A Weighty Issue: Obesity and Cancer Risk

Lisa Schulmeister, RN, MN, APRN-BC, OCN®, FAAN

Editor-in-Chief OncLive Nursing

Oncology Nursing Consultant, Adjunct Assistant Professor of Nursing Louisiana State Health Sciences Center in New Orleans, Louisiana

The “Bench to Bedside Lecture” delivered at this year’s Oncology Nursing Society Congress was on the topic of obesity and cancer risk. It is no surprise that increasing rates of obesity are linked to increasing cancer incidence, but what is interesting is just how bad things are now, and how bad they are predicted to become in the years ahead.

The National Cancer Institute (NCI) estimates that 69% of adults in the United States are overweight or obese (defined as a body mass index [BMI] >25). That means that 7 of every 10 adults now exceed healthy weight targets. And children are catching up: 3 in 10 are overweight or obese. If these trends continue, there will be a half million additional cases of cancer in the United States by 2030. That’s only 17 years from now, so many of us will be around to see if this in fact occurs, and if it does, we’ll have many more patients with cancer to care for.

So what’s behind the association of obesity and the increased risk of certain types of cancers, such as endometrial, colorectal, esophageal, pancreatic, renal, and postmenopausal breast cancers? Several possible mechanisms have been suggested. Fat tissue, for instance, produces excess amounts of estrogen, and high levels of estrogen have been associated with the risk of breast and endometrial cancers.

Obese people often have increased levels of insulin and insulin-like growth factor-1 in their blood, also known as insulin resistance, which may promote cancer development. Fat cells produce hormones (adipokines) that may stimulate cancer cell growth. The hormone leptin, which is more abundant in obese people, appears to promote cell proliferation, whereas adiponectin, which is less abundant in obese people, may have antiproliferative effects. Fat cells may also have direct and indirect effects on other tumor growth regulators, including mTOR and AMP-activated protein kinase.

Other possible mechanisms include oxidative stress, chronic low-level inflammation, altered immune responses, and effects on the nuclear factor kappa beta system.

If every adult reduced his or her BMI by just 1% (equivalent to a weight loss of about 2 pounds), for an adult of average weight, this would prevent the increase in the number of cancer cases and actually result in the avoidance of about 100,000 new cases of cancer each year in the years to come. Further reduction in cancer incidence would occur if obesity in our nation was reduced.

Several NCI Research-tested Intervention Programs (http://goo.gl/Am4pf) provide the evidence that interventions, such as awareness building and behavior modification, can increase healthier eating and promote weight loss. The most recent program added to the site in March 2013 is the Complete Health Improvement Program, a group lifestyle modification course for adults in community and workplace settings. An interesting aspect of this program is that participants are highly encouraged to enroll in the program with their spouses/partners. Having a buddy is a well-known weight loss strategy, and engaging the entire family in healthy eating behaviors and physical activity is even better.

Many people think that tobacco is the factor that most contributes to the risk of developing cancer; however, the number one factor is diet and obesity (tobacco accounts for a 30% risk while diet/obesity accounts for a 35% risk of cancer). The obvious conclusion is that the public should be encouraged to maintain a healthy weight, or if overweight, to lose weight.

Observational studies have found that people who have a lower weight gain during adulthood have a lower risk of colon and endometrial cancer, as well as postmenopausal breast cancer. However, many of these studies have not been able to evaluate whether the weight loss was intentional or not. Stronger evidence comes from studies of patients who have undergone bariatric surgery; these patients have lower rates of obesity-related cancers than obese people who did not have the surgery.

Once again, nurses are at the forefront of cancer prevention and have numerous opportunities to promote healthy behaviors at home, in the workplace, and in the community.