Differential energy metabolism in conjoined twins.

BACKGROUND/PURPOSE: Conjoined twins often have different body composition and growth rate before separation. This may be because of differences in energy metabolism. The aim of this study was to investigate the energy expenditure, body composition, and calorie intake of thoracopagus conjoined twins with shared hepatic circulation but separate gastrointestinal tracts. METHODS: The twins were studied at two periods: (1) before separation (age, 73 days) and (2) after separation (age, 97 days). Calorie intake over the study periods was carefully documented. Respiratory gas exchange was measured by computerized indirect calorimetry. The postseparation weight ratio of twin A to twin B was used to approximate the preseparation weights. Body composition (total body fat) was calculated from skinfold thickness and anthropometric measurements. RESULTS: The body composition of the twins was different: body weight and total body fat were higher in twin B. Resting energy expenditure and calorie intake were markedly different between the conjoined twins before separation. In both twins, the energy expenditure increased after separation. After separation, the resting energy expenditure of the twins was similar. CONCLUSIONS: This study illustrates the difference in energy metabolism in a set of thoracopagus conjoined twins. The authors speculate that twin A was supplying nutrients to twin B resulting in increased energy expenditure before separation. This would explain the lower calorie intake and higher fat mass of twin B.