The acute effect of dexfenfluramine on resting metabolic rate and postprandial thermogenesis in obese subjects: a double-blind placebo-controlled study.

The effects of dexfenfluramine (dFE: 30 mg per os) on energy expenditure were evaluated in seven young obese male subjects (mean +/- s.d.: age 30.9 +/- 6.1 years; BMI 39.8 +/- 4.4 kg/m2). Each subject was submitted, on a double-blind protocol and by random order, to four tests in which dFE or placebo (Pla) were administered either in the fasting state or in combination with a mixed test meal. Energy expenditure was measured by indirect calorimetry for 60 min before (BMR) and from 90 to 330 min after dFE or Pla. In those cases where the protocol required it, a mixed test meal (5 MJ, 1200 kcal; percentage of protein, carbohydrate and fat: 15, 55, and 30 respectively) was eaten 120 min after dFE or Pla. In the fasting state resting metabolic rate increased after dFE (mean +/- s.d.: 0.49 +/- 0.20 kJ/min) but not after Pla (-0.04 +/- 0.16 kJ/min) in comparison to BMR, the difference between the two tests being highly significant (P < 0.01). Post-prandial thermogenesis (over 3h) was also significantly higher after dFE than after Pla (232 +/- 85 kJ vs. 181 +/- 73 kJ; P < 0.025). On the other hand, dFE did not affect respiratory quotient (RQ), either in the fasting state or in the fed state. These results show that in obese subjects dFE increases energy expenditure in the post-absorptive state, as well as after the ingestion of food.