Findings from a large-scale analysis of three major prospective cohort studies revealed that increasing olive oil intake was inversely associated with long-term body weight changes among middle-aged U.S. adults, while other added fats showed positive associations with weight gain.

Study investigators examined data from 121,119 participants across the Nurses' Health Study (NHS, 1990–2010), Nurses' Health Study II (NHSII, 1991–2015), and Health Professional's Follow-up Study (HPFS, 1990–2014) over 20 to 24 years of follow-up.

"A long-term increase in olive oil intake was inversely associated with body weight in middle-aged adults in the [United States]. Conversely, increased consumption of other added fats—such as other vegetable fats, butter, and margarine—and refined grains was associated with increased body weight," the researchers reported in The American Journal of Clinical Nutrition.

The study found that consumption of each additional ½ tablespoon (7 g) per day of olive oil was associated with less weight gain after adjusting for sociodemographic and dietary variables. These results remained consistent when controlling for overall diet quality and other potential confounding factors. In contrast, equivalent increases in other vegetable oils and butter were positively associated with weight gain.

Substitution analyses demonstrated that replacing 7 g/day of other fats with olive oil was associated with less weight gain: –0.52 kg for butter, –0.18 kg for margarine, and –0.16 kg for other vegetable oils.

At baseline, mean body mass index across cohorts ranged from 25.9 to 26.1 kg/m². Average olive oil intake was 3.3 g/day in NHS, 3.9 g/day in NHSII, and 3 g/day in HPFS. The associations between olive oil intake and weight changes were particularly strong among participants with overweight or obesity at baseline.

In discussing potential mechanisms for the favorable association, the researchers noted several possibilities. "Oleic acid may stimulate thermogenesis, increase total energy expenditure, and enhance feelings of satiety, thus contributing to the regulation of energy balance," they wrote.

Study limitations included reliance on self-reported dietary intake and the inability to distinguish between olive oil varieties. However, the large sample size, extended follow-up period, and repeated measurements with validated questionnaires in the study may strengthen the findings, according to the authors.

These results support current dietary guidelines emphasizing fat quality over quantity and suggest that substituting olive oil for other fats may be a beneficial strategy for weight management in U.S. populations.

This work was supported by National Institutes of Health grants UM1 CA186107, U01 CA167552, R01 HL034594, R01 HL088521, and R01 HL35464. Authors reported funding from the National Heart, Lung, and Blood Institute, grant K01HL1694; and received olive oil used in the PREDIMED and PREDIMED-PLUS trials from The Fundaciòn Patrimonio Comunal Olivarero and Hojiblanca SA (Malaga, Spain). No other conflicts of interest were reported.