Mediterranean Diet Patterns Are Positively Associated with Maximal Fat Oxidation and VO2max in Young Adults: The Mediating Role of Leptin

Abstract

Background: Adherence to the Mediterranean diet (MedDiet) offers multiple metabolic benefits. However, its relationship with maximal fat oxidation (MFO) and cardiorespiratory fitness (VO2max), alongside the potential mediating role of leptin, remains underexplored in young adults. Objective: The objective was to investigate the associations between MedDiet adherence and the body mass index (BMI), MFO, and VO2max and to evaluate whether leptin mediates these relationships. Methods: Sixty-five young adults (n = 23 women), aged 18–38, were assessed for body composition, MedDiet adherence (14-Item Mediterranean Diet Adherence Screener), MFO, and VO2max through indirect calorimetry. Plasma leptin concentrations were measured in fasting conditions. Multiple linear regression models were performed, adjusting for sex, age, and both. Mediation analyses were conducted. Results: Higher MedDiet adherence was significantly associated with lower BMI (β = −0.339, p = 0.006) and leptin values (β = 0.284, p = 0.022) and higher absolute MFO (β = 0.338, p = 0.006) and VO2max values (β = 0.462, p < 0.001). These associations remained significant in all models except BMI and leptin when adjusted for sex and sex and age. Leptin was positively associated with the BMI (β = 0.550, p < 0.001) and inversely associated with absolute MFO (β = −0.650, p < 0.001) in all models. There was a trend in the association between leptin and VO2max (β = −0.233, p = 0.061) only in the unadjusted model. Mediation analysis revealed that the leptin levels significantly mediated the associations between MedDiet adherence and BMI (β = −0.358, 95% CI [−0.677, −0.077]) and VO2max (β = 1.043, 95% CI [0.280, 1.833]). Conclusions: MedDiet adherence is associated with a lower BMI and higher MFO and VO2max in young adults. Our findings further suggest that leptin plays a mediating role in how MedDiet adherence influences the BMI and VO2max.