Eating healthy foods does not necessarily ensure adequate nutrition. Foodstuff does not directly translate to nutrients. An enormous number of factors are involved in digestion and absorption: how well food is chewed, the proper secretion of enzymes and gastric juices, and the condition of the digestive tract.
Absorption is not even the final step: nutrients must reach the cells that need the energy and provided molecular building blocks. Transport varies in efficiency.
Intake and delivery are only half the story. For nutrition to occur, there must be a continuous and effective elimination process. Cells are unable to absorb and use new nutrients if crowded with the waste products of metabolism.
Just as coordination of inhalation and exhalation in breathing, in both rhythm and rate, are crucial to healthy respiration, the timing of feeding and tuning of the digestive system are important to nutrition.
Unlike breathing, which must be unceasing and continuous, breaks in the cycle of digestion and elimination are good for the system. Properly done, fasting breaks benefit body and mind.