High consumption of soybean oil has been linked to the risk of developing ulcerative colitis, a form of inflammatory bowel disease (IBD), characterised by chronic inflammation of the large intestine, a study in mice shows.
Soybean oil is the most commonly used edible oil in the US and is increasingly being used in other countries, particularly India, Brazil, and China.
Researchers at the University of California, Riverside, in the US examined the gut of mice that were consistently fed a diet high in soybean oil for up to 24 weeks in the lab.
They found that beneficial bacteria decreased and harmful bacteria — specifically, adherent invasive Escherichia coli — increased, conditions that can lead to colitis.
“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,” said Poonamjot Deol, an assistant professional researcher at the University of California, Riverside.
Deol, a co-corresponding author of the study published in the journal Gut Microbes, explained it is linoleic acid in soybean oil that is the main concern.
“While our bodies need 1-2 per cent of linoleic acid daily, based on the paleodiet, Americans today are getting 8-10 per cent of their energy from linoleic acid daily, most of it from soybean oil,” she said.
“Excessive linoleic acid negatively affects the gut microbiome,” the scientist added.
The team found that a diet high in soybean oil encourages the growth of adherent invasive E. coli in the gut. This bacterium uses linoleic acid as a source of carbon to meet its nutritional demands.
Several beneficial bacteria in the gut are not able to withstand linoleic acid and die off, which results in harmful bacteria growing out. Adherent invasive E. coli has been identified in humans to cause IBD, they said.
“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,” Deol said.
“Further, linoleic acid causes the intestinal epithelial barrier to become porous,” she added.
The barrier function of the intestinal epithelium is critical for maintaining a healthy gut. When disrupted, it can lead to increased permeability or leakiness, the researchers noted.
Toxins can then leak out of the gut and enter the bloodstream, greatly increasing the risk of infections and chronic inflammatory conditions, such as colitis, they said.
The researchers noted that the increase in IBD parallels the increase in soybean oil consumption in the US and hypothesise the two may be linked.
Previously, a high consumption of soybean oil has been linked to obesity and diabetes and potentially autism, Alzheimer’s disease, anxiety, and depression, they added.