Protein Intake to Support Muscle Mass and Function in Healthy Adults

1. Additional protein supported greater gains in lean body mass during resistance exercise

Across 62 trials involving resistance exercise, increasing daily protein intake produced a statistically significant additional improvement in lean body mass compared with control conditions.

The effect was modest in magnitude (standardized mean difference 0.22), and the certainty of evidence was rated moderate.

This suggests that additional protein can support the muscle response to resistance training, although the additional effect is limited in magnitude.

2. The evidence was much less clear without resistance exercise

Only a relatively small number of trials investigated increased protein intake without resistance exercise.

In these studies, additional protein did not produce a statistically significant improvement in lean body mass.

The evidence therefore does not support interpreting higher protein intake alone as an established strategy for increasing lean body mass in healthy adults.

3. Protein supported some measures of muscle strength

When combined with resistance exercise, increased protein intake was associated with improvements in some measures of strength.

Lower-body strength showed an additional benefit, particularly in studies in which total protein intake reached at least 1.6 g/kg/day, although the certainty of evidence for this outcome was low.

A small improvement in bench-press strength was also observed among adults younger than 65 years.

In contrast, the effect on handgrip strength was unclear.

4. Improvements in physical performance were limited

The effects of additional protein on tests of physical or functional performance were minimal and uncertain.

This distinction is important. Changes in lean body mass or individual measures of muscle strength do not necessarily translate directly into measurable improvements in overall physical performance.

5. The study does not establish one optimal protein intake for healthy aging

Among adults aged 65 years and older participating in resistance exercise, an improvement in lean body mass was observed in studies with total protein intake of approximately 1.2–1.59 g/kg/day.

However, the certainty of this evidence was low, and the association was no longer statistically significant after one influential study was removed in a sensitivity analysis.

There were also no relevant studies in adults aged 65 years and older combining resistance exercise with protein intakes of at least 1.6 g/kg/day.

These findings therefore should not be interpreted as defining a universal protein target or threshold for healthy aging.

Maintaining muscle mass and strength is an important part of preserving physical capacity, mobility and independence as we age.

This meta-analysis provides a useful perspective on the current interest in high-protein diets.

Protein is important for muscle health, but the evidence suggests that protein intake should not be considered in isolation.

The most consistent benefits of increasing protein intake were observed when it was combined with resistance exercise. Simply increasing protein intake without this training stimulus has much less supporting evidence.

For longevity, the relevant question is therefore not simply “How much protein should I eat?”, but also how nutrition and physical activity work together to preserve muscle health over time.

The findings support considering protein intake and resistance exercise together rather than viewing higher protein intake as an independent strategy for preserving muscle.

Several limitations are important when translating these findings into practice. Most included trials used animal-derived protein sources, many participants already had relatively high habitual protein intake, and trial duration, protein dose and exercise protocols varied considerably between studies.

The analysis also does not establish one optimal protein intake for all healthy adults or demonstrate that progressively increasing protein intake produces progressively greater benefits.

Protein intake should therefore be considered in the context of age, physical activity, overall diet and individual health status.