January 2, 2013 | 3 minute read

Just when New Years resolutions on weight loss are in full swing comes a large new study that suggests being pudgy may actually help us live longer, even as it finds being extremely obese increases our risk of premature death.

While the study has already spurred plenty of controversy among the experts, when it comes to cancer one point remains clear: having excess body fat increases the risk of seven types of cancers, including colorectal, post-menopausal breast, and endometrial. The more people weigh, the higher the risk.

“This study raises interesting questions about obesity and all-cause mortality,  but for cancer risk the evidence is clear,” said AICR Director of Research Susan Higginbotham, PhD, MPH, RD. “Our expert report and its updates show that body fatness increases the risk of several common kinds of cancer.”

The study was published today in the Journal of the American Medical Association.

Here’s what the researchers did: they looked at all the published studies of how mortality from any cause linked to body mass index (BMI), a measure of body fatness based on height and weight. In total, the researchers looked at 97 studies that included almost 2.9 million adults. The studies came from all over the world, including here in the United States, Europe, China and Israel.

Then the researchers calculated all-cause mortality risk for the various BMI categories compared to those in the normal BMI category, a BMI of 18.5 to <25. (A normal BMI is one indicator that you are at a healthy weight but it is only an estimate.)

When it came to obesity the results confirmed earlier findings: compared to those at a normal weight, being extremely obese – such as 100 pounds overweight – increases the risk of premature death. People in the two highest categories of obesity, with BMIs ranging from 35 to over 40, had a 29 percent increased risk of premature death compared to someone at a normal BMI. Yet those categorized as overweight had a 6 percent lower risk of death.

For example, take three women who are all 5’ 5” tall. One woman who weighs 140 pounds is categorized as a normal BMI. The BMI of a woman at 240 pounds puts her in a high level of obese category, and she is at increased risk of dying early compared to her normal BMI counterpart. But a third woman who weighs 160 pounds is considered overweight, and according to these findings she has a slightly lower risk of an earlier death.

The findings held after only looking at studies that the authors considered “adequately adjusted.” These studies took into account other factors, including age, sex, and smoking. Some of the studies included also adjusted for other lifestyle factors that influence cancer risk, including physical activity and alcohol consumption.

But as the authors point out, this study only shows a link between death and BMI, it does not look at what people died from or those who may have lived with a chronic disease such as type 2 diabetes and cancer.

There’s a lot researchers are still working to understand about the links between excess body fat, premature death and risk of chronic diseases. But if you have resolutions to make healthy lifestyle changes this year, don’t give up on them: studies are clear that a healthy lifestyle promotes good health.

And for cancer, eating a healthy diet and being physically active – two lifestyle choices that can help people get to and stay a healthy weight – lowers the risk, says Higginbotham.