Diet is a modifiable risk factor for healthy ageing and may influence telomere length (TL), a biomarker of cellular ageing. Telomere shortening is associated with increased biological ageing and disease incidence. This study investigated the effect of peanut butter supplementation on TL in community-dwelling older adults at risk of falls. In this 6-month randomised controlled trial, participants (≥65 years) were allocated to either 43 g/day of natural peanut butter (n=60) or usual diet (n=60). Buccal cell samples were collected at baseline and 6 months, and TL was measured as the normalised telomere-to-single copy gene ratio (T/S) using quantitative PCR (positive change indicating reduced biological ageing). The T/S changes in intervention and control groups were (median [IQR]) -0.0684 [0.99000] and 0.01380 [1.24000] respectively. Linear mixed-effects modelling showed no significant group × time effect on T/S measure over 6-months (β=-0.028, p=0.882). Telomere Shortest Length Assay (TeSLA) was also performed in an exploratory subsample (n=20), to enable high-resolution analysis of TL distribution particularly at the shortest telomeres. Median changes were directionally favourable in the intervention group for all TeSLA-derived measures: greater average TL indicating reduced biological ageing (+0.185 vs +0.06 kb), greater average TL of the 20% shortest telomeres indicating reduced age-related disease risk (+0.02 vs +0.005 kb), and greater reduction in the proportion of telomeres <1.6 kb indicating improved cellular health (-10.3% vs -1.675%). However, these between-group differences were not statistically significant. Although no statistically significant intervention effects were detected, the exploratory TeSLA findings suggest patterns worthy examining in adequately powered studies.