High-quality lean protein enables the body to recover and repair damaged muscle tissue. Because fat takes longer to convert to energy, consumption should be kept at a moderate level.
It's necessary to replace losses of sodium, potassium and other electrolytes during exercise. Keep in mind that under normal situations most exercisers are unlikely to deplete these minerals during regular training.
If you are serious about your success as a swimmer, or in any sport for that matter, you have to make time for nutrition and sleep in your daily routine.