New research suggests that for every 11 pounds (5 kilograms) a woman gains after being diagnosed with breast cancer, the chances of it proving fatal go up 14 per cent.

The study is by no means definitive, but gives the strongest evidence yet that controlling weight - a good idea anytime in life - may be especially important after breast cancer.

"There was a significant trend between increasing levels of weight gain and higher mortality," said Hazel Nichols, a doctoral student at Johns Hopkins Bloomberg School of Public Health.

"Lifestyle factors, the things you incorporate after a breast cancer diagnosis such as diet and exercise, do show potential to influence survival."

Nichols led the study and reported results on Friday at an American Association for Cancer Research conference in Philadelphia.

Researchers started with 4,021 women in Wisconsin, Massachusetts and New Hampshire who had been diagnosed with breast cancer from 1988 to 2001. They gave information on their height, weight, family history and breast cancer risk factors during telephone interviews.

From 1998 to 2001, all survivors were mailed surveys asking for updated information on these factors and lifestyle habits like exercise and diet.

After an average of six years of follow-up since their diagnoses, 121 breast cancer deaths and 428 non-breast cancer deaths had occurred. For every 11 pounds (5 kilograms) of weight gain after diagnosis, the risk of death from breast cancer or other causes increased by 14 per cent.