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
Why is regular exercise good for?
What is metabolism?
Appreciate that a combination of a
balanced diet and regular exercise is needed to help keep the
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.
need to be capable of stopping most microbes from getting in and dealing with any microbes which do get
You are expected to be able
... evaluate information about the effect of food
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
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?
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Diet and exercise
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.
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
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
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.
is your metabolism? What is metabolic rate?
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
Exercise increases the amount of energy expended by
Athletes or people engaged
in heavy manual work would need a greater energy (calorie) intake.
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.
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 ...
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