School biology notes: Diet, exercise and reducing risk from some non-communicable diseases

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KEEPING HEALTHY - Diet and Exercise

Balanced nutritious food intake and doing some regular 'aerobics' to help reduce the risk from some non-communicable diseases, obesity indexes

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 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?

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(a) What is a healthy balanced diet?

(b) Metabolism and body mass

(c) Aerobic exercise reduces risk from some non-communicable diseases

(d) Know that inherited factors also affect our health

(e) Measures of obesity - body mass index and waist-to-hip ratio

(f) Learning objectives

See also Respiration - aerobic and anaerobic

and Keeping healthy - non-communicable diseases - risk factors for e.g. cancers

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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.

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(b) Metabolism and body mass

  • What is your metabolism?   What is metabolic rate?

  • 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.

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

  • 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.

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(c) Regular aerobic exercise can reduce your risk from some non-communicable diseases

  • If you have a high resting heart rate (measured by your 'pulse') and you are slow to recover from physical exercise, you should be aware these observations are linked to an increased risk of developing heart disease (CVD, cardiovascular disease).

    • Regular exercise can reduce your resting heart rate and speed up your recovery rate after engaging in physical activity e.g. brisk walking, manual work, climbing stairs, jogging etc.

    • This has been clearly shown from scientific studies e.g.

    • You take a biggish number of volunteers (say a hundred) that do not exercise regularly.

    • Record their initial baseline resting heart rate.

    • Get them all to do the same physical exercise and record their recovery rate - that is the time it takes for the increased heart rate to fall back to the resting heart rate.

    • You then split the volunteers into two groups and ask one group to do some regular exercise every day e.g. brisk walking for an hour or 20 minutes on an 'aerobic exercise machine', and the other group asked to continue in their normal 'non-aerobic' lifestyle.

    • After, say 2 months, remeasure all their resting heart and recovery rates, and you should find a definite improvement in these figures in the group who did regular extra aerobic exercise.

  • 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.

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

  • Metabolic rate may be affected by inherited factors.

  • 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.

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

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(e) Measures of obesity (one measure of healthiness and well-being)


There is no such thing as the 'perfect weight', we come in all shapes and sizes, but there are limits within which we should be to be healthy!

In the medical profession, a doctor can't just simply that somebody is overweight, without reference to some kind of statistical index, usually by one/both of the ratios described below.

Equally healthy people can have quite different weights, but there are some reasonably good indicators as to when your weight is not what it should be 'ideally'.

In rich developed countries we are often dealing with 'overweight' people eating too much rich fatty food, but in poorer underdeveloped countries we are dealing 'underweight' people, particularly young children suffering from malnutrition.

Malnutrition means lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.

The Body Mass Index

The body mass index is a 'rough' guide to help the medical profession decide whether you are underweight, normal, overweight or obese - based on your height and height.

The higher your BMI the more fat you are carrying - but not necessarily unhealthily.

Body Mass Index (BMI) = (body mass in kg) / (height in m)2

When measured, you then consult a table of BMI values to se where you fit in!

Table of BMI values (from https://www.vertex42.com/ExcelTemplates/bmi-chart.html)

Body mass index Weight description
less than 18.5 underweight
18.5 to 24.9 normal
25.0 to 29.9 overweight
30.0 to 40.0 moderately obese
over 40.0 very obese

If you eat too much fatty sugary foods and don't take enough exercise, most people will put on weight and too much of it. You are taking in too much energy rich food for your daily needs.

The excess energy releasing food is stored as fat and gives you a raised BMI value.

Having a higher than normal BMI value increases your risk of developing type 2 diabetes.

Note of caution: Having a high BMI is not always unhealthy e.g. athletes train hard to build up extra muscle which is heavier than fat, so they will tend to have higher than 'normal' BMI values and would not be classed as overweight.

Note from 2020 on the covid-19 flue pandemic: Research has shown that obese people are more likely to be seriously ill with the virus than non-obese people - more severe fever, more likely to be hospitalised and more likely to die!

The waist-to-hip ratio should also be taken into consideration (see below).


The waist-to-hip ratio

Where the body stores fat is quite important.

If a lot of fat is stored around the abdomen you get a 'fat tummy' and this is associated with an increased risk of developing type 2 diabetes - hence the importance of diet and exercise.

Comparing the circumferences of waist and hips is another measure of whether you are 'overweight' and concentrates around one area where we can accumulate to much fat - the 'tummy'.

waist-to-hip ratio = circumference of waist (cm) / circumference of hips (cm)

The higher your waist-to-hip ratio the more fatty tissue you are carrying around the middle of your body.

When measured, you then consult a table of BMI values to se where you fit in!

Table of waste-to-hip ratios (from https://www.healthline.com/health/waist-to-hip-ratio)

Health risk waist-to-hip ratio (women) waist-to-hip ratio (men
low less than 0.81 less than 0.96
moderate 0.81 to 0.85 0.96 to 1.00
high (overweight) over 0.86 over 1.00

If you are female and your waist-to-hip ratio is over 0.86 you are classed as overweight.

If you are male and your waist-to-hip ratio is over 1.00 you are classed as overweight.

If you are above the moderate waist-to-hip ratio values you are carrying too much fat around your 'middle' - referred to as abdominal obesity.

Having a higher than normal waist-to-hip ratio increases your risk of developing type 2 diabetes.

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(f) Learning objectives

  • 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.

    • 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?

    • Note that knowledge and understanding of ...

    • See also Respiration - aerobic and anaerobic  gcse biology revision notes

    • Seeing computer simulations to model

      • the effect of ... balanced and unbalanced diets and exercise,

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General HUMAN BIOLOGY revision notes

See also cell biology index above

Introduction to the organisation of cells => tissues => organs => organ systems (e.g. in humans)

Examples of surfaces for the exchange of substances in animal organisms   gcse biology revision notes

See also Enzymes - section on digestion and synthesis  gcse biology revision notes

The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

Homeostasis - introduction to how it functions (negative feedback systems explained)  gcse biology revision notes

Homeostasis - control of blood sugar level - insulin and diabetes  gcse biology revision notes

Homeostasis - osmoregulation, ADH, water control, urea and ion concentrations and kidney function, dialysis

Homeostasis - thermoregulation, control of temperature  gcse biology revision notes

The brain - what the different parts do and the dangers if damaged gcse biology revision notes

An introduction to the nervous system including the reflex arc  gcse biology revision notes

Hormone systems - Introduction to the endocrine system - adrenaline & thyroxine hormones  gcse biology revision

Hormone systems - menstrual cycle, contraception, fertility treatments  gcse biology revision notes

Respiration - aerobic and anaerobic in plants and animals.  gcse biology revision notes

Keeping healthy - communicable diseases - pathogen infections   gcse biology revision notes

Keeping healthy - non-communicable diseases - risk factors for e.g. cancers   gcse biology revision notes

Keeping healthy - diet and exercise  gcse biology revision notes

Keeping healthy - defence against pathogens, infectious diseases, vaccination, drugs, monoclonal antibodies

See also Culturing microorganisms like bacteria - testing antibiotics/antiseptics  gcse biology revision

Food tests for reducing sugars, starch, proteins and lipids  gcse biology revision notes

The eye - structure and function - correction of vision defects  gcse biology revision notes

Optics - lens types (convex, concave, uses), experiments, ray diagrams, correction of eye defects (gcse physics)

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