Telomere shortening is a hallmark of biological ageing. Nuts and seeds contain several functional ingredients that may preserve telomere length; however, supporting evidence remains limited⁽¹⁾. This study examined the effects of peanut butter supplementation on telomere length in older adults and explored whether telomere length changes were associated with post-intervention functional outcomes including gait speed, muscle power and strength and global cognitive functions. In this six-month randomised controlled trial, 120 community-dwelling adults aged ≥ 65 years at risk of falls were allocated to consume 43 g/day of natural peanut butter (n = 60) or continue their usual diet (n = 60)(2). Average normalised telomere length, expressed as the telomere to single-copy gene ratio (T/S), was measured by quantitative polymerase chain reaction at baseline and six months. Linear regression models adjusted for the age, sex, BMI, physical activity, diet quality and baseline telomere length were used to estimate the intention to treat intervention effects. The association between change in average telomere length and follow-up functional outcomes was determined using linear regression models adjusted for the same covariates, intervention allocation and baseline values of the functional outcome measures. Telomere Shortest Length Assay (TeSLA) measurements were also obtained in an exploratory subsample (n = 20), with between-group changes compared using non-parametric tests. A total of 108 participants completed the study. At baseline, 70% were female, and the mean age and BMI were 76.1 ± 4.6 years and 27.5 ± 4.2 kg/m2, respectively. After six months, average telomere length decreased within the intervention group [2.024 (95% CI 1.992, 2.055) to 1.976 (1.947, 2.004); p < 0.05], while remaining unchanged in the control group [1.961 (1.926, 1.995) to 1.961 (1.934, 1.987); p = 0.989]. However, there was no significant between-group treatment effect (β = 0.037 T/S units; 95% CI −0.266, 0.340; p = 0.809). When pooling all data, an increase in average telomere length was associated with greater gait speed at follow-up (β = 0.036; 95% CI 0.007, 0.066; p=0.017), but not with other functional outcome measures. Although TeSLA-derived outcomes did not differ significantly between groups, median changes in shortest telomeres were directionally favourable in the intervention group; average telomere length (+0.185 versus +0.060 kb), average length of the shortest 20% of telomeres (+0.020 versus +0.005 kb), and proportion of critically short telomeres below 1.6 kb (−10.3% versus −1.7%). Six months of peanut butter supplementation did not affect average telomere length in older adults compared with the control condition. The observed association between telomere length change and gait speed warrants further investigation in adequately powered, longer-term trials.