Salt Lake City: Women who have extra fat around their middle may enjoy significant health advantages over slimmer hourglass-shaped females, says a 37-nation study in the journal, Current Anthropology.

Elizabeth Cashdan, a Utah University anthropologist, says that being thinner could mean missing out on the hormones that make women physically stronger, more competitive and better able to deal with stress.

Her study shows that across the world, women’s average waist-to-hip ratio is higher than the magic number of 0.7, the upper threshold of a classic hourglass figure – and the shape that anthropologists believe indicate female fertility to the opposite sex.

It is thought that bigger women have more androgens, a class of hormones that includes testosterone.Androgens increase the waist-to-hip ratio in women by boosting levels of visceral fat, which is carried around the waist. Raised levels of androgens are linked to increased strength, stamina and competitiveness in women, says Cashdan.

Trading the benefits of a thin waist for better ability to be independently resourceful may prove a good deal in many societies, she adds – and this in turn may alter male preferences.

Thus, in Japan, Portugal and Greece, where women tend to be less economically independent, the men say they place a higher value on a thin waist than do men in Britain or Denmark, where there tends to be more sexual equality.

And in some non-Western societies where food is scarce and women bear most of the responsibility for finding it, men prefer larger waist-to-hip ratios.

“Whether men prefer a waist-to-hip ratio associated with lower or higher androgen levels should depend on the degree to which they want their mates to be strong, tough, economically successful and politically competitive,” says Cashdan .