Do their <i>derri&egrave;res</i> look big? Battle of the bulge is all in the French mind

The typical French woman is slim and thinks that she is fat. The typical British woman is plump but is convinced that she is thin.

A French survey has charted wide discrepancies in the average weight of men and women in different European countries. The survey also finds that attitudes to weight – especially women's attitudes – vary enormously from one country to another. French women – whether the politician Rachida Dati, singer Vanessa Paradis or the simple mademoiselle dans la rue – are the thinnest in the EU but worry about their weight more than women in any other country. Britain has, on average, the most comfortably sized women in the EU but British women are also, on the whole, comfortable with their size (second only to the Danes). In other words, the actress Audrey Tautou thinks she looks like Susan Boyle and Susan Boyle thinks that she looks like Audrey Tautou.

A worldwide bestseller by Mireille Guiliano in 2004 was entitled French Women Don't Get Fat. It should perhaps be renamed French Women May Not Get Fat But They Think They Do.

The author of the study, Thibaut de Saint Pol, says that his research suggests that average national weight is not just a question of diet or exercise or genetics. It is strongly influenced by cultural differences and national attitudes to what constitutes an acceptably slender, or attractive, or – in the case of men – powerful body. In some social groups, in some countries, such as Greece, he points out, male fatness is still regarded as a symbol of power or strength.

French women are thin partly because they come under intense pressure from French men, but also from other French women, to stay thin. "What people consider to be the ideal weight in France is lower than in other countries," M. Saint Pol said. "If a French person who feels fat were to go to the United States, he or she probably wouldn't feel fat any more."

M. Saint Pol's study is published in this month's edition of Populations et Société, the newsletter of the French demographic institute, INED. The weight comparisons are based on adult body-mass index (BMI), the measure recommended by the World Health Organisation. To discover your BMI, you divide your weight in kilograms by your height in metres squared. A BMI below 18.5 is dangerously "underweight". The range 18.5 to 25 is ideal. Between 25 and 30 is "overweight". Above 30 is "obese".

French women tip the scales at 23.2, the slimmest in the EU. British women have, on average, a BMI of 26.2, just into the "overweight" range.

The survey suggests, unsurprisingly, that men across the EU are less concerned with their weight than women. Only French and Dutch men are, on average, within the ideal weight band. All the rest are overweight, with British men tipping the scales as the third plumpest, behind the Greeks and Finns.

Mireille Guiliano argues in her book that French women are slender not because they eat less but because they eat better and because they live busy, active lives.

French women have tended, traditionally, to drink less and not to eat fast foods. All of this is changing, however. Guiliano has herself admitted that her description of French womanhood is true mostly of the urban or suburban middle classes and above. A visit to any rural supermarket in France will reveal outsize male and female figures to rival those in Britain or the US. French surveys also suggest that binge-drinking and fast-food eating are rising sharply, among both young men and women. Either cultural attitudes to body weight are shifting in France or the burden of guilt is rising.