Why is Fiber Important for Digestive Health?

Gut Health: Fiber, Resistant Starch and Prebiotics

The digestive system is one of the most important organ systems in the human body. Besides converting food into energy and basic nutrients for the body, the gastrointestinal tract is responsible for mixing and movement of food, and excretion of wastes out of the body. This ensures proper flow of food and its wastes (Jenkins, et al, 2008). Without this proper movement, you could develop several complications. This include:

  • Gastroesophageal Reflux Disease (GERD).
  • Gallstones
  • Celiac disease
  • Crohn’s disease
  • Ulcerative colitis
  • Irritable Bowel Syndrome (IBS)
  • Haemorrhoids
  • Diverticulitis
  • Anal fissures

Among the various factors that ensure proper movement of food and waste, gut microbiota (gut flora) play a huge role. This community consisting of about 100 trillion microbial cells impacts our nutrition, metabolism, physiology and immune function. Any events that disrupt the microbiota balance could lead to obesity, depression, anxiety and the gastrointestinal disorders listed above. There are various nutritional substances known to improve the health of gut flora. These include fiber, starch, and prebiotics. In this post, you will know more about these substances, and how to achieve optimum gut health.



Also, known as bulk or roughage, dietary fiber is a complex carbohydrate that cannot be broken down by your own digestive system.  It makes up the edible, non-digestible portion of plants. Even then, roughage possesses a host of health benefits. This is because it is partially or fully fermented in the colon by the gut flora (Cummings, et al, 2010). Consuming the recommended intake of fiber, some people will notice an improvement in overall health status.

Unfortunately, some people with intestinal overgrowths or dysbiosis may notice worsening of symptoms with more fiber. In these cases, a lower fiber diet at least for a time may be beneficial.

for those who tolerate fiber, the health benefits include:

  • Easier weight loss- Fiber-rich foods are bulky and leave you feeling satiated for extended periods after consumption. This ‘fullness’ feeling reduces your appetite, and by extension your calorie intake. Thus, you can keep a healthy weight.
  • Reduced constipation and healthier bowel movements- Soluble fiber absorbs water as it moves along the GI tract. This guards one against developing diarrhea and constipation. In a study comparing bowel movements in members of African tribes and Americans, this benefit is more apparent. The study found out that the tribesmen, whose diet consists up to 100 grams of fiber daily, had a healthier stool, with no evidence of constipation, diarrhea or any diseases of the colon popular in the white population that buys processed foods.
  • Improved cardiovascular health- Fiber is also known to fight heart attacks and strokes! Taking fiber-rich foods interferes with the enterohepatic pathway- the network consisting of portal veins and the liver. Fiber ensures that Cholesterol from bile is transported along with other excretory wastes, reducing the levels of triglycerides and LDL cholesterol. This slows down the hardening of the arteries, lowering the chances of cardiac arrest and stroke.
  • Blood glucose regulation- since fiber is only partially broken down, consuming roughage does not raise blood glucose levels. Diabetics engaging in a fiber-rich diet report better control of blood sugar than those who don’t.

Types and Sources of Dietary Fiber

Generally, fiber is categorized according to how easily it absorbs water. There are two main types: soluble and insoluble fibers (Dreher, 1987).

Soluble fiber absorbs water, turning into gel while moving along the digestive tract. It helps to slow down digestion. Soluble fiber also helps improve cardiac health, regulate blood sugar, ease weight loss and improve bowel movement (Walters, et al, 2015). To increase your intake of soluble fiber, we advise that you take oat bran, barley, seeds, legumes, vegetables, and nuts.

Insoluble fiber mostly passes through our digestive tract intact, adding bulk to the excretory waste. Insoluble fiber helps ease the movement of food through the stomach and intestines. It helps improve weight loss and digestive health. It is mainly found in whole grains, wheat bran, and vegetables.


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Fiber deficiency and recommended intake

According to dietary experts, over 60% of the American population consumes less than half of the recommended daily intake (about 12 grams per day). This shocking statistic is evidenced by the common incidence of gut disorders, including Irritable Bowel Syndrome (IBS) and Crohn’s disease.

One major reason for this deficiency is the use of processed foods. Processes used in mass production and refining of foods typically strip the fiber content. The fact that these foodstuffs are convenient for today’s fast paced life only worsens the scenario, as processed foods make up about 45% of the American diet.

Medical and dietary experts agree on the optimum amount of fiber every individual needs. The table below shows the Recommended Daily Amounts (RDAs) for different classes of individuals.

 Above Age 50Between Age 18-50Ages 11-17Ages 6-10Ages 2-5
Children  25g/day20g/day15g/day


Fiber Intake Issues and Limitations

While it is hard to overstate the importance of roughage in our diets, we also need to watch how we incorporate it into our food schedule. Failure to do this may result in complications of the gut. Some considerations/limitations we should take into account include:

Switching suddenly from a low to high-fiber diet creates flatulence (gas) and may result in abdominal pain.

Experts warn those with gut inflammations, especially in the colon, to reduce fiber intake. This is because, fiber-rich foods take a while to digest, causing internal distress (Weston & Nguyen, 2016). In our clinic, we also observe that many of our clients who have gut issues that we identify on labs like Small Intestinal Bacterial Overgrowth (SIBO) do worse with more fiber until SIBO is fully resolved. They may temporarily do better with a lower fiber diet.

Diets with a large percentage of fiber are linked to a decrease in absorption of various crucial minerals. These include zinc, calcium, and magnesium. Partaking a fiber-rich diet could lead to a deficiency of these minerals in some individuals. Balancing fiber intake with nutrient dense foods and/or skillfully chosen supplements is recommended.

Resistant Starch (RS)

Many consider this a third classification of fibers. RS is a kind of starch that reaches the large intestines intact since it is not acted upon in the small intestines and stomach. Therefore, we do not gain a significant amount of calories or blood sugar when we ingest resistant starch. RS is mainly classified into four: Type 1, Type 2, Type 3 and Type 4.

RS stimulates beneficial gut flora within the colon. This helps maintain a regular balance of bacteria. By fermenting RS, gut flora produces short chain amino acids such as propionate, acetate, and butyrate (Clifton, et al, 2001). Butyrate is the main element behind the praise RS gets for its health benefits.

Cells along the intestinal wall prefer to use Butyrate as their main source of energy. Butyrate is also known for its anti-inflammatory properties and is useful in cancer protection, immunity, weight loss and therapy for digestive disorders.

RS also helps improve insulin sensitivity and regulate blood sugar levels. Its other benefits pertain to weight loss, as RS results in lower appetite and reduced fat storage in fat cells. RS also alters the gut flora, to favor a lean individual and to foster weight loss.


To add RS to your diet, incorporate green bananas, legumes, plantains, cooked and cooled parboiled rice and potatoes. You could choose other forms of RS supplementation too, including using Bob's Red Mill Unmodified Potato starch, 1-4 Tbsp starting slowly and psyllium husk fiber (Susan, et al, 2002).


While experts recommend that you include RS in your diet, it is important to take baby steps. In the first few weeks, about a ¼ teaspoon is enough for a day, with steady increases. As the gut flora gets acquainted with the new hang of things, you should expect some gas and bloat. Those with microbial dysbiosis may experience a bit of gut distress at the onset. If this persists with smaller doses of RS, it’s a clear indication that the starch feeds Small Intestinal Bacterial Overgrowth (SIBO) and you should seek medical care.


These are edible, non-digestible foods that promote healthy gut microbiota. Prebiotics differ from probiotics in that prebiotics improve/ maintain the health and balance of gut bacteria while probiotics introduce these bacteria into the system (Glenn, et al, 2004). In this post, we have already discussed two prebiotics; fiber and resistant starch.

Prebiotic fiber is abundant in a variety of fruits and vegetables including the husk of apples, bananas, beans, chicory root, artichoke, garlic, and onions. To reap maximum benefits, experts advise that you consume these foods on a regular basis.

Benefits of prebiotics

If you consume a diet high in prebiotics, you’ll enjoy various health benefits, including:

  • Reduced risk of cardiovascular disease.
  • Improved GI health.
  • Better digestion.
  • Lower stress response.
  • Improved immune function.
  • Favorable hormonal balance.
  • Reduced inflammation and autoimmune response.
  • Reduced likelihood of obesity and weight gain.

Having explored the various determinants of gut health, we should all strive to improve the health of our digestive tract, as it is crucial to the functioning of most other systems in our body.

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  1. Jenkins, D. J., et al. "Dietary fibers, fiber analogues, and glucose tolerance: importance of viscosity." Br Med J 1.6124 (2008): 1392-1394.
  2. Stephen, Alison M., and John H. Cummings. "Mechanism of action of dietary fiber in the human colon." (2010): 283-284.
  3. Dreher, Mark L. Handbook of dietary fiber. An applied approach. Marcel Dekker, Inc., 1987.
  4. Walters, R. L., et al. "Effects of two types of dietary fiber on faecal steroid and lipid excretion." Br Med J 2.5970 (2015): 536-538.
  5. Price, Weston A., and Trung Nguyen. Nutrition and physical degeneration: a comparison of primitive and modern diets and their effects. EnCognitive. Com, 2016.
  6. Topping, David L., and Peter M. Clifton. "Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides." Physiological reviews 81.3 (2001): 1031-1064.
  7. Pryde, Susan E., et al. "The microbiology of butyrate formation in the human colon." FEMS microbiology letters 217.2 (2002): 133-139.
  8. Gibson, Glenn R., et al. "Dietary modulation of the human colonic microbiota: updating the concept of prebiotics." Nutrition research reviews 17.02 (2004): 259-275.

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