The thermic effect of carbohydrate versus fat feeding in man.

Metabolic rate increases and heat is produced after eating a meal. This response has been termed the thermic effect of feeding. While some studies have found this response to be defective in obese subjects others have not. It is also unclear how dietary composition affects the thermic response to a meal. In this study, we evaluated the thermic response to both a high carbohydrate meal and a high fat meal in normal and obese subjects. Using the ventilated hood technique, metabolic rate was measured in seated subjects before and for 6 hours following a meal. Blood samples for insulin, glucose, and catecholamines were withdrawn each half hour to evaluate their possible role in regulating the thermic response. The overall response to the high carbohydrate meal was greater than to high fat (0.26 +/- .07 v 0.18 +/- 0.11 kcal/min; P less than .01). The thermic response to the high fat meal, however, was similar in the normal and obese groups. Although the 6-hour response to the high carbohydrate diet was not statistically different between the subject groups, there was a trend toward a diminished response in the obese relative to the normal group during the first 3 hours following the meal (0.30 +/- .06 v .22 +/- .09; P = .06). In our seated subjects, the thermic response to a meal accounted for 8%-13% of the total calories ingested, with the highest value found in the normal weight subjects after a high carbohydrate meal. No significant thermic response was noted when subjects were fed a noncaloric meal.(ABSTRACT TRUNCATED AT 250 WORDS)