Olive oil has long been praised as a healthy fat, often linked to heart health and a key part of the Mediterranean diet.
But new research suggests that when consumed in large amounts, it may actually lead to weight gain.
A study published in the journal Cell Reports shows that a high-fat diet containing large amounts of oleic acid—a type of fat found in olive oil—can increase the body’s ability to produce fat cells, raising the risk of obesity.
Oleic acid is a monounsaturated fat, which means it has one double bond in its structure. While it’s generally considered healthier than saturated fats, this study shows that high levels of it can have unexpected effects.
Researchers discovered that oleic acid causes the body to grow more fat cells by increasing a signaling protein called AKT2 and lowering the activity of another protein called LXR. This results in faster growth of the early-stage cells that turn into fat cells.
The research team, led by Dr. Michael Rudolph from the University of Oklahoma College of Medicine and the OU Health Harold Hamm Diabetes Center, worked with collaborators from Yale University and New York University.
They fed mice different types of fats, each commonly found in human diets—such as those in coconut oil, milk, lard, peanut oil, and soybean oil. Out of all these, oleic acid stood out as the only one that led to an increase in the growth of fat-making cells.
Dr. Rudolph explained it simply: “You can think of fat cells as an army. When you eat a lot of oleic acid, you’re recruiting more soldiers. That means your body becomes better at storing fat.
Over time, if you keep eating more energy than you burn, that army of fat cells fills up—and that’s when obesity can happen.” And obesity, in turn, raises the risk for heart disease and diabetes.
One complication is that people don’t eat only one kind of fat in a meal. A typical day’s food might include butter in your breakfast, oil in your lunch salad, and fat from meat at dinner.
This makes it hard to know exactly how much of each type of fat we’re eating. However, modern diets—especially those that rely on processed or fast foods—are seeing a rise in oleic acid levels.
So what does this mean for your olive oil? Should you throw out that bottle in your kitchen?
Not necessarily, says Dr. Rudolph. “The key is moderation,” he advises. “Fats from olive oil and similar sources can still be part of a healthy diet if you don’t overdo it. Try to get your fats from a variety of sources.”
This study offers an important reminder that even foods considered healthy can be harmful in excess. While balanced levels of oleic acid might have health benefits, consistently high levels could increase the risk of obesity and related health problems, especially in people already at risk for heart disease.
Scientists now hope to explore whether limiting oleic acid in the diet could be a helpful tool in preventing or managing obesity.
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