Can a healthy microbiome prevent depression or cancer?

“Every kind of living thing is dependent on communities of microbes we call microbiomes, and that includes humans,” says Lita Proctor.

Proctor is director of the Human Microbiome Project, an eight-year research mission of the National Institutes of Health to explore the role of our microbiome in human health and disease.

“So much of our human history of exposure to bacteria and viruses has been through infectious diseases and plagues, that it’s hard to wrap our heads around the idea that microbes also play a major role in supporting our health.”

In fact, they break down undigested food, make vitamins, prime our immune system, secrete neurotransmitters that allow nerve cells to communicate with each other, help defend us against invading bugs, and more.

Can that “more” include fighting off or even treating serious diseases?  Here’s some of what we know so far.

Diabetes.

In 2010, Dutch researchers reduced insulin resistance—which often leads to type 2 diabetes—in nine men by transplanting into their intestines solutions containing the gut microbiomes and feces of men who were not insulin resistant.  Can “fecal transplants” actually prevent—or even help reverse—diabetes? Several studies are looking.

Depression.

In an Irish study, the gut microbiomes of 34 people with serious depression had fewer and less diverse microbes than the gut microbiomes of 33 similar depression-free people.

Interestingly, rats that got transplants of fecal microbes from the people with depression were more likely to show signs of anxiety and less interest in appealing food than rats that got transplants from people without depression.

Autism.

Small pilot studies find that the gut microbiomes of children with autism are different from other children’s gut microbiomes.  But that doesn’t mean that the microbiomes caused the autism. Autistic children often have diarrhea or constipation or abnormal eating habits, which could alter their microbiomes.

However, when researchers at the California Institute of Technology transferred gut microbes from autistic children into mice, the animals started exhibiting repetitive behaviors and had trouble interacting with others, two characteristics of people with autism. The study hasn’t yet been published.

Colorectal cancer.

People with colo­rectal cancer have different gut microbiomes than people without the cancer, but that could be either a cause or a result of the disease.

The evidence for the microbiome as culprit isn’t clear. After being exposed to a carcinogen, mice that got fecal transplants from other mice with colorectal cancer developed more and larger tumors than mice that got fecal transplants from healthy mice.

But when researchers exposed mice to a carcinogen after giving them fecal transplants from humans with colon cancer, the mice had no more tumors than mice that got transplants from healthy people.

Heart disease.

Red-meat eaters have bacteria in their gut micro­biomes that convert the carnitine in meat into what eventually becomes TMAO, a compound that speeds up artery clogging. That may help explain why people who eat red meat have a higher risk of heart disease. Vegetarians have less of that kind of bacteria, and they don’t produce much TMAO when given a carnitine supplement.

To play it safe, avoid supplements that contain carnitine, unless they’ve been prescribed.

Asthma.

Children who are exposed to a host of microbes in the environment while growing up—if they live on a farm, for example­—are less likely to have asthma. But studies looking at whether more diverse gut microbiomes are linked to a lower risk of asthma are inconsistent.13 Nor have studies consistently implicated a specific group of microbes as risky.

And in four trials, children aged five months and younger who were given probiotics for 3 to 9 months were just as likely to develop asthma or wheezing as those given a placebo.

Ulcerative colitis.

The gut microbiomes of people with chronic inflammation and sores in the lining of their colon have lower diversity and a different makeup of microbes than the microbiomes of healthy people. But it’s not clear whether that’s a cause or a result of the disease.

Canadian researchers gave 38 UC patients weekly fecal-transplant enemas for six weeks. By the end of the study, 9 were in remission, compared with just 2 of 37 who got placebo enemas.

Best food for your gut microbiome.

While we wait for more research into the role of our microbiomes in health, the best food for your gut microbiome remains fiber.

“Eating dietary fiber is associated with a very different microbiome, one that’s richer, with a higher number of bacterial species compared with eating a low-fiber diet,” says Stanford University’s Elisabeth Bik.  More diversity appears to be a sign of a healthy microbiome.

“But you can’t get the fiber from a drink or a pill,” notes Lisa Proctor. “You have to present your microbes with a diverse array of fibers from a lot of different plant materials, such as beans and green vegetables.”

Think of yourself as a zookeeper for the community of little creatures inside you, adds Bik. “Eating fiber is good not just for us: It also keeps them happy.”

Sources: Gastroenterology 143: 913, 2012;  J. Psychiatr. Res. 82: 109, 2016; Microb. Ecol. Health Dis. 26: 26914, 2015; Microbiome 2: 20, 2014; MBio 4: e00692-13, 2013; N. Engl. J. Med. 368: 1575, 2013; Yale J. Biol. Med. 89: 309, 2016; Pediatrics 132: e666, 2013; Transplant Proc. 48: 402, 2016; Gastroenterology 149: 102, 2015.

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