What is the potential added benefit of increasing dietary protein on muscle growth?

From the Guidelines

Increasing dietary protein intake to 1.1 g/kg/d or higher may be beneficial for muscle mass maintenance in older adults, but the evidence suggests that there is limited benefit to exceeding this amount. The current international recommendation of 0.8 g/kg/d may be sub-optimal for maintaining muscle mass throughout adult life 1. Cross-sectional observational studies have reported positive associations between protein intake and muscle mass in older adults, but the evidence is not consistent, and some studies have found no further beneficial effects on muscle mass beyond a protein intake of 1.1 g/kg/d 1.

Some key points to consider when evaluating the potential benefits of increased dietary protein intake on muscle growth include:

• Protein quality is an important factor, with animal-based proteins generally considered high-quality due to their better essential amino acid profile and higher digestibility 1
• The timing of protein intake may also be important, with consuming 20-40 grams of high-quality protein within 2 hours after exercise and distributing protein intake evenly throughout the day (every 3-4 hours) potentially optimizing muscle protein synthesis 1
• Complete proteins containing all essential amino acids, particularly leucine, are most effective for stimulating muscle growth 1
• Plant-based proteins may not be as effective for muscle mass maintenance in older adults, but strategies such as increasing the dose of plant-based protein intake, mixing different plant-based protein sources, and adding leucine as an anabolic stimulant may help overcome this limitation 1

It is also important to consider the potential for metabolic adaptation to changes in protein intake, which may explain the null findings in some intervention studies 1. Overall, while increasing dietary protein intake may be beneficial for muscle growth, the evidence suggests that there is limited benefit to exceeding a protein intake of 1.1 g/kg/d, and that other factors such as protein quality, timing, and overall calorie intake should also be considered.

From the Research

Potential Added Benefit of Increasing Dietary Protein on Muscle Growth

• The current Recommended Dietary Allowance (RDA) for protein is defined as the minimum amount required to prevent lean body mass loss, but consuming higher-protein diets may have muscle-related benefits 2.
• Research has indicated that increased dietary protein intake (up to 1.6 g protein x kg(-1) x d(-1)) may enhance the hypertrophic response to resistance exercise 3.
• Ingestion of protein is crucial for maintenance of skeletal muscle mass, and the effect of protein intake on muscle protein accretion can be stimulated by prior exercise training 4.

Optimal Protein Intake for Muscle Growth

• Protein supplementation beyond total protein intakes of 1.62 g/kg/day resulted in no further resistance training-induced gains in fat-free mass (FFM) 5.
• Increasing daily protein ingestion may enhance gains in lean body mass (LBM) in studies enrolling subjects in resistance exercise, particularly in subjects ≥65 years old ingesting 1.2-1.59 g of protein/kg/day and for younger subjects (<65 years old) ingesting ≥1.6 g of protein/kg/day 6.

Effects of Protein Intake on Muscle Strength and Function

• Dietary protein supplementation significantly enhanced changes in muscle strength and size during prolonged resistance training in healthy adults 5.
• Lower-body strength gain was slightly higher by additional protein ingestion at ≥1.6 g of protein/kg/day during resistance exercise training 6.
• The effects of ingesting more protein are unclear when assessing handgrip strength and only marginal for performance in physical function tests 6.