GUT CHECK

Bad diets today can alter our great-great-grandkids’ biology

When we think of heritable traits, eyes and hair color are near the top of the list. But there’s a lot to be said for the attributes we can’t see, like our microbiome, the millions of tiny bacteria and other organisms that live in our bodies.

Researchers have compared (paywall) our microbiome, to an entirely separate organ for all of the work it carries out: The microbes living on and within us help make vitamins, break down foods, and even protect us from certain infections. We receive our microbiome from our mother as our “zeroeth birthday present” as Ed Yong put it in 2010. In the long-run, scientists think our microbiomes are likely shaped by the foods we eat, starting with breastmilk, and the company we keep; as we touch other people, tiny organisms are transferred from one body to another through contact with our skin.

Scientists at Stanford University found that over time, if a mother doesn’t have a diverse microbiome in her gut to pass down to her children, it becomes more difficult for her offspring to cultivate one. Their work was published (paywall) in Nature yesterday, Jan. 13.

Erica Sonnenburg, a microbiologist, and her team observed mice that had been given the same population of microbiomes that exist in people. According to Sonnenburg, the mice can act as hosts to human bacteria just as well as people do—and can pass them along in similar ways. Over time, the researchers fed some of the mice diets rich in fiber, similar to those that our ancestors likely ate, and other mice diets with less fiber, much like the average modern Western diet high in fat and protein.

By going through their stool samples, they found that mice with high-fiber diets had more diverse microbiota. Once the mice eating less fiber switched to a high-fiber diet, their gut microbiomes repopulated to have more diverse single-cell organism populations. “If you limit the amount of dietary fiber, the diversity [of the microbiota] drops; some of these species become so low in abundance they’re not being passed on,” Sonnenburg told Quartz.

Then, in a second part of the study, researchers followed the mice’s offspring. The offspring of mice that ate less fiber started off with less diverse gut microbiomes.

Yet even when these offspring were switched to high-fiber diets, their microbiomes didn’t repopulate with a wider diversity of organisms right away; it was only when these mice were given fecal transplants with additional bacteria that their microbiomes regained additional types of organisms. In other words, it was even harder to establish healthy levels of gut bacteria.

In acute cases of depleted microbiomes, like when we take antibiotics, having fewer gut microorganisms can leave our bodies susceptible to other infections. But in chronic cases, the science is murkier. “We don’t quite understand how a low diversity microbiota affects long-term health,” says Sonnenburg.

Existing research shows that populations that eat much more fiber, like the Hadza tribe living in Tanzania, have much richer (paywall) gut microbiomes. “We know that the microbiota is wired into our immune system,” says Sonnenburg, adding that the Hadza tribe doesn’t become sick with the same diseases like cancer and diabetes that Westerners do. “And so the question is, ‘Are less diverse microbiota at the root or an increased burden to Western disease?'”

In the meantime, she says that the best thing we can do is make sure our own diets contain foods that support as many gut bacteria as possible. This means supplementing our food intake with high-fiber foods, like green leafy veggies, oats, and starchy vegetables like sweet potatoes and corn.

If not for you, do it for those who may receive your microbiome one day.

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