| A nutrient is a quantiiable substance in food that provides structural or functional components or energy to the body. A essential nutrient is one which must be obtained from the diet because the body cannot make it in sufficient quantity to meet needs. Water is the most important nutrient as it constitutes about 70% of body mass and is essential for almost all body processes. Water can be consumed by drinking and eating or is produced as a result of metabolic processes. proteins supply amino acids to build or maintain tissues, secretory products and signalling molecules. 20 amino acids make up tissues, enzymes and hormones, twelve of these are manufactured in teh body and the other eight must be provided by the diet. Amino acids must be supplied or manufactured in the right amounts to enable proper function. Energy is a measure of a substance's ability to do a job/work. This is not an actual substance or nutrient such as protein or phosphorous. Carbohydrates are the body's main soruce of energy and there are two types of digestible carbohydrates; sugars and starches. SUgars are made up of monomers (one unit) or dimers (two units) typically of either glucose, fructose or galactose. Starches are polymers of linked glucose sub-units. Fats and oils are another source of energy. Fatty acid chains are linked by a glycerol unit tomake triglyceride and supply most of the body's energy during starvation and also transport nutrients such as fat soluble vitamins). Fat and oils provide precursors for the production of structural material of cells (membranes) and tissues (brain) as well as precursors for hormones and hormone like molecules (prostaglandins and steroids). Plant fibre is what gives plants their structure and support. Fibre is not digested and is absorbed in the small intestine and can be fermented (such as in the rumen and hindgut). Fibre is made up of two polymers of sugars, particularly glucose sub-units. There are two types of fibre based on structure; soluble and insolubule. Insoluble fibre is found in plant stems and leaves, bran of grains and vegetable skins. Soluble fibre is found in a variety of fruits and vegetables such as pectin from fruit. Vitamins are organic substances present in food that are required in small amounts for maintenance of normal growth and function as well as oxidation reactions and defences such as protection from free radical damage. B group and C vitamins are water soluble so are not stored in large quantities and excessive intake has no substantial consequences as it is simply excreted. Vitamins A, D, E and K are fat soluble so are stored in boy fat (liver and adipos) and hence can be toxic in excessive quantities are they are not excreted when consumed in excess. Minerals are non-organic elements and come in two classes; macrominerals and micro (or trace) minerals. Macrominerals are needed in large amounts and play a structural and functional role in bones and teeth, enregy exchange, electrolytes and electrical potential as well as protein structure and integrity. Micro- or trac minerals are needed in small amounts and usually participate in chemical reactions or asignallingrole such as inhormones, oxygen tansport or methyl group transfer reactions. Learn More UMass: Nutrients in Foods Questions
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