Diet & Energy Content of Food (WJEC GCSE Biology)
Revision Note
The Need for a Balanced Diet
A balanced diet consists of all of the food groups in the correct proportions
The necessary key food groups are:
Carbohydrates
Proteins
Lipids
Dietary Fibre
Vitamins
Minerals (mineral ions)
Water
Dietary elements functions and sources table
Dietary element | Function | Sources |
|---|---|---|
Iron | Iron is used to make haemoglobin, which is an essential chemical found in red blood cells that binds to oxygen and carries it around the body in the blood | Red meat, liver, leafy green vegetables like spinach |
Vitamin C | Forms an essential part of collagen protein, which makes up skin, hair, gums and bones | Citrus fruit, strawberries, green vegetables |
Fibre | Provides bulk (roughage) for the intestine to push food through it | Vegetables, whole grains |
Water | Needed for chemical reactions to take place in cells | Water, juice, milk, fruits and vegetables |
The nutritional requirements for individuals will vary throughout their lifetime
An individual will still require the same key food groups, but in different quantities depending on a number of factors such as age, height, sex, activity levels, pregnancy and breastfeeding
Variations in dietary requirements table
| Dietary needs |
|---|---|
Age | The amount of energy that young people need increases towards adulthood as this energy is needed for growth. Children need a higher proportion of protein in their diet than adults as this is required for growth. Energy needs of adults decrease as they age |
Activity levels | The more active, the more energy is required for movement as muscles are contracting more and respiring faster |
Pregnancy | During pregnancy, energy requirements increase as energy is needed to support the growth of the developing fetus, as well as the larger mass that the mother needs to carry around. Extra calcium and iron are also needed in the diet to help build the bones, teeth and blood of the fetus |
Breastfeeding | Energy requirements increase and extra calcium is still needed to make high quality breast milk |
Sex | Male average energy requirements tend to exceed that of females due to them having a larger proportion of muscle compared to fat |
Energy Content of Different Foods
Respiration is the chemical reaction carried out by all living organisms to provide energy for life processes as part of metabolism
The energy released during respiration comes from food, specifically carbohydrates and fats
Carbohydrates break down to glucose during digestion, which is a reactant for respiration
Fats contain a very high density of energy-storing chemical bonds
Foods that contain different quantities of carbohydrates or fats release different amounts of energy for the body to use, for example:
Sugary foods, like sweets, increase the level of glucose in the blood very quicky and can cause high energy hyperactivity as a result
Foods like pasta or potatoes contain the carbohydrate starch that breaks down slowly and releases glucose in the blood over a longer time span, this is why many athletes consume these foods before they compete
In a balanced diet, the quantity of fats and carbohydrates consumed would match the energy requirements of the person, such as the level of exercise
Consuming too many carbohydrates or fats for the energy requirements leads to the body storing the excess
Carbohydrates are stored as glycogen in the liver and muscle cells to be released when the level of glucose in the blood falls too low
Excess fats are stored under the skin and around organs
Too much fat storage in this way leads to obesity
Unhealthy foods diagram
Consuming too many foods high in fats and sugars can lead to obesity
Effects of Excess Sugar, Fat & Salt
Having an unbalanced diet can lead to malnutrition
Malnutrition can cause a variety of different health problems in humans
This is particularly linked to consuming too much sugar, fats and salt
Unbalanced diet causes and health effects table
Cause | Effect on health |
|---|---|
Excess sugar | Type 2 diabetes, obesity, tooth decay |
Excess fat | Obesity, heart disease, circulatory disease |
Excess salt | High blood pressure |
Examiner Tips and Tricks
You do not need to be able to explain these health effects in a lot of detail here, although heart disease does come up in topic 1.4 and type 2 diabetes is described in more detail in topic 2.5.
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