Nutrition involves understanding the foods necessary for health and growth. It focuses on how diseases and conditions can be prevented or lessened through a healthy diet, and how poor diet or allergies may cause health issues. Nutrition is the process of taking in food, digesting it, absorbing nutrients for growth, metabolism, and repair, then excreting waste. Complete nutrition requires ingesting and absorbing vitamins, minerals, carbohydrates, proteins, and fats, with dietary choices playing a key role in quality of life, health, and longevity.