Does being overweight boost your risk for cancer? The short answer is yes, if you’re among the third-plus of Americans that are obese – the CDC categorizes those with a body mass index of over 30.0 as such. Although evidence from studies show that larger percentages of body fat are strongly linked to increased risks of several cancer types, it’s a more complex story than that.
Dr. Neil Iyengar specializes in the link between obesity and cancer. “Our team became interested in the obesity-and-cancer question because there are strong epidemiologic observations linking obesity to breast and other cancers. The breast is a fatty organ — you have fat tissue sitting next to epithelial or ductal tissue. This leads to the logical hypothesis that changes in the fat tissue related to obesity promote the development of cancers in neighboring sites,” explains Iyengar, a medical oncologist and clinical investigator at Memorial Sloan Kettering Cancer Center. “Indeed, we see a similar correlation in other cancers.”
Fat, As It Relates to Cancer
So, what makes fat a cancer risk factor? One major reason is inflammation. Fat cells expand to store energy, but at a certain point, they become too large and wind up not functioning as they’re meant to (i.e. as energy storage vessels). These too-big cells start to die, and the immune system attempts to flush them. However, it’s an imperfect process — the area becomes inflamed instead. And, chronic inflammation changes the tissue itself, making it more prone to tumor growth. Scientists aren’t quite sure why chronic inflammation has this effect, but they’re working on it.
Another thing to consider is that fat cells help produce and house hormones. Excess estrogen brought on by excess fat may up the risk of breast cancer, for example. Obesity also lessens the chance of survival for patients with certain cancer types, like estrogen-receptor-positive breast cancer. This also happens to be the most prevalent variety of breast cancer, accounting for about 75% of cases.
The Broader Implications
This is all concerning for obvious reasons, but it’s also significant for the future of our society as a whole. In 2015, the CDC found that no state in the U.S. had a less than a 20% prevalence of obesity. Nationwide, more than a third of adults are obese, and that statistic is only growing. A 2012 report from The Trust for America’s Health and the Robert Wood Johnson Foundation predicted that by 2030, the majority of Americans will be obese. The types of cancer made more likely by way of obesity will become even more widespread — in fact, obesity is shaping up to be cancer’s biggest preventable risk.
“The trends suggest that obesity is becoming the leading risk factor for the development of cancer. As other traditional risk factors like smoking and alcohol use decline, obesity is becoming a more prevalent factor,” says Iyengar.
New Ways of Thinking About Prevention and Treatment
There’s hope. Looking at cancer from this perspective opens new doors for prevention and treatment. Experts at Memorial Sloan Kettering are working to identify those most at risk, and are finding that an unhealthy metabolism could be more of an indicator, particularly for breast cancer, than body mass itself, although they’re linked. (Only 10% of obese patients have a healthy metabolism, versus two-thirds of patients with a normal BMI). While scientists are still working through the connection between long-term inflammation and certain varieties of cancer, non-invasive inflammation screening options could be on the horizon.
There are also implications for patients already battling certain cancer types. Researchers are exploring how weight loss in breast cancer patients – whether through diet, exercise, or a combination of the two – can positively affect their prognosis. The effects of anti-diabetic and weight-loss drugs in obese cancer patients are also being tested.
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