The Big Question: What are superfoods, and are they really so good for our health?

Why are we asking this question now?

The term superfoods entered the language in the 1990s to denote foods packed with nutrients that supposedly have health-giving properties. Some are exotic, such as alfa alfa, spirulina and wheatgrass, and some prosaic such as broccoli, beans and beetroot.

The latest addition to the pantheon - watercress - was announced by scientists yesterday. Researchers at the University of Ulster, who fed large quantities of the peppery salad leaf to 60 men and women daily for eight weeks, showed it increased antioxidants in their blood and decreased DNA damage to their white blood cells. They concluded, in the American Journal of Clinical Nutrition: "The results support the theory that consumption of watercress can be linked to a reduced risk of cancer."

Are the watercress claims credible?

Not really. The research was funded by British watercress suppliers. Karol Sikora, professor of cancer medicine at Imperial College, delivered a delicious putdown yesterday.

He said: "The real problem is that it's not watercress specific - there's nothing magic there. The press release, from what is essentially a marketing association, is grossly overstated. We know that fruits and vegetables all do affect DNA damage, hence the five-a-day strategy to prevent cancer. There is absolutely nothing special about watercress."

What does the term superfood mean?

There is no definition of a superfood - and no definitive list. New candidates are regularly put forward, usually backed by a large dollop of marketing hype. Among the best known are oily fish (salmon, mackerel, tuna, etc) for omega 3 fatty acids, blueberries for vitamin C, brazil nuts for selenium, carrots for beta-carotene, tomatoes for lycopene, olive oil for the anti-inflammatory compound oleocanthal, red wine for resveratrol and garlic.

Health claims range from improving IQ to preventing cancer and heart disease, increasing sporting ability and enhancing appearance. Although their benefits are often overstated there is little doubt that they are a worthwhile addition to any diet.

Why not take vitamin pills and nutritional supplements instead?

Because eating is a pleasure - swallowing pills is not. Research on vitamins has also yielded confusing results with claims showing they protect against heart disease or cancer soon contradicted by new studies showing the opposite.

The argument for superfoods, which contain the vitamins in their raw unprocessed state, is that they are natural food sources, safe and easily absorbed. Calcium, for example, sold as calcium carbonate - chalk - is difficult to digest. In a glass of (low-fat) milk it is easily absorbed.

Does designating something as a superfood have an effect?

Yes. Sales of blueberries soared a couple of years ago after claims the fruit could help protect the body from a range of illnesses. Nutritionists say blueberries are bursting with vitamin C and offer one of the best sources of the antioxidant anthocyanin, believed to help keep the heart healthy and maintain youthful skin. In summer 2004, the US Department of Agriculture researchers revealed blueberries contained pterostilbene, which could be as effective as prescription drugs in helping lower cholesterol. Blackcurrant growers in the UK hit back with a campaign to promote the benefits of their "forgotten fruit", saying the berries contained more antioxidants than their foreign-grown rivals.

Which was the first superfood?

Hard to say as the term has been in widespread use only for a decade. But one vegetable with a claim to the title must be spinach. Sales peaked in the 1950s helped by the popularity of Popeye, the cartoon character who gulped down tins of the stuff to give him strength. A generation of children forced to eat it were turned off the dark green mush, some complaining they viewed it as a form of torture.

Half a century later, the leafy vegetable has shed its unlovely image to become one of Britain's trendiest foods. Sales soared 30 per cent last year after celebrity chefs and health gurus extolled its high vitamin and mineral content.

Which is the most widely used superfood?

Tea. It is drunk by millions, not because its healthy but because it is soothing, thirst-quenching and delicious. In recent years, research has shown it is high in antioxidants and may offer protection against cancer and heart disease. However, adding milk and, worse, sugar, may negate its health-giving benefits. For people who drink a lot of tea, the dash of milk in each cup adds up and can contribute significantly to the amount of fat in their diet increasing the risk of heart disease and cancelling the protective effect of the antioxidants.

Do scientists always get it right about superfoods?

No. One of the biggest upsets, scientifically speaking, occurred last year when research published in the British Medical Journal suggested the advice to eat more oily fish to benefit the heart, which had held sway for 20 years, was wrong. A review of 89 studies of omega 3 fatty acids, the key constituent of fish oils thought to protect against heart disease, found no clear evidence they were any help.

The claim that a diet high in fibre protects against bowel cancer, which has been promulgated since the 1970s, was based on the observation that the cancer was almost unknown in Africa, where the staple diet is fibre-rich vegetables and grains. However, epidemiological studies have proved inconclusive and researchers now think the presence of sugar in the gut, rather than the absence of fibre, may be the key factor.

What should we do about superfoods?

Eat them, enjoy them, but don't regard them as medicine - it will spoil your appetite. So-called superfoods, like all other foods, are best included as part of a balanced diet. The surest route to better health is to alter this balance gently. Up to one third of cancers and a high proportion of heart disease is thought to be associated with diet, and modifying the food we eat is one of the best defences against them. The standard advice is still the best - eat more fruit and vegetables, more starch and carbohydrate and less animal protein. Then try a square or two of chocolate - just for the pleasure it gives.

Should we increase the quantity of superfoods we eat?

Yes...

* They provide extra amounts of vitamins, minerals and fatty acids essential to growth and to the repair of DNA damage in the cells

* They offer more protection against cancer, heart disease and chronic conditions, such as dementia, than ordinary foods

* The nutrients they contain are easier to absorb than vitamin pills and nutritional supplements - as well as being tastier

No...

* Most superfoods contain the same nutrients as other foods, but in slightly higher quantities, so you need slightly less of them

* If you eat a balanced diet you will get all the vitamins, minerals and other nutrients you need to maintain your health

* There is no point in increasing your intake of vitamins and minerals unless you are deficient - the body simply excretes the excess