Short Term Increase in Prebiotic Fibers Makes a Big Difference

I’m on a bit of a fiber kick right now!

A study just came out of the University of California, Irvin, which caught my interest.  Did you know that on average, Americans eat way less than 50% of the recommended daily intake of fiber?   And that low fiber intake is associated with type 2 diabetes, heart disease and colon cancer?  (Well, you knew the colon cancer ‘cause I put up a post on it yesterday on the Biome Buzz Facebook page, which I’m sure you all look at daily…)  According to this article, “A profound decrease in the consumption of dietary fiber in many parts of the world in the last century may be associated with the increasing prevalence of type II diabetes, colon cancer, and other health problems. A typical U.S. diet includes about 15g of fiber per day, far less fiber than the daily recommended allowance. Changes in dietary fiber intake affect human health not only through the uptake of nutrients directly but also indirectly through changes in the microbial community and their associated metabolism” [i]

I’ve talked about this multiple times on this blog – how little fiber we consume in the industrialized world compared to preindustrial societies, where people typically consume 60-120 grams per day!  I was FLOORED when I read, in this paper, that in one study, exchanging a low-fiber western-type diet in African-Americans for a rural African high fiber diet (at least 40 grams per day of fiber) led to a “significant decrease in precancerous biomarkers.

And how’s this for a timely COVID-pandemic-era fact:  did you know that dietary fiber has been shown to protect against influenza?  And may influence vaccine efficiency?!

This study was to assess what even a short-term increase in fiber could do for the gut bacteria and metabolite production. The subjects: students in an undergraduate biology course.  The subjects were given 10 high fiber meals of unprocessed foods per week for 2 weeks.  During this time, they collected stool samples to track the fecal microbiome.  The students also recorded all their food consumption including macronutrients; they had to reach a goal of 50 grams of fiber per day during the 2 weeks.

The researchers compared the bacterial composition as well as short-chain fatty acid production, as well as specifically running extra tests to look at levels of Bifidobacterium, which are known fiber degraders.  They found that this short intervention significantly altered the gut microbiome, including a sizeable increase in the levels of Bifidobacterium, as well as an increase in Lactobacillus.  Prevotella levels, which, as you know are associated with plant-based diets, also increased. They did not, however, detect a change in levels of short-chain fatty acids.  Still, the results were dramatic enough that the researchers want to conduct longer tests, and to learn more about how fiber intake can promote good health.

A side note from a summary of this research on News-Medical Net: the comments of the course instructor struck me as particularly interesting – how both she and the students were amazed by what foods were high in fiber, specifically noting berries, avocados, beans and legumes.[ii]   The students raised their fiber intake by an average of 25 grams per DAY…and several started from essentially zero grams of fiber per day. According to the professor, in participating in this research the students became extremely interested in what they were eating:  “”I think this experience will have a life-long impact on how we all look at nutrition labels.”  It’s really a shame how little about nutrition we are taught when we are young.


[i] Andrew Oliver, Alexander., et al. (2021) High-Fiber, Whole-Food Dietary Intervention Alters the Human Gut Microbiome but Not Fecal Short-Chain Fatty Acids. mSystems.


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