## 1 Introduction  
The 1500 m event is the longest race in competitive swimming, aside from open-water events, and was first introduced at the Olympic Games in London in 1908, where [PERSON] won with a time of 22:48:40. Over the past 115 years, the qualifying times for the Olympics have improved by nearly eight minutes, alongside significant advancements in sports science and performance enhancement methods. Achieving a sub-15 min time in the 1500 m freestyle has become a prerequisite for success in international competitions. As a result, efforts have focused on understanding and addressing the optimal fueling and nutritional requirements for athletes during the competitive season [1]. Therefore, several studies suggest that developing optimal nutritional strategies supports swimming performance. Measuring resting metabolic rate (RMR) and body composition throughout the season may allow nutritionists and clinicians to propose better practical interventions [2, 3]. Indirect calorimetry represents the gold standard measurement of the RMR by assessing oxygen consumption and carbon dioxide production. It accounts for 60-70% of the total energy expenditure [4]. Thus, incorporating RMR testing into an athlete's routine is crucial for accurately determining energy needs and plays a vital role in maintaining optimal body fat levels, developing effective nutritional strategies, ensuring sufficient energy availability for training and competition, promoting metabolic function, and reducing symptoms of fatigue [5; 6]. Poor (imbalanced) nutrition in long-distance swimming events can significantly affect performance, recovery, and overall health. By examining comparative data from other endurance sports, such as athletics, cycling, and cross-country skiing, we can better understand the specific implications for swimmers. Energy deficiency and glycogen depletionLong-distance swimming requires sustained energy expenditure in a thermoregulated aquatic environment, where body heat dissipates rapidly. Insufficient caloric intake can lead to premature fatigue, reduced stroke efficiency, and the inability to maintain pace [7]. Glycogen stores serve as a primary fuel source during high-intensity intervals and sustained efforts in long-distance swimming. Suboptimal carbohydrate intake results in rapid glycogen depletion, diminished endurance capacity, and increased reliance on less efficient fat metabolism. In endurance running, energy deficits are linked to glycogen depletion [8]. Similarly, in cycling, insufficient energy intake reduces acceleration power during long races [9]. For swimmers, these energy gaps are exacerbated by the additional caloric demands of water resistance and thermoregulation [10]. HydrationSwimmers may underestimate fluid loss, as sweat is less noticeable in water. Suboptimal hydration impacts thermoregulation, muscle function, and cognitive focus, leading to impaired stroke mechanics and slower lap times. In cycling and running, dehydration is directly associated with cardiovascular strain and increased body temperature. While core temperature is less of a concern in swimming, dehydration still affects cardiovascular efficiency, a critical factor for sustained effort [11]. Electrolyte imbalancesElectrolyte loss occurs even in water, and inadequate replenishment can cause cramps, impair muscle function, and reduce neuromuscular coordination, compromising stroke efficiency [12]. Runners and cyclists often rely on electrolyte-rich drinks to prevent muscle cramps. Swimmers face unique challenges, as the aquatic environment can mask the dehydration symptoms, delaying corrective actions [13; 14]. Imbalanced (suboptimal or inadequate) nutrition has severe implications for performance in long-distance swimming, compounded by the sport's unique environmental and physiological demands. Comparative insights from athletics and cycling emphasize the critical importance of appropriate calorie, carbohydrate, protein, electrolyte, and hydration strategies tailored to the specific needs of swimming.