Oleic Acid Cancer Study May Not Apply to Olive Oil

A new Yale University study has found that diets rich in oleic acid promoted pancreatic tumor development in mice genetically predisposed to the disease, while diets high in polyunsaturated fatty acids appeared to suppress it. Published in Cancer Discovery, the research has prompted fresh questions about how findings tied to individual fatty acids translate, or do not translate, to real-world foods such as extra virgin olive oil.

The researchers designed a series of diets that provided the same number of calories but varied in fat composition and fed them to male mice prone to pancreatic ductal adenocarcinoma, the most common form of the disease. Diets rich in oleic acid, including those based on olive oil, high-oleic sunflower oil and high-oleic safflower oil, promoted tumor formation. Diets rich in polyunsaturated fats had the opposite effect.

The researchers relied on a well-established pancreatic cancer model known as the KC mouse, which carries a KRAS mutation restricted to the pancreas. Mutations in KRAS are found in more than 90 percent of pancreatic cancer patients and are considered a key driver of the disease.

Left untreated, these mice eventually develop pancreatic cancer. Christian Ruiz, the study’s first author, said the model allows researchers to study factors that may accelerate or suppress tumor formation, including diet.

“We found that the source of fat dictated the amount of disease the mice developed,” Ruiz told Olive Oil Times. “Diets rich in oleic acid caused more disease, while diets rich in polyunsaturated fats were less tumorigenic.”

The biological explanation, Ruiz said, centers on ferroptosis, a form of cell death caused by the iron-dependent accumulation of oxidized lipids in cell membranes. When polyunsaturated fats in membrane phospholipids undergo uncontrolled oxidation, cells can be driven into ferroptosis, a process that appears to act as a natural tumor-suppressive mechanism in the pancreas.

“Ferroptosis is a form of cell death that is due to uncontrolled lipid oxidation,” Ruiz said. “Oleic acid, because of its chemistry, is resistant to oxidation. And because it is resistant to oxidation, the cells become resistant to ferroptosis.”

In pancreatic cancer, ferroptosis appears to function as a tumor-suppressive mechanism.

“If you equip a tumor with oleic acid, then the tumor is protected from ferroptosis,” Ruiz said.

To look for parallel patterns in humans, the team analyzed blood samples and health records from nearly 488,000 participants in the U.K. Biobank, a large long-term British health database. Participants with higher amounts of monounsaturated fatty acids in their blood were more likely to develop pancreatic cancer, while those with higher ratios of polyunsaturated to monounsaturated fats appeared less likely to develop the disease.

The human data came with an important limitation.

“The short answer is no,” Ruiz said when asked whether blood levels of oleic acid can reveal its dietary source. “If you measure oleic acid in the blood, you can’t tell where it’s from. We actually make it ourselves as well.”

That distinction becomes a significant obstacle when translating the findings into dietary recommendations.

“Oleic acid does not equal olive oil,” Ruiz said.

Although one of the experimental diets used olive oil as its primary fat source, Ruiz cautioned against interpreting the findings as a direct assessment of olive oil as a food.

“One of the diets was olive oil and it did promote cancer in mice,” Ruiz acknowledged. “However, olive oil has many components to it, not just oleic acid.”

Those observations resonate with Mary Flynn, associate professor of medicine at Brown University, who has spent decades studying olive oil and Mediterranean dietary patterns. Speaking with Olive Oil Times, Flynn said that findings based on isolated fatty acids should be interpreted with caution when applied to human diets.

“Oleic acid is one of the most abundant fatty acids in the human body,” Flynn said.

She also noted that dietary fats are never consumed in isolation. Triglycerides, the molecules that carry fatty acids in food and in the body, always contain a mixture of saturated, monounsaturated and polyunsaturated fatty acids.

“You would not have a real-world situation that is all monounsaturated fats flooding the cells,” Flynn said.

Flynn further noted that it is not oleic acid that makes extra virgin olive oil healthy.

“While olive oil is rich in MUFA, the MUFA content does not explain why EVOO is healthy,” she said. “It is the phenols in EVOO.”

Studies comparing refined olive oil with extra virgin olive oil, Flynn noted, consistently point to phenolic compounds, not oleic acid, as the source of olive oil’s health benefits. The distinction becomes particularly important when interpreting observational studies based on blood biomarkers or dietary scores.

Flynn noted that monounsaturated fats can come from many sources besides olive oil. In the United States, for example, beef was historically one of the largest contributors of monounsaturated fats in the diet, with various vegetable oils now adding substantially to that total. As a result, higher blood levels of monounsaturated fats do not necessarily indicate higher olive oil consumption, making the U.K. Biobank associations more difficult to interpret.

Together, the researchers’ findings and Flynn’s comments highlight the challenges of translating research into practical dietary advice.

The Yale study provides new evidence that fatty acid composition may influence pancreatic cancer biology through mechanisms involving ferroptosis. At the same time, both Ruiz and Flynn emphasized that the relationship between oleic acid, dietary patterns and human health is highly complex.

“I love olive oil, don’t you?” Ruiz said. “This paper has not changed how I consume olive oil.”