Our nutritional needs change as we age - but the link between a good diet and staying healthy remains.

This is because every process in our bodies requires a specific mix of proteins, carbohydrates, fats, vitamins, minerals, trace elements and water to work correctly.

Dozens of nutrients are involved and their relationship with each other is often critical. For example, vitamin C makes it easier for the body to absorb iron.

When our diet is inadequate - that is, we aren't taking in the nutrients we need - problems occur. The health of our cardiovascular system and our bones depends on a good, balanced diet. Diet has also been linked to cataracts and age-related macular degeneration (AMD), which are the biggest cause of untreatable blindness among older people.

Here's some more examples of health problems and the deficiencies that cause them:

• Arteries can become clogged with 'bad' cholesterol (low density lipoproteins or LDL) as a result of eating too much saturated fat, (other nutrients protect the arteries).
• Anaemia can occur when the blood does not receive enough iron, vitamin B12 and folic acid.
• The immune system depends on adequate intakes of vitamin C, zinc and other nutrients.
• Poor wound healing may be the result of zinc deficiency.
• About one third of all cancers, including those of the lung, stomach, oesophagus, colon and breast, are thought to be linked to diet.
• Parkinson's and similar degenerative diseases are linked in part to oxidative damage, which may be caused by diet.
• Depression can be caused by lack of B vitamins.

Last but not least, obesity is the biggest nutritional disorder in the developed world and is especially common in middle-aged and older people. It increases the risk of stroke, coronary heart disease, type 2 diabetes, osteoarthritis, colon and breast cancer.