Does Body Weight Increase Cancer Risk?

By Stewart Lonky, MD

I often write about the obesity-cancer connection. And it seems especially important that we revisit the subject with World Cancer Day still in the rearview mirror. 

Let's start with some good news: The overall cancer death rate declined by 29 percent from 1991 to 2017, with a 2.2 percent decline from 2016 to 2017 alone, representing the most significant single-year drop in reported cancer mortality. The decline can be attributed to long-term reductions in death rates for the 4 primary cancers—lung, colorectal, breast, and prostate (lung cancer mortality accounts for 25 percent of all cancer deaths.

Here's the bad news: Obesity-related cancer deaths are rising. Thyroid, pancreas, and uterine cancers, all of which are linked to obesity, are up (overweight and obesity have been linked to 13 cancers). For some cancers, Millennials now face twice the risk that Baby Boomers did at the same age. Two of those cancers — pancreatic and gallbladder — are typically discovered in the advanced stages when the prognosis is very poor. 

And the culprit is all excess weight.

About 40 percent of all cancers diagnosed in the US are now linked to overweight or obesity — the same percentage associated with tobacco use — and the number is rising as our waistlines expand. Compounding matters, 40 percent of the US population is obese, and 71 percent are overweight or obese. Nearly one-third of all US children and adolescents are either overweight or obese," according to the CDC.

Obesity not only increases the risk of getting cancer but also speeds its development and makes it more likely to occur at a younger age, according to research published in the peer-reviewed journal obesity. 

Colorectal cancer is also on the rise in patients under 50, and younger patients are more likely than older patients to be diagnosed when the disease is in the advanced stages.

How Does Fat Drives Cancer?

So, we know that excess weight fuels cancer, but how does that happen, exactly? 

Right now, there are two main theories, both of which focus on visceral fat, or the fat collects around your internal organs.

Some researchers speculate that fat contributes to inflammation — specifically, chronic (long-term) inflammation, which has been linked to cancer. Researchers don't know why this happens, but they know it does.

The second theory boils down to the fact that fat cells produce a variety of hormones, including estrogen, which can disrupt the body's hormonal balance, explaining why hormone-regulated breast cancer and prostate cancer are among the cancers most often linked to obesity. Fat tissue produces more hormones than the body usually produces on its own, and this might drive cancer cell production. 

Recent studies have shown that when compared with normal weight breast cancer patients, obese postmenopausal women had a 34 percent higher death rate. Obese premenopausal women had a 75% higher death rate. Other research shows that obese men tend to have more aggressive prostate cancers and to have their disease first diagnosed in the advanced stages. Things are so bad that the National Cancer Institute (NCI) predicts that if these obesity trends are not reversed -and there's little indication they will be – that by 2030 the US could be dealing with an additional 500,000 cases of weight-related cancer.

While the NCI also estimates that 100,000 new cases of cancer could be prevented if every adult reduced his or her body mass index (BMI) by just one percent, even that small reduction in weight is easier said than done. We're headed in the opposite direction, with some experts predicting an adult obesity rate of 50 percent, and overweight and obesity rate of 80 percent by 2030. 

Despite the prevalence of weight-loss strategies and glut of diet books, most are useless and only effective – if at all –short-term, particularly for those who are morbidly obese. Among the morbidly obese, less than 5 percent succeed in losing a significant amount of weight and maintaining weight loss with non-surgical programs. 

Still, is there anything we can do? Check out my next blog to find out.