Your Microbiome May Determine Whether Your Diet Succeeds Or Fails

Switching to a healthier diet won't get you too far unless you have the right gut bacteria.
Scimat Scimat via Getty Images

A gut bacteria makeover may not be at the top of your list of resolutions for 2017, but you’d be wise to consider it if your goals have anything to do with improving your diet or losing weight.

New research finds that dietary sacrifices ― say, giving up pizza and hamburgers in favor of a healthy, low-calorie diet ― may be for naught if your intestinal flora are out of whack from a lifetime of eating a standard American diet.

The study, published last week in the journal Cell Host & Microbe, finds that switching from a diet high in calories and processed foods to a plant-based diet may not be very effective (at least initially) if there is still an overgrowth of unhealthy bacteria in the gut. This is because the microbiota already living in your gut determine how well you absorb and processes nutrients, which can affect weight loss, digestion and overall health.

But it’s not all bad news. Over time, a healthy diet will lead to a healthier microbiome ― it just may take longer than you’d like.

“If we are to prescribe a diet to improve someone’s health, it’s important that we understand what microbes help control those beneficial effects,” Dr. Jeffrey Gordon, a biologist at Washington University in St. Louis and senior author of the paper, said in a press release. “And we’ve found a way to mine the gut microbial communities of different humans to identify the organisms that help promote the effects of a particular diet in ways that might be beneficial.”

The gut microbiome ― the community of trillions of bacteria living in the digestive tract ― plays a significant role in the health of the digestive, nervous and immune systems, among other biological systems. These microbes can either aid or prevent weight loss. Diet is one of the main lifestyle factors influencing the makeup of bacteria in the gut, and research has shown that even short-term dietary changes (switching to either a meat-based or plant-based diet) can alter the gut microbial community.

A Tale Of 2 Microbiomes

For the study, the researchers first compared fecal samples of people who followed a calorie-restricted, plant-based healthy diet with those of people with a high-calorie, standard American diet.

As expected, they found that those with the standard American diet had less diverse microbiota, and that people with a plant-based diet had a more diverse (and therefore healthier) microbiome. A diverse bacterial community is beneficial because it helps with digestion, nutrient absorption and immune system function, while an unhealthy microbiome can contribute to inflammation, anxiety, depression, poor digestion and even autoimmune diseases.

Next, the researchers colonized groups of mice with human gut bacteria using the fecal matter samples. The mice were then fed either the native diet of their human donor, or the opposite diet.

Analyzing the microbial communities of the mice revealed that the gut bacteria of both groups of mice changed in response to their new diets. However, the mice with the bacteria of the American diet showed a weaker response to the plant-based diet ― their microbial communities didn’t increase and diversify as much as the mice colonized with the bacteria of the humans who ate a plant-based diet.

The illustration above depicts how gut bacterial communities change in response to dietary interventions.
Cell Host Microbe
The illustration above depicts how gut bacterial communities change in response to dietary interventions.

The researchers did find a way to improve the response of the mice to plant-based diets. When the American-diet mice were co-housed with the plant-diet mice, some of the microbes from the plant-based mice made their way into the microbial community of the mice with the less healthy gut bacteria. With the addition of the bacteria from the plant-based mice, the American-diet mice showed a stronger response to their new, healthier diet. It’s not clear whether bacteria in humans can be transferred from others in the same way.

“Many of these bacteria that migrated into the American diet-conditioned microbiota were initially absent in many people consuming this non-restricted diet,” study author Dr. Nicholas Griffin said in a press release.

All of this isn’t to suggest that your gut won’t benefit from a plant-based diet ― it just may take a little longer than you’d hope to see results. Dietician Meghan Jardine told The New York Times that adopting a more plant-based, high-fiber diet is probably the best way to build a healthier microbiome.

“When you look at populations that eat real food that’s high in fiber, and more plant-based foods, you’re going to see they have a more robust microbiota, with more genetic diversity, healthier species and fewer pathogenic bacteria living in the gut,” Jardine said, according to the Times.

Managing stress levels, eating more fermented foods and exercising also can help boost the level of healthy bacteria in the gut. If you follow a gut-healthy lifestyle, your bacteria will catch up soon enough.

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