Mediterranean Diet Adherence, Nutrition Knowledge and Lifestyle Factors in Physically Active Adults and Athletes: The NUTRI_ACTIVE Study

Background/Objectives: Unhealthy diets and poor lifestyle choices can increase athlete’s risk of low energy availability (LEA) and its negative consequences. Conversely, optimal nutrition, such as the Mediterranean Diet (MedDiet), promotes health, recovery, and performance. This study evaluates MedDiet adherence among athletes and physically active individuals, exploring its relationship with nutrition knowledge (NK), dietary intake, eating behaviors, and sleep quality. Methods: This single-center observational study evaluated Italian healthy active adults/athletes (18–65 years) categorized into four performance Tiers. Validated questionnaires analyzed MedDiet adherence (MEDI-LITE), NK (GeSNK), eating behaviour (EAT-26 and TOS), sleep quality (PSQI), and physical activity (IPAQ). Dietary intake was estimated via a 7-day food diary. Body composition (skinfolds/BIVA), and resting energy expenditure (indirect calorimetry) were assessed. Results: Analysis included 169 participants (32.3 ± 11.9 years; 52.7% females; 56.8% Tier 1), practicing 2.0 ± 0.9 sports with 7.1 ± 3.7 h/week of training. Mean MEDI-LITE score was 10.6 ± 2.2 (moderate adherence) across all Tiers and was significantly, positively associated with NK (p = 0.002). Mean EA was 31.3 ± 8.6 kcal/kg FFM/day; sex-specific cut-offs revealed a substantial proportion of high-tier participants with low/suboptimal EA. Eating disorder risk and orthorexic tendencies were low, sleep quality was generally good; none significantly correlated with MEDI-LITE score. Conclusions: Higher NK was positively associated with MedDiet adherence. However, high-tier athletes showed low or suboptimal EA. Targeted nutrition education must integrate MedDiet principles with sport-specific fueling strategies, optimizing diet quality and energy adequacy.