by Dr. Aaron Zadek ND, CISSN

Dietary fiber plays an important role in maintaining gut health and function.  Fiber is useful in helping feel full after meals, ensuring our bowel movements are regular as well as stimulating the growth of healthy bacteria to allow the gut microbiome to thrive. It is important that fiber, both soluble and insoluble, is included in everyday consumption to ensure optimal gut health (1). These fibers are found in a variety of different foods as well as prebiotic and full fiber supplements that can be used in times of bowel irregularity or for general health and maintenance. 

Fiber for healthy bowel movements 

Insoluble fibers are traditionally found in higher amounts in vegetables, wheat, and most grains.  They have the remarkable capacity to hold water and to bulk up stool, resulting in more gentle bowel movements that are softer, reducing incidents of constipation as well as the abdominal straining.  Reduction in abdominal straining is particularly important as straining is thought to potentially result in increased incidents of haemorrhoids, varicose veins as well as pressure related changes to the bowel known as diverticula. 

Useful in both diarrhea and constipation

One of the most interesting things to know about fiber is how it can alter the speed of transit of bowel contends depending on the situation. We’ve already discussed how insoluble fiber can help improve stool softness and increase transit time in times of constipation; it is important to note that soluble fiber can also do this to a lesser extent. In times of undesired loose bowel movements or diarrhea, insoluble fiber helps slow transit time so that loose stools can become more bulky.

Insoluble fiber is also used as fuel for the bacteria found in the colon, stimulating growth of a number of beneficial bacteria that ferment the fiber to form short chain fatty acids that improve the health of surrounding bowel and lower the pH of the intestine to improve gut flora (2). One type of insoluble fiber, Xylooligosaccharide (XOS), is particularly useful as a prebiotic that promotes growth of Bifidobacterium –important inhabitants of healthy guts known for helping provide stability and prevention of disease (3).   XOS is also able to lower cholesterol, improve blood sugar as well as absorption and production of B-complex vitamins (2).

Fiber to feel full

Soluble fiber, found in fruits, oats, barley as well as legumes, can combine with liquids to form a gel that slows gastric emptying. This gel can help activate stretch receptors in the stomach, providing a pronounced feeling of fullness which can decrease overeating. Soluble fibers are also especially useful in their ability to lower blood cholesterol by reducing fat abortion.   

Fiber to improve blood sugar

Both soluble and insoluble fibers have been shown to improve glycaemic control and reduce cholesterol in those with type 2 diabetes mellitus (4). Those that consumed a diet rich 50 g of fiber per day (fruits, vegetables, grains and legumes) for six weeks had significant improvements in their fasted blood glucose levels and urinary glucose levels. It was recommended that 50% of the fiber be soluble to help ensure that overconsumption of carbohydrates was limited and to delay gastric emptying so that carbohydrate levels in the small intestine were more consistent over time without quick increases. 

Works Cited

1. Gaby, Alan R. Nutritional Medicine. 1st. Concord : Fritz Perlberg Publishing, 2011. pp. 211-214.

2. Xylooligosaccharides: an economical prebiotc from agroresidues and their health benefits. Jain, Ira, Kumar, Vikash and Satyanarayana, T. 2015, Indian Journal of Experimental Biology, pp. 131-142.

3. The Role of Bifidobacteria in Health. Reyed, Reyed M. 2007, Research Journal of Medicine and Medical Sciences, pp. 14-24.

4. A diet containing food rich in soluble and insoluble fiber inmproves glycemic control and reduces hyperlipidemia among patients with type 2 diabetes mellitus. Mcintosh, Michael and Miller, Carla. 2, 2001, Nutrition Reviews, Vol. 59, pp. 52-55.

5. Mechanism and experimental and epidemiological evidence relating dietary fiber (non-starch polysaccharides) and starch to protection against large bowel cancer. Bingham, Sheila A. 1990, Proceedings of the Nutrition Society, pp. 143-171.

6. Polyphenols, glucosinolates, dietary fiber, and colon cancer: understanding the potentail of specific types of fruit and vegetables to reduce bowel cancer progression. Eid, Noura, et al., et al. 2014, Nutrition and Aging, pp. 45-67.

7. Soluble fiber polysaccharides: effects on plasma cholesterol and colonic fermentation. Topping, DL. 1991, Nutrition Review, pp. 195-203.