Several types of oil that are often considered to be ‘healthy’ may actually be fueling the growth of pancreatic cancer tumors, a study suggests.
Pancreatic cancer has earned a reputation as one of America’s deadliest cancers, killing the vast majority of patients, often in as little as a few months.
Overall, just 12 percent of patients survive for five years after diagnosis, and the majority do not live more than a year.
Experts believe this is because pancreatic cancer lurks silently in the early stages or causes vague, easily dismissed signs like a dull back ache, intermittent indigestion and unexplained fatigue.
And doctors are still unraveling the causes of the devastating disease. Studies have increasingly honed in on diet, focusing on processed meats, alcohol, ultra-processed foods and sugary drinks.
But in a new study, researchers at Yale University have found oleic acid – the main fat in olive, avocado and canola oils – may encourage tumor growth in pancreatic cancer.
The team created 12 different high-fat diets and assigned genetically modified mice to each one of the eating plans.
They found pancreatic cancer tumors grew the fastest when mice were fed diets high in oleic acid. This was particularly striking because foods high in this fat have long been associated with improved weight and heart health, which lower cancer rates.
Oleic acid, which is found in olive and avocado oil, may fuel the growth of pancreatic cancer tumors, a study suggests
‘It’s traditionally been considered a healthy type of fat for cardiovascular health,’ Dr Christian Felipe Ruiz, lead study author and associate research scientists in Yale School of Medicine’s Department of Genetics, said.
The researchers urged that more research on dietary causes of pancreatic cancer is crucial, as the disease affects 67,000 Americans and kills more than 52,000 each year.
According to the American Cancer Society, the lifetime risk of developing pancreatic cancer is one in 56 for men and one in 60 for women. While the disease remains rare in younger adults, incidence rates are rising steadily.
Between 2000 and 2021, pancreatic cancer diagnoses increased by 4.3 percent per year among Americans ages 15 to 34, and by 1.5 percent annually among those ages 35 to 54, according to a 2025 analysis.
While oleic acid was associated with tumor growth, the researchers also found omega-3 fatty acids, which are in fatty fish like salmon, as well as nuts, were the most protective against tumor growth.
‘It’s really the type of fat you’re consuming, not just total fat content,’ Ruiz said. ‘Depending on the type of fat that you consume, it can go completely different ways.
‘We found that some fats promote cancer, as we would expect, while other fats are really good at suppressing cancer.’
The above chart shows the US average survival rate of pancreatic cancer by stage
The study, published in the journal Cancer Discovery, looked at mice who were genetically modified to produce a disease that mirrors human pancreatic cancer. In humans, these mutations are usually found in the BRCA1, BRCA2, PALB2 and CDKN2A genes.
All 12 of the diets contained the same amount of calories and only differed in terms of the specific fat source.
Ruiz said this goes against decades’ worth of studies that instead gave mice lard-based diets, which involves pork fat, that do not mimic human eating patterns.
‘Exactly what components of dietary fat cause cancer has remained a mystery,’ he said.
Oleic acid is an omega-9 monounsaturated fatty acid, a type of fat long linked to lower LDL (bad) cholesterol, blood sugar control and lower levels of inflammation if they replace trans fats.
Uncontrolled, all of these factors can drive the development and growth of cancer.
Olive oil specifically has been shown to have antioxidant compounds, which banish harmful molecules called free radicals preventing oxidative stress that leads to inflammation.
In one 2022 review from the National Center for Biotechnology Information, individuals with the highest average olive oil consumption had a 31 percent lower risk of breast, gastrointestinal and urinary tract cancers than those with the lowest consumption.
Oleic acid is also found in seed oils like sunflower and safflower oils, which health authorities considered a healthier alternative to butter.
Most research has shown no increased cancer risk from seed oils, though one small 2024 study found seed oils may accelerate the growth of colon cancer, though the researchers cautioned larger studies are needed.
In contrast, researchers in the new study found omega-3 fatty acids, specifically those in fish oil, had the strongest protective effects against pancreatic tumors.
‘When we fed mice diets enriched with fish oil, we saw a 50 percent reduction in disease compared with mice fed a standard fat diet,’ Ruiz said.
The findings led the researchers to investigate ferroptosis, a form of cell death caused by lipid oxidation, which occurs when fatty acids react with oxygen.
The team found when fatty acids entered the membranes of pancreatic cells, polyunsaturated fatty acids like omega-3s were more vulnerable to oxidation, leading to ferroptosis and death in cancer cells.
Monounsaturated fatty acids like oleic acid, however, were more resistant to oxidation, which protected cancer cells.
Ruiz cautioned that the research has not yet been replicated in humans. However, the findings may provide insight on risk factors for people with genetic mutations making them prone to pancreatic cancer.
‘One of the most common questions clinicians get is “What can I change in my diet to prevent cancer?”‘ Ruiz said.
‘Right now, we don’t have clear answers, but this study begins to shed light on how we might address that question.’
