Abstract
Background: It is often advised to ensure a high-protein intake during energy-restricted diets. However, it is unclear whether a high-protein intake is able to maintain muscle mass and contractility in the absence of resistance training.Materials and Methods: After 1 week of body mass maintenance (45 kcal/kg), 28 male college students not performing resistance training were randomized to either the energy-restricted (ER, 30 kcal/kg, n = 14) or the eucaloric control group (CG, 45 kcal/kg, n = 14) for 6 weeks. Both groups had their protein intake matched at 2.8 g/kg fat-free-mass and continued their habitual training throughout the study. Body composition was assessed weekly using multifrequency bioelectrical impedance analysis. Contractile properties of the m. rectus femoris were examined with Tensiomyography and MyotonPRO at weeks 1, 3, and 5 along with sleep (PSQI) and mood (POMS).Results: The ER group revealed greater reductions in body mass (Δ −3.22 kg vs. Δ 1.90 kg, p < 0.001, partial η2 = 0.360), lean body mass (Δ −1.49 kg vs. Δ 0.68 kg, p < 0.001, partial η2 = 0.152), body cell mass (Δ −0.85 kg vs. Δ 0.59 kg, p < 0.001, partial η2 = 0.181), intracellular water (Δ −0.58 l vs. Δ 0.55 l, p < 0.001, partial η2 = 0.445) and body fat percentage (Δ −1.74% vs. Δ 1.22%, p < 0.001, partial η2 = 433) compared to the CG. Contractile properties, sleep onset, sleep duration as well as depression, fatigue and hostility did not change (p > 0.05). The PSQI score (Δ −1.43 vs. Δ −0.64, p = 0.006, partial η2 = 0.176) and vigor (Δ −2.79 vs. Δ −4.71, p = 0.040, partial η2 = 0.116) decreased significantly in the ER group and the CG, respectively.Discussion: The present data show that a high-protein intake alone was not able to prevent lean mass loss associated with a 6-week moderate energy restriction in college students. Notably, it is unknown whether protein intake at 2.8 g/kg fat-free-mass prevented larger decreases in lean body mass. Muscle contractility was not negatively altered by this form of energy restriction. Sleep quality improved in both groups. Whether these advantages are due to the high-protein intake cannot be clarified and warrants further study. Although vigor was negatively affected in both groups, other mood parameters did not change.
Highlights
During voluntary weight loss, as much lean body mass as possible should be maintained (Artioli et al, 2010)
While most of the studies revealed that energy restriction was associated with a significant lean body mass loss (Karila et al, 2008; Pikosky et al, 2008; Morton et al, 2010; Pasiakos et al, 2013; Rhyu and Cho, 2014), ranging from 34% (∼-1200 kcal/day; Morton et al, 2010) to 84% (∼-2500 kcal/day; Karila et al, 2008) of the total mass lost per week, some studies reported no significant lean body mass change during energy restriction (Huovinen et al, 2015; Wilson et al, 2015)
While lean body mass significantly declined over time in the energy-restricted group (ER) group [F(5,65) = 6.181, p < 0.001, partial η2 = 0.332], the control group (CG) increased lean body mass [F(5,65) = 4.369, p = 0.002, partial η2 = 0.252]
Summary
As much lean body mass as possible should be maintained (Artioli et al, 2010). While most of the studies revealed that energy restriction was associated with a significant lean body mass loss (Karila et al, 2008; Pikosky et al, 2008; Morton et al, 2010; Pasiakos et al, 2013; Rhyu and Cho, 2014), ranging from 34% (∼-1200 kcal/day; Morton et al, 2010) to 84% (∼-2500 kcal/day; Karila et al, 2008) of the total mass lost per week, some studies reported no significant lean body mass change during energy restriction (Huovinen et al, 2015; Wilson et al, 2015) Since all of these studies differ in total energy deficit, protein intake, sleep duration, baseline body fat, and type of physical activity performed, which are all known to significantly influence lean body mass change (Heymsfield et al, 2011), the exact reasons for the inherent interstudy differences remain unclear. It is unclear whether a high-protein intake is able to maintain muscle mass and contractility in the absence of resistance training
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