Benefits of a High-Fiber Diet

Specifically, the benefits of a high-fiber (>25 g/day) diet include:

Overall health and wellness

It is well known that increased consumption of dietary fiber helps to maintain health and wellness.  Fibers have numerous health benefits, more and more are being discovered every day.  They can reduce constipation and promote the health of your colon; lower cholesterol, blood pressure, and the risk of cardiovascular disease; and improve blood sugar control after a meal and aid in weight loss.  They can also help reduce diarrhea in some instances.

In particular, the specific benefits of particular types of dietary fibers include:

Reduced constipation (Bulking)

Dietary fiber, including fiber added to foods, can help reduce constipation by adding bulk to the stool.  Bulky feces move through the gut faster, resulting in an increased stool weight and improved regularity.  The increase in fecal bulk also “dilutes” the effect of toxic substances in the colon. Stool consistency, stool weight and frequency of defecation are indicators of colonic function. Increased bulking and decreased transit time are considered as the most widely known beneficial effects of dietary fibers in general. Different kinds of dietary fiber can have different bulking capacities, depending on the underlying mechanism. The bulking effect of dietary fiber that is poorly fermented in the colon is associated with the mass of fiber itself and enhanced in some cases by water binding, which is maintained throughout the whole gastrointestinal (GI) tract.  Fermentable dietary fibers provide a bulking effect mainly due to increased bacterial mass.

Reduced cholesterol levels (Viscosity)

Certain types of viscous fibers (i.e., beta-glucan, psyllium, guar gum) thicken the contents of the intestinal tract and reduce the absorption of cholesterol and glucose.

Studies have linked a high fiber diet with improvements in serum lipids, total cholesterol, low-density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), and triglycerides.  

Epidemiological studies have found reduced rates of coronary heart disease in individuals consuming high amounts of dietary fiber.  A study published in 2011 in the Archives of Internal Medicine reported that a high fiber diet reduced the risk of dying at an early age from a variety of causes, including heart disease, respiratory and infectious diseases, and, among men, cancer.

Reduced blood glucose levels (primarily Viscosity)

Similar to lowering cholesterol levels, viscous fibers also slow down the absorption of glucose and can lower the glycemic impact of foods (causing a lower rise in blood glucose levels). Unlike foods comprised of carbohydrates that are rapidly digested and absorbed in the small intestine, foods containing viscous fibers are associated with a much slower rise in serum glucose that does not reach as high a maximum level.  Similarly, the decline in serum glucose levels after reaching the peak is less rapid. Reduced post-prandial blood glucose levels are considered one of the traditional beneficial physiological effects related to viscous fibers.  Some non viscous soluble fibers such as resistant maltodextrin have also been shown to attenuate post prandial blood glucose response when taken with a meal although the mechanism is not explained by the viscosity.  Many types of fibers lower the glycemic (blood glucose) impact of foods because they substitute for high glycemic flours and sugars in food formulations. 

Increased digestive health (Bulking and Fermentation)

It is well known that dietary fiber promotes a healthy digestive tract.  Some types of fibers provide bulking and help with regularity. Fermentable fibers may be more important than bulking fibers for colonic health because the SCFAs produced by the fermentation actively facilitate digestive health. In particular, butyrate and propionate, two primary short-chain fatty acids produced by the fermentation of dietary fibers, are vital for health and well-being, as they optimize motor activity of the colon, help to regulate physiological intestinal mobility, and contribute to the defense mechanisms of the intestinal barriers. 

In addition, butyrate is the primary and preferred fuel for colon cells.  Emerging evidence suggests that SCFAs may contribute anti-inflammation and anti-cancer benefits as well.

Increased Mineral Absorption (Fermentation)

Fermentable fiber sources may improve the absorption of minerals, especially calcium.  There are several potential mechanisms to explain the favorable effect of prebiotic oligosaccharides on mineral absorption:

• Prebiotics are resistant to hydrolysis by the small intestinal digestive enzymes, and they reach the colon virtually intact, where they are selectively fermented by the microbiota. This colonic fermentation causes a substantial increase in the production of short chain fatty acids (SCFA) and other organic acids that contribute to lower luminal pH in the large intestine which, in turn, elicits a modification of calcium speciation and hence solubility in the luminal phase so that it’s passive diffusion is improved:
• The SCFAs are thought to have a direct effect on transcellular calcium absorption by increasing the exchange of cellular hydrogen for luminal calcium. Modulation of transcellular active calcium transport by increasing the level of the calcium-binding protein calbindin. This is the intracellular carrier protein involved in the translocation of calcium to the basolateral membrane of mucosal epithelial cells. The increased levels of calbindin may be mediated by butyrate.
• Prebiotics have a tropic effect on the gut e.g. cell growth and functional enhancement of the absorptive area.

In ovariectomized rats, Chonan et al. (1995) studied the effect of galacto-oligiosaccharides (GOS) on calcium absorption and prevention of bone loss. Rats fed a diet containing GOS absorbed calcium more efficiently than those on the control diet. More over bone ash weight and tibia calcium content of rats fed the GOS diet were significantly higher than those of the control animals. GOS fermentation, subsequent production of SCFA, lowering of cecum pH, and increase of calcium solubility are mentioned as important factors accounting for the observed effects which are also dependent on the calcium content of the diet.

In humans, the large intestine is not generally associated with calcium absorption, however, the fermentation of prebiotics in the large intestine have been shown to increase calcium absorption there (Macfarlane et al, 2006).

Increased immune support (Fermentation)

Specific fermentable fibers have been shown to provide support for healthy immune function.  Two mechanisms contribute to this benefit: increased levels of beneficial bacteria (i.e., Bifidobacteria, Lactobacillus) and reduced adhesion of pathogens to the colonic cell walls, which aids in flushing them from the digestive tract.

Increased insulin sensitivity (Fermentation)

One of the emerging benefits of dietary fiber is increased insulin sensitivity.  Resistant starch from foods as well as isolated from high amylase corn has been shown to increase insulin sensitivity.  Researchers are suggesting that fermentation in the large intestine may be contributing to this benefit, as the SCFAs produced by the fermentation of resistant starch triggers the production of hormones (Glucagon-like peptide-1 (GLP-1)) related to insulin sensitivity and Peptide YY (PYY)).

In addition, butyrate triggers nutrigenomic shifts in metabolism within the intestinal tract – it up-regulates the production of hormones important to lipid and carbohydrate metabolism, namely GLP-1, PYY and adiponectin. 

Epidemiological studies suggest that cereal fibers may provide a protective effect against type 2 diabetes.

Weight Management (Viscosity and Bulking)

Dietary fiber may contribute to maintaining a healthy weight.  Epidemiological studies have consistently showed that dietary fiber intake is lower for obese adults than for lean adults.  There is significant research investigating the weight management benefits of specific dietary fibers.  The overall data is inconsistent, suggesting that specific dietary fibers contribute weight management benefits, while other types of dietary fibers may have less significant effects.

All types of fiber are needed every day for the body to function well.

References

• Benefits of Fiber
• Mechanisms of Dietary Fiber
• Benefits of a High-Fiber Diet

• Did you know?
• When eaten regularly as part of a diet low in saturated fat, trans fat and cholesterol, soluble fiber has been associated with increased diet quality and decreased risk of cardiovascular disease.