Worldwide, more than a billion people have obesity—including 650 million adults, 340 million adolescents, and 39 million children1—a rate that has nearly doubled since 1980.2 In the United States alone, about two out of three adults are overweight or have obesity, and one out of three have obesity.3 A recent study by the World Obesity Atlas finds that if these trends continue unabated, more than half of the global population—over 4 billion people—will have obesity by 2035, and the economic impact could surpass $4 trillion.4
Commonly defined as a body mass index (BMI) or weight-to-height ratio of greater than or equal to 30 kg/m2, obesity is linked to the development of several major chronic diseases, including coronary artery disease, diabetes mellitus, and hypertension, as well as at least 12 major solid tumor cancers (including breast, colorectal, esophageal, kidney, uterine, gallbladder, stomach, pancreatic, ovarian, thyroid, liver, and brain cancers) and multiple myeloma, which collectively make up 40% of all cancers diagnosed in the United States.5
Studies show that excess body fat results in about a 17% increased risk of cancer-specific mortality.6 In addition, obesity may play a role in cancer recurrence and mortality in cancer survivors.
Cancer Risk Factors
Although the relationship between obesity and cancer development or recurrence is not well understood, several factors are believed to contribute to cancer risk, including the secretion of adipokines and anabolic and sex hormones, immune dysregulation, and chronic inflammation.6 Although several weight loss medications have been approved by the U.S. Food and Drug Administration for individuals with diabetes and cardiovascular disease, including the glucagon-like peptide-1 (GLP-1) receptor agonists tirzepatide and semaglutide, their use in reducing cancer risk has not been studied and remains unknown. And although studies suggest that bariatric surgery is an effective intervention for weight loss in some patients with severe obesity when diet and exercise interventions alone are not successful, the procedure is considered major surgery and carries risk.
In 2014, ASCO published Obesity and Cancer: A Guide for Oncology Providers, which offers strategies on weight loss and weight management that oncologists can recommend to their patients.7 (See sidebar on page 31.)
Colleen K. Spees, PhD, RD, FAND, FAHA
The increasing evidence linking obesity and cancer development was a major topic at the Union for International Cancer Control’s (UICC’s) 2023 World Cancer Leaders’ Summit, held October 2023 in Long Beach, California. The ASCO Post spoke with Colleen K. Spees, PhD, RD, FAND, FAHA, Professor, Division of Medical Dietetics at The Ohio State University College of Medicine, and a presenter at the summit, about the multifaceted underlying mechanisms associated with obesity-related cancers, the paradox of malnutrition in obesity, and interventions to promote weight loss in patients with obesity.
Changing Environment and Rising Global Obesity Rates
Why is the world seeing such an explosion in -obesity rates?
Obesity is a serious disease that develops from a complex interplay among genetic, environmental, socioeconomic, and behavioral factors. Because genetics are quite slow to change, the global obesity epidemic is likely related to our changing environmental exposures and diet quality. For example, we are seeing the adoption of more calorie-dense but nutrient-poor westernized dietary patterns and fast-food restaurants in low- and middle-income countries, as well as more screen time and less physical activity. These lifestyle behaviors can all contribute to increasing rates of overweight and obesity, as well as a higher risk of cancer.
These factors also play a role in the rising rates of obesity in the United States. The overconsumption of sugar-sweetened beverages and ultraprocessed foods combined with sedentary lifestyles with rising screen time can all contribute to increases in overweight and obesity in both adults and children.
Underlying Mechanisms
Why does having obesity increase a person’s risk of cancer and cancer-related mortality?
This is a question we are continuing to study. Several mechanisms have been identified to increase the risk of cancer development, recurrence, and prognosis in individuals with obesity, including the amount of adipose tissue in the body. Fat tissue produces excess amounts of hormones, such as estrogen, that increase the risk of breast, ovarian, endometrial, and other cancers. Individuals affected by obesity also have increased blood levels of insulin and insulin-like growth factor–1, which leads to insulin resistance, a risk factor for both type 2 diabetes and several types of cancer, including prostate, colon, and kidney cancers.
Another major association with obesity is systemic inflammation, which leads to oxidative stress that can increase the risk of DNA damage to the cells and promote carcinogenesis. Obesity can impair tumor immunity and change the body’s microenvironment, so instead of attacking cancer cells, it protects them and helps them thrive.
We need much more research to fully elucidate these mechanisms, as well as studies to inform how the microbiome may influence cancer prevention and risk in individuals with and without obesity. Taken together, these obesity-related mechanisms drive cancer progression, recurrence, risk of secondary primary cancers, and reduced mortality.
Measuring Patients’ Nutritional Status
During your presentation at the UICC World Cancer Leaders’ Summit, you talked about the dichotomy of having obesity while also being malnourished. Please explain how those two conditions can coexist.
Malnutrition refers to suboptimal nutritional status that encompasses both underweight and overweight individuals. Most people think about malnourishment only as it affects thin people, but that is just not the case.
In our current climate, malnutrition often presents with the phenotype of overweight and obesity. Often individuals may consume ample or excessive calories yet have specific macro- or micronutrient deficiencies. The literature reports that between 40% and 80% of patients with cancer are malnourished at some point in their cancer care, largely due to the physical and metabolic effects of cancer and its treatment.8 Malnutrition during the cancer journey is related to treatment toxicities and interruptions, increased hospital admissions and length of stay, reduced quality of life, and poorer overall prognosis. It is essential that oncology patients be screened for malnutrition regardless of weight status.
There are many validated tools to screen for malnutrition in patients with cancer. Early and ongoing malnutrition screening allows for nutrition interventions to prevent more severe malnutrition and associated consequences. One such tool is the Patient-Generated Subjective Global Assessment (PG-SGA; https://pt-global.org/pt-global), which tests for weight loss, food intake, symptoms, and physical function.
Reducing the Risk of Cancer
What does your research show regarding how individuals can reduce their risk of developing cancer and how patients with cancer can reduce their risk of recurrence and cancer-related death?
My research spans the cancer continuum from prevention and active treatment to posttreatment survivorship for vulnerable patients. Our biobehavioral interventions include access to healthy food provisions in tandem with intensive and tailored nutritional therapy and behavioral counseling. This is essential since patients with cancer and unmet social needs have additional challenges in meeting and maintaining their nutritional needs throughout cancer care.
My interventions align with the Food Is Medicine initiatives that are growing across the country, including one advocated by the U.S. Department of Health and Human Services. The intent of these programs is not to imply that food is replacing drug therapy, but rather that evidence-based guidelines for healthy eating should be part of the conversation during treatment and throughout survivorship to improve outcomes and reduce the risk of recurrence.
Providing Nutrition Therapy
How can oncologists help their patients with obesity lose weight and/or prevent weight gain during survivorship and maintain a healthy weight and healthy muscle mass?
The nutrition goal during active cancer treatment is to keep patients consuming whole, nutrient-dense food to minimize the risk of malnutrition and treatment-related symptoms, such as constipation and mucositis. Connecting high-risk patients with registered dietitians is critically important to provide medical nutrition therapy throughout the cancer continuum, to address specific nutritional needs and promote optimal nutritional status.
Unfortunately, nutrition services provided by dietitians in outpatient cancer settings, where more than 90% of patients are treated, are not currently covered as standard care by private health insurance or by Medicare and Medicaid. Although many oncologists would love to refer their patients to oncology dietitians, there is often an extra out-of-pocket cost that prevents many patients from receiving this level of care. It is shocking that with such high levels of malnutrition, the ratio is one dietitian for every 2,300 patients.
More research is needed to support the education and training of oncology providers, to promote referrals and overcome barriers to the implementation of weight management and physical activity programs for patients with cancer. In the meantime, combining lifestyle behaviors with high-quality dietary patterns, increased physical activity, and behavioral therapy can provide a successful path for weight management for patients.
Adopting Health-Protective Behaviors
What role do obesity medications such as tirzepatide and semaglutide have in helping prevent cancer in individuals with obesity or in helping survivors lose weight during cancer treatment and in long-term survivorship?
As a society, we are drawn to short-term fixes vs long-term changes in patterns of behaviors. Although these GLP-1 receptor agonists currently offer rapid results, we are now uncovering some unintended consequences, including pancreatitis, gastroparesis, and bowel obstruction. No long-term studies have been conducted in cancer prevention, and we have little information about how these drugs affect patients with cancer and obesity in active treatment and in posttreatment survivorship.
Until we know more, patients should discuss the implications and contraindications of these medications with their oncologists and adopt risk-reducing and health-protective lifestyle behaviors that include weight management and physical activity.
STRATEGIES FOR ADDRESSING WEIGHT MANAGEMENT WITH PATIENTS
To provide oncologists with weight management strategies to help their patients lose weight and lead healthier lives after a cancer diagnosis, in 2014, ASCO published Obesity and Cancer: A Guide for Oncology Providers. Here are some suggestions from the guide to begin the conversation about weight management with your patients.
1. ASSESS your patients’ weight by evaluating their body mass index (BMI), which can be calculated during an office visit by dividing an individual’s weight (in kilograms) by height (in meters) squared. (If calculated in pounds and inches, the result is multiplied by a conversion factor of 703.) Overweight is categorized as a BMI greater than or equal to 25 kg/m2; obesity is categorized as a BMI greater than 30 kg/m2.
2. ADVISE your patients to lose weight if you determine they are overweight or obese and weight loss is not contraindicated because of disease state or treatment. Weight loss is generally not recommended for patients with advanced disease or for those whose cancer treatment may lead to an inability to consume or digest sufficient calories (eg, patients with head and neck cancer). Encourage regular exercise and healthy eating at all points from diagnosis to long-term follow-up in all patients, regardless of weight and discuss the possibility of weight gain when patients initiate adjuvant therapy.
3. REFER patients to appropriate services. A referral to a dietitian is a good first step in helping patients develop a weight loss program. Dietitians who are members of the oncology nutrition dietetic practice group of the American Academy of Nutrition and Dietetics can be located at eatright.org. The cost of this service is dependent on medical insurance. There are also several free resources available to assist patients interested in losing weight. They include:
- U.S. Department of Agriculture: ChooseMyPlate offers a variety of resources, from weight management tips to calorie tracking tools (www.choosemyplate.gov)
- Obesity Action Coalition: brochures, guides, and fact sheets on obesity and related topics (www.obesityaction.org/educational-resources/brochures-and-guides)
- Fit Day: articles on nutrition and fitness, with tools to help participants count calories and track eating habits (www.fitday.com).
Source: Obesity and Cancer: A Guide for Oncology Providers. © 2014 American Society of Clinical Oncology.
DISCLOSURE: Dr. Spees reported no conflicts of interest.
REFERENCES
1. United Nations: Over one billion obese people globally, health crisis must be reversed—WHO. UN News. Available at news.un.org/en/story/2022/03/1113312. Accessed July 30, 2024.
2. Harvard T.H. Chan School of Public Health: Obesity has doubled since 1980, major global analysis of risk factors reveals. Available at www.hsph.harvard.edu/news/press-releases/worldwide-obesity. Accessed July 30, 2024.
3. Harvard T.H. Chan School of Public Health: Obesity prevention source. Available at www.hsph.harvard.edu/obesity-prevention-source/obesity-rates-worldwide. Accessed July 30, 2024.
4. World Obesity: Economic impact of overweight and obesity to surpass $4 trillion by 2035. Available at www.worldobesity.org/news/economic-impact-of-overweight-and-obesity-to-surpass-4-trillion-by-2035. Accessed July 30, 2024.
5. Centers for Disease Control and Prevention: Obesity and cancer. Available at www.cdc.gov/cancer/risk-factors/obesity.html. Accessed July 30, 2024.
6. Pati S, Wadeed I, Jameel A, et al: Obesity and cancer. Cancers (Basel) 15:485, 2023.
7. ASCO: Obesity and Cancer: A Guide for Oncology Providers. Available at society.asco.org/sites/new-www.asco.org/files/content-files/blog-release/documents/2014-Obesity-Cancer-Guide-Oncology-Providers.pdf. Accessed July 30, 2024.
8. Trabulo C, Lopes J, da Silva Dias D, et al: Assessment of nutritional status of oncology patients at hospital admission: A Portuguese real-world study. Front Nutr 9:972525, 2022.
