High-fat diets decrease good gut bacteria

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Researchers at Case Western Reserve University School of Medicine have shown a high fat diet may lead to specific changes in gut bacteria that could fight harmful inflammation — a major discovery for patients suffering from Crohn’s disease.

Crohn’s disease, a type of inflammatory bowel syndrome, causes debilitating intestinal swelling, cramping, and diarrhea.

The disease affects half a million people in the United States, but its cause is yet unclear.

“The finding is remarkable because it means that a Crohn’s patient could also have a beneficial effect on their gut bacteria and inflammation by only switching the type of fat in their diet,” said Alexander Rodriguez-Palacios, DVM, DVSc, PhD, first author on the study and Assistant Professor of Medicine at Case Western Reserve University.

“Patients would only need to replace a ‘bad’ fat with a ‘good’ fat, and eat normal amounts.”

The study is one of the first to identify specific changes in gut bacteria — our microbiome — associated with Crohn’s disease.

It is also the first to show how high fat diets can alter gut bacteria to combat inflammation. Rodriguez-Palacios presented his results at the annual Digestive Disease Week® conference in Chicago, Illinois earlier this month.

The study was one of six accepted for presentation at the conference out of the laboratory of Fabio Cominelli, MD, PhD, Professor of Medicine and Pathology at Case Western Reserve University, and Division Chief of Gastroenterology at University Hospitals Cleveland Medical Center.

Results from the study could help doctors identify bacteria to use in probiotics to treat patients suffering from inflammatory bowel syndromes.

“Ongoing studies are now helping us to understand which component of the ‘good’ and ‘bad’ fats make the difference in the gut microbes and make mice healthier,” Rodriguez-Palacios said.

“Ultimately, we aim to identify the ‘good’ fat-loving microbes for testing as probiotics.”

The researchers anticipate their findings may have varying effects for patients.

“Not all ‘good’ fats might be good in all patients,” Rodriguez-Palacios cautioned.

“Mice indicate that each person could respond differently. But diet is something we are very hopeful could help at least some patients without the side-effects and risks carried by drugs. The trick now is to really discover what makes a fat ‘good’ or ‘bad’ for Crohn’s disease.”

New research found that when people boosted their fat intake to 40 percent of their daily diet for six months, the number of “good” gut bacteria decreased while “unhelpful” bacteria amounts increased.

“The [study] result showed that a high-fat diet is linked to unfavorable changes in the type and numbers of gut bacteria – collectively known as the microbiome,” said the study’s senior author, Duo Li. He is chief professor of nutrition at the Institute of Nutrition and Health at Qingdao University in Qingdao, China.

In addition to changing the make-up of the microbiome, the study authors also noted an increase in inflammatory triggers in the body.

These changes may contribute to the development of metabolic disorders, such as diabetes and heart disease, the researchers noted.

Nutritionist Samantha Heller, from NYU Langone Health in New York City, said bacteria living in the digestive system appear to have broad-ranging impacts on human health, and that they “eat what we eat.”

“Research suggests that they thrive on plant fibers – such as those found in fruits and vegetables, legumes, nuts and grains – and that the typical Western diet, which is rich in fat, red and processed meats, cheese, sweets, refined grains and fast-fried junk foods, in a sense, poisons them,” she explained.

In China, where the study was done, a traditional diet has been low in fat and high in carbohydrates.

That, however, has been shifting to a diet higher in fat and lower in carbohydrates.

At the same time, the rates of obesity and type 2 diabetes have also been rising, the study authors said.

To see if changes occur in the gut microbiome when people transition from a low-fat diet to a higher-fat diet, the researchers recruited about 200 young people, who weren’t obese, for the study.

Their average age was about 23 years old.

Li said their average fat intake before the start of the study was about 31 percent.

The study volunteers were randomly placed into one of three groups for six months.

One group ate a diet comprised of 20 percent fat, another ate 30 percent of their daily calories from fat, while the third had a 40 percent fat diet.

The researchers altered carbohydrate intake – things like rice and wheat flour—to make up for the changes in fat intake.

The amount of fiber and protein in the diets stayed essentially the same.

All three groups had weight loss, but the lowest-fat group lost the most weight and had the greatest reductions in waist circumference, total cholesterol and bad cholesterol.

The low-fat diet group also had an increase in gut bacteria that have been linked to lower cholesterol levels.

Those on the higher-fat fare had an increase in a different type of gut bug – one that’s been linked to higher cholesterol levels.

Their diet was also associated with “significant” changes in long chain fatty acid metabolism, producing higher levels of chemicals that are thought to trigger inflammation.

Li said the findings may be relevant in developed countries where fat intake is high, but that further research needs to be done to see if similar changes occur in different populations.

“We suggest that fat intake for a general healthy population should not be more than 30 percent of total energy – at least in Asian populations,” Li said, and added that most fat should come from healthy fats, such as soybean, peanut or olive oil.

Nutritionist Heller said it’s important not to “interpret the findings of this study to suggest that dietary fat is unhealthy.

We need to eat fats to be healthy, unsaturated fats in particular.”

But, she added, you can have too much of a good thing. “Fad diets rich in animal fats – such as ‘Keto’ or ‘Paleo’ – over time, are likely to be deleterious to the gut microbiome and subsequently increase the risk of inflammation and chronic diseases,” Heller said.

To keep your microbiome happy and healthy, Heller recommended eating more vegetables, legumes, fruits, grains and nuts, while avoiding processed meats, limiting red meat and cheese, and balancing your intake of fats, carbohydrates and protein.

Results of the study were published online Feb. 19 in the journal Gut.

More information: Duo Li, Ph.D., chief professor of nutrition, Institute of Nutrition and Health, Qingdao University, China; Samantha Heller, M.S., R.D., NYU Langone Health, New York City; Feb. 19, 2019, Gut, online

Learn more about the microbiome from NutritionEd.org

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