More and more products claim to fight disease and boost wellbeing. But do 'functional foods' work?

After years of being blamed for people's expanding waistlines, Coca-Cola has joined forces with Nestlé to develop a calorie-burning fizzy drink. Enviga, which goes on sale in America next month and comes to Britain next year, is the latest in a growing array of "functional" foods and drinks which, the food companies behind them claim, will improve our health.

Broadly speaking, any food with a health benefit can be defined as functional, says Catherine Collins, the chief dietician at St George's Hospital, south London. "Cranberries, for example, have an innate health benefit because of the positive effect they have on infections in the urinary tract," she explains. "Now, however, most people use the term 'functional food' for food that has had health benefits thrust upon it."

Not so long ago, functional food meant cutting down on unhealthy components - for example, less or no fat, sugar or salt. Then food companies began fortifying foods with added vitamins and minerals. Today, the latest food technology enables them to put a broader range of natural and concocted health-giving components - so-called "positive additives" - into familiar products.

There are a number of different types of functional foods, each promising distinct health benefits. The best-known two are cholesterol-lowering spreads and probiotic yogurt drinks. Prebiotic foods are a fast-growing area. Then there are drinks such as Juice4Joints, containing glucosamine and chondroitin (ingredients said to help repair connective tissues, providing relief from arthritis).

Now, there's even a functional beer. It is claimed that the German brew Xan helps to reduce the risk of cancer as it contains 10 to 30 times normal levels of xanthohumol - a compound found naturally in hops that is thought to prevent some cancers. Czech researchers, meanwhile, have developed a non-alcoholic beer containing 10 times the normal amount of phytoestrogen to ease the effects of the menopause.

Small wonder, then, that by 2010 health-conscious Britons are expected to spend double the £1bn a year they currently do on functional foods, or "nutraceuticals", to use the unappetising term favoured by food companies.

Some claims made for functional foods have been evaluated independently, others have not. So what evidence is there to support promises made by the makers of functional products? More to the point; which - if any - actually work?

Why are these foods 'healthy'?

The health benefits claimed for functional foods are based on the positive additives contained by the various products. Typically, these are components extracted from a food in which they occur naturally. For example:

* Plant sterols are known to lower blood cholesterol, which is why they have been added to many functional spreads such as Benecol and Flora Pro-Activ

* Research shows that omega-3 fatty acids can help cognitive function and heart and eye health, which is why food companies have added it to eggs and dairy products .

* Insoluble fibre, found naturally in wheat and bran, can help to reduce the risk of breast and colon cancer.

* Soluble fibre, found naturally in psyllium plants, can help to lower the risk of cardiovascular disease.

* Positive additives can also be minerals such as selenium, which studies have found to benefit the immune system and help to regulate blood pressure. Waitrose recently introduced selenium-enriched bread.


What are they?

Canned drinks that help you to lose weight.

What's the theory?

Coca-Cola and Nestlé claim that extracts from green tea and caffeine contained in their new calorie-burning drink Enviga speed up the drinker's metabolic rate, which helps the body burn calories. In clinical trials, 32 people drinking three 355ml cans of the drink - equivalent to drinking three cups of black coffee - were found to burn an average of 106 calories as a result.

Do they work?

After news of the product's launch, some health experts warned that the drink could cause agitation in some consumers and that it might even pose a risk for people with heart conditions. However, Coca-Cola insisted: "We want to make clear that this is not a magic bullet to lose weight."


What is it?

Probiotic dairy products such as Yakult and Actimel aid digestion and gut health and improve general wellbeing, food companies claim.

What's the theory?

These products contain so-called "friendly bacteria" - lactobacillus acidophilus, to be precise - which help the existing friendly bacteria already in the stomach to fight bad bacteria.

Does it work?

The value of probiotic products is less clear-cut than cholesterol-lowering spreads.

According to Drug and Therapeutics Bulletin, a magazine for doctors published by the consumer watchdog Which?, no reliable research has yet proved that probiotic dairy products improve your general sense of wellbeing, as food companies claim.

There is some evidence to suggest that such products can help in certain cases, such as in young children with stomach upsets, or in diarrhoea caused by antibiotics and infections, or in preventing the flare-up of a known bowel disorder, according to Which?'s principal researcher Julie Lennard.

"The trouble is that it is as yet unclear which products work and which don't and for what condition, or even how much of a product is needed to have an effect," she says. "These products are perfectly safe to try - they won't do you any harm - but evidence of any claimed health benefit is patchy." Lennard also expresses concern that some probiotic products are high in sugar or saturated fat.

A report for the Food Standards Agency found that some of the "good bacteria" in probiotic products did not actually survive in the digestive system long enough to reach the parts they were supposed to help.

In spite of this, food companies continue to develop new probiotic products. The latest? Dancing Daisy, the UK's first probiotic semi-skimmed milk.


What is it?

Spreads such as Benecol and Flora Pro-Activ claim they can lower blood cholesterol.

What's the theory?

These products contain plant sterols and stanol esters, which can reduce the body's absorbtion of cholesterol.

Does it work?

Cholesterol-lowering claims for plant sterols have been researched and proven. The Government's expert committee on novel foods concluded that they were indeed effective in lowering cholesterol, but advised that foods to which they had been added - such as cholesterol-lowering spreads - "are suitable only for 'at risk' groups'; namely those who have been advised by their GP to reduce their blood cholesterol levels by altering their diet".

When judging the potential benefit of any functional food, it is essential to consider your particular circumstances. "It's important to remember that a food cannot be functional without the rest of a person's diet being healthy and balanced," Collins says. "It doesn't matter how many portions of Flora Pro-Activ you eat if you are obese - a condition clinically proven to increase your chance of getting cardiovascular disease and some cancers."


What are they?

While probiotic foods are designed to introduce more friendly bacteria to the body, prebiotics work by feeding the beneficial bacteria that are already in the gut.

What's the theory?

As the stomach is extremely acidic, some scientists claim that not enough of the friendly bacteria in probiotic drinks survive passing through it to improve the health of the large intestine, where most of the gut's bacteria actually live.

Do they work?

There is little consensus among experts on whether prebiotics can benefit health. However, given the concerns some have expressed about probiotics, the theory is regarded by many as sound. New prebiotic products include Little Squirts, a range of prebiotic spring waters for kids.


What is it?

Omega-3 is an essential fatty acid found naturally in oily fish. It can now be found in eggs, milk and dairy products.

What's the theory?

Omega-3 fatty acids are essential to promote brain and vision development and to protect against disease.

Does it work?

Research suggests that increasing omega-3 intake has benefits. However, always check the quantity of omega-3 in a functional food as some companies overstate the contribution their products can make. "An advertising campaign for Advance Omega-3 milk showed six pilchards being poured on to a bowl of cereal," Collins says. "But to get the equivalent of that much fish oil you would need to drink six litres of the milk - a quantity that would contain a high volume of fat."

If you consume more omega-3, cut your intake of omega-6, found in sunflower margarines and corn oil. Omega-6 will cancel any omega-3 effect.