Popular cooking oil found to sometimes cause severe brain inflammation

In a 20-week mouse experiment, a new study found that soybean oil led to more intense brain inflammation than lard when 35 percent of calories came from fat.

The work points to changes along the brain gut connection and shifts in gut microbes as key steps. Neuroinflammation, chronic immune activation inside the brain, can damage cells and dull the brain’s own defenses.

Soybean oil and inflammation

Researchers compared two diets that were matched for calories and protein but differed in the cooking fat source. One group ate soybean oil, and another ate lard, at either 15 percent or 35 percent of calories from fat.

Xiangyan Liu of Hunan Agricultural University (HAU) led the work with colleagues in Changsha, China. The team tracked brain structure, immune signals, antioxidants, and gut microbes across the 20 weeks.

At the higher fat level, the soybean oil group showed more damage to brain cells and stronger immune activation.

Microglia, immune sentinels that patrol brain tissue, appeared more activated, and proteins that turn on inflammatory genes were higher.

The soybean oil group also showed a drop in certain gut bacteria that track with better metabolic health. Akkermansia, a mucus loving species linked to a sturdy gut barrier, was lower, while Dubosiella rose.

Why the brain gut link matters

The brain and gut are in constant two way conversation. Brain gut axis, the network linking nerves, hormones, and immune signals between gut and brain, helps regulate stress, appetite, and inflammation.

Some gut species appear to help keep that conversation calm. Evidence suggests Akkermansia helps reinforce the intestinal lining and shapes immune tone, which can reduce inflammatory traffic to the brain.

When the gut barrier loosens, bacterial fragments can leak into blood and trigger immune responses. Cytokines, small proteins that coordinate immune activity, can then ramp up and signal the brain to mount a defensive response.

That pattern may explain part of the mouse results. If the high soybean oil diet weakened the gut barrier and shifted microbe balance, more immune traffic could have crossed into brain pathways that regulate inflammation.

Soybean oil, lard, and chemistry

Fat type matters. Soybean oil is rich in linoleic acid, an omega 6 polyunsaturated fat that the body uses to build signaling molecules, and excess linoleic acid may sensitize the brain to inflammation in animal models.

Lard, by contrast, carries more saturated and monounsaturated fats, which behave differently in membranes and signaling. That does not make lard a health food, but it can shape how cells react when immune alarms sound.

The mouse data suggest that, under a high fat plan, soybean oil pushed the brain’s immune system harder. The study also saw a stronger drop in antioxidant capacity, which could leave neurons more vulnerable to stress.

Context matters here. Both diets at 35 percent fat showed inflammation, and the oil source shifted the pattern and magnitude. The lower fat versions looked less harmful across measures, which fits broader nutrition science.

How this fits with human nutrition

Health authorities continue to advise limiting saturated fat in favor of unsaturated fats. The U.S. dietary guidelines recommend replacing sources like butter and lard with oils such as olive, canola, corn, soybean, peanut, safflower, and sunflower.

Cardiology groups reach similar conclusions on heart risk. An American Heart Association (AHA) advisory reports that swapping saturated fat with polyunsaturated vegetable oils lowers cardiovascular events.

These positions are based largely on human trials and long term population studies. Preclinical model, research in animals that tests mechanisms under controlled conditions, clarifies how a nutrient might act before clinical testing in people.

So this mouse work is a signal to study brain outcomes in humans under realistic eating patterns. It does not overturn guidance that favors unsaturated oils for heart health, which remains the best supported advice today.

Gut microbes don’t care about labels

One result that deserves caution is the rise of Dubosiella with soybean oil. Some studies link more Dubosiella to inflammation in mice, yet findings are not one way.

In colitis models, Dubosiella newyorkensis improved gut barrier function and boosted immune tolerance through specific metabolites. That means a microbe’s effect can flip with context, diet, or even the strain used.

Microbes act like a crowd, not solo performers. Strain, a genetic variant within a species, can behave differently from its cousins, which often explains why one lab’s results do not match another’s.

Future work should include careful microbe profiling in people eating typical amounts of different oils. Biomarker, a measurable signal that tracks a biological process, could help tie microbe shifts to brain immune activity without invasive tests.

The study is published in the Journal of Traditional and Complementary Medicine.

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