immune system.

Hence, they delay gastric emptying, regulate blood glucose levels, lower serum cholesterol levels, thereby help normalize stool formation by softening hard stool in constipation and firming loose or liquid stool in diarrhoea.

Soluble fibre is present in foods like oats, apples, citrus fruits, psyllium (isabgol), barley, flaxseed etc. Soluble fiber can help lower total blood cholesterol levels and lower low-density lipoprotein (LDL) levels. Soluble fiber can provide us with 2 kcal/g.

Insoluble Dietary fiber (IDF): IDF is not soluble in water and consists mainly of cell wall components and includes cellulose, hemicellulose, and lignin. In plants, cellulose gives rigidity and strength to plant cell walls. It is present in bran of cereals, millets, and pulses as well as nuts, vegetables (green leafy vegetables, immature /green beans), and fruits.

It provides bulk to the food and gives satiety and several health benefits such as weight management. It promotes movement of the material through the digestive system, and increases stool bulk and is helpful for persons who either have constipation or irregular stools.

The amount of soluble and insoluble fiber varies in different plant foods. To receive the greatest health benefit, eat a wide variety of high-fiber foods. Insoluble dietary fiber is also acted upon by the bacteria in the large intestines or colon. Including enough insoluble fiber in the diet could also help to manage blood sugar and reduce risk of developing type 2 diabetes.

So the benefits of a high-fiber diet are:

  • Normalizes bowel movements by increases the weight and size of your stool as well as softening it. Bulky stools are easier to pass, and decrease chance of constipation. Conversely, for a having loose, watery stools, fiber may help to solidify the stool because it absorbs water and adds bulk to stool.
partial view of woman holding paper made large intestine on grey background

partial view of woman holding paper made large intestine on grey background

  • Helps maintain bowel health, reduces our risk of developing hemorrhoids (piles) and problems like diverticular disease, colon cancer as well as blood pressure and inflammation.
  • Aids in achieving healthy weight. This is because foods that are high in fiber foods are more satiating and tend to be more filling. So we will not feel hungry soon as we do in case of low-fiber foods, so we are likely to eat less often and stay satisfied longer. Also more fiber generally means that the energy density of the food will be less i.e. they will be less “energy dense,” i.e. they have fewer calories for the same volume of food.
Female leg stepping on weigh scales
Female leg stepping on weigh scales. Healthy lifestyle, food and sport concept.

To reap the physiological effects of the fiber, several form of fiber like bran (wheat bran, oat bran, apple fiber, soy bran, etc.), guar gum, β-glucans are used by food processors to develop innovative, health promoting or functional products by modifying the texture, rheology and other properties of food systems and improve the marketability of food products. For example, bran is added to the wheat flour while making noodles. Other fiber rich cereal products in the market are whole grain bread, biscuits, and steamed bread etc.

Recommended intake of dietary fiber

The Indian Council of Medical Research and National Institute of Nutrition (ICMR-NIN, 2020) has recommended safe intakes of dietary fiber – as 40 g/2000 kcal. Even children in the age group of 1-9 years should consume fiber containing foods that can be in the form of fruits, green leafy vegetables and other vegetables along with whole pulses and whole grain cereals and millets, instead of refined foods.

mother feeding fibre food to child in the lap

Although there are no negative effects of dietary fiber, but in some people, it may cause abdominal discomfort because of flatus formation. Excessive intake of DF > 60g/d can lead to flatulence, abdominal distension and even diarrhea. Hence fiber intake should be gradually increased giving the gastrointestinal tract enough time to adapt. Drinking plenty of fluids is advisable along with consumption of high fiber diet in order to soften the fiber. Excess dietary fiber may reduce absorption of some minerals like calcium, iron, magnesium, copper, and zinc. Some evidence suggests consumption of fiber along with fluid and some fat is more beneficial as it promotes the smooth flow in the alimentary canal.

Dietary sources of dietary fiber

Dietary sources of dietary fiber

Ingredients for the healthy foods selection. The concept of healthy food set up on dark stone background.

Any food containing 2.5 g fiber /serving is considered a good source of DG. Animal foods including dairy do not contain any fiber. Fruits (sapota, pears, and oranges), vegetable (corn, peas, jackfruits, and broccoli), pulses (whole Bengal gram, green gram lentils, chickpeas, beans), and whole grains (wheat, maize, millets) are known to contain good amounts of DF. Though spices are consumed in lesser amounts but contain high amount of dietary fiber such as coriander seeds, and cumin seed. Flaxseed is an excellent source of DF containing lignan and used in several diseases. We must remember that milling, peeling and overprocessing the food strip away not only the DF content but the beneficial effect of that food item itself.


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