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.

Keywords: MFO; health; metabolic flexibility; nutrition; obesity.

Figure 1

Mediation analysis of leptin concentration between adherence Mediterranean diet (MedDiet) and BMI (A), absolute MFO (B), MFO relativized by body mass (C), and VO₂max (D). Abbreviations: p = p value; β = standardized regression coefficient; B = unstandardized regression coefficient; BMI = body mass index (kg/m²); MFO = maximal fat oxidation; Leptin = log-transformed leptin concentrations; VO₂max = maximal oxygen uptake.