The purpose of our work is to compare the resting metabolic rate (RMR) and thermogenic effect of food (TEF) in a group of vegetarians and a group of subjects consuming a Mediterranean diet. The composition of the diets was similar. Thirty-two subjects were studied: 16 vegetarians (age 34 +/- 9 years, BMI 21 +/- 2) and 16 omnivors (age 30 +/- 5 years, BMI 22 +/- 3). All were in excellent general health. Each subject consumed a dish of pasta (100 g) and bread (30 g) after RMR had been measured. TEF was measured over the next 3 h and calculated as the incremental area above RMR. Energy (vegetarians and omnivors 7,727 +/- 3,516 vs 8,970 +/- 2,273 kJ/day, respectively) and carbohydrate (vegetarians and omnivors 285.1 +/- 141.3 vs. 300.1 +/- 74 g/day, respectively) intakes of the 2 groups were similar. The vegetarian group consumed a higher quantity of fiber (30.5 +/- 16.7 vs. 16.5 +/- 7.9) and a lower amount of protein (44.9 +/- 18.3 vs. 70.1 +/- 14.9) than the omnivorous group. No significant differences were observed in RMR (4.23 +/- 0.96 vs. 4.06 +/- 0.54 kJ/min) and TEF (0.50 +/- 0.25 vs. 0.38 +/- 0.25 Delta kJ/min) between the groups. Results did not change after correcting for weight, age and gender. Our study failed to show any significant differences in RMR and TEF between vegetarians and subjects consuming a Mediterranean diet. We conclude that vegetarianism per se is not accompanied by a difference in RMR and TEF when the carbohydrate content of the diet is similar to a control group of nonvegetarians.