A new study published in the American Journal of Clinical Nutrition examines the effect of puberty on resting energy expenditure (REE) in white and African American adolescents, finding a general metabolic slowdown in both groups, which was greater in the African Americans. Compared to the whites, the African American subjects had greater lean mass in the limbs, but lower lean mass in the trunk. Since the metabolism of organ tissue in the trunk represents the major source of energy expenditure, the African American adolescents lesser proportion of calorie-burning organ tissue could account for a lower REE.
The 5-year study included 92 white and 64 African American children in Birmingham, Alabama, who began the study at an average age of 8 years old. Participants returned annually for repeated measurements of their REE and body composition. All of the boys maintained a higher REE than the girls throughout the study. The influence of maturation on body composition and REE was apparent at a younger age in African American children because they began puberty an average of 2 years earlier than whites.
In a related editorial, Dr. J. Yanovski questions whether the observed slowdown in metabolism during puberty is transient, as are many other humoral factors during this stage of life. However, the possibility that lower REEs among African-Americans may persist into adulthood is suggested by previous studies of African American adults that show that they too have a lower REE than whites. Whether this lower REE contributes to the development of obesity in African Americans cannot be proven at this time. The role of environmental factors such as food intake and physical activity, and how these factors contribute to the overall regulation of energy balance must first be determined in this ethnic group.