A balanced diet
...ing else as the correct enzymes to add double bonds after the ninth carbon to the carbon chain are not present. Two essential fatty acids are linoleic and linolenic acid which are found in vegetable oils such as soya, sunflower and maize. Fatty acids are needed for the formation of cell membrane phospholipids and also for the production of steroid hormones such as prostaglandins and thromboxin which have important roles in the renal, immune and circulatory systems as signalling chemicals. Deficiencies of essential fatty acids result in limited growth in children, poor healing of wounds, scaly skin and hair loss. Obesity is a result of a high fat intake in the diet and lack of exercise. Obesity is in fact a form of malnutrition as the diet is not balanced. The risk of developing diseases such as diabetes, hypertension, CHD, arthritis (due to extra pressure on joints), stroke and some cancers are increased dramatically with obesity. Proteins Protein is not a direct source of energy in the body, it is used primarily for growth and repair of body tissues although can be used as an energy source as a last resort. Proteins fulfil a wide variety of roles in the body, they are broken down in the stomach and intestines to amino acids which are then absorbed. The body can only form 8 amino acids to build proteins from, the diet must provide Essential Amino Acids (EAAs) which are synthesised into proteins which can be structural, i.e. collagen in bone, keratin in hair, myosin and actin in muscle; metabolic enzymes, haemoglobin, protective antibodies and communicative hormones. Sources of protein include meat, fish, eggs and pulses. The diet needs to provide 8 EAAs as the body is unable to synthesis proteins without these molecules. 2 other amino acids are synthesised from EAAs so if the diet lacks the original EAAs these other two will not be present either. Phenylalanine is converted to tyrosine and methionine is converted to cysteine. Cells draw upon a pool of amino acids for protein synthesis which either come from dietary protein digested and absorbed in the gut and the breakdown of body protein such as muscle. However, unlike fats and carbohydrates there is no store of amino acids for cells to draw on, any amino acid in excess of immediate bodily requirements is broken down into urea and excreted. It is therefore important to maintain the dietary intake of protein everyday. If the body lacks protein, muscle wasting occurs as muscle is broken down . If protein is lacked in a diet a person develops kwashiorkor which is caused when high levels of carbohydrates are eaten to overcome the lack of protein in the diet. One symptom of kwashiorkor is the abnormal collection of fluid around the abdomen due to the lack of protein in the blood. The body cannot retain water by osmosis and fluid accumulates in tissues causing them to become waterlogged. Vitamins Vitamins cannot be synthesised by the body so must be supplied by diet. Vitamins have no common structure or function but are essential in small amounts for the body to be able to utilise other dietary components efficiently. Vitamins fall into two categories, fat soluble vitamins such as vitamin A, D, E and K which are ingested with fatty foods and water soluble vitamins such as the B group vitamins and vitamin C. Vitamins are known as micronutrients because only small quantities are required for a healthy diet, in fact fat soluble vitamins can be toxic in high concentrations, for example the body stores vitamin A, or retinol, in the liver as it is toxic if kept in high concentrations in the blood stream, a dose of more than 3300mg of vitamin A can be considered toxic. Water soluble vitamins such as vitamin C and B groups vitamins can be excreted in the urine if in excess in the diet. Vitamins carry out a wide range of functions and prevent specific deficiency diseases. A diet that lacks a certain vitamin is not a balanced diet, vitamins have vital roles in the maintenance of a healthy body. An example of a deficiency is when the diet does not contain enough, or any vitamin A. Vitamin A is found in some animal foods such as milk, eggs, liver and fish liver oils, related compounds such as carotenoids e.g. b carotene, are in a wide variety of vegetables such as cabbages, carrots and spinach. Vitamin A is essential to the proper functioning of the retina in the eye and the epithelial tissues. A lack of vitamin A results in dry, rough skin, inflammation of the eyes, a drying or scarring of the cornea - xerophthalmia, which occurs when the secretion of lubricating tears is stopped, the eyelids become swollen and sticky with pus. Mucous surfaces of the eye may become eroded allowing infection to set in, leading to ulceration and destruction of the cornea. Night blindness - an inability to see in dim light can also occur. Rod cells in the retina of the eye detect light of low intensity, they convert vitamin A into a pigment, rhodopsin, which is bleached when light enters the eye. Rod cells resynthesis rhodopsin, but if there is a deficiency of the vitamin, rod cells can no longer function and the result is night blindness. Epithelial cells use retinol to make retinoic acid, an intracellular messenger used in cell differentiation and growth. Without retinoic acid epithelial cells are not maintained properly and the body becomes susceptible to infections, particularly measles and infections of the respiratory system and gut. Xenophthalmia is common among children who's diets consist of mainly cereals with little meat or fresh vegetables, this is common in Indonesia, Bangladesh, India and the Philippines. Vitamin D, or calciferol, is another fat soluble steroid vitamin which functions to stimulate calcium uptake from the gut and its deposition in bone. Vitamin D acts as a hormone when converted by enzymes in the gut and liver into an active form "active vitamin D", which stimulates epithelial cells in the intestine to absorb calcium. Vitamin D is therefore essential in growing children's diets to enable the growth of strong bones. Without adequate amounts of vitamin D children can develop rickets, which is the deformation of the legs caused when they lack calcium to strengthen the bones. In adults a lack of vitamin D in the diet can lead to osteomalacia, a progressive softening of the bones which can make them highly susceptible to fracture. Vitamin D is made by the body when exposed to sunlight and is stored in the muscles, however, if the skin is rarely exposed to the sunlight or is dark little vitamin D is produced. Foods such as eggs and oily fish are all rich in vitamin D. Vitamin K, phylloquinone, is found in dark green leafy vegetables such as spinach and kale. It is a fat soluble vitamin which is involved in the clotting process of blood. In the intestines bacteria synthesise a number of important clotting factors which need vitamin K. Without vitamin K cuts can fail to heal and internal bleeding can occur. Vitamin C is a water soluble vitamin, known chemically as ascorbic acid. It is found in citrus fruits such as oranges and lemons, and also in potatoes and tomatoes. The main function of vitamin C is the formation of connective tissues such as collagen. It is also known to be an antioxidant which helps to remove toxins from the body and aids the immune system. A lack of vitamin C leads to Scurvy, a condition experienced by sailors on long journeys when they did not have fruit in their diets. Scurvy causes painful, bleeding gums. As vitamin C is water soluble, it is not toxic in high doses as it can be excreted in the urine, very high doses can however cause diarrhoea. B group vitamins have a wide range of roles acting as co-enzymes in metabolic pathways. They are found in most plant and animal tissues involved in metabolism, therefore foods such as liver, yeast and dairy products are all rich in B group vitamins. Deficiency of B group vitamins include dermatitis, fatigue and malformation of red blood cells. Minerals Some minerals are considered to be macronutrients as they are required in fairly large amounts in the diet to maintain a healthy body. Minerals are required in their ionic state in the diet. Calcium, Ca2+, is a major constituent of bones and teeth and is required to keep bones strong. It is required in blood clotting as an activator of various plasma proteins and is also involved in muscle contraction. Calcium is used in synapses and also as an enzyme activator. A good source of calcium is in dairy products, eggs and green vegetables, the RDA for calcium is 800mg. Chlorine, Cl-, is required to maintain the osmotic anion / cation balance of the body and the formation of HCl in the stomach. It is found in table salt and is rarely deficient in the diet as it is used as a preservative to may foods. Sodium, Na+, is also found in table salt as well as dairy foods, meat, eggs and veget...