Women battling the bulge may be fighting more than just sweet temptation, according to new research showing a fat gene could be to blame.
Almost a third of women are believed to be affected by a mutated gene that leads to the development of fatty tissue, researchers at Maastricht University in Holland have discovered.
Women who have the gender-specific impaired DNA, called MMP2, are more than two-and-a-half times more likely to gain 15kg or more, the Daily Mail reported.
The researchers traced the weight gains and losses of more than 5000 men and women for 10 years, and analysed the participants' DNA for genes implicated in obesity.
Researcher Dr Freek Bouwman said while MMP2 was common in women who had gained weight, it wasn't in men, the Daily Mail reported.
However, if a woman had MMP2 it did not mean they were doomed to put on weight, said Waitemata specialist in endocrinology, diabetes and general medicine Dr Steven Miller.
"The investigators also observed women with the MMP2 mutation who did not gain excess weight, and excess weight gain in women without the MMP2 mutation.
"There are also numerous other factors that influence body weight to a greater or lesser degree," he said.
Genes were important in understanding an individual's risk of becoming overweight or obese, but behaviour and environment, such as food choices and physical activity levels also made contributions "that may be greater than any genetic predisposition", Dr Miller said.
Men don't escape completely, as the study showed they have their own fat gene that causes them to binge on junk food, said the researchers.
A flawed version of a known gene called FTO makes them gain weight, with those carrying it almost twice as likely to have gained more than a stone.
Named 'the junk food gene', it increases cravings for sugary and fatty foods, and men who have it can eat about 100 calories more per meal than average - - the equivalent of a small Kit Kat.
Over a week, the extra food eaten amounts to 2100 calories or a whole day's food.
"If you consume more energy than your body uses, over time the body will store the extra energy (as fat), and weight will rise. If less energy is taken in than is used, then the body's energy stores are used as a fuel and weight will fall," said Dr Miller.
He advised individuals with a genetic predisposition to obesity to combine increased exercise with caloric restriction in order to lose weight.