Background: The brown adipose tissue (BAT) is a potential target for the treatment of obesity and metabolic disorders. Its activation by cold exposure or adrenergic drugs can increase systemic insulin sensitivity and improve lipid metabolism; however, little is known about the effects of specific dietary components on BAT activity.

Objectives: We asked if a short-term (4 weeks) dietary intervention with olive oil could modify BAT activity in lean and overweight/obese volunteers.

Design: This was a 4-week open clinical trial in which all participants underwent a dietary intervention with extra-virgin olive oil supplementation. As the initial intake of olive oil was controlled all the participants were controls of themselves.

Results: The intervention resulted in significant increase in blood monounsaturated fatty acid levels, which was accompanied by increased BAT activity in lean but not in overweight/obese volunteers. In the lean group, an increase in leptin was detected after the intervention, and low leptin values at the beginning of the study were predictive of greater BAT activity after intervention. In addition, increase in leptin concentration was associated with increased BAT activity. Three known endogenous mediators of BAT activity, secretin, fibroblast growth factor 21 (FGF21), and 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME) were increased by intervention in lean, whereas only secretin and FGF21 were increased in subjects with excessive weight.

Conclusion: This study provides clinical evidence for the impact of monounsaturated fatty acids on BAT activity and an advance in the understanding of the beneficial health effects of olive oil.