The worst cooking oils for brain health, based on current research, are trans fats and partially hydrogenated oils, reused deep-frying oils, and certain common vegetable oils when overheated. A 2019 study in Neurology found that people with the highest blood levels of trans fats were 50% to 75% more likely to develop Alzheimer’s disease or dementia, while research presented at Discover BMB 2024 showed that consuming reused deep-fried oil led to significant neurodegeneration in rat brain tissue. Soybean oil and canola oil have also raised concerns in animal studies, though the evidence in humans remains limited.
This is not a simple story of “seed oils bad, olive oil good,” even though that narrative has gained traction online. The reality involves specific chemical reactions that occur during heating, the cumulative effect of dietary patterns over decades, and the important distinction between what happens in a mouse brain versus a human one. What follows is a detailed look at what the research actually says about each oil, where the evidence is strong, where it is preliminary, and what practical steps you can take to protect your brain without overhauling your entire kitchen.
Table of Contents
- Which Cooking Oils Are Worst for Brain Health and What Does the Science Say?
- What Soybean Oil Does to the Brain in Animal Studies
- Canola Oil and the Alzheimer’s Mouse Study That Made Headlines
- How Overheating Cooking Oils Creates a Toxic Compound Called HNE
- The Omega-6 Debate and Why “Seed Oils Are Toxic” Oversimplifies the Science
- What the Research Says About Olive Oil and Brain Protection
- Where Brain Health Oil Research Is Headed
- Conclusion
- Frequently Asked Questions
Which Cooking Oils Are Worst for Brain Health and What Does the Science Say?
The oil with the most damning evidence against it is one you probably no longer encounter very often: partially hydrogenated oil, the primary source of artificial trans fats. The American Academy of Neurology highlighted a study showing that each additional gram of daily trans fat consumption was associated with recalling 0.76 fewer words on memory tests. Among the highest-intake men, that translated to 12 fewer words recalled compared to those who consumed no trans fats at all. Trans fats get incorporated directly into brain cell membranes, where they alter the ability of neurons to communicate with one another. The U.S. banned trans fats in 2018, but they still appear in some imported products and older-formulation packaged foods, so checking labels remains worthwhile. Reused and reheated deep-frying oils come next in terms of evidence strength.
Research presented at the American Society for Biochemistry and Molecular Biology’s 2024 meeting found that rats consuming reheated sesame or sunflower oil showed increased oxidative stress, liver inflammation, and significant neurodegeneration. The mechanism is particularly concerning: reheated oils damaged the colon, altered liver lipid metabolism, and decreased the transport of DHA, a critical omega-3 fatty acid, to the brain through the liver-gut-brain communication network. Perhaps most troubling, offspring of the rats fed reheated oil also showed increased neuronal damage, suggesting transgenerational effects. If you eat fried food regularly from restaurants that reuse their oil throughout the day or across multiple days, this research is directly relevant to you. Beyond trans fats and reheated oils, the picture gets murkier. Soybean oil, canola oil, and other vegetable oils high in linoleic acid have all generated concerning headlines, but the research behind those headlines involves animal models, not human clinical trials. That distinction matters enormously when deciding what to cook with tonight.
What Soybean Oil Does to the Brain in Animal Studies
A UC Riverside study published in Endocrinology in January 2020 found that soybean oil diets in mice affected roughly 100 genes in the hypothalamus, which is the brain region responsible for regulating body weight, metabolism, body temperature, reproduction, and stress response. Among the affected genes was the one that produces oxytocin, sometimes called the bonding hormone. The researchers tested both regular soybean oil and a modified low-linoleic-acid version, and the effects were seen with both, meaning linoleic acid is not the culprit. The responsible chemical compound has not yet been identified. This finding is alarming on its surface, especially considering that soybean oil is the most widely consumed oil in the United States.
However, there is an important caveat that the researchers themselves acknowledged: this was a mouse study, and there is no proof that soybean oil causes these genetic changes in the human brain. Mice metabolize fats differently, consume oils at proportionally different levels, and lack the dietary variety that humans have. The study raises a hypothesis worth investigating further, but it does not establish that your stir-fry is rewiring your hypothalamus. Where the concern becomes more practical is in the sheer volume of soybean oil in the American food supply. It appears in salad dressings, baked goods, snack foods, and most restaurant fryers. Even if the direct neurological effects seen in mice don’t translate perfectly to humans, the cumulative exposure is enormous, and the oil is overwhelmingly consumed as a component of ultra-processed foods, which carry their own well-documented health risks.
Canola Oil and the Alzheimer’s Mouse Study That Made Headlines
Temple University researchers published a study in Scientific Reports in December 2017 that found mice genetically modeled for Alzheimer’s disease, when fed canola oil for six months, showed impaired working memory, significant weight gain, and decreased levels of post-synaptic density protein-95, a marker of synaptic integrity. The canola-fed mice also had an increased ratio of insoluble amyloid beta 42/40, which refers to the sticky amyloid plaques that are a hallmark of Alzheimer’s pathology. In plain terms, the mice that ate canola oil had worse brain function and more of the brain changes associated with Alzheimer’s than the control group. The study made waves in health media, but it drew sharp criticism from other researchers. An independent scientist from the University of Florida stated that the paper “does not show in any way that there is a causal link to disease in humans.” The mice were already genetically predisposed to develop Alzheimer’s-like pathology.
The study did not compare canola oil to other cooking oils, so there is no way to know whether soybean oil, corn oil, or any other fat would have produced similar or worse results. It also used a single, relatively high dose rather than testing a range of consumption levels. For someone caring for a family member with dementia or worrying about their own risk, this study is worth knowing about but not worth panicking over. Canola oil remains generally regarded as safe by major health organizations. The research is a signal that warrants further investigation, not a verdict.
How Overheating Cooking Oils Creates a Toxic Compound Called HNE
Here is where the research gets actionable regardless of which specific oil you use. When vegetable oils high in linoleic acid, including soybean, corn, sunflower, and safflower oils, are heated to 150 to 200 degrees Celsius, a cytotoxic compound called hydroxynonenal, or HNE, forms within just five minutes and reaches high concentrations in food after 30 minutes. This is well within the temperature range of normal pan-frying and deep-frying. HNE is not merely a theoretical concern. It accumulates in the brain cells of patients with both Alzheimer’s disease and Parkinson’s disease.
Research published in PMC shows that HNE triggers aggregation of amyloid beta peptide and alpha-synuclein, the two proteins most closely associated with Alzheimer’s and Parkinson’s respectively. It causes synaptic dysfunction and leads to neuronal death. The comparison here is straightforward: an oil used at low heat for a salad dressing is a fundamentally different exposure than the same oil heated to high temperatures for an extended period. This is why the distinction between an oil itself and how that oil is used matters so much. A drizzle of sunflower oil on a cold dish poses a very different risk profile than sunflower oil held at frying temperature in a restaurant fryer for hours. If you deep-fry at home, keeping oil temperatures moderate and never reusing oil are two of the most evidence-backed steps you can take for your brain health.
The Omega-6 Debate and Why “Seed Oils Are Toxic” Oversimplifies the Science
The claim that seed oils cause widespread inflammation and brain damage has become a popular health narrative, particularly on social media. But the science does not fully support the broadest versions of this claim. Johns Hopkins Bloomberg School of Public Health noted in 2025 that a 2017 meta-analysis found increased linoleic acid intake does not significantly increase inflammatory markers. Mass General has similarly pointed out that only about 0.2% of dietary omega-6 actually converts to arachidonic acid, which is the inflammatory precursor that concerns people. This does not mean there is nothing to worry about.
The real issue may be that seed oils are predominantly found in ultra-processed foods, and it may be the overall dietary pattern rather than the oil itself that is driving harm. When someone cuts out seed oils and reports feeling better, they have also likely cut out chips, fast food, packaged baked goods, and frozen meals. Disentangling the effect of the oil from the effect of the food matrix is extremely difficult in nutrition research. The limitation here is important for anyone making dietary decisions for themselves or for someone in their care: eliminating all omega-6 fats is neither practical nor desirable, as they are essential fatty acids. The goal should be reducing exposure to overheated and reused oils, minimizing ultra-processed food consumption, and increasing intake of omega-3-rich foods and oils with stronger protective evidence.
What the Research Says About Olive Oil and Brain Protection
For contrast, olive oil has the strongest evidence of any cooking fat for brain protection. A Harvard study published in JAMA Network Open in May 2024, following more than 92,000 participants over 28 years, found that consuming more than 7 grams of olive oil daily, roughly half a tablespoon, was associated with a 28% lower risk of dementia-related death. The study also found that replacing just 5 grams of margarine or mayonnaise daily with olive oil was linked to an 8 to 14% lower risk of dementia death. These are large numbers from a large, long-running human study, which gives them considerably more weight than the mouse studies behind the concerns about soybean and canola oil.
The practical tradeoff is cost and cooking suitability. Extra virgin olive oil is more expensive than soybean or canola oil and has a lower smoke point, making it less ideal for high-heat frying. For sauteing, roasting at moderate temperatures, and using as a dressing or finishing oil, it is an excellent choice. For high-heat applications, avocado oil offers a higher smoke point and a favorable fatty acid profile, though it lacks the same depth of long-term brain health research that olive oil now has.
Where Brain Health Oil Research Is Headed
The next several years of research will likely focus on two areas: identifying the specific compound in soybean oil responsible for the gene changes observed in the UC Riverside mouse study, and conducting larger human observational studies on reheated oil consumption, particularly in populations where deep-fried street food is a dietary staple. The transgenerational findings from the reheated oil research, where offspring of exposed rats showed neuronal damage, are likely to prompt further investigation into whether similar patterns appear in human populations.
For now, the strongest, most actionable evidence points to avoiding trans fats wherever they still appear, never reusing deep-frying oil, minimizing the duration and temperature of oil heating, and incorporating olive oil as a primary fat source. These are reasonable steps grounded in the best available research, and they do not require you to throw out every bottle in your pantry.
Conclusion
The cooking oils with the most evidence of brain harm are artificial trans fats, which directly alter neuronal communication and were associated with up to 75% higher dementia risk, and reused deep-frying oils, which generate toxic compounds and impair the brain’s supply of protective omega-3 fats. Soybean oil and canola oil have raised legitimate concerns in animal studies, but those findings have not been confirmed in humans. The formation of HNE when linoleic-acid-rich oils are overheated is a well-documented chemical process with clear links to Alzheimer’s and Parkinson’s pathology, making cooking temperature and oil freshness at least as important as oil selection. The most practical approach is not to fear every drop of vegetable oil but to shift your cooking habits based on what the research actually supports.
Use olive oil where you can. Avoid reusing frying oil. Check labels on imported or discount products for partially hydrogenated oils. And recognize that the biggest risk factor is not any single oil but a dietary pattern built around ultra-processed foods where these oils are consumed in their most damaged, most heated, most chemically altered forms.
Frequently Asked Questions
Is soybean oil proven to cause brain damage in humans?
No. The UC Riverside study that found soybean oil affected roughly 100 genes in the hypothalamus was conducted in mice. The researchers themselves noted there is no proof that soybean oil causes these effects in humans. The study is a basis for further investigation, not a confirmed health risk.
Are all seed oils bad for the brain?
The evidence does not support a blanket claim that all seed oils are harmful. A 2017 meta-analysis cited by Johns Hopkins found that increased linoleic acid intake does not significantly increase inflammatory markers. The concern is more specifically about overheated oils, reused frying oils, and the ultra-processed foods in which seed oils are most commonly consumed.
How does reheating cooking oil affect the brain?
Research presented at Discover BMB 2024 showed that reused deep-fried oil damaged the colon, altered liver lipid metabolism, and decreased DHA transport to the brain in rats. The result was significant neurodegeneration, and even the offspring of exposed rats showed increased neuronal damage.
Are trans fats still in the food supply if they were banned in 2018?
The U.S. ban on partially hydrogenated oils took full effect in 2018, but trans fats can still appear in some imported products and older-formulation foods. Checking ingredient labels for “partially hydrogenated” oil remains a useful habit.
What is the best cooking oil for brain health?
Olive oil has the strongest evidence. A Harvard study of over 92,000 participants over 28 years found that consuming more than 7 grams daily was associated with a 28% lower risk of dementia-related death. Replacing 5 grams of margarine or mayonnaise with olive oil was linked to an 8 to 14% lower risk.
Does it matter how hot I heat my cooking oil?
Yes. When vegetable oils high in linoleic acid are heated to 150 to 200 degrees Celsius, the toxic compound hydroxynonenal forms within five minutes and reaches high concentrations after 30 minutes. HNE accumulates in the brains of Alzheimer’s and Parkinson’s patients and triggers protein aggregation linked to both diseases.
