By Jonny Lupsha, News Writer

A new study published in The Journal of the National Cancer Institute says that sustained weight loss lowers breast cancer risk by one-third. Even gaining some of the weight back maintained lower breast cancer rates for women. Why does fat accumulation affect cancer rates?

According to the results of the recently published study, more than 180,000 women were observed over the course of 10 years. During this time, any weight loss of greater than 2 kg that wasn’t put back on in full was considered “sustained weight loss.” “Compared with women with stable weight (plus or minus 2 kg), women with sustained weight loss had a lower risk of breast cancer,” the paper said. “This risk reduction was linear and specific to women not using postmenopausal hormones.” Linking lifestyle choices to cancer rates has been a challenging process for doctors, but they’re starting to get results.

Difficulties in Studying Diet and Cancer Rates

Due to the countless variations in our individual diets and our individual bodies, studies correlating the two have been difficult to conduct—although researchers have tried.

“They took a bunch of different countries and asked the question, ‘If you look at the overall diet of everyone in the country and you say on a population basis, what’s the relationship between fat consumption in the diet and breast cancer?’” said Dr. David Sadava, Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center. “You get a graph that’s quite famous in the annals of cancer research.”

“Here’s a percent of calories as fat, and it ranged from 10 percent, that is a pretty low-fat diet, in Thailand, to about 45 percent in the United Kingdom,” Dr. Sadava said. “It goes up and you say, ‘Whoa, that means more fat means more breast cancer.’ But wait a minute, are the people who consumed the high-fat diet the same ones who got breast cancer?”

According to Dr. Sadava, a study of 337,000 women found that that wasn’t the case at all. “When you look at a case-control study of relative risk versus the percent of fat in a diet, so it ranges from 20 percent to 45 percent of fat in the diet, you find the relative risk on an individual basis is the same,” he said.

Obesity and Cancer Risk

Of course, a high-fat diet is still harmful for the body, but it doesn’t always correlate with the types of cancer one would expect. Obesity, as it turns out, is a far better metric.

Obesity is determined by one’s body mass index (BMI), which in turn is calculated by the relation of height to weight in an adult. The ranges on the BMI scale tell an individual if they’re underweight, normal, overweight, obese, or severely obese.

“People over a certain body mass index are at risk to getting cancer as well as many other things,” Dr. Sadava said. “It could be a descriptive risk factor—in other words, it could be a risk factor that makes these people more prone to getting cancer for other causes. Or it could be a causative risk factor, which means the fat that’s accumulating may actually cause the cancer.”

Most evidence suggests that the stored fat in those with high BMI’s is a causative risk factor, although as always, scientists are hesitant to definitively link one thing to another, since correlation does not imply causation. Regardless of whether fat is a descriptive or causative risk factor, this month’s published article in The Journal of the National Cancer Institute says a lot for weight loss as breast cancer prevention.

Dr. David Sadava is Adjunct Professor of Cancer Cell Biology at the City of Hope Medical Center in Duarte, CA. Professor Sadava graduated from Carleton University as the science medalist with a B.S. with first-class honors in biology and chemistry. A Woodrow Wilson Fellow, he earned a Ph.D. in Biology from the University of California, San Diego.