Relationship between Dietary Protein or Essential Amino Acid Intake and Training-Induced Muscle Hypertrophy among Older Individuals

Dietary protein intake is critical for maintaining an optimal muscle mass, especially among older individuals. Although protein supplementation during resistance training (RT) has been shown to further augment training-induced muscle mass in older individuals, the impact of daily variations in protein intake on training-induced muscle mass has not been explored thus far. Therefore, this study aimed to investigate the relationship between the dietary protein and amino acid intake and RT-induced muscle hypertrophy among older individuals. Ten healthy older men (n=10; mean age=69 +/- 2 y; body weight (BW)=61.5 +/- 2.2 kg; height=1.65 +/- 0.02 m) participated in progressive RT performed 3 times/wk for 12 wk. Body composition (using DXA) and nutritional assessments (using a 3-d dietary record) were performed before and after the training period. Leg lean mass (LLM) increased significantly (15.0 +/- 0.8 vs. 15.4 +/- 0.8 kg, p<0.05) after RT, with no change in dietary nutrient intake. The average dietary protein intake was 1.62 +/- 0.11 g/kg BW/d, while essential amino acids was 600 +/- 51 mg/kg BW/d. Although the correlation between the increase in LLM and dietary protein intake was not significant, a significant correlation was found between the increase in LLM and dietary essential amino acid (EAA) intake. Furthermore, there were significant correlations between the increase in LLM and protein as well as EAA (especially leucine) intake at breakfast among subjects with suboptimal protein intake (p<0.05). Our study findings indicate that dietary protein as well as EAA intake may be significant contributing factors in muscle hypertrophic response during RT among healthy older men.