This Common Cooking Oil Might Be Quietly Damaging Your Gut Health

If you cook regularly, there’s a good chance you’ve got soybean oil sitting somewhere in your kitchen. It’s one of the most common cooking oils in the United States, found in everything from salad dressings to snack foods and restaurant fryers. But according to recent research from the University of California, Riverside (UCR), this popular oil may be doing more harm than good—especially to your gut health.

The new study, published in the journal Gut Microbes, found that diets high in soybean oil—specifically its main component, linoleic acid—can disrupt the balance of gut bacteria, weaken the intestinal barrier, and make the body more vulnerable to inflammation and diseases like colitis, a type of inflammatory bowel disease (IBD).

What the Researchers Found

The UCR team, led by Poonamjot Deol, Frances Sladek, and James Borneman, fed mice a diet rich in soybean oil for up to 24 weeks. The results were striking. The mice showed a decline in beneficial gut bacteria and a rise in harmful bacteria, particularly a strain known as adherent invasive Escherichia coli (AIEC). This specific bacterium is already known to play a role in human IBD.

The harmful E. coli thrived in the presence of linoleic acid, using it as a carbon source for growth, while the “good” bacteria in the gut were unable to survive under those conditions. As a result, the microbial balance in the intestines tilted toward inflammation.

The study also revealed that linoleic acid caused the intestinal barrier—the thin layer of cells that keeps toxins and microbes from leaking into the bloodstream—to become more porous. When this barrier breaks down, bacteria and toxins can escape into the bloodstream, potentially triggering chronic inflammation and diseases like colitis.

The Bigger Picture: Soybean Oil’s Expanding Reach

Soybean oil isn’t some niche product—it’s the most consumed cooking oil in the United States and is rapidly growing in popularity in other major countries such as Brazil, China, and India. In the U.S., large-scale soybean farming began in the 1970s mainly to produce animal feed, and the oil was a convenient byproduct. Because soybeans are inexpensive and easy to grow, their use skyrocketed in the food industry.

Today, most processed foods in the U.S. contain soybean oil. It’s used because it’s cheap, stable, and has a neutral flavor, making it perfect for mass production. Unfortunately, this widespread use means many Americans are consuming far more linoleic acid than their bodies need.

Based on the research, humans only need about 1–2% of daily energy from linoleic acid, yet the average American gets 8–10%, mostly from soybean oil. That’s several times higher than what’s thought to be healthy.

Why Linoleic Acid Matters

Linoleic acid (LA) is an omega-6 polyunsaturated fatty acid, and the body needs small amounts of it for proper function. We can’t produce it ourselves, so it must come from food. It helps build cell membranes and supports normal growth and development.

But as with many nutrients, too much can backfire. When consumed in excess, linoleic acid can shift the body’s biochemical balance toward inflammation. It does this by converting into compounds called oxylipins and prostaglandins, which are known to promote inflammatory responses in the body.

In this study, the mice fed a high-soybean oil diet not only had more oxylipins but also had lower levels of endocannabinoids—natural, cannabis-like molecules made by the body that help regulate inflammation, pain, and mood. The imbalance between these two types of molecules could be one reason for the increase in inflammation and disease risk.

Rethinking “Healthy” Fats

For decades, people were told that saturated fats from animal sources were the enemy and that plant-based oils were always healthier. But this research challenges that old narrative.

While it’s true that unsaturated fats (like those in fish oil or olive oil) can support heart health, not all unsaturated fats behave the same way. Soybean oil, rich in linoleic acid, appears to have its own set of risks when consumed in large amounts.

The American Heart Association still recommends that 5–10% of daily calories come from omega-6 fats like linoleic acid to maintain heart health. However, this study suggests that going far beyond that range may lead to problems—especially for the gut.

How Soybean Oil Affects the Microbiome

The gut microbiome is a complex ecosystem of trillions of bacteria, fungi, and other microorganisms that play vital roles in digestion, immune function, and even mental health. When this system is disrupted—a condition known as dysbiosis—the consequences can ripple throughout the body.

The UCR researchers found that the high-linoleic soybean oil diet favored the growth of harmful E. coli while killing off beneficial species. This imbalance makes the gut more prone to inflammation, infection, and permeability issues.

Interestingly, the team observed that the mice’s microbiome changes were accompanied by a reduction in endocannabinoids and an increase in oxylipins, mirroring what’s seen in human inflammatory bowel disease. That link between microbiome disruption and molecular imbalance could be an important clue in understanding how dietary fats influence gut disorders.

The Gene Connection

The study also highlighted changes in a gene called HNF4α (hepatocyte nuclear factor 4 alpha), which is critical for maintaining the gut’s epithelial barrier and overall intestinal health. Alterations in this gene’s activity have already been linked to inflammatory bowel disease.

When the mice were fed soybean oil, certain HNF4α gene variants became more active, potentially worsening the barrier breakdown and inflammation.

This genetic component shows how a dietary factor (like linoleic acid) can interact with our genetic makeup, making some people more vulnerable to gut disorders than others.

Soybean Oil and Chronic Disease Links

The same researchers have studied soybean oil’s impact for years, and this isn’t the first time it’s raised red flags. Their previous work linked high soybean oil consumption in mice to obesity, insulin resistance, and even neurological effects such as changes in genes related to autism, Alzheimer’s, anxiety, and depression.

With this new study, ulcerative colitis—a chronic inflammation of the colon—is being added to the growing list of potential concerns tied to excessive soybean oil intake.

While these findings are from animal studies, they paint a clear picture that long-term overconsumption of high-linoleic oils could have far-reaching health consequences.

Is This Relevant to Humans?

That’s the big question—and the answer is not fully known yet. The researchers themselves emphasize that the study was done in mice, not humans. But the gut biology of mice shares enough similarities with humans to make the findings concerning.

So far, human studies on linoleic acid and gut inflammation are mixed. Some show no harm, while others hint at possible risks when omega-6 intake is much higher than omega-3 intake. The key may lie in balance—modern diets often have an omega-6 to omega-3 ratio of 15:1 or higher, when ancestral diets were closer to 2:1.

That imbalance could tip the body toward chronic inflammation, even if total fat intake seems reasonable.

The Role of the Intestinal Barrier

One of the most critical findings from the UCR study was the weakening of the intestinal epithelial barrier. Think of this barrier as the wall separating your internal body from the contents of your gut. When it’s healthy, it tightly controls what passes through. When it becomes “leaky,” toxins and bacteria can enter the bloodstream—an effect often called leaky gut.

This leakage can set off immune responses that contribute to chronic conditions such as IBD, arthritis, or metabolic diseases. The researchers suggest that the rise in IBD cases in the U.S. may parallel the dramatic increase in soybean oil consumption over the last few decades.

Healthier Alternatives

If you’re wondering what to cook with instead, the researchers—and most nutrition experts—suggest olive oil as a better option. Olive oil is lower in linoleic acid and rich in monounsaturated fats and polyphenols, which support heart and gut health.

Avocado oil and coconut oil are also solid choices depending on what you’re cooking. Coconut oil has mostly saturated fats, but these tend to be medium-chain triglycerides, which are metabolized differently than long-chain fats found in animal sources.

It’s also wise to limit processed foods, since they often contain large amounts of soybean oil. Reading ingredient labels and choosing whole, minimally processed foods can help reduce excessive linoleic acid intake.

Practical Takeaways

• Moderation is key. A small amount of linoleic acid is necessary, but overdoing it can be harmful.
• Watch your ratios. Try to balance omega-6 fats (from soybean, corn, or sunflower oil) with omega-3s (from fish, flaxseed, or chia).
• Cook smart. Air fryers and baking often need less oil, reducing overall intake.
• Focus on variety. Use different oils for different purposes—olive oil for salads, avocado oil for high heat, and small amounts of coconut oil for flavor.
• Be aware of hidden oils. Restaurant foods and packaged snacks often use soybean oil because it’s cheap and stable.

The Bottom Line

The evidence from the UC Riverside study adds to a growing body of research suggesting that too much soybean oil—specifically too much linoleic acid—can harm gut health by feeding harmful bacteria, damaging the intestinal barrier, and promoting inflammation.

That doesn’t mean you need to banish soybean oil from your kitchen forever. But it does mean being mindful of how much you’re consuming and where it’s coming from. Choosing a mix of oils, eating fewer processed foods, and keeping your omega-6 and omega-3 intake balanced could go a long way toward keeping your gut happy.

Research Reference:
Diet High in Linoleic Acid Dysregulates the Intestinal Endocannabinoid System and Increases Susceptibility to Colitis in Mice – Gut Microbes (2023)