Six Major Classes of Nutrients

There are six major classes of nutrients:  carbohydrates,  fats,  minerals,  protein,  vitamins, and  water. These nutrient classes can be categorized as either  macronutrients  (needed in relatively large amounts) or  micronutrients  (needed in smaller quantities). The macronutrients include carbohydrates (including  fiber), fats, protein, and water. The micronutrients are minerals and vitamins. 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 be used to generate energy internally, and in either case it is measured in  Joules  or  kilocalories  (often called â€Å"Calories† and written with a capital  Cto distinguish them from little ‘c' calories). Carbohydrates and proteins provide 17  kJ approximately (4  kcal) of energy per gram, while fa ts provide 37  kJ (9  kcal) per gram. ,[17]  though the net energy from either depends on such factors as absorption and digestive effort, which vary substantially from instance to instance.Vitamins, minerals, fiber, and water do not provide energy, but are required for other reasons. A third class of dietary material, fiber (i. e. , non-digestible material such as cellulose), is also required,[citation needed]  for both mechanical and biochemical reasons, although the exact reasons remain unclear. Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple  monosaccharides  (glucose, fructose, galactose) to complexpolysaccharides  (starch).Fats are  triglycerides, made of assorted  fatty acid  monomers  bound to a  glycerol  backbone. Some fatty acids, but not all, are  essential  in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, ox ygen, and hydrogen. The fundamental components of protein are nitrogen-containing  amino acids, some of which are  essential  in the sense that humans cannot make them internally.Some of the amino acids are convertible (with the expenditure of energy) to glucose and can be used for energy production, just as ordinary glucose, in a process known as gluconeogenesis. By breaking down existing protein, some glucose can be produced internally; the remaining amino acids are discarded, primarily as urea in urine. This occurs normally only during prolonged starvation. Other micronutrients include  antioxidants  and  phytochemicals, which are said to influence (or protect) some body systems.Their necessity is not as well established as in the case of, for instance, vitamins. Most foods contain a mix of some or all of the nutrient classes, together with other substances, such as toxins of various sorts. Some nutrients can be stored internally (e. g. , the fat soluble vitamins), wh ile others are required more or less continuously. Poor health can be caused by a lack of required nutrients or, in extreme cases, too much of a required nutrient. For example, both salt and water (both absolutely required) will cause illness or even death in excessive amounts.