Every time you eat whole grains, fresh fruit and vegetables – foods very rich in dietary fibre, which is a type of carbohydrate present in plants – you are not only taking care of your health, but also nourishing some of the trillion microbes inhabiting your gut that, in turn, take care of you. And as a new study suggests, your diet not only conditions your health and microbial community but also those of your children, grandchildren and even great grandchildren.
According to the results of research led by microbiologists of Stanford University and published in Nature, you do not just pass your genes on to your offspring, but also a whole gut ecosystem shaped in response to your dietary habits. If fibre intake plummets, so does the richness and diversity of bacteria living in the gut.
In a study conducted with mice, Justin and Erica Sonnenburg and colleagues at Stanford University wanted to simulate the effects of a low-fibre diet on the gut microbes of mice. To do so, they transplanted microbiota from a human donor (a 36-year-old American man) to a group of 10 germ-free mice.
They then separated the rodents into two groups: one was fed a diet rich in fibre and the other just the opposite. The animals were monitored for seven weeks and although in the beginning the microorganisms present in the mice’s guts in both groups were similar, after some weeks the rodents on the low-fibre diet showed a depletion in the diversity of their gut microbiota. In fact, they had 60% fewer bacteria species compared with the animals following the control diet.
Researchers switched the food regime of the microbiota-depleted mice and put them on the control diet to check whether they could recover some microbial diversity. This was partly achieved when a high-fibre diet was reintroduced, although 33% of all species remained at low or undetectable levels.
What about those mice’s offspring? Would they also suffer the consequences of this depletion? In order to answer this question, the scientists bred four generations of both groups of mice. They observed that the pups from the mice following a low-fibre diet showed a reduced microbial richness in every generation. Indeed, the fourth generation showed 72% less microbiota diversity. If those pups were switched to a high-fibre diet, their microbial community experienced a small recovery, but remained 67% lower than in rodents that had always been fed with a high-fibre diet.
Recent studies have linked the benefits of higher dietary fibre intake to less cardiovascular disease and lower body weight. Nevertheless, humans cannot metabolise the complex dietary carbohydrates found in fruit and vegetables nor obtain energy from them; rather, gut microbiota does it for us.
In light of the results of this research, it seems that once an entire population has experienced the depletion of key bacterial species, simply ‘eating right’ may no longer be enough to restore these lost species to the guts of individuals within that population.
We must not forget, however, that the study has been carried out with mice, so caution must be exercised before extrapolating results to humans. In fact, as the authors point out in their article, the next step will be to test whether the same results are relevant to humans.
Erica D. Sonnenburg, Samuel A. Smits, Mikhail Tikhonov, Steven K. Higginbottom, Ned S. Wingreen, Justin L. Sonnenburg. Diet-induced extinctions in the gut microbiota compound over generations. Nature, 2016; 529 (7585): 212 DOI: 1038/nature16504
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