Several leading American magazines have recently been carrying advertisements for a capsule called French Parad'ox. Its manufacturer, the French pharmaceutical company, Arkopharma, claims that it bestows the 'beneficial properties of red wine, without the disadvantages of alcohol'.

Demand for the capsules, which will soon be on sale in Britain, is based on the intriguing phenomenon called the 'French paradox': despite a penchant for fatty saucissons, buttery sauces and calorie-laden patisserie, the French have the lowest rate of deaths from coronary heart disease in the industrialised countries, apart from Japan.

The paradox has thrown nutrition experts into confusion. Epidemiological studies by august bodies such as the WHO and the OECD have shown that southern European countries with the legendary 'Mediterranean diet' - high in plant food, low in animal protein, saturated fat and sugar - tend to have less heart disease than northern European countries with fattier diets. The French, however, consume a relatively high amount of dairy products and a low amount of fruit and vegetables compared with Greece and Italy, for example.

For the past five years, Dr Serge Renaud, a leading scientist with the government-funded Institute of Health and Medical Research at Lyons, has been advancing the theory that the high French consumption of red wine may be at least part of the answer. So the French Parad'ox capsules contain what are believed to be the active ingredients in wine that protect against heart disease.

As early as 1786, doctors recognised that angina (heart pain) could be relieved by wine or spirits. During Prohibition in the United States in the Twenties, the only legal way to obtain red wine was on prescription for heart disease.

Now, according to Dr Renaud, 'all the studies show that a healthy diet for the heart is characterised by more fruit, less meat, more fish, less saturated fats. And certainly a moderate intake of alcohol - especially red wine at meals - is also an important part of the diet . . . By far the most potent drug to protect against all forms of mortality, not just coronary heart disease, is moderate wine consumption.'

His theory is based on the statistics of various countries' intake of items such as fats, fruits, vegetables and wine. Dr Renaud says that, when you look solely at food, France appears to contradict the rule that a high-fat diet leads to susceptibility to heart disease. 'But when you introduce just one parameter - wine - into the equation, you can show that France is no longer a paradox.'

Dr Renaud and his researchers are investigating the exact mechanism that renders red wine protective of the heart. To date, the theory is that the antioxidant effect of tannins and anthocyanins in grape skins, which distinguish red wine from other alcoholic drinks, prevent cholesterol depositions on the walls of the blood vessels.

Dr Renaud emphasises, however, that consumption of red wine is not an alternative to the health-giving Mediterranean diet - it is just an underemphasised part of the package. For instance, the inhabitants of Toulouse, who drink large quantities of red wine and eat a more or less Mediterranean diet, are the healthiest in France; but in northern Nancy - though groups drinking moderate amounts of wine appear to cut their risk of heart disease by almost 50 per cent - people generally are not so healthy, due probably to a fattier diet containing much less bread, fruit and vegetables.

Dr Renaud recommends a quarter of a bottle of red wine (two glasses) a day with meals as the ideal amount to protect not only against against heart disease but also cancer. A half-bottle does not significantly increase the protective effect, he says, and those who drink a litre will increase risks from other diseases such as cirrhosis.

His view was echoed earlier this year by Danish researchers at the Copenhagen Institute of Preventive Medicine, who showed that moderate drinkers are likely to live longer than total abstainers or heavy drinkers. But is a gin and tonic or a beer as good as a glass of red wine? Dr Renaud thinks not. An American study in 1982 of rabbits given red and white wine, whisky and beer resulted in the red-wine rabbits suffering less arteriosclerosis (thickening of the artery walls). Dr Renaud says other alcohols produce what is known as 'the rebound effect': they diminish the risk of thrombosis, but may leave the drinker predisposed to haemorrhages.

Tests on rats suggested that straight- alcohol drinkers suffered the rebound effect, red-wine drinkers did not, and white-wine drinkers came somewhere in between. 'Binge drinking leads to a huge risk of almost any health problem,' he says. 'But moderate consumption of red wine protects tremendously, and rapidly, against heart disease and, possibly, other chronic diseases, without side-effects.'

This is music to the ears of the French and American wine industries, which are facing increasing pressure to publish health warnings with their advertisements. But the latter is more likely to suffer from the incursions of the French Parad'ox capsule.

While French people, and to some extent the British, are likely to drink more red wine, the capsule may fare better in North America, where it is easier to deliver messages about weight control and health in the form of low-fat spreads and manic exercise programmes. In more northern European countries, where a glass of beer or vodka may be the regular tipple, the capsule may become a nibble with the peanuts and pretzels.