Updated: Jan 13, 2022
Your Ultimate Guide to understanding what dietary fiber is and its multi-fold impact on our body.
Dietary fiber is a plant matter that is non-digestible by human digestive enzymes.
Some can be fermented and digested by gut microbiota. They are carbohydrates and can be classified as polysaccharides which are present as cellulose in vegetables, hemicellulose in cereal fiber, pectins in fruits and vegetables, stabilizers in manufactured foods, gums, or as non-polysaccharides, present as lignins. In addition to this, they can be soluble fiber that dissolves in water forming gel-like material, and insoluble fiber does not dissolve in water.
TYPES - SOLUBLE AND INSOLUBLE FIBER, RESISTANT STARCH:
Soluble fibers have profound effects on carbohydrate and lipid metabolism. They are fermented to gas and short-chain fatty acids in the colon and contribute little to fecal bulk because the acids are rapidly cleared. On the other hand, insoluble fibers are responsible for increasing the bulk of the feces. In addition, soluble fibers appear to prolong the rate of gastric emptying and intestinal transit time. The insoluble fibers reduce gastric emptying and intestinal and colonic transit times.
Resistant starch is defined as a portion of starch that cannot be digested by amylase in the small intestine and passes to the colon to be fermented by microbiota. It has positive benefits on human health through prebiotic effects, laxation, hypocholesterolemic and hypoglycemic effects and reducing the risks of ulcerative colitis and colon cancer.
CARDIOVASCULAR HEALTH AND ROLE OF FIBER:
Cardiovascular diseases such as coronary heart disease (CHD), stroke, and hypertension, affects more than 80 million people and are the leading cause of morbidity and mortality.
Fiber improves heart health by binding cholesterol and bile salts in the gut, thus interfering in the enterohepatic circulation of cholesterol.
Changes in lipid metabolism suggest that fiber may exert actions in the intestine that facilitate the lipid- and cholesterol-lowering effects of fiber. These include effects on low-density chylomicron synthesis and the site of absorption of lipids. Alternative mechanisms embrace the altered very-low-density lipoprotein (VLDL) turnover. The viscous fiber in oats and apples decreases LDL cholesterol.
Soluble fiber acts like a sponge; it takes up bad cholesterol and takes it out of the body. It reduces bile acid recycling which stimulates the liver to take more amounts from circulation to replenish it.
In addition to that, oligosaccharides fermented in the lower gut produces Short-chain fatty acids which enter into the circulatory system and inhibit fatty acid mobilization and intestinal synthesis and decrease gluconeogenesis.
DIABETES AND ROLE OF FIBER:
Research suggest that consumption of high-dietary fiber especially soluble fiber has an impact on carbohydrate metabolism, lower total cholesterol, and low-density lipoprotein (LDL) cholesterol, and possess other beneficial effects in non-insulin-dependent diabetes mellitus patients (NIDDM). Soluble fiber-containing food takes longer to digest, hence resulting in satiety and weight control. In addition to that, the slowing rate of gastric emptying reduces postprandial hyperglycemia. The possible effects of both soluble and insoluble fiber within the small intestine include changes in mixing, motility, and convection, intraluminal digestion rates, inhibition of maximum transport capacity and altered pH profile.
Many studies concluded that the glucose-lowering effect of fiber as a result of decreased rate of carbohydrate absorption rather than increased total glucose utilization or suppression of hepatic glucose production.
On the other hand, fiber has been shown to reduce pancreatic enzyme activity and decrease pancreatic enzyme secretion.
WEIGHT MANAGEMENT AND ROLE OF FIBER:
Soluble fiber that gets fermented in the large intestine produces two gut hormones which play a major role in inducing satiety.
Dietary fiber may significantly decrease energy intake and thus, helps in maintaining weight.
Fruits and vegetables provides both soluble and insoluble fiber. It has been reported that consumption of both soluble and insoluble fibers increases satiety. A lower intake of dietary fiber indicates an increased risk of obesity. The viscous nature and water holding capacity of the fiber slow down the rate of digestion and absorption of macronutrients. Insoluble fibers that survive transit through the gut, which results in altered satiety and hunger cues, can be different from soluble fibers. Rather than modifying the rate of gastric emptying, insoluble fibers may affect satiety through changes in gut hormones or intestinal transit rate.
IMMUNITY AND THE ROLE OF FIBER:
Dietary fiber modulates properties of the immune system, including those of the gut-associated lymphoid tissues (GALT). As well it changes the intestinal microflora that may potentially mediate immune changes via the direct contact of lactic acid bacteria or bacterial products (cell wall or cytoplasmic components) with immune cells in the intestine; the production of short-chain fatty acids from fiber fermentation; or by changes in mucin production.
CANCER AND ROLE OF FIBER:
Men tend to have a higher risk of colorectal cancer than women.
A meta-analysis study stated that for every 10g of total dietary fiber consumed daily, the risk of cancer was reduced by 9%.
In addition to that, it was observed that dietary fiber from cereals was particularly significant in reducing the risk of colorectal cancer by increasing stool bulk, diluting fecal carcinogens, and slowing down transit time, thus helping in reducing the contact of carcinogens with the colorectal lining.
It has been hypothesized that dietary fiber also reduces breast cancer risk by inhibiting intestinal reabsorption of estrogens and increasing fecal excretion of estrogens.
In India intake of dietary fiber varies among different socioeconomic groups from 15 to 41 g/day. The fiber intake was observed to be lower in women (15-30 g/day) and much lesser in the tribal population (15-19 g/ day). Among the lower-socio-economic group particularly, nearly 80% of the fiber intake is attributed to the consumption of cereal-based diets.
Fiber recommendation depends upon g/1000 kcal and the caloric requirement of men is higher than women.
The Institute of Medicine, which provides science-based advice on matters of medicine and health, recommends 38 grams for men and 25 grams for women of Age 50 or younger, and 30 grams for men and 21 grams for women of age 51 or older.
If your fiber intake is not enough then boost your fiber intake by including the following foods in your diet:
Beans, peas, and other legumes
Nuts and seeds
WAYS TO INCORPORATE FIBER IN YOUR DIET:
Want to know more ideas to include fiber in your meals? Try this:
Maximize plant- based foods in your diet and reduce animal products including dairy.
Switch refined to whole grain: Include half of the grains as whole grains such whole- wheat, whole wheat flour, brown rice, bulgur wheat, amaranth, barley, buckwheat, quinoa, millet, oats, rye.
Include more fruits and vegetables: Eat 5 or more servings of fruits and vegetables a day as they are rich in vitamins and minerals. Add a salad to big meals. Eat fruits, don’t drink them.
Avoid baked foods: Use whole grain flour instead of white flour.
Consume legumes: They are an excellent source of fiber. Use them in nachos and salad
IN SUMMARY, HERE ARE THE 5 SALIENT FACTS ABOUT FIBER:
It is a longevity food as it protects us from many diseases such as heart attack, stroke, and diabetes by affecting insulin sensitivity and reducing developing colon cancer which are the main causes of death among the population. It is the healthiest ingredient in our diet.
The preferred food of gut microbiome: When you feed (fiber) your gut bugs they heal your body and they are the body’s best friends.
When gut bugs consume fiber, they produce short-chain fatty acids- butyrate, acetate, and propionate (post biotics) and as result, they heal the gut, empower good bacteria, suppress inflammatory bacteria namely Escherichia coli, Salmonella Shigella, prevents Alzheimer’s disease.
All different plants contain different types of fiber and they feed different types of the gut microbiome.
Eating a diversity of plants in the meal is the best way to optimize the diversity of the microbiome.
Aaron I. Vinik, MD David J.A. Jenkins, MD (1988) Dietary Fiber in Management of Diabetes, Diabetes care, Vol. 11 (https://care.diabetesjournals.org )
Position Of The Indian Dietetic Association: Dietary Fibre And Health December 2018 (http://idaindia.com/wp-content/uploads/2018/12/IDA-position-paper-fibre-24.12.18.pdf )
P. D. Schley and C. J. Field (2007) The immune-enhancing effects of dietary fibers and prebiotics British Journal of Nutrition (https://pubmed.ncbi.nlm.nih.gov/12088522/ )
Andrew N. Reynolds, Ashley P. Akerman (2020) Dietary fiber and whole grains in diabetes management: Systematic review and meta-analyses, PLOS medicine (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7059907/ )
“5 Facts About Fiber You Need To Know” (https://www.youtube.com/watch?v=EMsgV6RUZtc )
“Dietary Fiber: The Most Important Nutrient?” (https://www.youtube.com/watch?v=EtnTuTX4L24&t=4433s )
Diane F. Birt et al (2013) Resistant Starch: Promise for Improving Human Health, doi: 10.3945/an.113.004325