Tuesday 23 December 2008

Biology note -- Food and diet

Health is defined as physical fitness, mental health and social well-being. We should have appropriate food, enough exercise and rest in order to keep healthy. The important of food is that energy used for activities and keeping warm, raw materials for growth and repair and substances for maintaining health. Diet is what the person eat and drink each day. There are two types of nutrients: primary food nutrients and protective food nutrients. primary food nutrients means that without those nutrients, we will die. They include: carbohydrates, fats, proteins and water. Carbohydrates = C + H2O It is use for give out energy through respiration in cells. It’s the main energy source. In our body, they appears all places where any cells are found. We can get carbohydrates from cereal which contains starch. Starch is a large form of carbohydrates. It is not sweet but in the mouth, they will be broken down as maltose which is sweet. That’s why the food will become sweet after some time in the mouth. Maltose will be further broken down as glucose. Glucose will be used at once or turned into fat or glycogen which is a large chain of glucose for further use. Glycogen is also called animal starch that it’s usually found in animal’s body. They will be stored in liver and muscles. Fats is the energy reserves and it will only be used when carbohydrates is not enough. Fat gives double of carbohydrate’s energy supplies. It’s also use for transportation because some nutrients are only fat soluble and fat is used to transfer them. It’s also used for keeping our body warm. Fat also act as a solvent of nutrients which only fat soluble but not water soluble. Protein helps body to growth and repair. It’s also known as amino acid. There are 20 types of amino acid where 8 of them can be produced in our body. The left 12 types are called essential amino acid. Children needs a lot of protein because they grow rapidly. The deficiency disease is kwashiorkor. They will have swollen abdomens, weak muscles and poor mental development. Excess protein will be put into urine which passed out and fat stored. Water make up 70% of our body. It the most important component of diet that we can live even a week without water. Although it has no energy value, it has some important use. 1) Water act as medium of chemical reaction in our body; 2) Act as solvent of waste(urine) for us to take them out the body; 3) It’s use for transporting substances in the body, and 4) Helps regulating body temperature through sweating We lost water through many ways such as passing out urine, sweat and breathe out so we have to drink lots of water per day (6-8 glasses) We only need a small amount of protective food nutrients which includes vitamins, minerals and dietary fibre. Vitamins 1) Vitamin A -- Come from carrot, fish liver oil, fresh green veg.. It helps maintaining good vision because it helps forming pigment in the rod cells in our eyes. The deficiency disease is night blindness. 2) Vitamin C which also known as ascorbic acid. It is good for healthy gums, skin and teeth, helps healing wounds and resist diseases. The deficiency disease is scurvy -- bleeding easily occurs (usually in gums) 3) Vitamin D comes from diary products and fish liver oil, and our skin under sunlight. Minerals help us in different purposes. We mainly focus on Iron, calcium and iodine here. 1) Iron come from meat, yeast and green veg.. It’s used for making haemoglobin which is a pigment responsible for taking oxygen in the red blood cells. It’s deficiency disease is anaemia which no. of red blood cell is lower than normal, easily faint. 2) Calcium comes from milk, cheese and green veg.. It helps building up strong bones and teeth so that it’s deficiency disease is rickets which the bone become soft and bent. 3) Iodine comes from the product from sea(sea fish, seaweed, etc.), it help regulate body growth. It’s deficiency disease is simple goitre. Dietary fibre come from the roughage that there’s plant cell wall which called cellulose, and it cen’t be digested. It make the the muscles in intestinal wall to contract to make peristalsis and push the food forward. It prevent the food becomes bad inside our body and form constipation, piles and even colon cancer. We have various test to test the presence of nutrients. 1) Starch -- Iodine solution (Yellow brown → Blue black) 2) Glucose -- Clinistix paper, originally test for diabetes pink → purple 3) Protein -- Albustix paper, originally test for function of liver, yellow to green. 4) Fat -- Leave a translucent spot on a filter paper (spot test) We must have a balanced diet for those 7 food substances in right amount and proportions and refer to the food pyramid, and eat less of that in the higher level. We can measure the energy value by kilojoules (kJ) or kilocalories (kcal). Carbohydrates, fat and proteins have energy value of 17.1 38.9 and 18.2 kJ/g. People’s daily need of energy vary with sex, age, body size, occupation and physical activity. Over-eating(intake>need) will cause overweight, the more serious one is called obesity, they will have high blood pressure, and high risk of heart disease. Under-eating will cause malnutriention, thin, and various deficiency disease will occur. The more serious problem is the anorexia which is a mental health, which don’t want to eat, always thinks that they’re too fat. The food pyramid has the top of fat, salts and sweets, then diary product, vegetable and fruit,, grain and cereals at the bottom.

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