Effect of food palatability on early (cephalic) phase of diet-induced thermogenesis in nonobese and obese man

OBJECTIVE: To study the effect on the early (cephalic) phase of diet-induced thermogenesis (EDT) of palatable vs unpalatable food, in nonobese and obese man. SUBJECTS: Twenty-four nonobese volunteers and 19 obese clinic patients. DESIGN AND MEASUREMENTS: A palatable, liquid formula meal of Ensure (1048 KJ, 450 ml), and of Ensure made unpalatable by addition of aqueous KCl, were sipped on nonconsecutive mornings. O2 consumption (ml/min) was measured before, and starting 30, 60 and 90 min after beginning the test meal, from which EDT was calculated as KJ/min. RESULTS: Palatability of the test meal significantly increased EDT (palatability effect, P=0.004) but obesity status per se, did not affect EDT. Nevertheless, the effect of palatability on EDT was dependent on obesity status, being seen only in the nonobese. EDT was significantly greater in the nonobese after the palatable than the unpalatable meal: (mean±s.e.m.) 2.45±0.14 vs 1.83±0.14; P<0.0001, but not in the obese: 1.93±0.28 vs 1.73±0.20; P<0.21. Therefore only after the palatable meal was EDT less in the obese compared with the nonobese: P<0.05. The threshold for the unpleasant taste of added KCl was 31% higher in the obese than the nonobese: 4.2±0.4 vs 3.2±0.2 [g KCl]; P<0.025. CONCLUSIONS: The early (cephalic) phase of dietary thermogenesis (EDT) is significantly increased in the nonobese by palatability, but not in the obese, so that only after a palatable meal is EDT less, or ‘deficient,’ in the obese compared with the nonobese. Also, the obese have a higher threshold for the unpleasant taste of KCl (in Ensure) than the nonobese.