Fiber Focus Month Blog Post

By Vida Velasco-Popov, MS Student at PACE University

January for many is a time for change and new beginnings, so it seems fitting for RDs to celebrate this time as National Fiber Focus month! This topic is especially dear to me, as I am a strong advocate for increasing fiber consumption especially here in the United States where the average American only consumes about 15g of fiber per day When comparing this value to current dietary reference intakes, which are 38g/day for men and 25g/day for women, we see a clear need to encourage further consumption of fiber It is well known that adequate fiber intake plays a role in reducing cholesterol levels, improving blood glucose levels, easing bowl movements, and regulating body weight, all of which contribute to combating disease and improving overall health     

Fiber comes from a variety of different plant sources, and is categorized as non-starch polysaccharides, resistant starches, or resistant oligosaccharides Within these categories, fiber possesses different properties pertaining to relative solubility, viscosity, and fermentability, which influence overall function Fiber plays a critical function providing fuel for gut microbes resulting in the production of short chain fatty acids, vitamin K, and vitamin B12, all of which are essential components needed in healthy diets Though much is known with regards to health benefits gained by increasing fiber intake, still much remains unknown in terms of how fiber affects different gut microbe populations, and what microbial changes take place in response to specific dietary foods. Looking to the future, we see a tremendous opportunity for RDs to further new discoveries within this domain and to promote a shift toward advancing our current understanding of human nutrition.

When we think about the human gut microbiome, which contains 150 times more microbial genes than our own, it seems logical for so many researchers to take an interest in understanding the functions and optimization of this key system Though research is still ongoing with regards to fiber and prebiotics, we do know that dandelion greens, chicory roots, chia seeds, artichokes, garlic, almonds, flaxseeds, onions, oats, and barley all serve as prebiotics supporting the growth of healthy gut microbes Though beneficial effects of probiotics, or foods containing live health-promoting microbes are widely explored, prebiotics - the fuel source for probiotics, remain somewhat underrepresented. Prebiotics derived from fiber rich sources play a variety of beneficial roles, including supporting the immune system, promoting the growth of beneficial microbes, increasing production of beneficial metabolites, enhancing calcium absorption, and promoting the growth of lactobacilli species, which for women promotes vaginal health by reducing risk for infections Furthermore, fiber-rich diets have been associated with a higher prevalence of Firmicutes, a bacterial phylum with butyrate producing bacteria protective against colitis 

An interesting recent study conducted by researchers at Stanford University explored how fiber and probiotics influence the gut microbiome in 36 healthy adults ages 51±12 years over a 17-week period  Participants were assigned to one of two groups where they consumed either a high-fiber or high-fermented food diets. Food intake was recorded and submitted every two weeks to confirm compliance and assess dietary effects on the gut microbiome, overall health, and effects on the immune system. Data was collected using blood and stool samples to assess health biomarkers and varied microbial species. Baseline food intakes revealed the average participant followed primarily a western diet prior to the intervention phase In the high-fiber group, participants ate significantly less packaged food and were able to improve nutrient intake profiles while decreasing overall consumption of salt and animal-based proteins  Additionally, participants from the fiber-rich group reported an increase in softening of stool throughout the study

What I found particularly interesting were the findings related to changes in microbial species and overall effects on inflammation. Upon the conclusion of the study, microbiota within the high-fiber group was found to have enhanced capacity to degrade complex carbohydrates while bacterial growth increased significantly Though one might expect an overall decrease in inflammation in the high-fiber group, inflammatory biomarkers were surprisingly inconsistent across participants  One sector of the participants from the fiber rich group had increased inflammation while others were found to have decreased inflammation  After comparing baseline microbial genomes among fiber-rich group participants, researchers found that those showing higher inflammation at the end of the study had less microbial diversity and generally ate fewer plant foods than those who showed decreased levels of inflammation at the end of the study These results suggest a more nuanced approach for increasing fiber intake to improve gut health and support the immune system. Limited initial microbial diversity could limit the ability of a fiber-rich diet in supporting the immune system and decreasing inflammation.                

With regards to the high-fermented foods group, researchers found an overall increase in microbial diversity at the end of the study and an overall decrease in inflammatory cytokines In contrast with the high-fiber group, the high-fermented foods group did not show an increase in microbial proteins as we saw in the high-fiber group, this suggests microbial metabolic capacity within the gut may require fiber to increase capacity Furthermore, the simple introduction of microbial species from fermented foods alone may not contribute to enhancing overall capacity to degrade complex carbohydrates. Though the sample size was relatively small, and study focused on healthy participants, the implications behind this study open the door for further understanding how the gut microbiome varies in its response to the presence of fiber and how the combination of fiber and probiotics may serve to enhance gut health while supporting the immune system. There’s still much to learn with regards to fiber and the gut microbiome, which urges me to look toward the future in which the dietetic field is ever evolving. With the addition of new technologies, we may understand nutrition on an even deeper level, eventually seeing to the gut and its inhabitants as our true canary in the coal mine.

References

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3.                  Kaur AP, Bhardwaj S, Dhanjal DS, et al. Plant Prebiotics and their role in the Amelioration of Diseases. Biomolecules. 2021;11(3):440. doi:10.3390/biom11030440

4.                  Myhrstad MC, Tunsjø H, Charnock C, Telle-Hansen VH. Dietary fiber, gut microbiota, and Metabolic Regulation—current status in human randomized trials. Nutrients. 2020;12(3):859. doi:10.3390/nu12030859

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7.                  Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16). doi:10.1016/j.cell.2021.06.019