Background: Optimising protein nutrition alongside resistance exercise training (RET) is widely recommended to preserve muscle health and physical function during ageing. However, it remains unclear whether increasing protein intake provides additional benefits when older adults already consume relatively adequate amounts of protein, or whether these effects depend on RET intensity. We investigated the combined and independent effects of a dietary protein intervention and RET performed across a wide range of intensities on dietary intake, muscle strength, body composition, cognitive and psychosocial outcomes in frail community-dwelling older adults.
Methods: The 12-week TEAMS randomised controlled trial included 295 frail community-dwelling older adults (74±6 years; 69% female). Participants performed supervised RET twice weekly at intensities ranging from 20–80% of one-repetition maximum (1-RM) and were randomised to RET alone or RET plus a dietary protein intervention (RET-Pro). RET-Pro included dietary counselling and daily provision of 20 g protein, targeting 1.2–1.5 g protein/kg/day. Outcomes included dietary protein and amino acid intake and distribution, 1-RM leg-press strength, body composition, executive function, depressive symptoms, fear of falling and quality of life. Linear mixed models examined intervention effects (P<0.05).
Results: Baseline protein intake was relatively high (~1.2 g/kg/day). RET-Pro increased protein intake by ~29 g/day, including essential amino acids (+14.5 g/day) and leucine (+3.1 g/day; all P<0.001), and increased protein intake across all eating occasions. RET substantially increased leg-press strength (~24 kg, P<0.001), with improvements across the full range of training intensities. RET also improved depressive symptoms, executive function and quality of life, independent of training intensity. Despite substantial improvements in protein and amino acid intake, RET-Pro did not provide consistent additional benefits for muscle strength, lean mass, executive function or quality of life. RET-Pro reduced fear of falling but increased total energy intake (~209 kcal/day) and fat mass (+0.7 kg).
Conclusion: In frail older adults with relatively adequate habitual protein intake, a targeted protein intervention substantially improved protein quantity, amino acid intake and protein distribution, but provided limited additional benefits beyond RET. In contrast, RET to volitional failure produced substantial improvements in muscle strength and broader healthy ageing outcomes across intensities from 20–80% 1-RM. These findings highlight the importance of considering habitual protein intake when prescribing additional protein and support flexible RET prescriptions tailored to the capacity and preferences of frail older adults.