Currently, the Centers for Disease Control and Prevention estimates that nearly 42 percent of U.S. adults have obesity and nearly 10 percent have severe obesity, according to a June 2021 report (Natl Health Stat Report 2021; http://dx.doi.org/10.15620/cdc:106273). Estimates suggest that by the year 2030, nearly half of all adults in the United States will have obesity (defined as a body mass index or BMI between 30 and 34), and nearly a quarter will have severe obesity (a BMI of 35 or higher).
That's concerning to oncologists because high BMI is linked to an increased risk of several cancers, including the following: adenocarcinoma of the esophagus, breast cancer (in women who have gone through menopause), cancer in the colon and rectum, uterine cancer, gallbladder cancer, upper stomach cancer, kidney cancer, liver cancer, ovarian cancer, pancreatic cancer, thyroid cancer, meningioma, and multiple myeloma.
According to the American Cancer Society, excess body weight is estimated to be responsible for 11 percent of cancers in women, 5 percent of cancers in men, and 7 percent of all cancer deaths. After smoking, obesity is the second most common preventable risk factor for cancer, and it's estimated to become the top preventable risk factor for cancer in the coming decades with obesity's wider spread, according to Ali Aminian, MD, Director of Cleveland Clinic's Bariatric & Metabolic Institute. "That's why it's very important to study the role of obesity in cancer pathogenesis and development," he noted.
And that's why research like that from Aminian's group is important. They published a paper in JAMA that followed cohorts of thousands of patients with severe obesity. One cohort had undergone bariatric surgery and one had not, and researchers considered incidence of obesity-related cancers and outcomes after an average of 6 years of follow-up (2022; doi:10.1001/jama.2022.9009). Patients who had undergone bariatric surgery had significantly lower risk of getting these cancers and significantly lower risk of dying from these cancers than those who hadn't undergone surgery.
"The question here was if we can help patients lose weight and if we can help the patients to keep it off for a long period of time; can we reverse the effects of obesity on cancer development?" Aminian noted. The data showed bariatric surgery did indeed help people lose weight and keep it off, and protect them from obesity-related cancers.
Another study from earlier this year looked at the association between following the American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention and obesity-related cancer incidence in Women of Color (Cancer 2022; https://doi.org/10.1002/cncr.34428).
"Very few studies in the field focus on racial and ethnic [minority] groups, so we wanted to provide new evidence that was specific for these groups and can inform clinical practice and future work in these populations," noted Margaret S. Pichardo, MD, PhD, MPH, a resident physician in general surgery in the Department of Surgery at the Hospital of the University of Pennsylvania, and the study's lead author.
Pichardo's group looked at data from Black and Latina women who had taken part in the Women's Health Initiative, which is a large, randomized clinical trial and observational study conducted across 40 U.S. clinical centers. The data confirmed that indeed women who followed the lifestyle guidelines had a 28 percent to 42 percent reduced risk of obesity-related cancers. She said that she's not aware of previous studies that had examined the incidence of obesity-related cancers or less common obesity-related cancers in relation to guideline adherence. Here are the details of both investigations.
Surgery for Severe Obesity
For Aminian's recent JAMA paper, he and his colleagues enrolled 30,318 patients with a BMI of 35 or greater at the start of the study and followed them for an average of 6 years. The first cohort included 5,053 patients who underwent bariatric surgery (including Roux-en-Y gastric bypass and sleeve gastrectomy). The second cohort included 25,265 matched control patients who had not undergone weight loss surgery.
Of the bariatric surgery cohort, 2.9 percent of patients developed an obesity-related cancer compared with 4.9 percent of patients in the non-surgery group. Rates of cancer mortality were 0.8 percent for the group who underwent surgery and 1.4 percent for the nonsurgical group. That's a 32 percent reduced risk of developing an obesity-related cancer in people with severe obesity who underwent bariatric surgery compared to those who did not undergo surgery, and a 48 percent reduced risk of dying from any cancer. The researchers controlled for several baseline characteristics, including race, ethnicity, and preexisting comorbidities.
Aminian noted he and his colleagues weren't surprised by these findings because they knew at the outset that obesity is a major risk factor for these cancers. "But the magnitude of effect was surprising," he said. "The effect size was very large."
Another meta-analysis published in October in the journal Surgery for Obesity and Related Diseases found a similar beneficial effect for people with obesity who underwent bariatric surgery and their subsequent risk for developing colorectal cancer (2022; doi.org/10.1016/j.soard.2022.10.003). The research included 13 papers that followed a total of 3,233,044 patients. Patients who had bariatric surgery had a 37 percent lower risk of getting colorectal cancer compared with patients who had not had surgery.
This benefit of bariatric surgery on cancer risk and outcomes is an important one because the threshold of weight that needs to be lost to reduce disease burden when it comes to cancer is much greater than when it comes to reducing the risk of other obesity-related diseases, Aminian says. Losing 5-10 percent of body weight for someone with obesity can reduce the risk of complications from diabetes, metabolic diseases, and heart disease, while greatly increasing quality of life.
But for cancer, someone with obesity needs to lose 20-25 percent of their body weight or more to see a significant reduction in risk of developing an obesity-related cancer. That's why surgery can be such a powerful tool, Aminian noted.
Lifestyle Interventions
For their analysis of the American Cancer Society's Guidelines on Nutrition and Physical Activity for Cancer Prevention and obesity-related cancer risk, Pichardo's group looked at data from 9,301 Black and 4,221 Latina postmenopausal women. Additionally, ACS guideline adherence was examined in a subset of less common obesity-related cancers and potential effect modification by neighborhood socioeconomic status and smoking.
The researchers conducted an analysis whereby they assigned a composite score to the women that measured their adherence to the guidelines that was based on diet, physical activity level, BMI, and alcohol intake reported when the women enrolled in the study. They followed the women for a median follow-up of 11 years. The data showed that high ACS guideline adherence was associated with the following:
* a lower incidence of obesity-related cancers for Black women (28-29% lower) and Latinas (41-42% lower); and
* fewer common obesity-related cancers for Black women (31%) and Latinas (63%) separately, and among all women combined (41%).
While previous work hasn't looked at obesity-related cancer incidence and guideline adherence specifically, other research has investigated guideline adherence and incidence of any cancer. Data suggests that guideline adherence may have a greater effect in terms of lowering cancer risk for People of Color, Pichardo noted. "More and more evidence is suggesting that, among People of Color, the guidelines are really important, maybe even more important, and if followed may likely confer protection against obesity-related cancers."
Pichardo said the next step of her group's work is looking at other factors that influence guideline adherence, including environmental, socioeconomic, and neighborhood ones (like segregation and gentrification). "I'm also working to understand what motivates and deters cancer survivors of color from adopting the guidelines through qualitative research that can provide greater insight to mechanisms that quantitative data may not."
Aminian said the bottom line from their work is that bariatric surgery can help certain patients with severe obesity potentially lower their risk of developing obesity-related cancers. Some people will be good candidates for surgery, and others will not-but clinicians should have those conversations with people with severe obesity about these options and refer them to bariatric surgery centers to further discuss their eligibility, he noted. Bariatric surgeries are extremely safe, he added, with low risk of complications. "If you don't start the conversation, there's no chance of moving ahead with it."
Pichardo said it's important to keep in mind when looking at the success of interventions like bariatric surgery in helping reduce cancer risk in people with severe obesity, it's important to consider access. "Who has access is a totally different question and needs to be addressed," she stated.
For clinicians, the takeaway from Pichardo's work is to stay current with the cancer prevention guidelines, as well as the ones specific to cancer survivors. "Engage in active and continuous counseling about behavior change. Tailor lifestyle counseling to patient's unique needs, including the environment in which they live," she stated.
Sarah DiGiulio is a contributing writer.