KEEPING HEALTHY - Diet and Exercise

Doc Brown's Biology Revision Notes

Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent

This page will answer many questions e.g.

What constitutes a healthy balanced diet?

Why do we need protein in our diet?

Why do we need both fats and carbohydrates in our diet?

Why is regular exercise good for?

What is metabolism?



Keeping healthy

  • Appreciate that a combination of a balanced diet and regular exercise is needed to help keep the body healthy.

  • Be aware that our bodies provide a good environment for many microbes to live and multiply at our expense and can make us ill once they are inside our body.

  • Our bodies need to be capable of stopping most microbes from getting in and dealing with any microbes which do get in.

  • You are expected to be able to ...

    • ... evaluate information about the effect of food on health,

    • evaluate information about the effect of lifestyle on development of disease,

    • and analyse and evaluate claims made by slimming programmes, and slimming products.

      • There are lots of slimming products on the market eg from special diets ('Atkins Diet'), diet pills, low calorie milkshakes, soups, ready made meals etc. but how do you know which is likely to be effective?

        • BUT has the diet been properly scientifically tested and evaluated?

        • Have different research groups agreed on the effectiveness or otherwise of a particular diet strategy?

        • Is the only information on the diet, that supplied by the manufacturer?, so no independent review of the diet's effects on body weight, just the non-verified company's opinion!

        • In the end for many people the best thing is to take in less calories and eat a smaller better balanced nutritious diet AND take more exercise.

      • In all cases the necessary data and information will be provided in the exam paper.

      • Even a study of food labels is useful eg what energy does a food provide, what is the protein, carbohydrate/sugar, fat, fibre, minerals (salt, calcium, iodine) content etc. pictures?

      • What are the health implications for the content of the food in a meal OR what is the meal deficient in? ie are you having a good balanced diet meal?


Diet and exercise

  • a) What is a healthy balanced diet?

    • Know that a healthy diet contains the right balance of the different foods you need and the right amount of energy and the different food groups are ...

    • Carbohydrates and fats are needed to provide energy for your body chemistry to function correctly, and of course to keep you warm at 37oC,

      • but, not too much, or excessive fats or carbohydrates build up in your body which can lead to obesity.

      • Obesity is a common disorder in developed countries eg in Europe and the US.

      • Obesity is defined as 'having a body mass of at least 20% greater than the maximum recommended body mass.

      • Although the usual causes of obesity are overeating, lack of sufficient exercise and bad diet, hormonal problems can also help cause obesity.

      • Obesity can contribute to other medical problems eg arthritis (joint inflammation), type 2 diabetes (failure to control blood sugar levels), high blood pressure and heart disease and even some types of cancer.

      • If you have too much saturated fat in your diet, your blood cholesterol levels are raised above what is needed and deposits form on the walls of your blood vessels leading to higher blood pressure.

    • Proteins are used by the body to build cells - growth of new tissue, cell repair and cell replacement.

    • Mineral ions and vitamins are needed in small amounts for healthy functioning of the body - organs, skin, bones etc.

      • You do need mineral salts containing eg sodium, calcium, potassium and chloride ions BUT too much salt (sodium chloride) can cause high blood pressure and heart problems.

    • Fibre keeps everything moving smoothly through your digestive system.

    • A person is malnourished if their diet is not balanced.

    • Lack of a good healthy diet can cause a person to be overweight or underweight.

    • An unbalanced diet may also lead to deficiency diseases or conditions such as Type 2 diabetes.

    • You need to eat the right types of healthy food and in the right amounts/proportions to maintain a healthy body.

    • People who live on a poorly balanced diet are malnourished and malnourishment is common in the poorer developing countries of the world eg in Africa.

      • Don't confuse with starvation, where there is not enough food of any description to maintain life - the pictures you see on your TV of very thin people in Africa, on the edge of life exemplifies this pitiful state.

      • However, malnourished people can be overweight as well as thin, from an imbalanced diet eg those fat people who live off too much junk food and excess fat are as malnourished in some ways just as much as a 'thin' person in a poor third world country!

      • The effects of malnutrition do depend on what is missing from the diet but common symptoms are slow growth in children (arrested development), weight loss in adults, poor resistance to disease and infection, fatigue (low physical activity, lack of energy).

      • Particular deficiency diseases are caused by lack of specific vitamins or minerals eg lack of vitamin C causes scurvy which leads to problems with gums, the skin and joints. Tissue is not efficiently repaired and ulceration is common.

  • b) A person loses mass when the energy content of the food taken in is less than the amount of energy expended by the body.

    • What is your metabolism? What is metabolic rate?

    • You need energy to fuel the chemical reactions in your body to keep you alive and these reactions are called your metabolism.

    • Different people have small differences in their resting metabolic rates because eg muscle needs more energy than fatty tissue, so more muscular people tend to have a higher metabolic rate because of the higher ratio of muscle to fat.

    • Bigger people tend to have a higher metabolic rate because more energy is needed to maintain a greater mass of cells.

    • On average men tend to have a greater metabolic rate because they tend to have a greater proportion of muscle.

    • Exercise increases the amount of energy expended by the body.

      • Athletes or people engaged in heavy manual work would need a greater energy (calorie) intake.

        • eg the energy need for cycling at low speed is about 4x that you need for sleeping, and you need 4x the energy for cycling to rapidly climb stairs!

      • Your metabolic rate can stay up even after you have finished engaging in more physical exercise, particularly if it has been strenuous.

      • Regular exercise can increase your metabolic rate because it builds muscle as well as using more energy due to performing more physical activities than just sitting around.

      • People who have more active physical jobs need more energy and hence more carbohydrates or fats ie your dietary needs vary with your occupation.

      • Exercise increases the amount of energy (via fat/carbohydrate etc.) used by the body and so decreases the amount stored as fat, hence less chance of suffering from obesity.

      • Exercise also builds up muscle which boosts your metabolic rate.

      • If you do little exercise and have a job sitting in an office, you should reduce your carbohydrates and fats intake accordingly because you need less energy to get through the day.

      • A note of caution - being fit does not necessarily mean you are healthy, a common assumption! You can be unhealthy because of a lack of balanced diet but you could still be physically non-obese and fit.

  • c) The rate at which all the chemical reactions in the cells of the body are carried out (the metabolic rate) varies with the amount of activity you do and the proportion of muscle to fat in your body.

    • Metabolic rate may be affected by inherited factors.

  • d) Know that inherited factors also affect our health e.g. ...

    • Your DNA profile ==> gene expression ==> inherited characteristics, can have some bearing on your metabolic rate eg an underactive thyroid gland which can lower metabolic rate, increase fatigue and ultimately cause obesity. Any energy not used will be stored as fat.

    • People can inherit factors that affects the blood cholesterol level.  Cholesterol is an essential fatty substance for good health and its in every cell in the body but if it is too high it causes fatty deposits on the inner surfaces of blood vessels causing higher blood pressure and heart disease.

  • e) People who exercise regularly are usually healthier than people who take little exercise.

  • Note that knowledge and understanding of ...

    • the specific functions of nutrients and the effects of any deficiency in the diet is not required here.

    • the effect of exercise on breathing and heart rate is not required here either.

  • Seeing computer simulations to model

    • the effect of ...

      • balanced and unbalanced diets and exercise,


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