A new study tries to answer the question that has perplexed women for generations, why they store fat more efficiently than men.
It has long been suspected that female sex hormones are responsible for their ability to store fat more efficiently than men, despite eating proportionally fewer calories.
Now, a University of New South Wales (UNSW) research review has for the first time drawn a link between one hormone, oestrogen, and its impact on fat storage for childbearing.
On an average, women have 6 to 11 percent more body fat than men.
Previous studies have shown that oestrogen reduces a woman's ability to burn energy after eating, resulting in more fat being stored around the body.
The review suggests that the likely reason is oestrogen's impact on fat storage for childbearing.
"Female puberty and early pregnancy, times of increased oestrogen, could be seen as states of efficient fat storage in preparation for fertility, foetal development and lactation," the study's author Associate Professor Anthony O'Sullivan, from UNSW's St George Clinical School, said.
The findings may have implications for dietary advice given to women during pregnancy and the design of exercise regimes.
"From an energy balance point of view there is no explanation why women should be fatter than men, particularly since men consume more calories proportionately," O'Sullivan said.
He added: "In fact, women burn off more fat than men during exercise, but they don't lose body fat with exercise as much suggesting women are more efficient fat storers at other times. The question is why does this paradox exist?"
O'Sullivan said that an obvious answer is that fat storage by women gives an evolutionary benefit. However, additional research was needed to provide more insights into the role of oestrogen in the regulation of body fat.
O'Sullivan said that while oestrogen's effects on postprandial fatty acid oxidation provide a mechanism for fat accumulation, the findings do not explain why some women are obese.
He said that factors contributing to obesity are complex and include both genetic and environmental factors.
The study appears in Obesity Reviews, the journal of the prestigious International Association for the Study of Obesity.