# Nutritional Recommendations for Breath-Hold Divers
## 1 Introduction  
Presently, breath-hold diving (BHD) is practiced in recreational, hunting, military, and competitive manners. At the elite level, freedivers can hold their breath for an impressive time of ~10 min, can reach depths > 200 m, or dive into pools longer than 300 m depending on the specific diving discipline [1]. The two main disciplines are static apnea and dynamic apnea. The periods of prolonged apnea that these athletes endure make the BHD environment extreme. Such extremity is pronounced especially in a competitive context, where the ultimate limits of the body's ability to withstand intense hypoxic and hypercapnic states are tested in hyperbaric conditions [1, 2, 3, 4, 5, 6]. Frequent exposure to such physiological and physical limitations increases the risk of potential dangers to the health of freedivers [7, 8]. Furthermore, it can be speculated that the specific requirements of long-term diving apnea make inadequate nutrition a greater obstacle in this sport. This speculation can be observed from nutritional recommendations in other aquatic sports [9, 10]. Also, performance insynchronized swimming, defined with shorter periods of apnea, could be improved with proper diet [11]. Hence, the nutritional recommendations for these athletes may present a potentially important factor in performance. General Recommendations for a Healthy Daily Diet for Freedivers: Mediterranean and Alkaline Diet  
Diving is a specific sport that requires exceptional physical and mental fitness [12]. Proper nutrition not only provides the energy needed for training and competitions but also supports complex biochemical mechanisms such as the regulation of acid-base balance and the management of oxidative stress, which are especially endangered during the practice of apnea diving. This is why it is necessary to develop a permanent habit of daily healthy and balanced eating. It is not only a matter of personal discipline, but also of understanding the importance of nutrition in improving physical and mental characteristics. A balanced, varied, unprocessed, and high-quality diet could be a prerequisite for achieving maximum diving abilities, safer diving, and long-term health. The combination of the Mediterranean and alkaline diet offers an optimal nutritional basis for achieving and maintaining these goals. The Mediterranean and alkaline diets share many common features, such as an emphasis on the intake of large amounts of fruits, vegetables, and minimally processed foods, but they are not completely identical [13,14]. The Mediterranean diet (MD) also includes acid-forming foods such as fish and dairy products, while the alkaline diet tends to eliminate such foods [14]. A combination of the principles of both diets can provide a balanced and healthy approach to nutrition, especially for the specific needs of freedivers. Due to the high demands of this sport and the significant energy expenditure, freedivers are forced to carefully balance between these two nutritional approaches, depending on the training periodization. In the phase of the predominantly physical conditioning phase, when a higher protein intake is needed for recovery and muscle mass building, the Mediterranean diet provides optimal nutritional support. On the other hand, in specific apnea and/or competition phases, when it is crucial to reduce oxidative stress and optimize the body's acid-base balance, an alkaline diet can play an important role. By combining these nutritional principles on a daily basis in accordance with the phase of the planned training process, while respecting the characteristics and intensity of operational loads and the necessary recovery during microcycles and individual training sessions, divers can ensure optimal intake of nutrients. This allows them to support endurance and performance, as well as improve diving safety and efficiency. The literature review showed a lack of studies that examined the diet of BHD and gave full recommendations for different disciplines.