Thermic effect of glucose in obese subjects studied by direct and indirect calorimetry

Abstract

I . The thermic effect of a glucose load (50 g) was studied in ten control and eleven obese female subjects, using both direct and indirect calorimetry simultaneously. Experiments were done under conditions of thermal equilibrium (28O and 30 % relative humidity).2. Thermal balance (heat production measured by indirect calorimetry minus heat losses measured directly) was negative in the control group during the fasting period (heat deficit -14.2 _+ 5.0 kJ/m2 per h), whereas that of the obese group was in equilibrium (+ 1.4 t4.8 kJ/ma per h). 3.After the glucose load, metabolic rate increased 13.0 f 1.5 and 5 2 1.3 % in the control and obese groups respectively. 4.In contrast to the metabolic rate, total heat losses were not significantly altered in either group after the glucose load. Total heat losses of the obese group were significantly lower than those of the control group throughout the experimental period.5. During the experiments the amount of heat stored was increased in both groups. Thermal balance in the control group became positive while that of the obese group remained positive.6. During the fasting period, the control subjects oxidized more carbohydrates (90.4 mglmin) than lipids (68.8 mglmin), whereas obese subjects oxidized more lipids (103.7 mglmin) than carbohydrates (50.2 mg/min). After the glucose load, the oxidation rate of carbohydrates was increased in both groups to 158-1 mg/min in control subjects and 95-6 mg/ min in obese subjects.7. The mean skin temperature of the control subjects was significantly higher than that of the obese subjects and remained higher throughout the postprandial period.8. These results indicate that: (a) during the fasting period, the energy sources utilized and the thermal balance of the two groups were different; (b) the thermic effect of glucose was less in the obese subjects and, therefore, might be a factor contributing to their low energy expenditure.

A study of the thermic responses to a meal and to a sympathomimetic drug (ephedrine) in relation to energy balance in man

“…(In the present study the subjects were sitting rather than lying down so that the values obtained for RMR were probably 20-30% higher than the true values of RMR.) Rose & Williams (1961) were also unable to show any difference in the RMR between the large and small eaters in their study. However, it is clear that whereas the RMR comprises the major proportion of energy expenditure in the LEI group, it accounts for less than half the daily energy expenditure of the HE1 group.…”

“…Although the LEI group was fatter than the HE1 group, their mean energy intake was less than half that of the HE1 subjects, an illustration of the great diversity of metabolic efficiency that can be observed in man which has been reported on many previous occasions (Widdowson, 1947;Rose & Williams, 1961;Garrow, 1974). This efficiency could not be related to a lower RMR in the LEI group.…”

“…It has been suggested that TEF is potentiated by simultaneous exercise (Miller et al 1967, Bray et al 1973) but these studies have been criticized by Garrow (1978) who concludes that if it exists the potentiation is very small. A reduction in the size of the thermic response to an individual meal has been reported in obese subjects (Kaplan & Leveille, 1976;Pittet et al 1976). That such a defect might contribute to the energy imbalance of obesity rather than be secondary to the obese state is suggested from the observation that the thermic response to feeding remains diminished in thin anorectics with a previous history of obesity (Stordy et al 1977).…”

“…The reasons for the conflict in findings between the present study and that of Rose & Williams (1961) is unclear but could reflect a number of factors such as (1) only a single meal size of 3.39 MJ was used, a level at which any difference in response might be masked, (2) a difference in the composition and absorption rates of the commercial meal preparation used in this study and the 'English breakfast' used in the Rose &Williams (1961) study, (3) the effect of the previous exercise of the subjects in the study of Rose & Williams (1961). It has been suggested that TEF is potentiated by simultaneous exercise (Miller et al 1967, Bray et al 1973) but these studies have been criticized by Garrow (1978) who concludes that if it exists the potentiation is very small.…”

Brown Adipose Tissue in Man: A Review

“…Further, it should be possible to demonstrate that obese people have a reduced capacity for thermogenesis. Pittet et al (1976) found differences between lean and obese women in the size of response to a small meal (50 g glucose), but this was not confirmed by other workers (Kaplan & Leveille 1976, Clough & Durnin 1970. Blaza (1980) found no differences in the response of five lean and five obese women to a 1000 kcal (4.2 MJ) meal and moderate exercise although there were some differences in response to warm and cool environmental temperatures (all within 20-30"C and described by the subjects as 'comfortable').…”