Women find it harder to lose weight than men because their brains are wired differently, a new study reveals.
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Neurons that regulate appetite also control physical activity and energy expenditure in males - but not in females.
The findings could explain why women suffer higher rates of obesity , scientists say. They could also lead to gender-based diet regimes.
Previous research has shown men tend to be more successful than women at sticking to diet programmes and subsequently shedding more pounds .
But the new study shows that the brain controls physical activity, energy expenditure and weight gain in a different way from men to women.
This means it really could be harder for women to slim because of the vital role played by key brain hormones in the battle of the bulge.
In experiments on mice, researchers were able to transform obese males with increased appetite and reduced physical activity into lean, healthy specimens.
But the same transformation did not occur in the females, reports Molecular Metabolism.
Professor Lora Heisler, of Aberdeen University, said: "The World Health Organisation (WHO) reports higher rates of obesity in women worldwide - reaching twice the prevalence of men in some parts of the world.
"Currently there is no difference in how obesity is treated in men and women.
"However what we have discovered is the part of the brain that has a significant influence on how we use the calories that we eat is wired differently in males and females.
"This study reveals a sex difference in physical activity, energy expenditure and body weight is driven by a specific source of brain POMC peptides.
"This could have broad implications for medications used to combat obesity, which at present largely ignore the sex of the individual."
A study of 34,000 dieters by Slimming World found men lost more weight than women both in absolute terms and as a percentage of their body weight.
Men were also more likely to complete the programme.