The Link between Obesity and Cancer
Diabetes, heart disease, high blood pressure, osteoarthritis, sleep apnea - the list of health concerns linked to obesity is long and well known. The connection between cancer and weight, however, still takes many by surprise ... including some healthcare providers.
Nigel Brockton, PhD
Nigel Brockton, PhD, director of Research for the American Institute for Cancer Research (AICR), recently returned from the annual Obesity Week Conference, a joint meeting of The Obesity Society and the American Society for Metabolic and Bariatric Surgery. Attending numerous scientific sessions, Brockton said the defining moment for him was when cancer researcher Stephen Hursting, PhD, MPH, simply and compellingly stated: "We need to stop asking, 'Is obesity a risk factor for cancer?' Yes. It is. Now we need to focus on how to reduce the impact of obesity on cancer risk and outcomes."
Brockton added the research community has spent the last few decades looking at the link between weight and cancer. "We now know 11 cancer sites where obesity is strongly associated with risk," he said.
Research has provided sound evidence that overweight and obesity directly influence risk for esophageal, liver, kidney, stomach, colorectal, advanced prostate, post-menopausal breast, gallbladder, pancreatic, ovarian, and endometrial cancers. Additionally, an October 2017 report by the Centers for Disease Control and Prevention (Vital Signs: Trends in Incidence of Cancers Associated with Overweight and Obesity - United States, 2005-2014) found increasing rates of most cancers associated with overweight and obesity, with the exception of colorectal cancer. From 2005-2014, incidence rates of cancers not known to be related to weight declined by 13 percent, but cancers linked to overweight and obesity rose by 7 percent during that timeframe when excluding colorectal cancer (which saw a significant decrease of 23 percent, possibly tied to increased screening).
Although not new knowledge, Brockton said it's important to remember fat tissue is metabolically active and affects the whole body. "It's not this sort of inert, storage substance," he pointed out. "Excess adipose tissue ... fat tissue ... is a major source of hormones and growth factors in the body."
More Research Needed
While research has clearly uncovered ties to cancer, not all results have been as expected. The Continuous Update Project (CUP), a joint effort of AICR and the World Cancer Research Fund (WCRF), has found being overweight between the ages of 18-30 actually has a slight protective factor when it comes to pre- and post-menopausal breast cancer. "But from a public health point of view, it's a very tricky message to navigate," noted Brockton, adding the research also shows that women who continue to be overweight past 30 increase their risk for the cancer type.
Alice Bender, MS, RDN
Alice Bender, MS, RDN, director for Nutrition Programs at AICR, pointed out significantly improved treatments for breast cancer mean women have to consider other health concerns that come along with weight gain that far outweigh any slight protective gain. "Many survivors don't die from recurrence of breast cancer but from heart disease," she said of the reality for many women. "And we know that losing weight will help with those health outcomes."
Other areas that need to be explored when it comes to weight and cancer research include residual effects of losing weight on prevention, active treatment and survival. Similarly, Brockton said differences between the impact of being overweight vs. obese need to be more thoroughly vetted and stratified by cancer site.
"In overweight and obesity, we don't know if being formerly obese has the same effect as being formerly a smoker," he pointed out. "We need more research done, and the CUP reports have helped identify which aspects we need to address more carefully."
Bender noted results are beginning to be published from researchers who have put the AICR/WCRF's 10 recommendations for cancer prevention (see box) to the test with promising results. Since the release of the evidence-based steps, researchers have analyzed the impact on populations in ongoing studies of diet, activity and disease risk. Consistently, the findings have shown adherence to the AICR recommendations cuts cancer risk, improves the health of cancer survivors and protects against other chronic diseases.
And new evidence is coming online all the time. "In our latest CUP report on colorectal cancer, whole grains stood out with particularly strong evidence of decreasing risk," she said.
Empowering Patients & Providers
Despite the established evidence that compels providers to enhance patient education on the relationship between weight and cancer, there remains a disconnect across the country.
"We know that surveys find half of Americans are not aware of the link between obesity and cancer risks," said Bender.
Providers, she continued, could help bridge the gap. "It's a really tough conversation to have, but we help equip doctors and healthcare providers to know how to start those conversations," she said, noting AICR has brochures, infographics, and other helpful tools to get the ball rolling.
Brockton added, "It's important for healthcare providers to know that second to smoking, obesity is the most important lifestyle issue for preventing cancer." He continued, "I think it's important to position it in a way that empowers the patient to make those changes."
Bender said AICR also has tools to do just that. The aicr.org website includes a quiz to assess current diet, information on establishing a cancer-protective diet, nutrition facts, healthy recipes and easy-to-follow information on the positive impact of phytochemicals in food and the negative effects of too much processed meat, sugar and alcohol.
Twice a year, Bender continued, the organization hosts 'The New American Plate Challenge," a 12-week online program that encourages participants to fill two-thirds of the plate with plant-based foods and only one-third or less with food from animals. In addition, there are a series of weekly challenges to encourage healthier eating and increased physical activity.
The next round starts February 2018. By participating in the fun, interactive cancer prevention challenge, Bender concluded, "You are well on your way to a diet that can lower your risk for cancer and other chronic diseases."
Ten Recommendations for Cancer Prevention
And a bonus rule for all - don't smoke or chew tobacco.