The last few yeards have seen a huge increase in the marketing of so-called 'functional foods'. From cholesterol-reducing spreads and yoghurts to drinks packed with friendly bacteria, it seems that the supermarket shelves are bursting with foods that are specially designed to do us good.

It could be said, of course, that all foods are functional to some extent, as any food helps to fill us up and provide us with the nutrients and energy to keep us going.

But the term 'functional foods' was coined in Japan in the 1980s to describe foods that have been purposely produced or specially fortified to have particular health-giving properties.

Perhaps the most high-profile types of funtional foods are spreads, yoghurt and milk products designed to help cut cholesterol. They contain substances called plant-sterols, chemicals that are not absorbed by the body and which can help to reduce the amount of cholesterol we absorb from our diet.

If you are concerned about your digestive system, there are lots of probiotic products on the market to help keep it running smoothly. Often yoghurt-based, these aim to give you a daily dose of good bacteria in the gut that may be upset by modern diets, medication or antibiotics. It is also claimed that a regular intake of probiotics can help to boost your immune system, as well as increase energy and vitality.

Although many of the products have only been around for a few years, functional foods are not particularly new. Breakfast cereals have been fortified with vitamins for many years, and the beneficial effects of probiotics have been talked about for nearly a century.

But now there are a new breed of products that have added extras to help people get all the essential nutrients they need. Some types of bottled water and fruit juice have added calcium, some kinds of squash come with added fibre and for those people who are not eating enough oily fish, you can buy eggs that contain high levels of omega-3 fatty acids.

All of these foods claim that their added extras have health benefits and many studies suggest that, if eaten reularly, they can have the desired effect. But it's important to remember that even if you use these products to boost your health, they are no substitute for a healthy, balanced diet.