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Macro nutrients constitute the bulk of the food we eat, they provide energy and chemical building-blocks for tissues.
Proteins consists of long chains of amino acids , to which it is broken down to in the digestive system. Much of these amino acids are reconstituted by the body to form human proteins. Human proteins are universal in the body: as enzymes they regulate chemical reactions within cells and the blood, they form tendons and ligaments which hold the body together, and they provide muscle with its ability to contract. Excess protein can be converted to sugar by the liver.
consists of sugar, and chains of sugar molecules called starches. Starches are broken down in a similar manner to protein. In plants and bacteria, carbohydrates provide structure, but in animals they are used for energy.
consists of fatty acids (lipids), which are chain of carbon atoms with a acid group at the end. These fatty acids are linked in groups of three by glycerol. Once again,. this structure is broken down in the gut, only to be re-formed in fat cells. Some fatty acids have special functions, but mostly fat is a store of energy.
Rightfully a drug, but its energy component, between fat and protein, can be significant in some people. There is no recommended intake for alcohol, but their are recommended maximum intakes, these being 40g a day for men and 20g a day for women. [1]
A total calculated from the above, which is expressed in both kilocalories (the traditional unit in chemistry), and kilojoules (the physicist's unit).
There is a base requirement for energy, which can be estimated by age and weight. However, muscle mass requires more energy to maintain than fat mass, so persons of the same weight can have widely different base energy requirements. In addition, active people will obviously need more energy.
is indigestible by human enzymes, and is largely excreted, or digested by bacteria in the large intestine. Nevertheless, it is very important, and often deficient in first-world diets. It dilutes toxins that build up the gut and retains water. It softens faeces and increases its volume, making bowel motions more efficient. Deficiency causes constipation, and has been linked to bowel cancer.
Arguably the most important nutrient, in terms of amount (two-thirds of the body), and essentiality (people die of thirst long before they starve).
[1] | according to the Drug and Alcohol Centre, St. Vincent's Hospital, Melbourne, Australia. |
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