Diet & Energy Content of Food (WJEC GCSE Biology: Combined Science)

• 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

• 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

• 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