How can divers ensure their health while diving?

The correct choice emphasizes the importance of adhering to medical guidelines, managing stress, and maintaining proper hydration and nutrition as essential practices for divers to ensure their health while diving.

Medical guidelines are crucial because they provide divers with essential information about their fitness for diving, including assessments of their physical health and any pre-existing conditions that may affect their safety underwater. Managing stress is equally important, as stress can lead to poor decision-making and increased risks during dives. Proper hydration and nutrition are vital because dehydration can lead to serious health issues such as decompression sickness, while proper nutrition supports overall energy levels and physical performance.

The other options present practices that do not adequately address comprehensive health management for divers. Eating heavily before dives might lead to discomfort and increase the risk of serious health issues, such as nausea or vomiting. Diving only during the daytime does not inherently ensure health, as night dives can also be conducted safely with proper training and preparation. Exclusively practicing shallow dives limits a diver's experience and skill development, without necessarily improving health or safety.