Diet & Deficiencies (Cambridge International IGCSE Biology)
Balanced diet
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7.1.1· Describe what is meant by a balanced diet State the principal dietary sources and describe the importance of: (a) carbohydrates (b) fats and oils (c) proteins (d) vitamins, limited to C and D (e) mineral ions, limited to calcium and iron (f) fibre (roughage) (g) water
Balanced diet
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A balanced diet consists of all of the food groups in the correct proportions
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The necessary food groups are:
- carbohydrates
- proteins
- lipids
- vitamins
- minerals
- dietary fibre
- water
Food groups table
| Food type | Function | Sources |
|---|---|---|
| Carbohydrate | Source of energy | Bread, cereals, pasta, rice, potatoes |
| Protein | Growth and repair | Meat, fish, eggs, pulses, nuts |
| Lipid | Insulation and energy storage | Butter, oils, nuts |
| Dietary fibre | Provides bulk (roughage) for the intestine to push food through it | Vegetables, whole grains |
| Vitamins | Needed in small quantities to maintain health | Fruits and vegetables |
| Minerals | Needed in small quantities to maintain health | Fruits and vegetables, meats, dairy products |
| Water | Needed for chemical reactions to take place in cells | Water, juice, milk, fruits and vegetables |
Vitamin and mineral requirements table
| Vitamin / mineral | Function | Sources |
|---|---|---|
| Vitamin C | Forms an essential part of collagen protein, which is found in skin, hair, gums and bones | Citrus fruit, strawberries, green vegetables |
| Vitamin D | Helps the body to absorb calcium (and so required for strong bones and teeth, see below) | Oily fish, eggs, liver, dairy products, also made naturally by the body in sunlight |
| Calcium | Needed for strong bones and teeth and involved in blood clotting. Deficiency can lead to osteoporosis later in life. | Milk, cheese, eggs |
| Iron | Needed to make haemoglobin, the pigment in red blood cells that binds oxygen to transport it around the body | Red meat, liver, leafy green vegetables (e.g. spinach) |
Varying dietary needs of individuals table
| Factor | 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 compared to adults as this nutrient is required for growth. Energy needs of adults decrease as they age. |
| Activity levels | The more active, the more energy required for movement as muscles are respiring more to contracting more. |
| Pregnancy | During pregnancy, energy requirements increase as energy is needed to support the growth of the developing foetus, as well as the increased 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 foetus. |
| Breastfeeding | Energy requirements increase and extra calcium still needed to make high quality breast milk |
Scurvy & rickets
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7.1.1· State the causes of scurvy and rickets
Scurvy
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Scurvy is the name for a severe vitamin C deficiency
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Scurvy is caused by a lack of vitamin C in the diet for over 3 months
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Symptoms of scurvy include:
- anaemia
- exhaustion
- spontaneous bleeding
- pain in the limbs
- swelling
- gum ulcerations
- tooth loss
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Scurvy is a condition that was commonly seen in sailors between the 15th to 18th centuries
- Long sea voyages made it very hard to access a ready supply of fresh produce rich in Vitamin C
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Scurvy can be treated with oral or intravenous vitamin C supplements
Rickets
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Rickets is a condition in children characterised by poor bone development
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Symptoms of rickets include:
- bone pain
- lack of bone growth
- soft, weak bones (sometimes causing deformities)
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Rickets can be caused by a severe lack of vitamin D
- Vitamin D is required for the absorption of calcium into the body; calcium is a key component of bones and teeth
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The body can naturally produce a form of Vitamin D when a substance in the skin (derived from cholesterol) is exposed to UV radiation in sunlight
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Vitamin D can also be found in some foods e.g. fish, eggs and butter
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The treatment for rickets is to increase consumption of foods containing calcium and vitamin D
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Alternatively, vitamin D supplements can be prescribed
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