The American Cancer Society has just published a strong guideline document for preventing cancer (Ca: a Cancer Journal for Clinicians, June 9, 2020; https://doi.org/10.3322/caac.21591). Their recommendations are:
• Avoid overweight and avoid weight gain in adult life.
• Be physically active. Adults should engage weekly in 150 to 300 minutes of moderate intensity physical activity, 75 to 150 min of vigorous intensity physical activity, or an equivalent combination; exceeding the upper limit of 300 minutes is optimal. Children and adolescents should engage in at least one hour of moderate or vigorous intensity activity each day. Limit sedentary behavior, such as sitting, lying down, and watching television, and other forms of screen based entertainment.
• Follow a healthy eating pattern at all ages. Eat a variety of vegetables—dark green, red, and orange, fiber rich legumes (beans and peas), and others; fruits, especially whole fruits with a variety of colors; and whole grains. Restrict or avoid red meat and processed meats, sugar sweetened beverages, highly processed foods and refined grain products.
• It is best not to drink alcohol.
Obesity and Cancer Risk
The National Health and Nutrition Examination Survey found that nearly 70 percent of U.S. adults age 20 years or older are overweight or obese. Being overweight markedly increases cancer risk (N Eng J of Med, 2016; 375(8):794-798), particularly:
• Endometrial cancer: four times increased risk (J of Clin Onc, 2013;31(20):2607-2618)
• Esophageal cancer: double increased risk (Int J of Epid, 2012;41(6):1706-1718)
• Gastric cancer: double risk (Canc Epidem, Biomark & Prev, 2013;22(8):1395-1408)
• Liver cancer: double risk (Cancer Research, 2016;76(20):6076-6083)
• Kidney cancer: double risk (Int J of Can, 2014;135(7):1673-86)
• Multiple myeloma: 20 percent increased risk (Europ J of Cancer, 2011;47(11):1606-161515)
• Meningioma: 50 percent increased risk (Neurology, 2015;85(15):1342-1350)
• Pancreatic cancer: 1.5 times increased risk (Int J of Cancer, 2011;129(7):1708-1717)
• Colorectal cancer: 30 percent increased risk (PLoS One, 2013;8(1):e53916)
• Gallbladder cancer: 20 percent increased risk (Obesity (Silver Spring), 2016;24(8):1786-1802)
• Breast cancer: 20-40 percent increased risk (Epidemiologic Reviews, 2014;36:114-136)
• Ovarian cancer: slightly increased risk (PLoS Medicine, 2012;9(4):e1001200)
• Thyroid cancer: 10 percent increased risk (Thyroid, 2016;26(2):306-318)
How Does Obesity Increase Cancer Risk?
• Full fat cells cause inflammation, and exercise helps to prevent inflammation. Overweight people are at increased risk for inflammation in which your own immune system attacks the DNA in your cells to turn them into cancer cells. (An Rev of Imm, 2011; 29:415-445).
• Full fat cells produce large amounts of the female hormone, estrogen, that can overstimulate and cause breast, endometrial, ovarian, and other cancers.
• Obese people usually have high blood levels of insulin and insulin-like growth factor-1 (IGF-1), both of which stimulate cells to grow. Excessive levels of each of these hormones increase cancer risk (Physiological Reviews, 2015; 95(3):727-748).
• Full fat cells produce large amounts of leptin that markedly increases cell growth to increase cancer risk (J Cell Physiol, 2006;207:12-22).
• Full fat cells cause oxidative stress that damages DNA to increase cancer risk (Annual Review of Medicine, 2010; 61:301–31631).
Prolonged Sitting Time Increases Cancer Risk
A review of 18 studies of more than a million individuals showed that sitting for many hours each day is associated with increased cancer risk (J of the Nat Can Inst, July, 2014;106(7):dju098). In a review of 18 articles on exercise predicting cancer survival, the authors found 10 articles that showed that sedentary behavior increased recurrence rate in cancer survivors (Cancer Epidemiol Biomarkers Prev, 2010;19(11):2691–709.
How Exercise Reduces Risk for Cancer
Exercise appears to help reduce risk for various types of cancers in many different ways, including:
• reducing the likelihood of obesity (Diabetes Spectr, Aug 2017;30(3):157–160)
• lowering levels of estrogen, other sex hormones and growth factors that have been associated with breast and colon cancer (Cancer Causes and Control, 2011; 22(6):811-826)
• reducing inflammation and improving immunity (Europ J of Physiology, May 20, 2019;472:235–244)
Obesity Increases Risk for COVID-19 Complications
A review of 4,103 patients found that obesity and its resultant inflammation, heart disease and diabetes are the most common conditions found in patients requiring hospitalization with COVID-19 (Physician’s Weekly, published online April 14, 2020). Another study of 3,615 patients found that in patients under 60 years of age, being obese more than doubled the chance of needing to be hospitalized (Clinical Infectious Diseases, April 9, 2020). Other studies show that obesity (body mass index or BMI greater than 30) is a major risk factor for dying from COVID-19 (Lancet, April 1, 2020), and the more you weigh, the more likely you are to need to be put on a ventilator, which markedly increases your chance of dying (Obesity, April 9, 2020).
Lack of exercise also increases risk for COVID-19 complications (Nature Medicine, 2019;25:1761-1771). It decreases immunity by increasing risk for insulin resistance (Acta Physiol, 2019;226:1-16), and prevents your body from responding to infections and mounting a full attack on invading viruses (Cell Physiol Biochem, 2015;37:735-746).
Researchers at Queen Mary University of London predict that lack of exercise caused by isolation for the COVID-19 pandemic and obesity caused by the food industry’s increased advertising of unhealthful foods and drinks will markedly increase the cancer rate in North America, where 70 percent of the population is already overweight (BMJ, June 11, 2020).
If the COVID-19 pandemic is keeping you at home and away from group activities, and your house is full of food, realize that eating more food and exercising less sets you up to gain extra fat, which will increase your risk for severe COVID-19 disease. Gaining fat also increases your risk for cancer.
Try to exercise at home or outdoors in activities that keep safe social distances. Unless you are underweight, you should probably avoid bringing foods that make you fat into your home. Follow the ACS diet guideline (above), and drink only fluids that contain no calories (water or unsweetened coffee or tea).