Diet & Deficiencies | Cambridge O Level Biology Revision Notes 2023

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 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 / 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

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 gums

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 in 3 children

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 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 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