A balanced diet is one that contains the correct amounts of all the necessary nutrients needed for healthy growth and activity. An imbalanced or poor diet can contain too much or too little of a particular nutrient. If you have too little of a particular nutrient, we say that you have a deficiency in that nutrient. For example, fibre is needed to keep food moving through the intestines easily, and people who have a fibre deficiency in their diet may get constipation.

Mineral deficiencies

Goitre, a neck swelling caused by iodine deficiency

You only need small amounts of the different minerals in your diet to stay healthy, but mineral deficiencies can make you ill. For example:

• iron deficiency can cause anaemia, where there are too few red blood cells
• iodine deficiency can cause a swelling in the neck called goitre

Vitamin deficiencies

Bleeding gums and loose teeth caused by scurvy

Like minerals, you only need small amounts of the different vitamins in your diet to stay healthy, but you become ill if you do not get enough. For example:

• vitamin A deficiency can cause blindness
• vitamin C deficiency causes scurvy, which makes the gums bleed
• vitamin D deficiency causes rickets, which makes the legs bow outwards in growing children