The trillions of microorganisms residing in our guts play fundamental roles in many aspects of human health, including immune function and metabolism. However, the reduced microbial diversity observed in Western populations to that in populations living traditional lifestyles presents the question of the contributing factors driving changes throughout modernization. Microbiota-accessible carbohydrates (MACs) found in dietary fiber play a critical role in shaping this microbial ecosystem but are notably reduced in the Western diet, which is high in fat and simple carbohydrates and low in fiber, compared with a more traditional diet.
Fiber is important: doctors and nutritionists alike have probably told us all at one point in our lives that we need to include more fiber in our diets. Many Western populations, including the US, eat significantly less than the recommended daily intake of 25 to 38 grams of fiber, which is dramatically affecting our future health.
You probably also know that fiber helps keep you regular; however, did you know that it also feeds your microbiota?
Surprisingly, new research has also shown that including the recommended daily dose of fiber in your diet may also benefit your offspring.
Low-Fiber diets and the microbiome
In one study, researchers transferred gut microbes of a “healthy” human into germ-free mice and fed two groups either high- or low-fiber diets.
Scientists observed a significant decrease in diversity within the low-fiber diet group after a few weeks. However, when two mice from each group bred, microbial changes in the low-fiber group were passed on to the next four subsequent generations. In offspring from the high-fiber group, diversity flourished within each new generation.
The scientists attempted to reverse diversity loss in the low-fiber diet group by increasing their fiber. Although this experiment seemed to succeed in the first generation of mice, it was less effective in subsequent generations. The lowest microbial diversity was observed in the last generation studied, the fourth generation, despite eating a high-fiber diet. Only a quarter of the bacterial species found in previous generations were found in their gut microbiome. Researchers did succeed in restoring microbial health in these mice through fecal transplants.
These results indicate that prolonged, cross-generational damage to the gut microbiome may not be reversible merely through diet, and could ultimately explain why obesity in humans prevails despite dieting and exercising.
Researchers believe that the low-fiber diet group of mice likely lost bacteria that were capable of digesting fiber.
Humans produce thousands of enzymes that aid in breaking down dietary fiber that otherwise would be useless. The leftovers are not only fuel for the bacteria digesting the fiber, but for human cells as well.
Sonnenburg, E.D., Smits, S.A., Higginbottom, S.K., et al. Diet-induced extinctions in the gut microbiota compound over generations. Nature, 2015. DOI: 10.1038/nature16504