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A history of fad diets Which diets are designed for weight loss? Which diets have a scientific basis? 3 of 36 © Boardworks Ltd 2006

You are what you eat! When food is digested its components enter the blood. carbohydrate glucose fatty acids + glycerol protein amino acids Molecules used for growth and repair become part of the body. Those used as energy sources are lost as CO 2 and H 2 O. 4 of 36 © Boardworks Ltd 2006

What are cells made from? Different nutrients are incorporated into each part of a cell: nucleus: protein membrane: fats and carbohydrate cytoplasm: protein and water 5 of 36 © Boardworks Ltd 2006

You are what you eat! What could this food label represent? A human! 6 of 36 © Boardworks Ltd 2006

Different nutrients 7 of 36 © Boardworks Ltd 2006

Dietary guidelines vitamins and minerals (1%) carbohydrate (50%) protein (14%) fat (35%) The amount of each type of nutrient a person needs varies between individuals. What factors might affect how much a person needs? 8 of 36 © Boardworks Ltd 2006

Lack of protein Proteins in meat and fish are called first-class proteins because they contain all the essential amino acids that humans need in their diet. Recommended daily allowance (RDA) of protein (g) = 0. 75 x body mass (kg) What is the RDA of protein for a 60 kg student? RDA = 0. 75 x 60 kg = 45 grams A protein deficiency illness called Kwashiorkor can cause a swollen belly and weak immune system, and is common in developing countries. 9 of 36 © Boardworks Ltd 2006

Why do some people need more food? Metabolism is the series of chemical reactions or ‘life processes’ in the body. Different amounts of energy are used in different life processes. digestion (10%) exercise and warmth (20%) growth and repair (70%) Metabolic rate is the rate at which cells uses energy, and this varies between individuals. Why does metabolic rate increase during exercise and cold weather? 10 of 36 © Boardworks Ltd 2006

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Chemical and physical digestion 12 of 36 © Boardworks Ltd 2006

Enzymes at work Enzymes digest food in the mouth, stomach and small intestine. Enzymes break down large food molecules into smaller ones that can be absorbed by the blood. This is called chemical digestion. Different types of food are broken down by different enzymes. 13 of 36 © Boardworks Ltd 2006

Enzymes of digestion 14 of 36 © Boardworks Ltd 2006

Helping enzymes Enzymes are not the only substances involved in chemical digestion. Hydrochloric acid in the stomach provides the right conditions for protease enzymes to break down protein. Bile is a substance produced by the liver and stored in the gall bladder. It helps the digestion of fats by turning them into small droplets. This is called emulsification. How does this help lipase enzymes? The smaller droplets have a larger surface area, which speeds up the rate at which lipase digests the fat. 15 of 36 © Boardworks Ltd 2006

Which enzyme? 16 of 36 © Boardworks Ltd 2006

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What is BMI? Body Mass Index (BMI) measures the relative amounts of fat and muscle in the body. BMI = body mass (kg) (height)2 (m) Gloria: 1. 45 m and 66 kg BMI = 31 BMI Conclusion <20 underweight Zak: 20 -25 normal 25 -30 overweight >30 obese 1. 85 m and 66 kg BMI = 19 What are their health risks? Obese people have an increased risk of arthritis, diabetes and heart disease. People who are underweight tend to have poor immune systems and often get ill. 18 of 36 © Boardworks Ltd 2006

Are you right for your height? In 2002, 22% of boys and 28% of girls aged 2 -15 in the UK were overweight or obese. Statistics show that obesity levels, among both young people and adults, are rising. Calculating a person’s BMI can be useful, but the formula can overestimate the proportion of body fat in people who are muscular. This is because muscle is denser than fat. This means it is helpful to use extra measures to help judge how healthy a person is, such as waist circumference. 19 of 36 © Boardworks Ltd 2006

What is blood pressure? Blood pressure is a measure of the pressure exerted by the blood against artery walls. Blood pressure varies with: l heartbeat strength l blood volume l fitness l health l age. Blood pressure is measured as two numbers, e. g. 120/80. What do these numbers show? The numbers show pressure readings in mm of mercury. 20 of 36 © Boardworks Ltd 2006

Systolic and diastolic “Blood pressure one-twenty over eighty. ” The big number (‘ 120’) is the systolic pressure. This is the blood pressure during a heartbeat. The small number (‘ 8’) is the diastolic pressure. This is the blood pressure in-between heartbeats. 21 of 36 © Boardworks Ltd 2006

How does blood pressure affect health? High blood pressure can make blood vessels more likely to burst, and can cause strokes and kidney damage. Low blood pressure can cause dizziness, fainting and poor circulation. Age Systolic Diastolic The older you get, 10 80 -100 60 the higher your 15 90 -110 60 blood pressure 20 110 -125 70 naturally becomes. 40 130 -150 80 Kevin is 38 years old and his blood pressure is 180/90. What advice would you give him? 22 of 36 © Boardworks Ltd 2006

Lifestyle assessment Kevin’s GP quizzed him about his lifestyle, tested his blood and referred him to a health centre. Excess salt is known to increase blood pressure in about 30% of the population. What else could Kevin do to improve his health? 23 of 36 © Boardworks Ltd 2006

Health and fitness Health and physical fitness are different. l A healthy person is free from disease or abnormality. l A fit person has good cardiorespiratory, aerobic and muscular endurance. Kevin’s GP wants his cardiovascular fitness to improve so that he puts less strain on his body. His personal trainer wants other sorts of fitness to improve. What types of exercise should Kevin do? 24 of 36 © Boardworks Ltd 2006

What is wrong with fast food? Fast food and takeaways such as curries, burgers and pizzas are high in unhealthy nutrients such as saturated animal fats, sugar and salt. Fast food usually contains very little fibre, vitamins, minerals or unsaturated vegetable oils, which are important for a health diet. 25 of 36 © Boardworks Ltd 2006

Unhealthy diets? 26 of 36 © Boardworks Ltd 2006

What is cholesterol? Cholesterol is a lipid found in cell membranes and is used in the production of hormones and bile. Cholesterol is transported in the blood by molecules called lipoproteins, of which there are two types: l high-density lipoprotein (HDL): often called ‘good cholesterol’ l low-density lipoprotein (LDL): often called ‘bad cholesterol’. Cholesterol levels depend on diet and genes, but high levels of LDL have been linked to eating lots of saturated fats and few mono/polyunsaturated fats. 27 of 36 © Boardworks Ltd 2006

Good and bad cholesterol How do ‘good’ and ‘bad’ cholesterol affect a person’s health?

Cholesterol and heart disease Why is LDL called ‘bad cholesterol’? Excess LDL is deposited on the walls of blood vessels, which can lead to clots in the arteries. This can starve the heart of oxygen and cause heart disease. Why is HDL called ‘good cholesterol’? HDL returns cholesterol to the liver where it is metabolized. The risk of heart disease may be reduced by: l lowering blood cholesterol l eating more HDL than LDL l gentle daily exercise. 29 of 36 © Boardworks Ltd 2006

Taking action Kevin’s blood test showed high cholesterol, but not high enough to require drug therapy to reduce it. This margarine claims to cut blood cholesterol by 10%, but it costs four times as much as normal margarine. Should Kevin buy the margarine? What extra information would help him decide? 30 of 36 © Boardworks Ltd 2006

What are statins? The plant extracts in margarine that lower cholesterol are less effective than cholesterol-lowering drugs called statins. Should these drugs be available without a prescription? Yes! People should be allowed to self-medicate. No! People with normal cholesterol might take them and they wouldn’t be checked for side-effects like liver damage. What do you think? 31 of 36 © Boardworks Ltd 2006

Glossary (1/2) l blood pressure – The pressure in the arteries during and between contractions of the heart. l body mass index – A measure of a person’s weight in relation to their height. l chemical digestion – The process of breaking large food molecules into smaller ones using enzymes. l fitness – Strength, stamina, flexibility, agility, speed and cardiovascular efficiency. l health – Freedom from disease and injury. l heart disease – An abnormal condition of the heart or the arteries that supply the heart. 33 of 36 © Boardworks Ltd 2006

Glossary (2/2) l lipoproteins – Molecules that carry cholesterol in the l l l blood and which are either high density or low density. metabolic rate – A measure of how fast chemical reactions occur in cells. obese – A person who is very overweight and has a BMI of over 30. physical digestion – The breaking up of pieces of food by chewing it in the mouth and churning it in the stomach. saturated – A type of animal fat that raises blood cholesterol levels and increases the risk of heart disease. unsaturated – A type of fat from vegetable and fish oils that helps lower blood cholesterol levels and reduce the risk of heart disease. 34 of 36 © Boardworks Ltd 2006