Sleeping metabolic rate and body size in 12-week-old infants.

OBJECTIVE

Sleeping metabolic rate (SMR) is influenced by body size and body composition. In order to be able to compare SMR between individuals and groups, the best way to remove the effect of body size and body composition was sought.

DESIGN

A cohort of 50 infants was studied at 12 weeks. SMR was measured by indirect calorimetry, and body size and body composition by anthropometry and a stable isotope technique. Regression analysis was used to calculate the best way to remove the effect of body size and body composition on SMR.

RESULTS

Regression analysis showed that SMR was adjusted for body weight and fat-free mass by 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 powers 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 both 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.