Nutrition is the study of how the nutrients in food affect the body and support human health. Nutrients are molecules in food that maintain vital processes such as digestion, energy production, development, growth, and reproduction. The two main classifications are macronutrients and micronutrients. Macronutrients consist of carbohydrates, proteins, fats; while the micronutrients are vitamins, minerals and water. The required amounts of the essential nutrients differ by age and the state of the body. Nutrition guidelines are established by the United States Department of Agriculture. Nutritional status is the state of one’s health as determined by what is consumed. It is assessed in several ways, including anthropometric (i.e. physical body measurement), food intake and biochemical measurement. Body mass index (BMI) is generally a good indicator of nutritional status, as it considers weight and height, and correlates well with total body fat expressed as a percentage of body weight. However, BMI is inaccurate for measuring nutritional status in body builders & high-performance athletes; pregnant women; elderly; people with a physical disability who are unable to walk and may have muscle wasting. A healthy diet includes a lot of natural foods, and should consist of fruits and vegetables, especially ones that are red, orange, or dark green; whole grains, such as whole wheat and brown rice. For adults, dairy products should be non-fat or low-fat; protein e.g. lean meat and poultry, seafood, eggs, beans, legumes, and soy products such as tofu, as well as unsalted seeds and nuts. Good nutrition also involves avoiding certain foods such as high sodium foods; heavily processed foods; refined grains; fried, fatty and sugary foods. Poor nutrition can lead to a lack of energy, digestive problems, food allergies, weight gain, nutritional deficiencies, depression and anxiety as well as chronic diseases e.g. coronary heart disease, cancer, ADHA.