The Obesity - Cancer Connection

Jill Weisenberger, M.S., R.D., C.D.E.

Environmental Nutrition

Expect to see higher rates of cancer as America packs on the pounds. Overweight and obesity come with plenty of bad news, including aches and pains and increased risks for heart disease, high blood pressure, diabetes, osteoarthritis and several types of cancer.

If you didn't know that excess body fat is a risk factor for cancer, you're not alone. According to a 2009 survey by the American Institute for Cancer Research (AICR), only about half of Americans know of the relationship. Extra fat does more than make us uncomfortable and self-conscious; it is actually busy at work, generating as many as 100 substances. Some are hormones and chemicals that set the stage for cancer and other chronic diseases. Maintaining low body fat, says the AICR, could prevent over 100,000 cases of cancer each year in the U.S. Specifically, excess body fat is linked to cancers of the colorectum, endometrium, esophagus, gallbladder, kidney, pancreas and postmenopausal breast cancer.

Fat's dirty work

A lot goes on in the body when excess fat is hanging around. Here are some of the most significant issues impacting cancer risk:

Estrogen

One of those hormones produced by fat is estrogen, says Tim Byers, M.D., M.P.H., interim director of the University of Colorado Cancer Center. From puberty to menopause the ovaries produce estrogen, helping to regulate a woman's menstrual cycle and enabling normal breast development. A woman's lifelong exposure to estrogen affects her cancer risk. After menopause, when the ovaries stop producing estrogen, body fat is the major source of this hormone. The more fat a woman has, the more estrogen is pumped into her bloodstream raising her risk for endometrial cancer and postmenopausal breast cancer. Estrogen may promote cancer by stimulating cell division in the uterus and breast.

Insulin Resistance

Excess body fat can promote insulin resistance, a condition in which the body doesn't respond adequately to the hormone insulin. In the early stages of the condition, the pancreas tries to compensate by producing more and more insulin, causing insulin levels in the blood to become very high. According to a 2009 study in the International Journal of Cancer, high levels of insulin in the blood are linked to postmenopausal breast cancer. Researchers at Albert Einstein College of Medicine of Yeshiva University collected multiple blood samples from 5,450 women participating in the Women's Health Initiative, a multicenter study that examined the effect of various factors, such as diet and supplementation on women's health. In their study, the participants were categorized into three groups based on their insulin levels. Researchers found that women with the highest insulin levels, suggesting insulin resistance, were more than twice as likely to develop breast cancer as women with the lowest insulin levels.

"This high level of insulin and the resulting increased availability of insulin-like growth factor tends to promote cell growth and reproduction, including that of cells with damaged DNA that can develop into cancer," explains Karen Collins, M.S., R.D., nutrition advisor to the AICR.

Insulin resistance is a quiet, insidious condition. Because it comes on slowly over many years, it often brutalizes the body long before the problem is recognized. If left unchecked, the body's production of insulin will eventually dwindle, and blood glucose levels will rise, possibly reaching the level of type 2 diabetes. Though blood glucose is frequently checked at routine medical appointments, insulin levels are not. In the early stages of insulin resistance, blood glucose is likely to be normal because of the excess insulin available, thus masking that something is awry. Insulin resistance may explain, in part, the connection scientists found between type 2 diabetes and several cancers. According to the AICR, people with diabetes are twice as likely to get cancer of the liver, pancreas and endometrium, and 20 to 50 percent more likely to develop cancers of the colorectum and bladder, as well as postmenopausal breast cancer.

There may still be many other, as yet undiscovered ways in which insulin resistance boosts cancer risk. Another theory is that insulin and insulin-like growth factor inhibit apoptosis, the body's normal, programmed "death" of abnormal cells.

Inflammation

Body fat also secretes cytokines, proteins important in the communications between cells. An overabundance of fat cells produces an overabundance of cytokines. As they circulate through the body, these proteins promote chronic, low-level inflammation. Inflammation then leads to the production of free radicals that can damage the cells' DNA and start the cancer process, explains Collins. Additionally, inflammation may bolster cancer by stimulating the development of new blood vessels that allow cancer cells to grow and then spread.

Heartburn

You may want to tough it out, but if you have chronic heartburn, also called acid reflux, you need to seek treatment. When acid from the stomach backs up into the esophagus, it irritates or injures the tissue because the esophagus lacks a protective coating like the one found in the stomach. Over time, this reflux damage increases the likelihood that esophageal cancer will develop, says Byers. Obesity plays a role because it increases pressure within the stomach and allows the stomach contents to flow backward into the esophagus.

Apples and pears

If you were a fruit, what would you be? In other words, do you carry extra weight at your midsection (apple) or around your hips (pear)? Fat around the hips and thighs is stored just beneath the skin, but abdominal fat nestles deep around the liver and other organs. This deep fat, called visceral fat, is more harmful because it produces hormones and cytokines linked to insulin resistance and inflammation, says Collins. In general, men have more visceral fat than women, but women tend to lay down fat in the middle as they age. See "Measure Your Middle" (SIDEBAR) for another way to assess your cancer risk.

Take action

Both the Nurses' Health Study and the Iowa Women's Health Study, two large-population studies, suggest that overweight women can reduce their risk for postmenopausal breast cancer by losing weight, explains Collins. Other research has demonstrated that when overweight individuals lose just 5 to 10 percent of their body weight (10 to 20 pounds for someone weighing 200 pounds), both insulin resistance and inflammation decrease. "Since cancer development is an ongoing process, this suggests by changing the factors that promote the development of cancer, we can reduce risk," adds Collins.

If you are overweight, make efforts to stop gaining. The next step is to lose weight if possible. "Focus on small changes that you repeat day after day -- forget perfection," Collins urges, adding "You have to be in it for the long haul." Start by walking 10 minutes and changing one meal or one snack. Or dump sugary drinks in favor of water or tea. For more help, check out AICR's New American Plate (www.aicr.org), a long-term approach to managing what and how much you eat. Be sure to discuss your risk factors for cancer and all chronic diseases with your health care provider. If your risk is higher than average, you may need earlier screening for certain conditions.

Measure Your Middle

Keep an eye on your waistline. For a lower cancer risk, a woman's waist should be no more than 31.5 inches, and a man's waist should not exceed 37 inches, states Karen Collins, M.S., R.D., nutrition advisor to the American Institute for Cancer Research. Follow this two-step process to measure your waist. Contrary to popular belief, the waist is not the skinniest point of the midsection.

Circle a tape measure around your midsection immediately above your hipbone.

Exhale and check the number on the tape.

Environmental Nutrition is the award-winning independent newsletter written by nutrition experts dedicated to providing readers up-to-date, accurate information about health and nutrition in clear, concise English.

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