To examine the influence of dietary protein on lean body mass loss and performance during short-term hypoenergetic weight loss in athletes.
In a parallel design, 20 young healthy resistance-trained athletes were examined for energy expenditure for 1 wk and fed a mixed diet (15% protein, 100% energy) in the second week followed by a hypoenergetic diet (60% of the habitual energy intake), containing either 15% (∼1.0 g·kg−1) protein (control group, n = 10; CP) or 35% (∼2.3 g·kg−1) protein (high-protein group, n = 10; HP) for 2 wk. Subjects continued their habitual training throughout the study. Total, lean body, and fat mass, performance (squat jump, maximal isometric leg extension, one-repetition maximum (1RM) bench press, muscle endurance bench press, and 30-s Wingate test) and fasting blood samples (glucose, nonesterified fatty acids (NEFA), glycerol, urea, cortisol, free testosterone, free Insulin-like growth factor-1 (IGF-1), and growth hormone), and psychologic measures were examined at the end of each of the 4 wk.
Total (−3.0 ± 0.4 and −1.5 ± 0.3 kg for the CP and HP, respectively, P = 0.036) and lean body mass loss (−1.6 ± 0.3 and −0.3 ± 0.3 kg, P = 0.006) were significantly larger in the CP compared with those in the HP. Fat loss, performance, and most blood parameters were not influenced by the diet. Urea was higher in HP, and NEFA and urea showed a group × time interaction. Fatigue ratings and "worse than normal" scores on the Daily Analysis of Life Demands for Athletes were higher in HP.
These results indicate that ∼2.3 g·kg−1 or ∼35% protein was significantly superior to ∼1.0 g·kg−1 or ∼15% energy protein for maintenance of lean body mass in young healthy athletes during short-term hypoenergetic weight loss.
1School of Sport and Exercise Sciences, University of Birmingham, Birmingham, UNITED KINGDOM; 2Department of Agricultural and Food Sciences, ETH Zurich, Zurich, SWITZERLAND; and 3English Institute of Sport, Sheffield, UNITED KINGDOM
Address for correspondence: Kevin D. Tipton, Ph.D., School of Sport and Exercise Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom; E-mail: K.D.Tipton@Bham.ac.uk.
Submitted for publication August 2008.
Accepted for publication June 2009.