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Experts say fast foods can produce higher levels of destructive bacteria that harm the gut. Luka TDB/Getty Images
  • Researchers say consuming too much fast food and other unhealthy foods can harm your gut microbiome.
  • They said people who have a diet high in processed and animal-derived fatty foods develop greater levels of destructive bacteria.
  • They recommend a diet that consists mainly of vegetables, fish, nuts, and legumes.

Eating too many Big Macs could hit you right in the gut, a new study suggests.

Researchers from the Netherlands report that a diet full of high fat and high sugar foods – items found in most fast foods – can lead to an unhealthy gut microbiome.

The gut microbiome is the collection of bacteria, fungi, and viruses that live in your bowels that affect everything in your body, from inflammation to heart health.

An unhealthy microbiome increases your risk for inflammatory bowel disease and irritable bowel syndrome, as well as diabetes and even cancer.

In the study with 1,425 people in the Netherlands, researchers said that those who consumed a diet high in processed and animal-derived fatty foods had greater levels of destructive bacteria that produce toxins that harm the gut.

On the flip side, people whose diets consisted of more plants and fish had higher levels of healthy bacteria with anti-inflammatory effects.

“The microbiome contains trillions and trillions of microbes and microorganisms,” said Dr. Rudolph Bedford, a gastroenterologist at Providence Saint John’s Health Center in Santa Monica, California. “The gut microbiome essentially helps to train the immune system in childhood and adulthood, recognize and react to various harmful microbes that may enter the body also helping to the immune health. The microbiome is a very important aspect of our general health.”

The study dug into which dietary habits increase colonies of healthy bacteria, particularly Roseburia, Faecalibacterium, and Eubacterium.

“We showed that dietary patterns comprising legumes, breads, fish and nuts are associated with a lower abundance of clusters of opportunistic bacteria, pathways for the synthesis of endotoxins and inflammatory markers in stool,” the study authors write. “Higher proportions of these bacteria and pathways have been implicated in IBD and colorectal cancer.”

Conversely, diets too high in fatty foods and meat were associated with higher levels of more harmful bacteria.

“We here observed a positive association of the total fat intake and meat consumption with [bacteria] species that are dominant in the upper GI tract and oral cavity, while the opposite direction was found for plant-derived foods,” they wrote. “Higher colonization of these bacteria in the intestine has been reported in IBD, liver cirrhosis, colon cancer.”

Aside from the health benefits of lowering your fat, animal protein, and sugar intake, consider that what you eat determines the health of an entire living ecosystem within you.

“I like to think of the microbiome as a 3- to 5-pound garden that we have living inside of us,” Dr. Elroy Vojdani, the founder of Regenera Medical in Los Angeles, told Healthline.

“What you feed that garden dictates what type of plants grow in that garden. If you feed it fuel that supports anti-inflammatory healthy bacteria, such as plant-based fibers and plant-based fats then you get a garden that has healthy, good bacteria and yeast living inside of it,” he explained. “If you feed the garden processed foods, sugar, and animal fat, then weeds will grow in that garden. Essentially, it’s a living and breathing biomass that is very responsive to what you put into it. When you put in healthy things, you get healthy things out.”

And if you have to eat fast food regularly, stay away from the burgers and fries.

“Vegetables, vegetables, vegetables,” Bedford told Healthline. “Salad if you have to go to a fast food restaurant, and cut down on the amount of dressing as they typically contain a lot of sugars. But that’s really about it – there are not too many other good fast foods out there, so to speak.”