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Being Overweight Increases Risk for Many Cancers

Pinch the skin over your belly. If your fingers are three or more inches apart, you are at increased risk for diabetes, high blood pressure, heart attacks, strokes, and certain cancers (J Am Coll Cardiol, 2013;62(10):921-925). Harvard University researchers show that being overweight increases risk for most cancers (American Society of Clinical Oncology conference in Chicago, May 29, 2015), probably because belly fat specifically is associated with excess fat stored in your liver. A fatty liver can cause higher blood levels of sugar, insulin, and insulin-like-growth factor-1, all of which can increase cancer risk (Oncologist, 2010; 15(6):556–565).

The 2008 National Health and Nutrition Examination Survey (NHANES) showed that 68 percent of U.S. adults age 20 years and older were overweight. The number in 1994 was 56 percent. Now the estimates run as high as 80 percent. Excess weight has been associated with increased risk for the following types of cancers:
• Colon and rectum
• Breast (after menopause)
• Endometrium (lining of the uterus)
• Kidney
• Esophagus
• Pancreas
• Thyroid
• Gall Bladder
• Prostate
• Ovary
• Liver

How Excess Fat Can Increases Cancer Risk
Nobody knows exactly why overweight is associated with increased risk for so many types of cancer, but the most likely explanation is that storing fat in your belly means that you store excess fat in your liver. Your liver controls blood sugar levels. When blood sugar levels rise too high, the pancreas releases insulin which lowers blood sugar levels by driving sugar from the bloodstream into your liver. Having extra fat in your liver prevents sugar from entering the liver to keep blood sugar levels high. This raises blood insulin and insulin-like growth factor-1 (IGF-1) levels even higher to overstimulate cells, which can lead to cancer (Annual Review of Medicine, 2010; 61:301–316). Extra fat in your liver also turns on your immunity to cause inflammation, which is associated with increased risk for many cancers (Cell, 2010;140(6):883–899).

Colorectal Cancer: Storing fat in the belly is a major risk factor for colon and rectal cancers (PLoS One, 2013;8(1):e53916). Having extra belly fat means that you have extra liver fat that cause high blood sugar, insulin and insulin-like growth factor-1 levels that can turn normal cells into cancers. Red meat is also associated with colon cancer, probably primarily because it blocks insulin receptors to raise blood sugar and insulin levels.

Breast Cancer (after menopause): Fatty tissue produces large amounts of the female hormone, estrogen. Estrogen stimulates the breast to grow and too much estrogen overstimulates the breast which can lead to cause cancer. The riskiest time to have too much estrogen is after the menopause (BMJ, 2007 Dec 1;335(7630):1134). Taking estrogen after menopause increases cancer risk, and taking estrogen with the second female hormone, progesterone, increases breast cancer risk even more. Women who have a delayed menopause and go into menopause after age 55 are at increased risk for breast cancer because of their prolonged exposure to estrogen. Gaining a lot of weight from age 18 to 50 also increases breast cancer risk after the menopause. Women who start menstruating before age 10 are at increased risk for breast cancer because of their prolonged lifetime exposure to estrogen. A program of diet and exercise that gets women to lose weight after treatment for breast cancer helps to prevent recurrences (Journal of the National Cancer Institute, 2009; 101(9):630–643).

Endometrial Cancer: Women who are overweight are two to four times more likely to suffer cancer of the inner lining of the uterus, and the more overweight a woman is, the more likely she is to suffer endometrial cancer (Int J Cancer, Jan 15, 2007;120(2):378-83). Women who are given estrogen without also receiving the second female hormone, progesterone, are at high risk for uterine cancer. Estrogen stimulates the inner lining of the uterus to grow, while progesterone stops the stimulation. Taking estrogen without also taking progesterone stimulates growth of the inner lining of the uterus all the time to cause cancer. Anything that raises blood sugar levels increases risk for endometrial cancer: diabetes, lack of exercise, eating and drinking foods and fluids with added sugar, and so forth.

Kidney Cancer: Storing fat in the belly is associated with renal cell cancer, the most common form of kidney cancer (Br J Cancer, 2001 Sep 28;85(7):984-90). Having extra belly fat raises blood insulin levels. Insulin constricts arteries to raise blood pressure. High blood pressure is associated with increased risk for kidney cancer.

Esophageal Cancer: Being overweight is associated with increased risk for esophageal adenocarcinoma, but not esophageal squamous cell cancer (Ann Oncol, 2013 Mar;24(3):609-17). Overweight can cause reflux of acid from the stomach to the esophagus, and the esophagus is damaged by the acid. This can cause inflammation that leads to a precancerous condition called Barrett's esophagus.

Pancreatic Cancer: Obesity is associated with increased risk for pancreatic cancer (Ann Oncol, 2012 Apr;23(4):843-52). Storing fat in the belly raises blood sugar levels, which causes the pancreas to constantly make more insulin that overstimulates the pancreas. Other risk factors for pancreatic cancer include smoking, diabetes, eating red meat, processed meats and fried foods, and exposure to pesticides, dyes and various other chemicals. A diet high in fruits and vegetables reduces risk for pancreatic cancer.

Thyroid Cancer: Patients who are overweight tend to have increased risk for thyroid cancer, particularly the types that kill (Archives of Surgery, published online May 21, 2012). Other risk factors include being iodine deficient, a family history of thyroid cancer, having a bowel condition called familial adenomatous polyposis, growth hormone tumors or diabetes, or exposure to large amounts of radiation, particularly for treatment of other cancers in early life. Having other cancers such as non-Hodgkin’s lymphoma, breast cancer, esophageal cancer, or testicular cancer also increase risk for thyroid cancer.

Gall Bladder Cancer: Being overweight increases risk for having gall stones, and gall stones are associated with increased risk for gall bladder cancers (Br J Cancer, 2007 May 7;96(9):1457-61).

Prostate Cancer: Obesity is associated with a slight increased risk of prostate cancer, but it is strongly associated with increased risk for the aggressive type of prostate cancer that can kill (World Cancer Research Fund International. Continuous Update Project Report: Diet, Nutrition Physical Activity, and Prostate Cancer, 2014). Obesity increases levels of growth factors such as Insulin-Like Growth Factor-1 that can stimulate normal cells to become cancerous.

Ovarian Cancer: Being overweight is associated with a slight increased risk for premenopausal ovarian cancer, but not for ovarian cancer after menopause.

Liver Cancer: The most common known causes of liver cancer are chronic infections with the hepatitis viruses. However, being overweight is associated with increased risk for liver cancer in people who are not infected with these viruses (Eur J Cancer, 2012 Sep;48(14):2137-45). Storing extra fat in your liver, called a fatty liver, turns on your immunity to cause inflammation, which increases risk for many different cancers.

Bariatric Surgery Reduces Cancer Risk in Obese Patients
Obese people who have bariatric surgery to help them lose weight are at reduced risk for developing these obesity-related cancers, compared to those who did not have the surgery (Cancer, 2011; 117(9):1788–1799). Bariatric surgery is more effective than anything else to help grossly obese people lose weight. Bariatric surgery, combined with lifestyle changes, usually gets people to lose more than 30 percent of their weight, while ordinary dieting rarely results in loss of more than 7-10 percent of body weight.

My Recommendations
If you have more than 100 pounds to lose, you may want to consult a bariatric surgeon. If you need to lose less than 100 pounds, I believe that the most effective method for permanent weight loss is Intermittent Fasting, combined with a regular exercise program. For detailed instructions on weight loss with intermittent fasting I recommend The Fast Diet by Michael Mosley. Once you have lost your desired amount of weight, you can keep the weight off by continuing a less-stringent but lifelong program of healthful eating, intermittent fasting and exercise.
• Eat all the fruits and vegetables you want.
• Restrict red meat, processed meats, fried foods and sugar-added foods and drinks.
• Two days a week (not consecutive days), "fast" by having oatmeal for breakfast, and then having only occasional snacks of whole fruit or nuts for the rest of the day. Drink as much water, unsweetened tea or coffee as you want.
• Try to exercise at least 30 minutes every day. You can pick any activity that keeps you moving continuously.

Also see Being Overweight Increases Risk for Premature Death

September 27th, 2015
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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