Soybean Oil-Rich Diet Can Hurt Your Gut Health, Potentially Leading to Colitis: Study

Soybean oil in a supermarket. (ShutterStock)

Hold onto your stir-fry pans! New research has sizzled its way onto the food scene, suggesting a diet high in soybean oil might not be as gut-friendly as previously thought.

Soybean oil, by far the most widely consumed and produced edible oil in the United States, has been linked to ulcerative colitis, a chronic inflammatory bowel disease, according to a new study (pdf).

“Our work challenges the decades-old thinking that many chronic diseases stem from the consumption of excess saturated fats from animal products and that, conversely, unsaturated fats from plants are necessarily more healthful,” Poonamjot Deol, an assistant professional researcher in the Department of Microbiology and Plant Pathology and a co-author of the paper, said in a press release.

The researchers conducted experiments on mice using a total of five diets. They also performed in vitro experiments using cultured bacteria. The findings indicated that a high-fat diet based on soybean oil could accelerate the onset of colitis, disrupt the gut microbiome, impair immune cell regulation, and impact gut metabolites.

“It’s the combination of good bacteria dying off and harmful bacteria growing out that makes the gut more susceptible to inflammation and its downstream effects,” Ms. Deol said.

What Makes Soybean Oil Unhealthy?

Excessive intake of linoleic acid, one of the five fatty acids found in soybean oil, is what concerns the researchers. Typically, soybean oil contains approximately 55 percent linoleic acid.

Linoleic acid is an essential polyunsaturated fatty acid necessary for normal growth and development. However, it cannot be produced within the body and must be obtained through the diet.

Although it is estimated that the human body requires 1 to 2 percent of total calories from linoleic acid on a daily basis, excessive intake has already been associated with an increased risk of coronary heart disease, potential adverse effects on brain function, and potential links to various metabolic issues. “Americans today are getting 8 to 10 percent of their energy from linoleic acid daily, most of it from soybean oil,” Ms. Deol said.

Results from the study revealed that although the soybean oil-rich diet alone does not directly cause colitis, it does hurt intestinal barrier function, resulting in increased susceptibility to colitis.

Furthermore, it disrupts the balance of a crucial protein known as hepatocyte nuclear factor 4 alpha (HNF4A), which has been linked to both colitis and colon cancer.

Additionally, a metabolomic analysis indicated an imbalance between omega-6 and omega-3 fatty acids.

These factors, whether individually or in combination, are likely to contribute to an unfavorable gut environment that can lead to the development of colitis.

This may also explain why the study's authors also noted a parallel between the rise in inflammatory bowel disease cases and increased soybean oil consumption in the United States, suggesting a possible connection.

Furthermore, the study's authors discovered that olive oil and a genetically modified soybean oil variant containing 7.42 percent linoleic acid did not elevate susceptibility to colitis.

These findings suggest that the elevated linoleic acid content in regular soybean oil may be the determining factor in its potential connection to colitis.

Linoleic Acid Composition in Cooking Oils

Soybean oil is one of the most used edible oils in restaurants thanks to its low price, high smoke point, neutral flavor, and generally allergen-free properties.

Oils With Higher Linoleic Acid Content

Various vegetable oils, such as corn, safflower, grapeseed, and sunflower, have higher linoleic acid content than soybean oil, according to a study (pdf).

Oils with higher linoleic acid content. (The Epoch Times)

Oils With Lower Linoleic Acid Content

Canola oil generally contains less linoleic acid than soybean oil, averaging about 20 percent. Coconut, palm, and avocado oils have even lower linoleic acid content, ranging from approximately 2 to 14 percent.

Animal fats contain lower levels of linoleic acid. Lard typically consists of about 10 percent linoleic acid, while butter has a mere 2 percent.

Oils with lower linoleic acid content. (The Epoch Times)

The researchers acknowledged the need for further studies to determine the safe daily intake of linoleic acid.

“We recommend keeping track of the soybean oil in your diet to make sure you are not consuming excessive linoleic acid,” Ms. Deol said. “That is our take-home message.”