BEING slim is not enough to ward off breast cancer.
It's exercise that is crucial - whatever your weight, say experts.
A study has found that being unfit raises a woman's risk of the disease, whether she is fat or thin.
The researchers warned that women who were slim should not be complacent, because it was also important to be active.
Even ordinary, everyday activities such as carrying the shopping home and playing with children would help, the world's leading obesity conference heard.
And the Swedish researchers said it was "never too late" to become more active.
They quizzed more than 19 000 women with an average age of 56 about their health and habits, including how much exercise they got, then checked on their health again 13 years later.
About 900 of the participants had been diagnosed with breast cancer in that time.
Analysis showed their odds of developing the disease were clearly linked to how active they were.
Those who did the least exercise were 40 percent more likely to have developed breast cancer than those who did the most, the International Congress on Obesity heard.
Crucially, the link with exercise applied whatever their weight.
Researcher Ylva Trolle Lagerros, an obesity doctor from the Karolinska Institute in Stockholm, said that women did not necessarily need to sweat it out in the gym to see a benefit - everyday activities such as walking to work, playing with grandchildren and gardening all counted.
The professor said: "Usually what you do in the gym is only a small part of your total activity for the day. Your body doesn't really care if you are carrying groceries home or if you are at the gym; it is the total amount of exercise in the day that matters, independent of where you get it."
Professor Trolle Lagerros found that being overweight raised a woman's risk of the disease, even if she exercised. Being obese raised the odds of breast cancer by 58 percent, while merely being overweight increased the likelihood by 20 percent.