Protein intake and its interaction with dietary patterns on clinical outcomes among older adults.

Adequate protein intake is increasingly recognized as a key determinant of healthy aging, yet its independent and diet-dependent effects on functional decline and mortality remain uncertain. Using data from 532 adults aged ≥65 years in the English Longitudinal Study of Ageing, we examined cross-sectional and longitudinal associations between multiple protein-related parameters and clinical outcomes over six years. We also evaluated whether protein intake modified or mediated the effects of two healthy dietary patterns-the Mediterranean diet (MED) and the World Health Organization Quality Diet Index (WHO-QDI). Results indicated that high protein intake, whether adjusted for body weight ( ≥ 0.8-1.0 g/kg/day) or expressed relative to total energy consumption ( ≥ 18%), was consistently associated with lower risks of falls, mobility limitations, activities of daily living (ADL) disability, frailty status, declines in walking speed, and mortality. Protein intake, particularly from animal sources, also mediated beneficial associations between the MED diet and WHO-QDI with mobility outcomes. These findings underscore protein intake-especially at or above 1.0 g/kg/day and with substantial contributions from high-quality animal proteins-as a key component of dietary strategies aimed at preserving physical function and promoting healthy aging.