<P> Human nutrition deals with the provision of essential nutrients in food that are necessary to support human life and health . Poor nutrition is a chronic problem often linked to poverty, food security or a poor understanding of nutrition and dietary practices . Malnutrition and its consequences are large contributors to deaths and disabilities worldwide . Good nutrition helps children grow physically, promotes human biological development and helps in the eradication of poverty . </P> <P> The human body contains chemical compounds, such as water, carbohydrates, amino acids (in proteins), fatty acids (in lipids), and nucleic acids (DNA and RNA). These compounds are composed of elements such as carbon, hydrogen, oxygen, nitrogen, phosphorus . Any study done to determine nutritional status must take into account the state of the body before and after experiments, as well as the chemical composition of the whole diet and of all the materials excreted and eliminated from the body (including urine and feces). Comparing food to waste material can help determine the specific compounds and elements absorbed and metabolized by the body . The effects of nutrients may only be discernible over an extended period of time, during which all food and waste must be analyzed . The number of variables involved in such experiments is high, making nutritional studies time - consuming and expensive, which explains why the science of human nutrition is still slowly evolving . </P> <P> The seven major classes of nutrients are carbohydrates, fats, fiber, minerals, proteins, vitamins, and water . These nutrient classes are categorized as either macronutrients or micronutrients (needed in small quantities). The macronutrients are carbohydrates, fats, fiber, proteins, and water . The micronutrients are minerals and vitamins . </P> <P> The macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built), and energy . Some of the structural material can also be used to generate energy internally, and in either case it is measured in Joules or kilocalories (often called "Calories" and written with a capital' C' to distinguish them from little' c' calories). Carbohydrates and proteins provide 17 kJ approximately (4 kcal) of energy per gram, while fats provide 37 kJ (9 kcal) per gram, though the net energy from either depends on such factors as absorption and digestive effort, which vary substantially from instance to instance . </P>

Nutrients needed in large amounts for the human body are known as