A Franco-US study has discovered the secret of why the French stay slim on rich diets: they eat less.

A group of researchers from France’s CNRS research institute and the University of Pennsylvania have compared restaurant eating habits, cookery book measurements and prepared meals in supermarkets – in both countries.

Their results, published in the September issue of Psychological Science , show that only seven per cent of French people are obese, compared to 22 per cent of Americans. Despite higher cholesterol levels in the French diet, rates of heart disease are lower than in the US.

The French are also served much smaller portions – an average 9.8 ounces, than their US counterparts, who receive an average of 12.2 ounces, or around 25 per cent more on their plates. Also ready-made meals in French supermarkets are smaller than those on sale in the US.

Paul Rozin, professor of psychology at the University of Pennsylvania, said while the French eat more fat than Americans, they probably eat slightly fewer calories, which over a few years can amount to substantial differences in weight.

Observations in French restaurants showed that the French took longer to eat their meals, which in turn meant they often felt full with less food in their stomach.

Cans of soft drinks are sold in cans over 50 per cent larger in the US than France and US hotdogs are 63 per cent bigger.

“The French, with smaller portion sizes and probably lower level of snacking, have created a friendlier environment oriented toward moderation. The American emphasis on changing the individual to control weight has been generally unsuccessful,” added Rozin. Details: crns.fr