Skeletal muscles are not only important for movement but also for overall health. For instance, muscles are the primary reservoir of amino acids that support protein synthesis in vital tissues and organs when amino acid absorption from the gut is insufficient. Muscle strength and function are central to recovery from injuries and severe illnesses. Maintaining adequate muscle mass contributes to healthy bone mineral density and reduces the risk of diabetes.
While protein intake and exercise are known to be critical for maintaining muscle mass, the exact protein requirement for optimal muscle gain remains unclear. The recommended dietary allowance for protein for adults is 0.8-0.9 g/kg of body weight per day, but some studies suggest that higher doses—up to 1.6 g—may be more effective.
Researchers from the Department of Kinesiology at McMaster University in Canada sought to determine:
- Whether additional protein intake can increase muscle mass and strength in adults.
- How the effects of higher protein intake depend on age and physical activity.
The researchers conducted a systematic review and meta-analysis of 74 randomized controlled trials. Most of the studies lasted between 8 and 12 weeks. Participants were healthy, non-obese adults aged 18 and older. Some participants engaged in resistance exercises. The participants were divided into groups:
- Intervention Group: Consumed between 1 and 4.4 g of protein/kg per day.
- Control Group: Consumed between 0.8 and 2.3 g of protein/kg per day.
Meta-Analysis Results
Additional protein intake leads to a modest increase in muscle mass and strength. The most significant muscle mass gain was observed in individuals under 65 who consumed more than 1.6 g of protein/kg daily, especially those who performed resistance exercises.
As people age, they develop anabolic resistance—even with adequate nutrients and physical activity, muscles become less responsive to growth and recovery stimulation. Therefore, older adults likely require higher protein doses to increase muscle mass.
Conclusion
Current recommendations for protein intake for healthy young and elderly individuals are 0.8-0.9 g/kg of body weight per day. This meta-analysis showed that additional protein, especially when combined with resistance exercises, promotes muscle growth and improves muscle function. Significant effects were observed in physically active individuals under 65, only when consuming more than 1.6 g of protein/kg daily. This level of protein intake is twice the current recommended for healthy adults. For individuals over 65, higher doses of protein may be necessary to achieve muscle mass gain.
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