Nutrition is : the act or process of nourishing or being nourished; specifically : the sum of the processes by which an animal or plant takes in and utilizes food substances.
Nutrition is the science that interprets the interaction of nutrients and other substances in food in relation to maintenance, growth, reproduction, health and disease of an organism. It includes food intake, absorption, assimilation, biosynthesis, catabolism, and excretion.
The diet of an organism is what it eats, which is largely determined by the availability and palatibility of foods. For humans, a healthy diet includes preparation of food and storage methods that preserve nutrients from oxidation, heat or leaching, and that reduce risk of food-borne illness.