Study: High-fat diets affect immune health, brain function

A recent study of three different high-fat diets found all three diet patterns caused changes in intestinal gene expression, associated with issues like obesity and irritable bowels, as well as immune health and brain function.

For the study, published in Scientific Reports, researchers fed mice one of four diets over a period of 24 weeks. Three of the diets studied a different type of fat: coconut oil, high in saturated fats; genetically modified (GM) soybean oil, high in monounsaturated fats; and conventional soybean oil, high in polyunsaturated fats. In addition, some mice were assigned to a low-fat, high-fiber control diet.

The high-fat diets were designed to replicate the current American diet, providing 40% of calories from fat and low fiber.

Researchers studied the microbiome of the mice, as well as genetic changes in all four parts of the intestines. Compared to a low-fat, high-fiber control diet, the high-fat diets altered the expression of certain intestinal genes. Genes that were affected by the high-fat diets included those linked to the immune system, brain function and the gut.

“The majority of dysregulated genes can be grouped into one of two categories — metabolism (generally increased) and the immune system (typically decreased) — and are associated with various pathological conditions and diseases ranging from colon cancer, inflammation and inflammatory bowel disease (IBD) to leaky gut and infectious diseases, including Covid-19,” researchers wrote.

For example, the high-fat diets negatively affected the genes that recognize infectious bacteria, as well as genes that affect cytokine signaling. Both play a role in regulating the body’s susceptibility to infectious diseases, including Covid-19.

Similarly, the high-fat diets dysregulated genes related to neurotransmitter signaling.

The findings support the impact of the diet on the gut-microbiome-brain axis to not only affect immune health and metabolism, but brain health as well, the researchers contended.

“There were … several genes involved in the metabolism or transport of neurotransmitters — including endocannabinoids, dopamine and serotonin, gamma-aminobutyric acid (GABA), glutamate and glycine — that are dysregulated by the [high-fat diets] and could impact brain health,” the researchers wrote.

In the microbiome, researchers noted the high-fat diets increased populations of some pathogenic and opportunistically pathogenic bacteria in the small intestines and the colon, compared to the control diet. They also indicated a “notable” decrease in beneficial bacteria in the small intestines and colon among the mice that consumed the high-fat diets, compared to control.

Importantly, coconut oil showed the most changes in terms of gene expression, followed by the conventional soybean oil. The greater impact of conventional soybean oil on intestinal gene expression is likely the result of its content of linoleic acid, per the study.