<p>The Eatwell Guide represents the UK’s principal healthy eating model and understanding whether adherence to UK dietary recommendations can attenuate age-related functional decline is essential to inform healthy ageing strategies. In up to 157,457 participants from the UK Biobank, we explored cross-sectional and prospective associations between adherence to the Eatwell Guide and markers of physical function (grip strength, fat-free mass percentage, self-reported walking pace, and falls). Eatwell Guide adherence scores were derived from 24-h dietary recall data (Oxford WebQ), and quantified using a graded, food-based scoring system. Differences between population subgroups including by age, sex, physical activity, and protein intake level were explored. Higher Eatwell Guide adherence was cross-sectionally associated with higher grip strength, greater fat-free mass percentage, higher odds of brisk walking pace, and lower odds of falls (all <i>p</i> &lt; 0.001). Prospectively, greater adherence was associated with attenuated fat-free mass decline (β = 0.02, SE = 0.001, <i>p</i> &lt; 0.001) and slower grip strength decline (β = 0.01, SE = 0.002, <i>p</i> &lt; 0.01). For walking pace, the positive cross-sectional association attenuated over follow-up (EWG × time interaction OR = 0.998, 95% CI 0.997–0.999, <i>p</i> = 0.002), whereas the protective association with falls remained stable over time (OR = 1.000, 95% CI 0.998–1.000, <i>p</i> = 0.89). Higher Eatwell Guide adherence was associated with preserved muscle mass, modest attenuation of grip strength decline over time, and a reduced risk of falls, supporting its relevance for musculoskeletal health and physical function in aging populations.</p>