Whey beats five rival proteins for ageing muscle

Sarcopenia, the age-related loss of muscle mass, strength and mobility, is one of the biggest threats to independent living in later life. Resistance training is the established countermeasure, and protein supplementation has been shown to augment its effects in older people, but protein comes from many sources: whey, milk, casein, meat, soy and peanut all appear in trials. Whether the source matters, and which works best, has been hard to answer because few trials compare sources head to head. Ranking them requires pooling both direct and indirect comparisons across the whole evidence base.

The researchers searched online databases for randomised controlled trials that combined a protein supplement with resistance training in untrained middle-aged and older adults, spanning community-dwelling people as well as hospitalised or institutionalised residents with acute or chronic health conditions. In total, 78 trials with 5272 participants were included. Using network meta-analysis, the team compared six protein sources and ranked the probability that each was the most effective for muscle mass, handgrip strength and walking speed. They also ran meta-regression to identify factors that moderated treatment efficacy.

Whey protein topped the rankings on all three headline outcomes, showing the largest effects on muscle mass, handgrip strength and walking speed when added to resistance training. The ranking scores placed whey ahead of milk, casein, meat, soy and peanut protein. The moderator analyses added nuance: a participant's health condition influenced the muscle mass result, sex influenced the handgrip strength result, and supplementation dose influenced leg strength. In other words, who takes the protein, and how much they take, shifts how well the supplement works.

This extends earlier evidence that protein supplementation boosts the returns from resistance training in older adults by asking the next question: which protein? The result gives whey the strongest pooled backing among the six sources compared. Open questions remain, though. Many included participants were hospitalised or living with health conditions, so whether the same ranking holds in healthy, trained populations is unknown, and rankings built partly on indirect comparisons can still be overturned by direct head-to-head trials.

For an older adult doing, or considering, resistance training, this is a reason to think the type of protein may matter, with whey currently holding the best pooled evidence among the six sources compared. It does not establish an ideal amount, since dose mattered differently for different outcomes here. Nor does it suggest supplements can replace training: every trial in the analysis paired protein with resistance exercise. Because people with health conditions featured heavily in these trials, the findings speak most directly to that group.