Q&A: The Link Between Body Weight and Cancer

Having obesity does not mean you will get cancer, but it does mean you are more likely to get cancer than if you maintained a healthy weight. Excess body weight is thought to be responsible for about 11 percent of cancers in women and about 5 percent of cancers in men in the U.S., as well as about 7 percent of all cancer deaths, according to research from the American Cancer Society.

Sarah Ro, MD, is a UNC Health weight management physician, and Young Whang, MD, PhD, is a UNC Health medical oncologist. We asked them common questions about the link between excess body weight and cancer.

Is there a link between obesity and cancer?

Research shows that carrying extra body fat increases your risk of several cancers, including breast, uterine, prostate, pancreatic, gallbladder, thyroid, colorectal, head and neck, and esophageal cancers, Dr. Whang says.

“The link between obesity and cancer is clear,” he says.

Not everyone who carries excess weight will develop cancer, but people are more likely to get cancer if they have obesity than if they have a healthy weight.

How many people have obesity-related cancers?

Although cancer is the second-leading cause of death in the United States, cancer prevalence and deaths are decreasing thanks to scientific advances. There is one exception, though. Obesity-associated cancers are on the rise, accounting for about 40 percent of all cancers and affecting more than 684,000 people each year, Dr. Ro says.

The most common obesity-associated cancers are breast cancer after menopause for women and colorectal cancer for men.

“More than 90 percent of new obesity-related cancers occur in people who are age 50 or older,” Dr. Ro says. “More alarmingly, cancer among younger people is on the rise in the United States, and experts believe rising obesity rates in children may be a contributing factor.”

What increases the risk of obesity-associated cancer?

Several factors can increase a person’s risk of obesity-associated cancer. These include:

  • Degree of weight gain—the more weight gain, the higher the risk.
  • Length of time carrying extra weight—the longer it’s carried, the higher the risk.
  • Losing weight and gaining it back over and over.
  • Obesity during childhood, which is associated with a higher cancer mortality rate during adulthood.

How does obesity cause cancer?

There are several reasons why carrying excess body weight can increase cancer risk, Dr. Whang says. These include:

  • Excess body fat causes long-lasting inflammation, which increases the risk of cancer.
  • Fat tissue produces sex hormones such as estrogen that increase the risk of breast cancer.
  • Excess body weight increases the levels of insulin and insulin-like growth hormones that can cause cancer to develop.

Why should people with obesity be screened for cancer?

For people with obesity, it is crucial to keep up with all recommended cancer screenings.

Screening tests can detect cancer in its earliest stages, when it’s easier to treat and there is a better chance of survival. Here are four common screening recommendations:

  • Women ages 40 to 74 should get a mammogram every other year to screen for breast cancer.
  • Women ages 21 to 65 should get a Pap smear to screen for cervical cancer every three years. From ages 30 to 65, women can screen with a Pap test and HPV testing every five years to lengthen the screening interval.
  • People with an average risk of developing colon cancer should be screened for colon cancer beginning at age 45.
  • According to the American Cancer Society, men at average risk should get a prostate-specific antigen (PSA) test starting at age 50 and at age 45 for African Americans and people with a family history.

Those at higher risk of breast and colon cancers may need to start earlier. Talk to your doctor to determine your risks.

“If available, women living with obesity should request 3D mammography, which increases rates of detection of invasive breast cancer by 40 percent,” Dr. Whang says.

When it comes to prostate cancer screening, men living with obesity tend to be less likely to have elevated PSA levels that could indicate cancer, leading to delayed detection and treatment.

“Prostate cancer in men with obesity may be detected at more advanced stages and less likely to be cured. Thus, prostate cancer in men with obesity tends to have higher mortality rates,” Dr. Whang says. “One study showed promise with using MRI in high-risk men with obesity, which can help with screening for prostate cancer for those at risk.”

How can I reduce my cancer risk if I am overweight or have obesity?

Losing as little as 5 to 10 percent of your body weight—that’s 10 to 20 pounds for a 200-pound person—can decrease your risk of cancer, Dr. Ro says. Here are some strategies to do that:

  • If you smoke, quit smoking. Talk your doctor about smoking cessation
  • Trade soda, juice and other sweetened beverages for water. Drinking water instead will help you decrease your daily calorie intake, which will help you lose weight.
  • Skip the drive-thru. Eating out regularly at fast-food places and sit-down restaurants will sabotage your efforts to lose weight. Eating out one meal can provide enough calories for the whole day. Preparing meals at home can help you eat out less often and lose weight.
  • Don’t crash diet. The promise of short-term weight loss is appealing, but it’s usually not sustainable, and the yo-yo effect of repeated cycles of weight loss and gain increases the risk of cancer.
  • Lace up your walking shoes and hit the pavement, trails or the gym. The health benefits of physical activity are clear. Find an activity you like and keep doing it weekly for one month. Soon it will become a habit. Regular physical activity will prevent future weight gain.
  • Talk to your doctor about anti-obesity medications to see if you might benefit. Also, if your body mass index (BMI) is greater than 35, consider asking for a referral to a weight management clinic, where experienced obesity physicians will work closely with you to adopt healthy lifestyle habits and discuss all treatment options.
  • If you have a BMI over 35, talk to your doctor about weight-loss surgery, also called bariatric surgery. “The long-term benefits of bariatric surgery are clear. Studies show the surgery reverses many chronic diseases like diabetes, decreases cancer risks and prolongs life by about six years,” Dr. Ro says.

Obesity is a chronic disease that is difficult to treat, but losing even a small amount of weight has health benefits, and healthcare professionals now have a range of treatment options, Dr. Ro says.

“It is bringing hope to many people living with obesity,” she says. “Effective obesity treatments are available to help them decrease their cancer risks, improve their quality of life and improve their overall health.”

Concerned about your cancer risk? Talk to your doctor. Need a doctor? Find one near you.