The Oil Americans Cook With Most Feeds a Gut Bacterium Linked to Colitis

Your vegetable oil is soybean oil

Pick up the bottle you cook with most nights. Flip it around. The label reads vegetable oil. Underneath, in smaller type: soybean. More than half of all cooking fat sold in America is soybean oil. It sits in your mayo, dressings, snack bags, and most frozen dinners.

So the oil you pour every week comes from one bean. It has been the country's main cooking fat for decades. But a century ago, it barely existed.

1,000-fold The increase in US per capita soybean oil consumption from 1909 to 1999

Blasbalg et al., American Journal of Clinical Nutrition, 2011

By 1999, soybean oil delivered more than seven percent of all American food calories. In 1909, it was near zero. Researchers at UC Riverside wondered what that load of one fatty acid was doing inside the gut.

A 24-week mouse study linked soybean oil to invasive gut bacteria

Poonamjot Deol and Frances Sladek at UC Riverside fed mice a diet heavy in soybean oil for 24 weeks. Other groups ate olive oil or a modified soybean version stripped of one fatty acid. The team published its findings in Gut Microbes, 2023.

Soybean oil is 51% linoleic acid, an omega-6 fat. In the mice that ate it, a strain called adherent invasive E. coli took over. This strain shows up in human Crohn's disease patients. Lactobacillus bacteria died off. And the olive oil group showed none of these changes.

One fatty acid fed the invader. The other left it hungry. But how does linoleic acid sort the bacteria in a living gut?

The wrong E. coli eats linoleic acid for fuel

Adherent invasive E. coli feeds on linoleic acid as a carbon source. Give it enough and it multiplies. Some Lactobacillus species are inhibited by the fatty acid. In the mice fed soybean oil, the invader grew and the protectors shrank.

In mice, linoleic acid also weakens a protein called HNF-4α that holds the gut wall together. With less of it, the gut wall loosens. Food particles and bacteria that should stay inside start slipping through… and swelling follows.

No oil sits in more American kitchens—and it is loaded with linoleic acid.

IBD rates rose alongside the linoleic acid surge

Crohn's disease and colitis have climbed in America for decades. The UC Riverside team notes the parallel with soybean oil consumption. They stop short of claiming the oil caused it. But the mouse data point in the same direction.

Soy protein is not the concern. Tofu, edamame, and soy milk are fine. The problem is the extracted oil and its concentrated linoleic acid… sitting in bottles labeled vegetable oil on every shelf. But the other bottles in the aisle carry a very different load.

Six cooking oils, ranked for your gut bacteria

Each oil below is ranked by its linoleic acid content and the gut evidence behind it, from worst to best.

🫘 Soybean oil ("vegetable oil") 51% linoleic acid, fed invasive E. coli in mice	🌽 Corn oil 54% linoleic acid, same concern, no separate gut study
🫙 Canola oil 19% linoleic acid, no gut shift in a 30-day human trial	🥥 Coconut oil 2% linoleic acid, grew Bifidobacterium in a pig study
🥑 Avocado oil 10% linoleic acid, whole avocado boosted fiber-fermenting bacteria	🫒 Extra virgin olive oil 10% linoleic acid plus polyphenols, greater gut diversity in a study of 656 adults

The distance between the top and bottom of this list is one bottle swap.

Swap your vegetable oil for extra virgin olive oil

Put the bottle labeled vegetable oil back on the shelf. Pick up a bottle of extra virgin olive oil instead.

🚫 Reach for the bottle labeled vegetable oil

✅ Cook with extra virgin olive oil

Avocado oil handles high heat if you need it. For dressings, sauces, and medium heat, extra virgin olive oil gives your bacteria the polyphenols and the low linoleic acid at the same time. So one swap tips the balance.