Background and aim: Despite advances in research on training and nutritional supplementation, it is largely unknown how micronutrient intake modulates the response to training in older adults. This study investigates the relationship between nutrient intake and response to training in older women at risk of sarcopenia. Methods: A randomized clinical trial with two parallel groups (high-speed resistance training (H-RT) and multicomponent training (MT)) was conducted over a 32-week intervention involving 80 older women at risk of sarcopenia (mean age: 77.36 ± 6.71 years). A food frequency questionnaire was administered to assess whether nutrient intake influenced strength outcomes measured by the Five Times Sit-to-Stand Test (5STS) and other functional variables. Results: Significant improvements in the five times sit to stand test (5STS) were observed in both groups post-intervention (p < 0.001), with no significant differences between them (p = 0.127), suggesting comparable effectiveness. In both groups, lower levels of vitamin B12 (H-RT: rp = −0.52; MT: rp = −0.50) and vitamin D (H-RT: rp = −0.55; MT: rp = −0.69) were associated with worse 5STS performance. Additionally, in the H-RT group, lower levels of vitamin E (rp = −0.36), magnesium (rp = −0.48), iron (rp = −0.43), and potassium (rp = −0.47) were also correlated with poorer performance. Conclusions: The results indicate that improvements in strength are related to micronutrient sufficiency rather than macronutrient sufficiency. Deficiencies in vitamin D and B12 negatively impacted muscle strength gains in both H-RT and MT, while vitamin E, potassium, magnesium, and iron influenced H-RT outcomes. The lesser effect of micronutrient deficiencies on MT suggests it may be more suitable for individuals with mild deficiencies, as it requires fewer specific nutrients for muscle strength. Registration: The study is registered at ClinicalTrials.gov under the identifier NCT05870046.
