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The three nutrients required in the largest quantities are:

• carbohydrates
• proteins
• lipids (fats and oils)

Other nutrients required in smaller quantities are:

• vitamins
• minerals
• dietary fibre
• water

To obtain these nutrients humans, as omnivores, eat a varied diet.

Carbohydrates, proteins and lipids

Here are the sources and main functions of the different components in a balanced diet.

Vitamins

Vitamins are only needed in small amounts to maintain a healthy body. A lack of vitamins in the diet leads to deficiency symptoms.

Vitamin C

Vitamin C (ascorbic acid) is needed to help heal wounds and maintain healthy connective tissue (which gives support to other tissues and organs).

Good sources of vitamin C include:

• citrus fruits (such as oranges, lemons and limes)
• leafy green vegetables (such as sprouts and broccoli)

Vitamin C deficiency leads to scurvy. The symptoms of scurvy include bleeding and swelling of the gums, loss of teeth, tiredness and muscle and joint pain.

Mineral ions

Like vitamins, mineral ions are only needed in small amounts to maintain a healthy body. A lack of the correct mineral ions in the diet also leads to deficiency symptoms.

Iron

Iron is needed to produce haemoglobin, found in red blood cells.

Good sources of iron include:

• liver
• red meat
• beans and nuts
• dried fruits such as dried apricots

Iron deficiency causes anaemia. People with anaemia become tired and weak because their blood does not transport enough oxygen.

Water and dietary fibre

Water and dietary fibre (roughage) are also important components in the diet.

Water

Sources of water include:

• food
• drinks
• metabolic processes, such as aerobic respiration

Dietary fibre

Sources of fibre include:

• fruit
• vegetables
• cereals

Dietary fibre is important because it provides bulk, which helps the walls of the intestine move food and faeces along the gut. Lack of dietary fibre can lead to constipation.