Obesity and Cancer 3

The Connection Between Obesity and Cancer

February 24, 2020

To understand the link between obesity and cancer risk, and the health implications of excess body weight, we must first understand how to define obesity. The World Health Organization (WHO) defines obesity as an “abnormal or excessive fat accumulation in adipose tissue, to the extent that health is impaired” [1].

The accepted classification of obesity uses the body mass index (BMI). BMI is a calculation that takes into consideration one’s height and weight and can be calculated using the assistance of an online BMI calculator. A BMI of 25 falls in the overweight category, and obesity begins at a BMI of 30.

Excess body weight is a problem that affects over 2 billion individuals worldwide. The United States accounts for the highest population BMIs across the globe, with 71% of men and 62% of women falling into the overweight or obese categories[2]. These numbers have only been climbing in the past several decades.

This is important for the health of the American population because several chronic illnesses are more common at a BMI of 25 and above. These include diabetes, stroke, cardiovascular disease, sleep apnea, arthritis, fatty liver disease, and certain cancers[3]. An increased incidence of these chronic conditions is also responsible for a large percentage of premature mortality, or early death, in those with excess body weight[4].

The Link Between Obesity and Cancer Risk

This article will focus on the link between obesity and cancer risk. Researchers at the American Cancer Society report that excess body weight is linked to 8% of all cancers in the United States.

More specifically, there is a cause and effect relationship between excess weight and cancers of the colon, female breast, endometrium, kidney, and esophagus[5]. According to the National Institute of Health, overweight people are also twice as likely to develop liver cancer and 1.5 times as likely to develop pancreatic cancer compared to normal-weight people.

Those with larger waistlines, called central obesity, are more likely to experience colorectal cancer, no matter their BMI. Thus, the distribution of fatty tissue in the body plays a role as well. Endometrial cancer is 2-4 times more likely to develop in an obese female compared to one of normal weight, making it one of the cancers most strongly linked to obesity.

Endometrial cancer exhibits an increasing risk as weight gain increases, implying a linear relationship with cancer risk and degree of obesity for certain cancers.

Excess body weight is not only tied to cancer development, but also to cancer deaths. A large study demonstrated that excess body weight accounted for 14% of all deaths from cancer in men and 20% of those in women². This includes cancer of the esophagus, colon, rectum, liver, gallbladder, pancreas, kidney, non-Hodgkin’s lymphoma, and multiple myeloma. There is also a higher chance of cancer recurrence in those that are obese compared to those of normal weight.

Finally, we are seeing a rise in rates of weight-related malignancies, such as colorectal cancer, at earlier ages than we have seen in the past. A high incidence of obesity in American adolescents of about 29% may explain this phenomenon.

The Metabolic Syndrome

What is the explanation behind an increased incidence of cancer in those with excess body weight? Adipose, or fatty, tissue functions primarily in energy storage.

Recently, however, it has also been identified as an endocrine or hormonal organ that can react to and release different factors. These factors become disturbed in obesity, leading to a morbidity known as “metabolic syndrome.” The metabolic syndrome is characterized by insulin resistance, in which the body has a reduced response to insulin.

To compensate for this reduced response to insulin and maintain normal blood sugar levels, the body increases the production of insulin. A chronic state of insulin over-production is linked to cancer development and specifically to colon, endometrial, pancreatic, and breast cancers[6].

Insulin and its breakdown products directly promote tumor development by reducing cell death and stimulating cell growth. This abnormal cell overgrowth is the first step in cancer development.

Obesity and insulin resistance lead to a state of chronic inflammation in the body. This inflammation leads to mutations in cells and damaged DNA, both of which contribute to cancer development[7]. Also, high levels of the breakdown products of fats can impair the normal function of non-fatty cells, leading to altered cellular pathways, which can lead to cancer downstream.

Finally, obesity has been linked to increased blood levels of sex steroids, such as estrogen. Sex steroids can stimulate cell production, inhibit cell death and therefore increase the chance of those cells becoming cancerous. Insulin resistance also plays a role in the overproduction of sex hormones, further fueling the problem. The role of sex steroids has been linked to endometrial, breast, prostate, and colorectal cancers[8].

Obesity is the Second Leading Cause of Preventable Death

Obesity is the second leading cause of preventable death in the United States, trailing just behind cigarette smoking. Research has shown that the treatment of obesity can improve mortality by reducing the incidence and severity of several chronic medical conditions. Is this also true for the development of cancer?

Several clinical trials are currently examining this question and showing promising results. How much weight loss do you need to reduce your risk of cancer development? The answer is unclear, but avoiding weight gain is an important first step.

Data suggests that a five percent reduction in body weight has a beneficial impact on blood sugar levels and inflammation, which in turn can play a role in reducing chances of getting cancer.

Is there an optimal way to achieve this weight loss and maintain it? As an experienced bariatric (weight loss) surgeon, I can sing the praises of weight loss surgery and its positive impact on health conditions in the obese population. Bariatric surgery is recognized as the most effective means for achieving significant weight loss, up to 70% of excess body weight, and for maintaining a healthy BMI several years down the road.

As a result of this weight loss, several medical comorbidities are improved as well. What is the role of bariatric surgery and reducing cancer risk? Recent studies examined patients several years after bariatric surgery and found they had a 33% reduction in developing cancer compared to similar patients with obesity who did not undergo surgery.

Specifically, there was a reduction in the rates of obesity-associated cancers such as colorectal, esophageal, pancreatic, post-menopausal breast, and endometrial cancers after bariatric surgery[9].

There is a direct relationship between excess body weight, cancer risk, cancer recurrence, and cancer-related deaths. With the United States leading the world in rates of obesity, this becomes a major public health concern. More than 90,000 deaths per year in the United States could be prevented if all adults maintained a BMI under 25 throughout life. Bariatric surgery is likely one of the best options in achieving this healthy weight and therefore reducing cancer risk and cancer-associated deaths.

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References

  1. Schauer D, Feigelson H, Koebnick C, Caan B, Winmann S, Leonard A, Powers J. Bariatric surgery and the risk of cancer in a large multisite cohort. Annals of Surgery 2019. 269 (1):  95-101.
    Obesity: preventing and managing the global epidemic. Report of a WHO consultation. World Health Organ Tech Rep Ser 2000;894:1-253.
  2. Calle EE, Rodriguez C, Walker-Thurmond K, Thun MJ. Overweight, obesity, and mortality from cancer in a prospectively studied cohort of US adults. N Engl J Med 2003;348:1625-38.
  3. Ceschi M, Gutzwiller F, Moch H, Eichholzer M, Probst-Hensch NM. Epidemiology and pathophysiology of obesity as a cause of cancer. Swiss Med Wkly 2007; 137: 50-56.
  4. Manson JE, Willett WC, Stampfer MK, Colditz GA, Hunter DK, Hankinson SE, et al. Body weight and mortality among women. New Engl J Med 1995;333:677-85.
  5. IARC. Weight control and physical activity. IARCPress, Lyon;2002.
  6. Kaaks R, Lukanova A. Energy balance and cancer: the role of insulin and insulin-like growth factor-1. Proc Nutr Soc 2001; 60: 91-106.
  7. Hussain SP, Hofseth LJ, Harris CC. Radical causes of cancer. Nat Rev Cancer 2003;3:276-85.
  8. Reed MJ, Purohit A. Aromatase regulation and breast cancer. Clin Endocrinol 2001; 54:63-71.
  9. Schauer D, Feigelson H, Koebnick C, Caan B, Winmann S, Leonard A, Powers J. Bariatric surgery and the risk of cancer in a large multisite cohort. Annals of Surgery 2019. 269 (1):  95-101.
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ABOUT THE AUTHOR

Dena Arumugam, MD, is a board-certified general surgeon who specializes in minimally invasive surgery, general surgery and bariatric surgery. She earned her medical degree at the Albert Einstein College of Medicine and completed a general surgery residency at Rutgers Robert Wood Johnson Medical School. She refined her laparoscopic surgery skills at New York University Winthrop Hospital with fellowship training in advanced gastrointestinal and bariatric surgery, before returning to New Jersey to practice at Jersey Shore Advanced Surgical Associates.