Study finds high-fat diets harm immune, gut and brain health

A UC Riverside study that could motivate your New Year’s resolutions shows that high-fat diets affect genes linked not only to obesity, colon cancer and irritable bowel, but also to the immune system, functions brain and potentially at risk of COVID-19.

While other studies have examined the effects of a high-fat diet, this one is unusual in its scope. The UCR researchers fed mice three different diets over a 24-week period, in which at least 40 percent of calories came from fat. Next, they looked not only at the microbiome, but also at genetic changes in all four parts of the gut.

One group of mice were fed a diet based on saturated fats from coconut oil, another received a modified monounsaturated soybean oil, and a third received an unmodified soybean oil high in polyunsaturated fats. Compared to a low-fat control diet, all three groups saw changes in gene expression, the process that turns genetic information into a functional product, such as a protein.

“Word on the street is that plant-based diets are better for your health, and in many cases this is true. However, a diet high in fat, even from a plant, is one case where this is not the case. is simply not true,” said Frances Sladek, UCR professor of cell biology and lead author of the new study.

A new Scientific reports An article on the study documents the many impacts of high-fat diets. Some gut changes didn’t surprise researchers, such as major changes in genes related to fat metabolism and the composition of gut bacteria. For example, they observed an increase in pathogenic E. coli and a suppression of Bacteroides, which helps protect the body against pathogens.

Other observations were more surprising, such as changes in genes regulating susceptibility to infectious diseases. “We saw pattern recognition genes, those that recognize infectious bacteria, take a hit. We saw cytokine signaling genes take a hit, which helps the body control inflammation,” he said. Sladek said.

“So it’s a double whammy. These diets alter the genes of the host’s immune system and also create an environment in which harmful gut bacteria can thrive.”

The team’s previous work on soybean oil documents its link to obesity and diabetes, two major risk factors for COVID. This paper now shows that all three high-fat diets increase the expression of ACE2 and other host proteins that are used by COVID spike proteins to enter the body.

Additionally, the team observed that high-fat foods increased signs of stem cells in the colon. “You would think that would be a good thing, but in reality, they can be precursors to cancer,” Sladek said.

In terms of effects on gene expression, coconut oil showed the greatest number of changes, followed by unmodified soybean oil. The differences between the two soybean oils suggest that polyunsaturated fatty acids found in unmodified soybean oil, primarily linoleic acid, play a role in altering gene expression.

The negative changes in the microbiome in this study were more pronounced in mice fed a soybean oil diet. This was not surprising, since the same research team had previously documented other negative health effects linked to high soybean oil consumption.

In 2015, the team discovered that soybean oil induced obesity, diabetes, insulin resistance and fatty liver in mice. In 2020, the team of researchers demonstrated that the oil could also affect genes in the brain linked to diseases like autism, Alzheimer’s, anxiety and depression.

Interestingly, in their current work, they also found that the expression of several neurotransmitter genes was altered by high-fat diets, reinforcing the notion of a gut-brain axis that may be influenced by diet.

The researchers noted that these findings apply only to soybean oil and not to other soy products, tofu, or soy itself. “There are some really good things about soy. But too much of this oil is just not good for you,” said UCR microbiologist Poonamjot Deol, co-first author of the current study with UCR postdoctoral researcher Jose Martinez-Lomeli.

Additionally, the studies were conducted on mice, and studies on mice do not always translate to the same results in humans. However, humans and mice share 97.5% of their functional DNA. Therefore, the results are concerning because soybean oil is the most consumed oil in the United States and is increasingly used in other countries, including Brazil, China, and India.

By some estimates, Americans tend to get nearly 40 percent of their calories from fat, which mirrors the diets of the mice in this study. “A certain amount of fat is necessary in the diet, perhaps 10 to 15 percent. However, most people, at least in this country, consume at least three times the amount they need,” Deol said. .

Readers should not panic over just one meal. It was the long-term habit of consuming a lot of fat that caused the observed changes. Recall that the mice were fed these diets for 24 weeks. “In human terms, it’s like starting from childhood and continuing into middle age. A night of indulgence is not what these mice ate. Rather, it’s a lifetime of nourishment,” Deol said.

That said, researchers hope the study will make people take a closer look at their eating habits.

“Some people think, ‘Oh, I’ll just exercise more and everything will be fine.’ But eating regularly this way could impact your immune system and brain function,” Deol said. “You may not be able to just eliminate these effects.”