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Mouse guts demonstrate the multi-generational impact of low-fiber diets on microbial diversity

The next time you’re in the grocery store, consider the idea that you’re not just shopping for yourself. In addition to the enjoyment and nutrients you might gain, what you eat also makes an impact on the multitudes of bacteria that live in your digestive tract. In addition to the nutritional needs of your microbiome, recent research has found that what you munch on might also make a difference in the guts of your children, as well as your grandchildren. So what are all these microbes interested in eating? Fiber, and lots of it.

Fiber isn’t easy for us to digest, at least not on our own. Unlike animals that have multiple stomachs to help break down tough bits of cellulose, dextrins or pectins, humans have to get what we can from dietary fiber in the first round of digestion. Fortunately, bacteria living in our guts can help with this, as they help break down fiber by targeting what are known as microbiota-accessible carbohydrates. By fermenting these carbs, the bacteria feed themselves, and make a bit of fuel that our bodies can reclaim as well. If that weren’t enough of an incentive, well-fed microbes have also been linked to lower rates of allergies, infections and autoimmune diseases.

Starving the microbiome in sterile mice

Researchers at Stanford University wanted to see how long a gut’s microbiome could last without its favorite foods, checking to see just how strict a diet these bacteria were on. This would be a difficult test to control in humans, so mice were raised in a sterile environment, and with no natural bacteria of their own. That way, the starting microbiome could be controlled by seeding the mice’s’ guts with bacteria laden feces from a healthy human. It doesn’t sound appealing, but it made for mice that could healthily digest meals without any problems.

After a few weeks of a healthy, high-fiber diet, half the mice were switched to meals lacking in fiber, which made a clear impact on their gut bacteria. Bacteria populations declined in 60 percent of the sampled species in just seven weeks. Unfortunately, putting giving those mice extra whole grains and veggies didn’t really undo the damage— returning to a high-fiber diet restored some bacterial diversity, but the mouse guts were still 33 percent more homogeneous than before.

This simplified gut ecology persisted, even in other mice. Researchers compared gut bacteria in multiple generations of mice, and continued to see the impact of even temporary low-fiber diets. Fourth-generation low-fiber mice showed 72 percent less microbial diversity, and could only recover five percent of their stunted microbiome when switched to a high-fiber diet. Aside from the loss of bacterial diversity, researchers also noted a decline in glycoside hydrolases, the proteins that bacteria use to help digest fiber in the first place.

Is your bacterial diversity doomed already?

It’s good to keep in mind that this study was in an unusually controlled environment with a small number of mice. It shouldn’t be taken as a perfect proxy for human digestion, as we generally get exposed to a variety of bacteria in our everyday life, and usually eat a wider variety of foods than mice do. So while the mice needed to be isolated from these factors in order to properly test the possible impact of food, the degree of isolation likely makes a difference. With that said, most Americans don’t eat their recommended helping of 25 grams of fiber a day, and so it probably couldn’t hurt to eat more fresh produce, beans and whole grains in our diets. We can’t say for sure if our great-great grandchildren will notice the effects, but we’ll probably feel better while we wait for them to be born.

Source: Low-fiber diets make gut microbes poop out by Bethany Brookshire, Scicurious

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