Covid risk likely to increase by immune changes induced by high-fat diets: Study

Diets high on fat have been found to affect genes linked to the immune system, brain function, and potentially COVID-19 risk in a new study.

Researchers said that it was the long-term consumption of high-fat diets that were seen to cause the observed changes, and that readers should not panic about a single meal.

The researchers at the University of California - Riverside (UCR), US, fed mice three different diets over the course of 24 weeks where at least 40 per cent of the calories came from fat. They then looked at all four parts of the mice's intestines, along with their microbiome. A fourth control group of mice was fed a low-fat diet.

Compared to the low-fat diet group, all the other three groups were found to experience "concerning" changes in gene expression. These groups were made to consume diets based on saturated fat from coconut oil, monounsaturated, modified soybean oil and unmodified soybean oil high in polyunsaturated fat.

"Word on the street is that plant-based diets are better for you, and in many cases that's true. However, a diet high in fat, even from a plant, is one case where it's just not true," said Frances Sladek, a UCR cell biology professor and senior author of the study published in the journal Scientific Reports.

Further, it may not be possible to "just exercise away these effects", according to UCR microbiologist Poonamjot Deol, the study's co-first author.

"Some people think, 'Oh, I'll just exercise more and be okay'. But regularly eating this way could be impacting your immune system and how your brain functions," said Deol. The team advised about 10-15 per cent of fat consumption everyday.

Some of the intestinal changes brought about by high-diets did not surprise the researchers, they said, such as major changes in genes related to fat metabolism and the composition of gut bacteria.

However, other observations were more surprising, such as changes in genes regulating susceptibility to infectious diseases, including those recognising infectious bacteria and those controlling inflammation, they said.

"So, it's a double whammy. These diets impair immune system genes in the host, and they also create an environment in which harmful gut bacteria can thrive," said Sladek.

The team has previously linked soybean oil-based diets to obesity and diabetes, both of which have been studied to be major risk factors for Covid.

Their latest work examining the impacts of the three high-fat diets have found them to heighten the expression of ACE2 and other host proteins, used by spike proteins of Covid-causing virus to gain entry into the body.

The coconut oil diets were found to impact gene expression the most, followed by the unmodified soybean oil diets, suggesting that polyunsaturated fatty acids in unmodified soybean oil play a role in altering gene expression.

Microbiome changes, on the other hand, were observed to be more pronounced in mice fed with diets based on soybean oil, which the researchers said was the most commonly consumed oil in the US, and is increasingly being used in other countries, including Brazil, China, and India.

They also noted that the findings applied only to soybean oil and not to other soy products, tofu, or soybeans.

Further, the experimental mice being fed these high-fat diets for 24 weeks was like "starting from childhood and continuing until middle age" in human terms, according to Deol.

"One night of indulgence is not what these mice ate. It's more like a lifetime of the food," said Deol.

The team hopes that the study makes people look more closely at their eating habits.