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• Researchers report that a diet high in fat can increase the risk of diseases such as colon cancer.
• They add that high-fat eating habits can also affect the immune system and brain function.
• Experts say that even small changes in a person’s diet can have a positive impact on overall health.

Researchers at the University of California Riverside say high fat diets affect genes linked to obesity, colon cancer, and irritable bowels.

They add that the high-fat diets also adversely affect the immune system, brain function, and a person’s risk of getting COVID-19.

In their study published in the journal Scientific Reports, the authors acknowledged other studies have examined the effects of a high-fat diet, but that their research “is unusual in its scope.”

Details from the high fat diet study

For their research, scientists fed mice three different diets over 24 weeks. At least 40% of the calories from the diets came from fat.

The researchers then examined genetic changes in all four parts of the mice’s intestines.

One group of mice consumed a diet based on saturated fat from coconut oil. The second group took in a diet based on monounsaturated, modified soybean oil. The third group consumed an unmodified soybean oil diet high in polyunsaturated fat.

Even though mouse studies don’t always translate to humans, researchers noted that mice share 97% of people’s working DNA.

When compared to a low-fat control diet, all three groups of mice “experienced concerning changes in gene expression,” which is the process of turning genetic information into functional substances like protein.

“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, the study’s lead author and a UC Riverside cell biology professor, in a press release.

The significance of the findings on high fat diets

The team said the findings are concerning because people in the United States consume more soybean oil than any other oil. It’s also increasingly used in countries such as China, India, and Brazil.

Researchers said some of the changes they observed weren’t surprising, such as those they saw in genes related to gut bacteria and fat metabolism.

What was surprising was the changes seen in genes regulating susceptibility to infectious diseases.

“We saw pattern recognition genes, ones that recognize infectious bacteria, take a hit. We saw cytokine signaling genes take a hit, which help the body control inflammation,” the study authors wrote. “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.”

The research also showed all three high-fat diets increased the expression of ACE2 and other host proteins used by COVID-19 spike proteins to enter the body.

Researchers added that high-fat food increased signs of stem cells in the colon.

“You’d think that would be a good thing but actually they can be precursors to cancer,” said Sladek.

Soybean oil vs. coconut oil

In the study, coconut oil showed the greatest number of changes in terms of gene expression, followed by unmodified soybean oil.

The team reported differences between the two soybean oils, suggesting polyunsaturated fatty acids in unmodified soybean oil — primarily linoleic acid — help alter gene expression.

The team found negative changes to the microbiome were more pronounced in mice given soybean oil. They said this wasn’t surprising as they’d previously documented other negative health effects of high soybean oil consumption.

They noted they had previously found the oil could affect genes in the brain related to autism, anxiety, depression, and Alzheimer’s disease.

The researchers said the findings only apply to soybean oil and not to other soy products, tofu, or soybeans themselves.

Reaction to the high fat diet story

Dr. Anton Bilchik, a surgical oncologist as well as the chief of medicine and the director of the Gastrointestinal and Hepatobiliary Program at Saint John’s Cancer Institute in California, told Medical News Today that the study provides important information.

“It’s showing three different fat diets negatively impact the immune system and microbiome throughout the entire intestinal tract – from the duodenum to the colon,” said Bilchik, who was not involved in the study. “High fat diets suppress genes that are important in the immune system and alter the function of the trillions of bacteria throughout our bodies (the microbiome).”

“The result of this is that we don’t have the defenses to fight diseases such as inflammatory bowel disease and colon cancer,” he added. “These changes can have a deleterious effect on brain function.”

Dr. Babak Firoozi, a gastroenterologist at MemorialCare Orange Coast Medical Center in California, told Medical News Today that the high fat diets did appear to alter gene expression.

“What that means is that in the cell, certain genes can be overactivated and certain genes can have their activity reduced,” said Firoozi, who was not involved in the research. “Based on the study, this effect increased metabolism and decreases the immune response.”

“It also appears to negatively affect the gut bacteria or microbiome, leading to a higher presence of pro-inflammatory bacteria,” he added. “This translates into an increased risk of developing inflammatory bowel disease, diabetes, and cancer.”

Dr. Sudarsan Kollimuttathuillam, an oncologist and hematologist at City of Hope Orange County in California, told Medical News Today that consuming high levels of fat doesn’t alter the sequencing of DNA directly.

“But the evidence demonstrates the foods you eat affect how your body expresses – turns ‘off’ or ‘on’ – the myriad genetic possibilities your DNA has encoded within it,” said Kollmuttathuillam, who also was not involved in research. “Gene expression ultimately plays a major role in cell functions that increase or decrease the long-term risk of diseases such as obesity, heart disease and cancer.”

Advice on high fat diets

How should people respond to the study?

“I see many patients who say they are benefiting from limiting their intake of unhealthy fats, refined sugars, and highly processed foods,” Kollmuttathuillam said. “These patients often report improvement in side effects of their cancer treatment and increased overall health and wellness. Research also suggests that a diet rich in plants, whole foods, healthy fats and high-quality carbs – a Mediterranean-like diet, for example – helps reduce the risk of several of the most common types of cancer, including colorectal, prostate, and breast cancer.”

Dr. Shiara Melissa Ortiz-Pujols, an obesity medicine specialist and surgeon at Northwell Health in Staten Island, New York, told Medical News Today people can improve their health by making small changes in their diet.

“Eating less processed foods and less fast foods can help us to be healthier,” said Ortiz-Pujols, who was not involved in the study. “Even changing our cooking oils to olive oil is a small but realistic change that can promote positive changes in our microbiome.”

“Small changes in our diet can lead to big changes in our health,” she added. “When we talk about diets, we often think about restriction and short-term commitments. I would recommend not thinking about changing what you eat as a diet. Instead, think about making small changes to what and how we eat that will become lifelong habits. If we focus on making small changes, we are more likely to be successful.”