The American Association for Cancer Research reports that being overweight is linked to 25 percent of cancers, and adding lack of exercise and eating pro-inflammatory foods raises the risk to 33 percent of newly diagnosed cancer cases in the U.S. The International Agency for Research on Cancer (IARC) reported that being overweight increases risk for 17 different cancers: colon, rectum, esophagus, kidney, breast (women), endometrium, stomach, liver, gall bladder, pancreas, ovary and thyroid, as well as fatal prostate cancer and breast cancer in men, meningioma, multiple myeloma and B-cell lymphoma (N Engl J Med, Aug 25, 2016;375:794-798). Overweight is associated with almost five million cancer deaths each year.
• Cancer risk is associated particularly with belly fat, rather than having fat in other places (Circulation, 2008;117(13):1658–1667). It is belly fat that markedly increases inflammation.
• Full fat cells turn on your immunity to cause inflammation, insulin resistance and oxidative stress (Br J Nutr, Dec 2011;106 Suppl 3:S5-78). Obese people have higher blood levels of these markers.
• The foods that cause the highest rises in blood markers of inflammation include sugar, animal fats and fried foods (AGEs). See Anti-Inflammatory and Pro-Inflammatory Foods.
• Obesity increases levels of cell growth stimulators: insulin, insulin-like growth factor-1 (IGF-1) and leptin. It also decreases adiponectin, a cell growth inhibitor. Cell growth stimulators are associated with increased cancer risk.
• Fat cells produce large amounts of estrogen, too much of which can stimulate breast and uterus cells to grow at a very fast rate, which raises risk for cancers of the breast and endometrium.
How Does Excess Weight Increase Cancer Risk?
The most likely explanation for the link between obesity and cancer is an overactive immunity (Archives of Physiology and Biochemistry, 2009;115(2):86–96). Your immunity is supposed to kill germs that invade your body and as soon as the germ is gone, it is supposed to reduce its activity. If your immunity stays active, it then uses the same mechanisms that it uses to kill germs on you. This is called inflammation. Your immunity attacks your own genetic material called DNA. Your DNA tells your cells that they are supposed to divide a certain number of times and then die, having been replaced by new cells. However, if the DNA in cells is damaged, the cells can forget to die and keep on dividing. For example, breast cancer cells do not kill a person as long as they stay in the breast. They kill by becoming so abundant that they spread from the breast to invade and destroy your brain, lungs, bones and whatever other organs they invade.
Risk for many types of cancers is reduced by:
• restricting calories, which lowers insulin and insulin-like growth factor-I (Frontiers in Physiology, 2012;3(318):1–10), and inflammation (Cancer Research, 2012;72(9):2314–2326).
• regular exercise (Nature Reviews Cancer, 2008;8(3):205–211).
• eating lots of fruits, vegetables and other anti-inflammatory foods (British Medical Journal, 2006;333(7578):1109–1111, and BMJ. Nov 10, 2011;343).
Obesity Worsens Chances of Survival after a Cancer Diagnosis
The American Cancer Society reports that obesity was linked to increased death rates from the most common forms of cancer in men (prostate 34 percent, kidney 70 percent, colorectal 84 percent, esophagus 91 percent, stomach 94 percent, pancreas 2.5-fold, liver 4.5-fold) and women (colorectal 46 percent, ovary 51 percent, breast 2-fold, cervical 3-fold, kidney 5-fold, uterine 6-fold). See my recent report on How Excess Fat Can Spread Cancer
If you are overweight, you are increasing your risk for many types of cancer. Particularly if you store most of your fat in your belly, your excess weight turns on your immunity and keeps it active to cause inflammation that is associated with increased cancer risk. I recommend Intermittent Fasting as the most effective way to lose weight and to control weight permanently once you have reached your goal.