FLUOXETINE INCREASES RESTING ENERGY-EXPENDITURE AND BASAL BODY-TEMPERATURE IN HUMANS

Humans lose weight when administered fluoxetine, an inhibitor of serot onin reuptake by nerve terminals. To determine whether increased energ y expenditure contributes to this weight loss we admitted 20 nondepres sed obese women to a metabolic unit where they were randomly assigned to 3 wk of a 1.76-MJ/d formula diet and either 60 mg fluoxetine/d or a placebo. Resting energy expenditure of the control subjects fell belo w normal after 5.6 +/- 0.6 d of energy restriction, whereas that of th e fluoxetine-treated subjects increased by 4.4 +/- 1.8% (P < 0.005) wi thin 3 d of commencing treatment. This increased resting energy expend iture then reversed and fell below normal after 9.8 +/- 0.9 d of energ y restriction. Basal body temperature of the control subjects decrease d insignificantly during the period of energy restriction, but that of the fluoxetine-treated subjects increased by 0.28 +/- 0.10 degrees C (P < 0.05) within 3 d of commencing diet and drug treatment. Urinary n orepinephrine excretion and the serum triiodothyronine concentration d ecreased equally in both groups. Despite identical energy intakes and equal nitrogen balance, the fluoxetine-treated subjects lost weight fa ster than the control subjects during the final week of energy restric tion (P < 0.05). We propose that serotonin reuptake inhibition increas es energy expenditure by increasing basal body temperature.