Protein Intake Is Associated with Lower Body Fat and Higher Skeletal Muscle Mass in Late Adolescence

Abstract

Longitudinal data evaluating the effects of dietary protein during later childhood and adolescence on body composition are sparse. While short‐term trials suggest higher morning protein intake improves satiety and higher total protein, especially in combination with vigorous exercise, increases muscle protein synthesis, questions remain about the long‐term effects of protein timing and amount on changes in body fat and skeletal muscle mass among adolescents. The objective of this study was to investigate the effects of total and morning protein intake on late adolescent body composition. Data from 2105 girls followed for 10 years (until 17–20 years of age) in the National Heart Lung and Blood Institute's National Growth and Health Study were used for this analysis. Diet was assessed by means of three day food records collected annually. Girls were classified according to average weight‐adjusted protein intake per day and during the morning hours in early to mid‐adolescence (ages 9–17 years). The following body composition outcomes were collected at the end of follow‐up (ages 17–20 years): percent (%) body fat assessed with a bioelectrical impedance analyzer (BIA), truncal fat measured by subscapular and suprailiac skinfolds, and % skeletal muscle mass (SMM) estimated using race‐specific BIA‐based equations. Analysis of covariance models were used to control for potential confounding; race, socioeconomic status, height, television/video viewing, and percent calories from carbohydrates were retained in the final models. Total % body fat decreased linearly with increasing weight‐adjusted total protein intakes (<55 g, 55–<65 g, 65–<75 g, ≥75 g) in early adolescence (32.0%, 31.8%, 30.5%, 30.0%, respectively; p‐trend: <0.0001). Truncal fat also decreased with increasing total protein intake (36.2%, 34.2%, 32.1%, 30.1%; p‐trend: <0.0001) while % SMM increased from 33.1% to 34.5% with increasing intakes of total dietary protein (p‐trend: <0.0001). Girls with higher intakes of protein during the morning hours also tended to have higher total protein intakes during the day. With increasing amounts of morning protein (<8 g, 8–<12g, 12–<15g, ≥15 g), total % body fat decreased (31.5%, 31.2%, 30.9%, 30.7%; p‐trend: <0.0327), while % SMM tended to increase (33.4%, 33.6%, 33.8%, 33.9%; p‐trend: 0.0771). Although the amount of protein consumed during the morning hours was not independent of total protein intake, girls who generally had a morning eating occasion, regardless of its macronutrient content, tended to have lower levels of body fat and higher levels of SMM in later adolescence. These results suggest that higher total protein intake through childhood and early adolescence is associated with lower levels of percent body and truncal fat and higher levels of SMM in later adolescence. In this study, girls who consumed more protein in the morning tended to acquire less body fat and have a higher percent SMM during adolescence, although these effects appeared to be partially explained by a higher total daily protein intake.Support or Funding InformationNIDDK and a dissertation fellowship from the American Egg Board/Egg Nutrition Center