Healthy Eating

From AQA GCSE Science Textbook,

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  • Created by: Cristina
  • Created on: 29-09-09 18:06

Diet and Exercise 1

What makes a healthy diet?

A healthy diet contains:

  • Carbohydrates
  • Proteins
  • Fats
  • Vitamins
  • Minerals
  • Fibre
  • Water

If your diet isn't balanced, you will end up malnourished.

Not taking in enough vitamins and minerals can lead to deficiency diseases such as scurvy which is caused by lack of vitamin C.

If we take in too much energy we get fat however if we don't eat enough we get too thin.

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Diet and Exercise 2

How much energy do you need?

The amount of energy you need to live depends on lots of different things:

  • Gender
  • Age
  • Activity

The metabolic rate

This is the rate at which all the chemical reactions in the cells of the body take place. The metabolic rate varies from person to person.

The proportion of muscle to fat in your body affects your metabolic rate.Men generally have a higher metabolic rate than women. You can change the proportion of muscle to fat in your body by exercising and building up more muscle.

Exercise increases your metabolic rate for a time even after you stop exercising.

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Weight Problems 1

BMI (Body/Mass Index) compares your height to weight;

BMI = Weight / (height)²

Most people have a BMI in the range 20-30. If you have a BMI of below 18.5 or above 35 then you may have some real health problems.


If you take in more energy than you use, the excess is stored as fat. Some body fat is needed to cushion your internal organs, and also act as an energy store for when you don't feel like eating. However, too much can make you obese.

Obesity can lead to; arthritis (worn joints), diabetes (high blood sugar levels), high blood pressure and heart disease. They are more likely to die young than slimmer people.

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Weight Problems 2

Losing weight

  • Reduce energy intake by cutting back on the amount of food you eat.
  • Increase the amount of energy you use up by taking up more exercise.
  • The best way to lose weight is to do both.


The symptoms of starvation include;

  • Loss of weight and muscles waste away so people become very thin.
  • The immune system doesn't work properly so people pick up infections very easily.
  • If you are female, your periods become irregular and may stop altogether.
  • Deficiency diseases due to lack of vitamins and minerals.

These symptoms can also occur in the mental disorder anorexia nervosa.

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Fast Food 1


As well as obesity, the amount and type of fat you eat also seems to affect the levels of cholesterol in your blood.

Cholesterol is a substance made in your liver and is carried around your body in your blood. It helps make the membranes of your body cells, your sex hormones and the hormones that help your body deal with stress.

High levels of cholesterol in your blood increase your risk of getting heart disease or diseased blood vessels.

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Fast Food 2

Controlling Cholesterol

The amount of cholesterol in your blood depends on two things:

  • The way your liver works, which can sometimes be inherited and cannot be changed.
  • Amount of fat in your diet.

Cholesterol is carried around your body by two types of lipoproteins:

  • Low-density lipoproteins (LDLs) are known as 'bad' cholesterol. Raised levels increase your risk of heart problems.
  • High-density lipoproteins (HDLs) are known as 'good' cholesterol and they reduce risk of heart disease.

The balance of LDLs and HDLs in your blood is very important for a healthy heart.

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Fast Food 3

There are three main types of fats in the food and they seem to have different effects on your cholesterol.

  • Saturated fats increase blood cholesterol levels. You find them animal fats like meat, butter and cheese.
  • Mono-unsaturated fats seem to have two useful effects. Reduce your overall blood cholesterol levels and improve the balance between LDLs and HDLs. You find them in food like olive oil, olives, peanuts and margarines.
  • Polyunsaturated fats are even better at reducing your blood cholesterol levels than mono-unsaturated fats. You find them in corn oil, sunflower oil, margarines and oily fish.


Vital in our diet. Without it, your nervous system would not work and the chemistry of all your cells would be in chaos. Too much salt can lead to high blood pressure. This can damage your heart, kidneys and increase your risk of stroke. Found in 'processed foods'.

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Statins are chemicals that are found in plants that are used to reduce people's cholesterol levels. Statins work by blocking a certain enzyme in the liver which is needed to make cholesterol.

The disadvantages of using Statins are;

  • They can cause liver damage,
  • Many side effects e.g. nausea, headaches etc.
  • Have to be used for life
  • High cost

The advantages of using Statins are;

  • Increase general health
  • Lower the chances of strokes and heart attacks
  • Reduces 25% total cholesterol
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