ntroduction: Relative Energy Deficiency in Sport (RED-S) results from low energy availability and negatively affects athlete health and performance. Data on RED-S prevalence among Indian athletes remain limited. This study aimed to quantify the prevalence of RED-S risk and examine whether lower energy intake is associated with impaired physical performance among young athletes. Methods: A total of 316 endurance state and national-level athletes (18-25 years) from Tamil Nadu, India, were recruited using purposive sampling. RED-S risk was assessed using the Relative Energy Deficiency in Sport Screening Tool (RST). Dietary intake was evaluated using a 24-hour dietary recall and food frequency questionnaire, and physical fitness performance was assessed using standardized tests of cardiovascular endurance, muscular endurance, muscular strength, and flexibility. Group differences were analysed using chi-square tests and ANOVA. Results: Moderate-to-high RED-S risk was observed in 73% of female and 51% of male athletes (?²=8.58, p<0.01). Mean energy and nutrient intakes were below ICMR-RDA 2024 recommendations in both sexes. Athletes classified as low RED-S risk demonstrated significantly superior cardiovascular endurance, muscular endurance, and flexibility compared to high-risk athletes (p<0.05). Associations between lower energy intake and poorer performance outcomes were more pronounced among females. Conclusion: This study provides first quantitative evidence of a high prevalence of RED-S risk among Indian athletes and demonstrates its association with inadequate dietary intake and reduced physical performance. Early screening and targeted nutrition interventions are essential to protect athlete health and optimize performance.
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