Does Being Obese Cause Cancer?
By Durado Brooks, MD, MPH
Suppose that, during your next doctor's visit, you look at your medical record and your doctor has written "53- year-old diabetic white female, here today for a check-up." Would you be bothered by that description? Probably not. Your doctor is just discussing your medical condition, right? But what if, instead of "diabetic" the note read "53-year-old obese white female?" How would you feel now? Hurt? Angry? Sad? Would you think, "Why is my doctor being so mean?" For many, the term "obese" brings to mind a massively overweight individual (like "Fat Albert" in the old Saturday morning cartoons). In reality most obese people don't look like Fat Albert.
OBESITY IS A MEDICAL TERM
Obesity is actually a precise medical term that is based on a measure of body fat called the Body Mass Index (BMI). The BMI is calculated from a person's height and weight. In general, a higher BMI indicates a higher amount of body fat. Adults with a BMI between 18 and 25 are in the "healthy" body fat/weight category. People with a BMI between 25 and 30 are considered overweight, and a BMI greater than 30 signifies obesity. Many people who view themselves as having a "normal weight" (or at most "pleasingly plump") are shocked when they do this calculation and realize that 180 pounds on their 5 feet 6 inch frame means they are medically obese.
Our obsession with body image creates an emotional context for obesity that doesn't exist for most other medical issues. But make no mistake about it - obesity is a medical condition, and like other medical problems it has important long-term implications for health and well-being.
OBESITY'S LINK TO CANCER NOT WIDELY KNOWN
Over the past few years a growing body of evidence (pun intended) has demonstrated links between being overweight or obese and many diseases, including arthritis, diabetes and heart disease. The general public is becoming more aware of many of these associations.
However, researchers have found that there is a lack of recognition of the ties between obesity and one important disease: cancer. Exactly how or why obesity increases the risk of cancer is not clear. Scientists believe it may be in part related to insulin and other hormones that are produced by the body to regulate fat storage and blood sugar levels. Inflammation may also play a role. Regardless of the underlying cause, the evidence is clear that excess weight leads to a higher risk of cancer and higher death rates.
OBESITY'S LINK TO COLON CANCER ESPECIALLY STRONG
Obesity is known to raise the risk of many types of cancer, but studies have demonstrated a particularly strong link between obesity and cancer of the colon or rectum (often referred to as "colorectal cancer" or just "colon cancer"). Being overweight or obese raises the risk both of being diagnosed and dying from this disease. The good news is people can change their risk by changing their behavior.
Most cases of colorectal cancer start as a non-cancerous growth called a polyp. Studies have found that people who are overweight or obese are more likely to develop these polyps, and higher weights are associated with higher polyp risk. It has also been shown that people who are obese are more than twice as likely to die from colorectal cancer as those with healthy weights.
In addition to our weight, what we eat also has a big impact on colorectal cancer risks. A diet that is high in red meat and processed meat (like luncheon meats and hot dogs) increases the risk of developing the disease. Diet certainly plays an important role during cancer treatment, and more and more studies now suggest that after treatment, eating habits may influence recurrence and survival. A recent study examined the eating habits of a group of people who had been treated for colorectal cancer. The researchers found that cancer survivors who ate a "Western pattern" diet, characterized by eating a lot of meat, fat, refined grains and desserts, and whose diet had a high "glycemic load" (meaning it was more likely to cause spikes in blood sugar) were almost twice as likely to die or have their cancer return than those who had the lowest dietary glycemic load. On the other hand, a diet made up of mostly fruits and vegetables, poultry, and fish was not significantly associated with cancer recurrence or death.
HOW YOU CAN LOWER YOUR COLON CANCER RISK
On the other hand, taking steps to achieve or maintain a healthy body weight can protect against colorectal cancer. A diet high in vegetables, fruits, and whole grains, and low in red and processed meats, sugar, and processed grains is good for your waistline and is associated with a lower risk of colorectal cancer. Physical activity has also been shown to decrease the risk of colorectal cancer. One study found that people who were the most active over a 10-year period cut their risk by half.
Physical activity doesn't necessarily mean vigorous activities like running or working out at the gym. Taking a brisk walk, roller skating, or playing golf are examples of moderate intensity activity, and when done regularly can lower your disease risk. The American Cancer Society recommends that adults get at least 150 minutes of moderate intensity or 75 minutes of vigorous intensity activity each week (or a combination of these), preferably spread throughout the week.
So if your doctor labels you "obese," recognize that this isn't name-calling; he or she is simply pointing out that you have an important (and correctable) medical condition. Follow these common-sense recommendations to address the problem and to lower your risk of colorectal and other cancers, as well as other chronic problems like diabetes and heart disease:
• Achieve and maintain a healthy weight. Start by calculating your BMI. If it's in the "healthy" range make sure you keep it there, and if it's in the overweight or obese range, get to work on bringing it down.
• Eat a healthy diet, with an emphasis on plant foods. Limit red meat and processed meats, eat at least 2 ½ cups of vegetables and fruit each day, choose whole grain foods instead of refined grains, and limit sugary foods and sugar-sweetened beverages.
• Get regular physical activity. Don't be a couch potato - get up and move! Moderate or vigorous activity is best, but even a little bit of activity (housework or a leisurely walk) is better than sitting. Men older than 40 years, women older than 50 years, and people with chronic illnesses or risk factors for heart disease should check with their doctor before starting a vigorous activity program.
And finally, remember that while you can cut your risk of colorectal cancer by following the advice above, it's also important to get screened. If you are 50 or older, be sure to talk to your doctor about recommended screening tests and decide which test is right for you.
Dr. Brooks is director of colorectal and prostate cancers for the American Cancer Society.
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