PURPOSE: To examine the effects of dietary intake, with or without energy, on faculatative diet-induced thermogenesis in human skeletal muscle. METHODS: Five healthy males (age: 28.6 ± 1.5 (SD) yr.; height: 172.4 ± 5.2 cm; body weight: 63.6 ± 7.8 kg) participated in the study. Forearm muscle oxygen consumption (VO2mus) was measured by near infrared continuous wave spectroscopy (NIRcws; HEO-200, Omron Inc.), using the brief arterial occlusion method (Hamaoka et al. 1996, Sako et al. 2001). Pulmonary oxygen uptake (VO2pul) was measured using the breath-by-breath gas analysis method (AE-280, Minato Medical Science Co., Ltd.). Subjects were given a meal equivalent to total energy content of 10 kcal/kg body weight (ML), or an equal amount of placebo with no calorie-content (PLC), or no meal at all (CON) on each subsequent days. VO2mus and VO2pul were measured before (pre), and after meal or placebo intake (post 15, 30, 45, 60, 90, 120 and 150 min.). RESULT: ML induced a significant increase in both VO2pul (pre: 226 ± 11 (SE) ml/min., post 120 min. (the peak value): 258 ± 14 ml/min.) and in VO2mus (pre: 1.41 ± 0.15μM O2/s, post 120 min.: 2.13 ± 0.37μM O2/s). In contrast, CON did not show any increase in either VO2pul or VO2mus. While PLC showed an early increase in VO2pul (pre: 217 ± 9 ml/min., post 15 min.: 241 ± 10 ml/min.), in VO2mus there were no changes throughout the experiment. CONCLUSION: The results indicate that ML and PLC induced a significant increase in whole body metabolism. This was mainly due to obligatory thermogenesis, and facultative thermogenesis that occurred only after dietary energy intake. Facultative thermogenesis in skeletal muscle may be of importance for the regulation of energy output in humans.