Yes, it's common for highest-level athletes to have their diets controlled or guided by coaches and/or sports nutritionists, particularly in sports that require specific body compositions or energy expenditure. Coaches, alongside other specialists like strength and conditioning trainers, often play a key role in educating athletes about sports nutrition. 

Coaches often provide guidance on nutrition, emphasizing the importance of fueling the body for optimal performance and recovery. They may discuss the impact of certain foods on energy levels, recovery, and overall health. 

While not always strict control, many athletes work with a sports dietitian to create a tailored diet plan that aligns with their training goals and specific sports requirements. This may involve monitoring calorie intake, macronutrient ratios, and specific nutrient needs. 

Nutrition is crucial for athletes because it directly impacts training, recovery, and performance. A well-balanced diet provides the necessary energy and nutrients to support intense training, promote recovery, and maintain body composition. 

Athletes may have different nutritional needs depending on their sport, training intensity, and individual goals. For example, endurance athletes may need to prioritize carbohydrate intake for energy, while strength and power athletes may need to focus on protein intake for muscle building. 

In addition to dietary guidance, some athletes may also be advised on the use of supplements to address specific nutrient needs or enhance performance, according to the article on Sports Nutrition Knowledge.