A series of four trials was carried out to investigate the effects of caffeine and coffee on the metabolic rate and substrate utilization in normal weight and obese individuals. In the first trial 8 mg/kg caffeine was compared with a placebo in normal weight subjects. Metabolic rate increased significantly during the 3 hr after caffeine ingestion. While plasma glucose, insulin, and carbohydrate oxidation did not change significantly, plasma free fatty acid levels rose from 432 +/- 31 to 848 +/- 135 muEq/liter and were accompanied by significant increases in fat oxidation during the last hour of the test. In the second and third trials the effects of coffee providing 4 mg/kg caffeine were studied in control and obese subjects. Metabolic rate increased significantly in both groups; however, significant increases in fat oxidation were only observed in the control group. Plasma free fatty acids did not change in the obese. In the fourth trial, coffee was taken with a 3080 kJ meal. The thermic effect of the meal was significantly greater after coffee than after decaffeinated coffee and again fat oxidation was significantly greater after coffee. In conclusion caffeine/coffee stimulates the metabolic rate in both control and obese individuals; however, this is accompanied by greater oxidation of fat in normal weight subjects.

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.

I. A new apparatus is described with which it is possible to measure the volume (and hence density) of obese patients without requiring them to immerse totally in water. Replicate measurements of subjects with 6, 23 and 38 kg body fat had a standard deviation not greater than 0.3 kg fat.2. In nineteen obese women body fat was measured by density, total body water, and total body potassium at the beginning, and again at the end, of a period of 3-4 weeks on a reducing diet, during which they lost 5.43 (SD I. 83) kg in weight. The composition of weight loss was also estimated both by energy balance and nitrogen balance during the interval between the two measurements of body composition.3. The estimates of fat content of the nineteen women at the start of the balance period were 45.63(SD 1450) kg by density, 48.07 (SD 13.88) kg by K and 47.09 (SD 13.85) kg by water. The correlation coefficient between the density and K estimate was 0-949, and for the density and water estimate it was 4. It is concluded that measurement of density by the new method provides a convenient method for estimating body fatness, and change in fat content, which compares favourably with estimates based on total body water or total body K. However, these methods cannot be used to provide an accurate estimate of the composition of a small weight loss in an individual since deviations up to 4 kg fat occur between fat loss based on change in density and those based on the more reliable (but more tedious) energy balance method. 0,971.

I. In order to reinvestigate the classical concept of specific dynamic action of food, the thermic effect of ingested glucose (jo g) or essential amino acids (50 g) or both was measured in seven healthy male subjects dressed in shorts, by using both direct and indirect calorimetry simultaneously. Experiments were performed under conditions of thermal comfort at 28". 2. Energy 'balance' (heat production minus heat losses) was negative during the control period (mean heat deficit: -16,0+0.8 kJ/ma per h.3. Metabolic rate increased 1 3 6 + 1.8 yh after the glucose load, 172t1.40/o after amino acids, and 17'3 f 2.9 yo after both glucose and amino acids : thus there was no additive thermic effect when both nutrients were given together.4. I n contrast to the metabolic rate, heat losses were not significantly altered after nutrient ingestion; consequently, the energy 'balance' became rapidly positive.5. These results show that: (a) the food-induced thermogenesis, for a moderate energy intake, is less dependent on the nature of the nutrients than was classically admitted; (b) this increased heat production mainly induces changes in heat storage rather than in heat losses during the first hours following ingestion of a meal.An increased heat production following food ingestion was described by Rubner (1902) at the beginning of the century. Lusk (1930) showed that the stimulation of heat production varied according to the composition of the diet. Proteins had the greatest effect, increasing the metabolic rate by 30% of the ingested energy, whereas the augmentation was 6 and 4% for lipids and carbohydrates respectively. The term 'specific dynamic action' was used to describe this effect. It is to be emphasized that most of these early experiments were performcd on animals given large amounts of nutrients.The concept of specific dynamic action (SDA) has been recently challenged by various authors Ashworth, 1969; Garrow & Hawes, 1972; Garrow, 1973;Miller & Mumford, 1973). According to Miller & Mumford (1973), the term ' thermic effect' appears more appropriate to account for the incrcased metabolic rate following food ingestion.Since precise quantitative findings on the thermic effect of food in human subjects are scarce in the literature, the present study was undertaken to measurc the energy balance of subjects receiving glucose or amino acids or both. For this purpose, determinations of metabolic rate were made simultaneously with measurements of heat losses in a direct calorimeter.

No abstract