BACKGROUND: Endurance athletes' competitions have increased over the decades and marathon races are becoming increasingly popular. Proper nutrition is critical for optimal performance and long-term health in marathon athletes. This study aimed to investigate runners' nutritional intake, especially fluids, food, and supplements, competing in the Seville Marathon. A descriptive and cross-sectional study was carried out to obtain information on the consumption of liquids, food, and supplements. A total of 160 runners (aged 42.2 ± 7.3 years) who were primarily men (87.5%) who participated in the 2022 Seville marathon took part in the study. RESULTS: There was no significant difference (p >
0.050) between marathon finish time (from 2 h 12 min to 5 h) or sports experience and fluid, carbohydrates (CHO), sodium, and caffeine intake pre- and post-competition. However, according to the results obtained, the athletes who met CHO intake recommendations during the competition (60-90 g/h) were more likely to finish the marathon in less than 180 min (p = 0.035). CONCLUSIONS: The intake of CHO (35 ± 17 g/h), sodium (192 ± 150 mg/h) and caffeine (57 ± 49 mg/h) was low compared to the current recommendations during the competition. The intake of fluids (466 ± 279 mL/h) was at the lower limit of recommendations. Most athletes did not receive nutritional counselling by a sport dietitian, which may explain why athletes failed to meet specific nutrient recommendations. Future investigations with a larger sample size are warranted to assess the relationship between dietary intake and finish time.