Olive oil prevents weight gain while butter and margarine add pounds, study finds

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Feb 20 2025

New research challenges the myth that olive oil leads to weight gain—showing that quality of fat, not quantity, matters most for long-term weight control.

Study: Changes in olive oil consumption and long-term body weight changes in three U.S. prospective cohort studies. Image Credit: Prostock-studio / Shutterstock

In a recent study published in The American Journal of Clinical Nutrition, researchers conducted a long-term (20-24 years) large cohort (n = 121,119 final eligible participants) study to evaluate the impacts of olive oil on participant weight. Olive oil is known to benefit cardiovascular health, but its implications on weight remain contentious. Most people worry that its high-calorie density contributes to obesity and similar weight gain-associated complications.

The study found that consuming olive oil (7 grams per day) was associated with reduced weight gain while consuming equal amounts of margarine, vegetable oils, or butter resulted in weight gain. These findings remained significant irrespective of participants' age or baseline body mass index (BMI), highlighting the benefits of olive oil and the distinction between healthy and unhealthy fat sources.

Background

Overweight and obesity are global public health concerns, with 2022 estimates revealing that one in every eight people (>1 billion) live with these conditions. Characterized by body mass indices (BMIs) exceeding 25 kgm⁻² and 30 kgm⁻², these conditions are associated with severe medical conditions, including cardiovascular diseases (CVDs), cancers, and premature mortality.

Unfortunately, despite several public health initiatives tailored towards curbing this global epidemic, overweight and obesity prevalence continues to rise annually, highlighting the need for novel approaches aimed at combatting unwanted weight gain.

Dietary interventions, particularly those involving 'healthy diets' like the Mediterranean diet pattern, are popularized for their numerous health benefits, including improved cardiovascular health and pthe otential to mitigate weight gain.

"Current recommendations highlight the importance of dietary patterns including healthy sources of dietary fats, particularly those high in unsaturated fatty acids and low in saturated fatty acids (SFA), for preventing cardiometabolic diseases, including obesity."

Olive oil, a rich source of monounsaturated fatty acids (MUFA), is traditionally the foremost source of fat in the Mediterranean diet. Unfortunately, several people express concerns with olive oil's potential for weight gain, citing its high calorific value as a cause for its sparing use or substitution. Olive oil has been scientifically verified as safe and healthy for human consumption, and its cardiovascular benefits are well documented. However, its impacts on long-term weight changes remain underexplored.

About the Study

The present study seeks to investigate the relationship between olive oil consumption and long-term weight changes in three United States (US) cohorts, namely the Nurses' Health Study (NHS), the Nurses' Health Study II (NHSII), and the Health Professionals' Follow-up Study (HPFS). Together, these studies initially enrolled 121,700 females (age 30-55 years) in 1976, 116,429 females (25-42 years) in 1989, and 51,529 males (40-75 years) in 1986, respectively. However, after applying exclusion criteria (age, pre-existing chronic diseases, missing data), the final analysis included 121,119 participants.

"The NHS, NHSII, and HPFS prospective cohorts enrolled 121,700 females (age 30-55 years) in 1976, 116,429 females (25-42 years) in 1989, and 51,529 males (40-75 years) in 1986, respectively."

Study data collection included self-administered questionnaires comprising personal characteristics, lifestyle details, medical history, and other relevant baseline clinical data, with updates submitted every 2-4 years. Participants above the age of 65 years or those with severe chronic conditions (diabetes, CVD, cancers, respiratory ailments, kidney diseases, etc.) were excluded from the present analyses.

Dietary data was obtained using semiquantitative food frequency questionnaires (FFQs) comprising 130 items, administered every 4 years. Special attention was placed on fat consumption, including those used in cooking. Changes in participant weight were recorded biennially. Other health behaviors, including smoking status, physical activity, prescribed medications, sleep habits, and television times, were recorded once every 2 years.

Multivariable generalized linear regression models were used to evaluate participant-specific changes in body weight and how these changes correlated with reported fat consumption. Models were adjusted for several variables, including ethnicity, socioeconomic status, smoking status, alcohol intake, etc. Substitution models were also employed to evaluate the impact of replacing other dietary fats with olive oil.

Study Findings

Study results revealed that increased olive oil consumption was inversely associated with weight gain (higher olive oil consumption was linked to less body weight gain) independent of sociodemographic or other dietary factors. On the other hand, most other fat sources, particularly margarine, vegetable oils, and butter, resulted in weight gain, especially in participants who were already overweight or obese at the start of the study.

Substitution analyses confirmed that replacing margarine, butter, or vegetable oils with olive oil was associated with less weight gain over time. This supports clinicians' hypothesis that the quality, not quantity, of calorific intake contributes to unwanted weight gain.

"These findings support dietary guidelines emphasizing the importance of fat quality over fat quantity, even within the framework of weight management."

Together, these findings highlight the benefits of olive oil in protecting against CVD risk and promoting healthy weight management. Importantly, the study did not differentiate between extra-virgin and refined olive oils, meaning its conclusions apply broadly across olive oil types. While the present study was unable to differentiate between different types of olive oils (e.g., virgin versus extra-virgin), its findings suggest that olive oil's benefits extend beyond its traditional Mediterranean context, making it relevant to diverse populations.

Conclusions

The present study establishes that increasing olive oil intake is linked to lower weight gain over time and addresses concerns regarding its potential to trigger overweight or obesity. While these findings were restricted to US-based cohorts, the study's duration (20 to 24 years) and size (n = 121,119 final eligible participants) enhance its credibility and potential applicability to other populations. This study emphasizes the "quality over quantity" principle, demonstrating that substituting higher-calorie fats such as vegetable oils, margarine, and butter with olive oil may help in long-term weight management.