Weight gain and metabolic syndrome are not a rite of passage, though some people seem to think they just come with the territory of getting older. Dr. Laura C. Bridgewater, professor of microbiology and molecular biology at BYU, asks: “How did we come to think that’s a normal way to age? Because it’s really not.”

At a recent gerontology conference on campus, she said that at least 25% of the adult population in most of the United States is obese, according to reports from Centers for Disease Control and Prevention. Quite a bit of research has been done on obesity and its causes. 

The Myth of Obesity Causes

While there is some evidence that obesity is genetic, it’s not enough to explain it entirely, says Bridgewater. “You look at families and think ‘okay, it runs in the family.’ There is a genetic component, but on the other hand, people who live together often share dietary habits and exercise habits.”

Lack of willpower can’t be the sole culprit either. “We all know people who seem to live on junk food and never gain weight,” she said. There is one aspect, however, that seems to play a crucial role in obesity and overall health: gut microbiota.

What is Gut Microbiota?

Gut microbiota is made up of all the microbes that live in the gut, with bacteria being the most abundant, explains Bridgwater. Healthy gut microbiota can do wonders for our bodies: they make vitamins, protect us from infection, regulate our metabolism, and harvest calories and nutrients from foods that are otherwise indigestible. Diversity in the gut microbiota makes the whole system more resilient. The more diverse the microbiota, the more good it can do.

Gut Microbiota in Research

“The evidence [that] gut microbiota [are related]…to obesity is very strong,” said Bridgewater. Researchers who transferred gut microbiota from obese mice to lean mice found that, over time, the mice who had received the gut microbiota from the obese donors ended up obese. Lean mice who received gut microbiota from lean donors stayed lean.

Researchers in Malawi found that the same process works with human microbiota. They took gut microbiota from severely malnourished children and from healthy children and transferred them into germ free mice. All of the mice were then fed a typical Malawian diet of roots and grains. The mice with the gut microbiota from the malnourished children stayed malnourished and the mice with the gut microbiota from the healthy children stayed healthy. Although they were eating the same thing, the gut microbiota from the malnourished children couldn’t harvest all the nutrients from the diet.

Research at BYU and U of U

Bridgewater has been involved in an ongoing study with colleagues from the University of Utah and BYU. The study, which is being funded by the BYU Gerontology Program, looks at how diet affects the gut microbiota and, by extension, overall health. The researchers started with two groups of mice. Each group was composed of both mutant mice with a high metabolic rate and wild mice. They fed each group a specific diet for six months.

Group one was fed a western style diet. It was composed of 40% fat, 43% simple carbohydrates, and 17% protein. Group two was fed normal mouse chow, which was plant-based and consisted mostly of corn, grains, soybeans, etc. The researchers tested the mice monthly to collect gut bacteria samples and check for diabetes.

After six months, Bridgewater and her fellow researchers observed that all the mice on the western-style diet had gained weight, whether or not they had a high metabolic rate, while the majority of the mice on the normal chow diet had stayed at a healthy weight. They also found a striking trend: all of the mice on the western-style diet had less diversity in their gut microbiota. Some had also developed diabetes.

Eating a Western Diet is Risky

Eating a western style diet is risky, says Bridgewater. While not all the mice on the western- style diet in the study developed diabetes, some did. It just depended on how their gut microbiota changed. All the mice on the western style diet lost diversity in their gut microbiota, making them more vulnerable to other illnesses and diseases.

While gut microbiota, genes, and diet all have an impact on obesity, some of those contributors also impact each other. There is evidence that gut microbiota influence diet by causing cravings, says Bridgewater. Certain bacteria want a certain type of nutrients. For example, if your gut microbiota is made up of a kind of bacteria that can thrive on dietary fats, they can make you crave foods that are high in fat. Eating that food will keep the bacteria happy, but according to Bridgewater, “these might not be the kind of bacteria you want growing.”

What You Can Do

According to Bridgewater, the best thing you can do to support a healthy gut microbiota is to feed it good food. Eating plant foods that provide a lot of plant fiber, like vegetables and grains, is really important. This fiber is indigestible to us, but our gut microbiota can digest it. The healthy microbiota use this fiber to produce metabolites that help us. A lot of things, including genes, impact our gut microbiota, says Bridgewater, but research shows that “we do have some control over what grows in our gut.”

Dr. Bridgewater is a professor of Microbiology and Molecular Biology in BYU’s College of Life Sciences. She served as chair of the Department of Microbiology and Molecular Biology from 2011 to 2014. She holds a PhD in Genetics from George Washington University and a BS in Microbiology from BYU