Option A - Diet and Human Nutrition

From KstructIB

Base content by Samar

A.1 Diet

A.1.1. Diet is the total food taken in by an individual. Nutrition can be defined as the study of the efficiency of food to nourish the body.

A.1.2. Nutrient- A substance needed in the diet of an organism. Nutrients are the chemical components of food, which has the function of producing energy, promoting growth and repair of tissues, and regulates these processes, once it is absorbed by the body.

A.1.3/4 Constituents of a diet:

Carbohydrates- filling, slow-burning energy. It is stored in humans as glycogen in the liver and muscles. In plants, carbohydrates are synthesised during photosynthesis. Found in bread/potatoes/cereals/pasta

Lipids (fats)- contain essential fatty acids which are necessary for the formation of cell membranes. Also provide energy. Lipids also influence the contraction of involuntary muscles (e.g. intestine and blood pressure). Found in butter/cooking oil/cream/chocolate

Proteins- needed for growth in tissues, and for tissues in repair or replacement. They are also necessary as a source of amino acids. Some amino acids are essential because they can’t be made by the body. A constant supply of amino acids is needed for the production of enzymes and proteins in the cell membrane. Found in meat/eggs/fish

Water- takes part in body building when protein is laid down in body tissues. It also acts as a catalyst in some body reactions, and works as a lubricant . Found in everything wet.

Minerals- these are inorganic nutrients which participate in a wide variety of body functions. Iron- making haemoglobin (found in liver/red meat) Calcium- making teeth and bones (found in milk/cheese) Sodium- proper function of nerves (found in salt) Fluoride- hardening of tooth enamel. (found in milk)

Vitamins- are only required in trace amounts. They are essential for good health. They prevent deficiency diseases. Found in vegetables/fruit/cereal

Fibre- It affects the balance of other nutrients present. It protects against ‘diseases of affluence’; it basically regulates the amount of stuff you have in your body. It helps you do number 2s better too, as well as lowering cholesterol levels and blood-glucose levels. Found in vegetables/fruit/cereals.

A.1.5 A balanced diet is an equilibrium between food intake and energy expenditure. It meets bodily needs for growth, replacement and heart functioning.

A.1.6 /7 Self- explanatory stuff.

A.2 The Biochemistry of Nutrition

A.2.1 Monosaccarides: (glucose, dextrose) : grapes, honey, onions

Disaccharides: (maltose, lactose, sucrose) : milk, sugar cane, most fruits

Polysaccarides: (cellulose, starch) : most vegetables, potatoes, cereal grains.

A.2.2. Carbohydrates are broken down into simple sugars. Glucose is then oxidised to provide a continual source of energy which can be used for synthesising ATP (energy) for cell respiration. The end products of digestion of carbohydrates, fats and proteins can all be used as energy sources. Energy release from these components occurs by a series of enzyme-controlled reactions. Energy is released when glucose forms the products carbon dioxide and water through catabolism (the breakdown of larger molecules). The digested carbohydrates are diffused out of the small intestine into the hepatic portal vein and are transported to the liver. Carbohydrates are the preferred substrate for cell respiration, and the brain cells of mammals can only use glucose. Fats from the ‘first reserve’ are mainly used when the carbohydrate reserves have been exhausted. Excess carbohydrates are converted and stored as fats and glycogen.

A.2.3 Sources of lipids: margarine, pork, peanuts, olive oil

A.2.4 Fats are used as a source of energy when carbohydrates are in short supply or when the demand for energy is particularly high for cell respiration. The products of fat digestion are transported to the surfaces of the intestinal epithelial cells into which they are absorbed through diffusion. These absorbed fats bypass the liver and travel to the thoracic lymphatic duct from where they enter the venous bloodstream. Fats are also stored in tissue around the heart, the kidneys and in the mesenteries (fat which attaches the stomach and intestine to the peritoneal wall). The liver removes lipids from the blood and either oxidises them with the transfer of energy, or modifies them chemically before they are sent to the body’s fat depot for storage. Fats may be oxidised in the body to give energy, carbon dioxide and water. Fats are also used in the growth of membranes.

A.2.5 See Table 14.2, Page 244 Yellow Book.

A.2.6. Sources of Protein: meant, fish, eggs, cheese.

A.2.7 The liver’s main contribution to protein metabolism is to synthesise the non-essential amino acids by transamination. It also gets rid of excess proteins. This is because the body is unable to store proteins or amino acids, and any surplus is destroyed in the liver. The amino acids are first deaminated by the liver cells: the amino group is removed from the amino acid molecule with the formation of ammonia. The rest of the amino acid is then fed into carbohydrate metabolism and respired.

A.2.8 Essential amino acids are those which must be ingested and cannot be synthesised.

A.2.9 Calcium- Involved in selective permeability of plasma membranes and intracellular communication; activates certain enzymes; constituent of bones, teeth and plant cell walls. Iron- Constituent of haemoglobin and myoglobin; involved in electron transfer, activates certain enzymes including catalase. Iodine- Constituent of thyroxine. Potassium- Helps determine anion-cation balance in cells. Activates many enzymes; involved in stomatal openings.

A.2.10 Retinol (Vitamin A) – enters into photochemical reaction in rods in retina of eye. Cyancobalamin (Vitamin B12)- plays a vital role in the activities of several enzymes. Important in the production of the genetic material of cells and in the production of red blood cells in the bone marrow. Ascorbic acid (Vitamin C)- Required for formation of intracellular material. Calciferol (Vitamin D)- Absorption and utilisation of Ca2+ for bone formation. Tocopherol (Vitamin E)- Not known.

A.2.11 High fibre diets are known to prevent diverticulitis of the colon, and are thought to reduce the incidence of bowel cancer and colitis.

A.3 Diet and Health

A.3.1 People in the Western World have too much fat in their diet. Body fat acts as a store of energy, protects internal organs from injury and insulates the body. However, there are problems.

BMI (Body mass index) = weight (kg)/height (m)2

The best range for health lies between 20 and 25.

People who are overweight have an increased risk of: Gall bladder disease, high blood pressure, diabetes, some cancers.

Coronary heart disease (CHD): Common in Western World. It arises from the failure of the coronary arteries to supply sufficient blood to the heart tissue. It is usually caused by: - atherosclerosis of the coronary arteries - angina: a pain in the chest caused by exercise.

Excess amounts of fat in a diet cause the coronary arteries to become clogged up with fat which lessens the amount of blood which reaches the heart. To prevent cardiovascular disease, fibre and starch should be eaten while fat and saturated fats should be reduced.

Risk factors with CHD: - Genetic History - Lack of exercise - Stress - High blood pressure - Diabetes - Obesity A.3.2 There are many kinds of fat. Each contains particular fatty acids. Now some fatty acids are saturated, whereas others are unsaturated (an unsaturated fatty acid is one which contains less than the maximum amount of hydrogen possible). Fatty acids which are very unsaturated are called polyunsaturates. In general animal fats contain a high proportion of saturated fatty acids, whereas plant oils contain a high proportion of polyunsaturated fatty acids. For good health we should eat mainly polyunsaturates. The reason is that polyunsaturates reduce the amount of another substance in the body: cholesterol.

A.3.3 Cholesterol interacts with the hydrocarbon chains of the phospholipid molecules just behind the polar heads. This enhances the mechanical stability and flexibility of the membrane. Cholesterol is found in the membranes of animals cells where it helps to keep the membranes fluid. Other important steroids are derived from cholesterol. They include the sex hormones progesterone and testosterone, and the hormone aldosterone secreted by the adrenal cortex. Bile salts, such as glycocholate and taurocholate, are polar metabolic products of cholesterol needed for the normal digestion of lipids.

A.3.4 The amount of cholesterol in the blood is largely determined by dietary intake in conjunction with the activities of the liver. If there is a considerable excess in the blood, some of it may be deposited in the walls of certain arteries, obstructing the smooth passage and often leading eventually to an intravascular clot. If this occurs in one of the coronary arteries serving the heart, a coronary thrombosis (heart attack) may result.

A.3.5/6 Vegetarians’ diet includes animal products such as milk and eggs, but not the animals themselves. Vegans only eat food of vegetable origin. A vegetarian diet that includes dairy products can provide everything needed for a healthy life. Plants can provide lots of fibre, vitamins and polyunsaturated fat, so a vegetarian diet is good in that respect. Vegans have to make sure that their food gives them all the substances they need. In general their diet needs to be bulky and varied. This will ensure that they get enough carbohydrate and protein, together with the full range of vitamins and essential amino acids. Vegans have problems with vitamins D and B12 , neither of which are present in plant products. There should be no problem if vegans ensure that they have adequate exposure to sunlight and most vegans take vitamin B12 supplements. Iron and calcium are also important (must be taken in supplement form). Often vegetarian diets are high in fibre which tends to bind minerals and render them unavailable. There are also lacto-vegetarians, pesco-vegetarians (fish) and ovolacto-vegetarians (egg and milk products).

A.3.7 Calcium- If a child does not get enough calcium, its bones remain soft and become deformed (rickets). Calcium is also needed for making muscles contract, and it helps blood to clot when you cut yourself. Iron- Iron is needed for blood. Shortage of iron results in the blood containing too little haemoglobin (this is a type of anaemia). The oxygen-carrying ability of the blood is reduced, resulting in tiredness and lack of energy. Calciferol- deficiency may occur in people with poor diet, premature infants, in those deprived of sunlight and in dark-skinned people, particularly in foggy urban areas. Deficiency develops rickets. Cyancobalamin- deficiency is usually due to an inability to the intestine to absorb the vitamin, most commonly due to pernicious anaemia.

A.3.8 Malnutrition- The result of feeding on a diet that is not balanced.

A.3.9 Self-explanatory

A.3.10 Find this online

A.3.11 Vitamin Deficiency- Deficiency in fat soluble vitamins is due to a disorder in which intestinal absorption of fats is impaired or to a poor/restricted diet. Deficiencies in water-soluble vitamins is more common due to prolonged cooking, storage, processing.

A.3.12 Chemical additives can act as preservatives, antioxidants, colouring, flavouring, stabilisers and acid-regulators.

A.3.13 Some additives may have deleterious effects. Some individuals seem to be sensitive to certain colourings, flavourings or preservatives. For example: Tartazine (E102)- a commonly used yellow colouring in fizzy drinks, convenience foods and medicines. It can be the cause of skin rashes, hay fever, blurred vision, purple patches on the skin, and may possibly be linked with hyperactivity in children, or with asthma. Sunset Yellow (E110)- A yellow colour widely used in convenience foods. It may produce skin rashes.

A.3.14 Self-explanatory