This “healthy” oil may actually raise the risk of one of the deadliest cancers

A new study has raised questions about oleic acid, the main fatty acid in olive oil and a compound long praised for its heart-health benefits. Researchers reported in Cancer Discovery that in mouse experiments, diets rich in oleic acid appeared to speed up the growth of certain pancreatic tumors, while some other fats seemed to slow tumor progression.

The study was designed to test whether the type of fat matters as much as the total amount consumed. Scientists created 12 different diets with the same calorie content but varying fat sources and fed them to mice genetically predisposed to develop pancreatic cancer, one of the most aggressive forms of the disease. The results showed that mice receiving a diet high in oleic acid developed tumors more quickly than those on other fat profiles.

Oleic acid is found not only in olive oil, but also in sunflower oil, peanuts, and lard. The researchers said the findings suggest that the biological effects of fat may differ significantly depending on its chemical composition. According to the study’s lead researcher, Christian Felipe Ruiz, it is not only the amount of fat that matters, but also the type of fat being eaten. Some fats may promote cancer growth, while others may help suppress it.

The study also pointed to omega-3 fatty acids, such as those found in fish oil, as potentially protective. In the mouse experiments, diets enriched with fish oil were associated with about a 50% reduction in disease compared with a standard high-fat diet. The researchers proposed that the mechanism may involve oxidation: omega-3 fats are more easily oxidized, which could make cancer cells more vulnerable, while oleic acid may resist oxidation and help tumors survive longer.

Despite the striking findings, the researchers emphasized that the work was done in mice, not humans, and the results should not be interpreted as proof that olive oil is harmful in people. Olive oil’s cardiovascular benefits remain well established, and it is still widely regarded as a healthy dietary fat. The study instead suggests that variety in fat sources may be important, and that diets including more fatty fish and omega-3-rich foods could offer a better balance than relying on olive oil alone.

The findings may be especially relevant given the severity of pancreatic cancer, which remains among the deadliest cancers. In France, nearly 16,000 new cases are diagnosed each year, and the five-year survival rate is only 11%.