Food is an integral part of human life providing energy for cellular activities to keep us healthy. According to World Health Organization (2013), healthy nutrition is ingesting an adequate and well balanced diet in relation to the body’s dietary needs and when combined with regular physical activities is the cornerstone to good health. A diet containing the right portions of all the five food groups of the Eatwell Plate (figure1 and appendix1 for recommended servings) known as a balanced diet will provide the organic macronutrients including proteins, carbohydrates and lipids and the micronutrients, vitamins and minerals to sustain life. Only ingested carbohydrates, proteins and lipids will count towards total caloric intake and will be digested into monomers like glucose for absorption and assimilation. National Health Service (2012) recommends daily caloric intake of 2500Kcal and 2000Kcal which will be derived from the proteins, lipids and carbohydrate sources in a diet for average adult males and females respectively. Age, sex, health condition and physical activities influence dietary needs. This essay will discuss a balanced diet for an adult including the structure, sources, functions, recommended daily allowance (RDAs), deficiency and excessive effects of the macronutrients. Also the micronutrients and water which are not considered as nutrients will be discussed.
THE FOOD PYRAMID
Carbohydrates contain carbon, hydrogen and oxygen. British Nutrition Foundation (2013), recommends that 47.7% (203g) and 48.5% (275g) of daily energy should come from carbohydrates for females and males respectively with 29g being roughages. Carbohydrates exist naturally or refined as monosaccharides that are reducing sugars. Monosaccharides build the complex carbohydrates, disaccharides and polysaccharides through dehydration synthesis. Monosaccharides have general formula (CH2O)n where ‘n’ determines whether pentose(5Carbons) or hexose (6Carbons). Glucose found in maple syrup, fructose in corn syrup and galactose in honey are hexose-isomers; having the same formula, C6H12O6 but different structures.
The disaccharides with the general formula C12H22O11 are sucrose made from fructose and glucose, maltose from two glucose molecules and lactose from galactose and glucose. Sucrose is derived from beet sugar, lactose from milk and maltose from vinegar. The polysaccharides with general formula (C6H10O5)n where 40≤n≤3000, exist as starch or non-starch polysaccharides (NSPs) which can be soluble or insoluble. Starch consists of glucose molecules joined by glycosidic bonds. The NSPs include oligosaccharide (raffinose) and cellulose (dietary fibre). Potatoes, yams and cassava are rich in starch and are very digestible. Whole grain cereals, legumes (appendix2), fruits and storage vegetables like asparagus and cabbage are rich in the NSPs. Raffinose is an indigestible trisaccharide of fructose,glucose and galactose with formula C18H32O16. Animal sources of carbohydrates are liver and scallops.
Carbohydrates provide sweetness and are the primary source of energy especially for brain and blood cells. Cellular respiration converts glucose monomers into ATP. Fats cannot be oxidised without glucose. Most NSPs are partially digestible or indigestible due to lack of α-galactosidae (enzyme) in GI Tract. They reduce glycaemia index and plasma cholesterol levels, increase bile acid excretion, promote normal laxation and prevent breast cancer, gallstones, haemorrhoids, and irritable bowel syndrome (Kumar et all 2012). Furthermore, Kumar (2012) concluded that excessive carbohydrates will cause dental decay, kidney damage, stroke, diabetes due to obesity and short term conditions like hyperglycaemia. Carbohydrate deficiency will cause constipation, fatigue, weak immunity, muscle cramps and ketosis; this is very rare as 50g/day of carbohydrate is needed to prevent ketosis.
THE DEHYDRATION SYNTHESIS TO FORM MALTOSE...
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