SLEEPING METABOLIC-RATE AND BODY-SIZE IN 12-WEEK-OLD INFANTS

Objective: Sleeping metabolic rate (SMR) is influenced by body size an d body composition. In order to be able to compare SMR between individ uals and groups, the best way to remove the effect of body size and bo dy composition was sought. Design: A cohort of 50 infants was studied at 12 weeks. SMR was measured by indirect calorimetry, and body size a nd body composition by anthropometry and a stable isotope technique. R egression analysis was used to calculate the best way to remove the ef fect of body size and body composition on SMR. Results: Regression ana lysis showed that SMR was adjusted for body weight and fat-free mass b y raising body weight to the power 0.41, and by raising fat-free mass to the power 0.44. When SMR was at its minimum level, the optimum powe rs were 0.41 for body weight and 0.45 for fat-free mass. Conclusions: SMR can be adjusted for body weight, or fat-free mass thereby taking b oth body size and body composition into account, by expressing SMR in terms of weight or fat free mass raised to powers close to 0.50.