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Diet & Deficiencies (Cambridge O Level Biology)
Revision Note
Balanced Diet
- A balanced diet consists of all of the food groups in the correct proportions
- The necessary food groups are:
- Carbohydrates
- Proteins
- Lipids
- Vitamins
- Minerals
- Dietary Fibre
- Water
- A balanced diet provides everything needed for successful growth and repair of tissues
- There must also be enough energy that can be used for metabolic processes
- There must also be enough roughage to maintain the function of the digestive tract
- A diet can be unbalanced by having too little of a food group (called a deficiency) or by having too much (a surplus)
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, oil, 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 Sources and Functions Table
| Vitamin / Mineral | Function | Sources |
| Vitamin C | Forms an essential part of collagen protein, which makes up skin, hair, gums, and bones. Deficiency causes scurvy. | Citrus fruits, strawberries, green vegetables |
| Vitamin D | Helps the body absorb calcium and so required for strong bones and teeth. | Oily fish, eggs, liver, dairy products. Also made naturally by cells in sunlight. |
| Calcium | Needed for strong teeth and bones and is involved in the clotting of blood. Deficiency can lead to osteoporosis later in life. | Milk, cheese, eggs |
| Iron | Needed to make haemoglobin, the pigment in red blood cells that transports oxygen. | Red meat, liver, leafy green vegetables like spinach |
Varying Dietary Needs of Individuals Table
| Factor | Dietary needs | Age |
| Growth | A higher proportion of protein | Children |
| Activity levels | More energy is required for movement as muscles are contracting more and respiring faster | All ages |
| Pregnancy | Extra energy and calcium are needed to support the growth of the developing fetus and the larger mass of the mother | Pregnant women |
| Breastfeeding | Extra energy and calcium still needed to make high-quality breast milk | Breastfeeding women |
Scurvy, Rickets & Anaemia
Scurvy
Bleeding gums caused by scurvy
Centers for Disease Control and Prevention, Public domain, via Wikimedia Commons
- Scurvy is the name for a severe vitamin C deficiency
- It is caused by a lack of vitamin C in the diet for over 3 months
- Its symptoms include:
- Anaemia
- Exhaustion
- Spontaneous bleeding
- Pain in the limbs
- Swelling
- Gum ulcerations
- Tooth loss
- It 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
- Scurvy can be treated with oral or intravenous vitamin C supplements
Rickets
Rickets as seen in three children
Friends' Relief Mission, Vienna, CC BY 4.0, via Wikimedia Commons
- Rickets is a condition in children characterised by poor bone development
- Symptoms include:
- Bone pain
- Lack of bone growth
- Soft, weak bones (sometimes causing deformities)
- Rickets is caused by a severe lack of vitamin D or a lack of calcium in the diet
- Vitamin D is required for the absorption of calcium into the body
- Calcium is a key component of bones and teeth
- Vitamin D is required for the absorption of calcium into the body
- Vitamin D mostly comes from exposure to sunlight but it can also be found in some foods (fish, eggs and butter)
- The treatment for rickets is to increase consumption of foods containing calcium and vitamin D
- Alternatively, vitamin D supplements can be prescribed
Anaemia
- Anaemia is caused by a lack of iron in the diet
- Iron is an important component of the blood pigment haemoglobin
- Haemoglobin carries oxygen to all cells and tissues inside red blood cells
- A lack of iron in the diet can cause a decrease in the number of red blood cells circulating in the blood
- This can cause the person's skin to appear pale (called 'pallor')
- Anaemia can also cause fatigue and exhaustion because there is not enough haemoglobin to carry oxygen to respiring cells all over the body
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