We are constantly trying to find what causes cancer. Almost every patient I diagnose with cancer asks why it happened. As a society we’ve accepted that tobacco and alcohol cause cancer, and we suspect there are tons of chemicals out there that are also carcinogenic. A recent review in the British Medical Journal shows that there is one more carcinogen we are all exposed to, but have the ability to control — our weight.
By combing the literature and reviewing over 200 studies, the authors were able to analyze the association between excess body weight and cancer. Given that there were multiple studies contributing to the review, there was variability in how “excess weight” was measured. Some studies used body mass index (weight in kilograms to height, known as m2) others’ waist or hip circumference, waist-to-hip ratio, weight gain over time, and so forth. Thirty-six anatomic sites were studied, of which 11 were found to have a significant association to weight. Some of the associations between weight and cancer were gender specific.
For instance, for every 5 kilograms/m2 gain of body mass index, there was a 9 percent increase in the risk of colon cancer and a 56 percent increase risk of biliary tract (such as gallbladder) cancer in men. For postmenopausal women not using hormone replacement therapy, every 11-pound weight gain increased the risk of breast cancer by 11 percent. The affect was cumulative, meaning being overweight by 25 pounds increases the risk of breast cancer by 25 percent. Even scarier, the risk of endometrial (lining of the uterus) cancer increased by 21 percent for every 1/10th increase in the ratio of waist circumference to hip circumference. For those of you who have heard that being “pear-shaped” is better than “apple-shaped,” meaning carrying your extra weight on your hips, this is one of those cancers that highlight the difference.
Having your excess weight more centrally is also related to developing Type II diabetes. A major downside is that you don’t get to choose where your extra weight accumulates.
Other cancers with increased risk related to body mass index included esophageal adenocarcinoma, multiple myeloma, and cancers of the kidney, stomach and pancreas. The only bright spot was that being overweight somehow seemed to lower your risk for lung cancer.
The study was full of numbers that are hard to keep straight or fully understand, so let’s put it into terms of known carcinogens. A woman 50 pounds overweight has a greater risk of developing breast cancer than a soldier who was exposed to Agent Orange during the Vietnam War developing prostate cancer. Agent Orange has been classified as a carcinogen by the Environmental Protection Agency and is known to increase the risk of prostate cancer. In terms of cigarettes, this newest research links obesity with almost as many cancers as smoking.
Other studies have tried to determine how excess fat contributes to cancer. In a postmenopausal woman, fat is the main source of estrogen. Obese women can have twice as estrogen as normal weight women. This excess estrogen is believed to be the source of increased risk for breast and uterine cancer.
Obesity also increases insulin levels. The theory is that insulin triggers cells to divide. This, in essence, is stimulating cancer cells to divide. Taken one step further, this is why some people say sugar feeds cancer or causes cancer. It’s not the sugar — it is any excess intake of calories. These excess calories, in the form of unhealthy foods, have their own associations to cancer as well. A diet of processed foods is not only high calorie, but typically low vegetable and low fiber. This in itself is a risk factor for colon cancer.
Recognizing the association between weight and cancer is important. It empowers the individual to take control of a situation that has significant health risks. Many people eat organic food to avoid potentially dangerous chemicals when there is hardly any research that shows that doing so protects them from cancer. Even chemicals that were deemed risky, such as aspartame and saccharin, have never been proven to cause cancer in humans. Rather than spending so much time and money to circumvent potential chemical exposures, we should be focusing our energy into staying in shape.
Don’t get me wrong — every chemical we add to our food supply should be well-studied. But leave that to the scientists while you maintain your weight.
Dr. Salvatore Iaquinta is a head and neck surgeon at Kaiser Permanente San Rafael and the author of “The Year They Tried To Kill Me.” He takes you on the Highway To Health every fourth Monday.
