Short‐Term Dietary Intervention Alters Physiological Profiles Relevant to Ageing

Ageing is a complex process influenced by modifiable factors such as diet, which may accelerate or decelerate physiological decline. While chronological age increases uniformly, biological ageing varies between individuals, reflecting differences in health status and the resilience of biological systems. The Klemera-Doubal Method (KDM), a composite biomarker-based index often used as an estimate of biological age, has been associated with morbidity and mortality in large cohorts. This study examined whether dietary manipulation of protein source and macronutrient composition affects KDM estimates in older adults. We analysed data from the Nutrition for Healthy Living study, a 2 × 2 factorial dietary intervention trial involving 104 participants aged 65-75 years. Participants were randomised to one of four diets: omnivorous/high-fat (OHF), omnivorous/high-carbohydrate (OHC), semi-vegetarian/high-fat (VHF) or semi-vegetarian/high-carbohydrate (VHC). KDM-derived δAge (the difference between KDM- and chronological-age) was calculated before and after a 4-week intervention. The OHF group, most like participants' baseline diets, showed no meaningful change in δAge. Compared to OHF, participants in the OHC group showed a significant reduction in δAge. The VHF and VHC groups showed similar reductions in δAge, relative to OHF, though not all reached statistical significance. KDM-derived δAge appears responsive to dietary change within 4 weeks and may offer a useful proxy for evaluating shifts in physiological status. Caution is warranted in interpreting such changes as evidence of biological age reversal as observed shifts may reflect acute physiological responsiveness to dietary inputs rather than altered ageing trajectories. Longer-term treatment would be needed to assess changes in age-related disease risks.