Introduction to nutrition Nutrition is defined as the processes by which an animal or plant takes in and utilizes food substances. Essential nutrients include protein, carbohydrate, fat, vitamins, minerals, and electrolytes. Normally, 85% of daily energy use is from fat and carbohydrates and 15% from protein. In humans, nutrition is mainly achieved through the process of putting foods into our mouths, and chewing and swallowing it. The required amounts of the essential nutrients differ by age and the state of the body, for example, physical activity, diseases present (e.g. prostate cancer, breast cancer, or weakened bones – known as osteoporosis),