Patients with inflammatory bowel disease often present with weight loss. Among possible causes, an elevated energy expenditure has frequently been suggested but is the least documented. In this study resting metabolic rate (RMR) and total daily energy expenditure (TDEE) were measured in 15 outpatients with inflammatory bowel diseases and in eight healthy control subjects. Measured RMR as a percentage of that predicted from fat-free mass was not significantly different for control subjects (102 +/- 9.8%, mean +/- SD) and patients (100 +/- 13.3%). TDEE, expressed as a multiple of RMR, was 1.70 +/- 0.31 for control subjects and 1.78 +/- 0.24 for patients. When patients were subgrouped as greater than or equal to 90% or less than 90% desirable body weight, a mean increase over RMR predicted from fat-free mass was seen in the underweight patients (106 +/- 9.3%) but not in normal-weight patients (99.0 +/- 15.6%). Mean TDEE/RMR values for the patient subgroups were 1.70 +/- 0.30 and 1.88 +/- 0.08, respectively. We conclude that stable outpatients with inflammatory bowel disease have only a minimal increase in energy needs.