Extra virgin olive oil has long been praised for its heart-healthy benefits, but many people still shy away from it due to its calorie content — worried it might lead to weight gain. But is that concern really justified?
A new study published in The American Journal of Clinical Nutrition (February 2025) sheds light on this question, showing that increasing olive oil intake may actually help reduce long-term weight gain — even in populations outside of the Mediterranean region.
What the Study Looked At: Does Olive Oil Cause Weight Gain?
Researchers, led by Marta Guasch-Ferré, analyzed data from three large, long-running U.S.-based cohort studies:
- Nurses’ Health Study (NHS) (1990–2010)
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Nurses’ Health Study II (NHSII) (1991–2015)
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Health Professionals Follow-up Study (HPFS) (1990–2014)
In total, the study included over 121,000 men and women under age 65 who were free of chronic diseases at the start.
Participants self-reported their weight and completed food frequency questionnaires every four years, including detailed questions on cooking oils — from olive oil to butter, margarine, and vegetable oils.
Olive oil intake was calculated based on its use in salad dressings, drizzled on food or bread, or used in baking and frying.
Key Findings: Olive Oil and Weight Gain
Over the four-year intervals, the average weight gain was modest:
- NHSII participants gained 1.8 kg on average
- NHS: 1.2 kg
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HPFS: 0.9 kg
But here’s the kicker: For every additional 7 grams (about half a tablespoon) of olive oil consumed per day, participants gained less weight — even after accounting for diet quality, physical activity, and other lifestyle factors. This inverse association held true across genders and ethnic backgrounds, though it was stronger among those with Southern European ancestry.
By contrast, increased intake of margarine, vegetable oils, and butter was linked to more weight gain — especially in those who were already overweight or obese at baseline.
Substitution models revealed that swapping out butter, margarine, or refined grains for olive oil was consistently associated with less long-term weight gain.
Why Might Olive Oil Help?
Researchers point to a few possible reasons:
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Satiation: Fat, especially when paired with nutrient-dense foods like vegetables, can help you feel fuller longer and reduce mindless snacking.
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Oleic acid: The main monounsaturated fat in olive oil may boost thermogenesis (heat production) and energy expenditure.
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Polyphenols & bioactives: Olive oil contains compounds like oleocanthal, which may influence metabolism in ways we’re just beginning to understand.
Most importantly, this research highlights that the quality of fat matters more than the quantity. It’s not just about calories — it’s about what those calories do in your body.
Bottom Line: Don’t Fear the Olive Oil
This study offers powerful reassurance: when used in place of other fats, olive oil isn’t just safe — it may actually help prevent weight gain over time.
If you’re new to using olive oil in everyday cooking, here are a few easy ways to start:
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Use it in salad dressings and marinades
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Drizzle it over veggies, grains, or toast
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Use it in baking instead of butter
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Roast, sauté, or grill with it
And remember — weight management is about more than food. Movement, sleep, stress, and emotional health are all part of the equation. Don’t hesitate to team up with a doctor, dietitian, or wellness coach to find an approach that works for you.
