But the study, which is collecting information on more than 18,000 breast cancer survivors in the U.S. and China, also had a silver lining: most won’t pack on a large number pounds, at least not so many as to put their health at risk.
“I thought it was quite impressive,” says Mary Jo Nissen, PhD, senior health services researcher at Park Nicollet Health Services in Minneapolis, Minn.
“It was sort of a ‘good news, bad news’ message, that moderate weight gain did not seem to be predictive of increased risk of recurrence or death,” says Nissen, who has also studied weight gain after breast cancer, but was not involved in the current research.
“But the bad news, of course, is that there is a real risk for those women who gain a lot of weight.”
“There have been previous reports consistent with this finding, but this seems to be a large, thoroughly analyzed study so I think it’s important,” Nissen tells WebMD.
Weight Gain After Breast Cancer
Researchers analyzed data from the After Breast Cancer Pooling Project, which is following 18,339 breast cancer survivors from four different sites -- three in the U.S. and one in Shanghai, China.
The average weight change reported in the study in the two years following diagnosis was an increase of 3.5 pounds.
However, about one in six women in the study gained what researchers called “extreme” amounts of weight -- more than 10% of their original body weight.
Regardless of their starting weights, women who saw extreme gains had a 14% greater risk of seeing their cancer come back compared to women whose weight didn’t change during the study.
When researchers took a closer look to determine which women were most likely to see dangerous gains, they found something surprising; it was women who were thin or normal weight, with a BMI of less than 25, when they were diagnosed who were most likely to scale up a few sizes.
Among women who were lean at diagnosis, 20.2% gained moderate amounts of weight, which was defined as an increase of 5% to 10% of pre-diagnosis weight;19.4% saw an extreme gain of 10% or more, which amounted to a minimum of about 12-15 pounds in this group.
“The normal weight or underweight women were most at risk for gaining weight, and the normal weight or underweight women were also the ones with the biggest effect of weight gain, if they gained that 10%,” says study researcher Bette Caan, DrPH, a senior research scientist at the Kaiser Permanente Division of Research in Oakland, Calif.
Women who were normal weight at diagnosis and experienced extreme weight gains over the next two years had a 25% increased risk of breast cancer death, and an increased risk of recurrence, compared to women with stable body weights.
Extreme weight gain also appeared to be particularly dangerous for women whose tumors were responsive to estrogen and for nonsmokers with an increase in their risk of overall death of 25% and 29% respectively.
After Cancer, Fighting the Scale
The weight gain that can follow breast cancer is disheartening and catches many off guard, says Cheryl Rock, PhD, RD, professor in the cancer prevention and control program at the University of California, San Diego School of Medicine, because most people are used to thinking of cancer as a wasting disease.
“If you go through the process of being diagnosed with a life-threatening illness and then having surgery and everything and then on top of that you gain 20 pounds, it’s not happy thing,” Rock says.
But researchers who have followed women with breast cancer as they go through their daily routines have made some important discoveries as to why many breast cancer patients soon see the numbers on the scale creeping higher.
And the forced menopause that often followed chemotherapy causes women to lose lean body mass, which can dramatically slow the body’s metabolism.
The result, explains Rock, is that “it’s very easy to gain weight after eating not a lot more food.”
The next wave of studies will focus on helping women with breast cancer keep off extra pounds. Rock, for example, is leading a study, funded by the National Cancer Institute, which is looking at the effects of different interventions on body weight after breast cancer.