Excess Weight May Contribute Up to 40 Percent of US Cancer Diagnoses

If you’re overweight or obese, your risk of multiple types of cancer increases, but the good news is that losing even a moderate amount of weight may help lower that risk.

By Rachael Bieschke

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Your weight plays an important role in your overall health, including your risk of many chronic diseases — cancer included. In fact, being overweight or obese — defined as a body mass index (BMI) of greater than 25 or 30, respectively — is believed to cause up to 40 percent of all cancer diagnoses in the U.S. Overall, 13 different types of cancer have been “firmly linked” with obesity, according to Dr. Damien Hansra, medical oncologist at Cancer Treatment Centers of America® (CTCA) in Newnan, Georgia. This includes:

  • Meningioma
  • Multiple myeloma
  • Adenocarcinoma of the esophagus
  • Thyroid
  • Postmenopausal breast
  • Gallbladder
  • Stomach
  • Liver
  • Pancreas
  • Kidney
  • Ovaries
  • Uterus
  • Colon and rectum (colorectal)

Obesity-Related Cancers Are on the Rise

While rates of non-obesity-related cancers declined from 2005 to 2014, the opposite held true for obesity-related cancers, which increased by 7 percent during that time, the U.S. Centers for Disease Control and Prevention (CDC) reports. The exception is colorectal cancer, which decreased by 23 percent, likely because increased screening has prevented an upswing in new cases.

Despite its prevalence — about 630,000 Americans were diagnosed with cancer related to overweight or obesity in 2014 — “many people are not aware that obesity and cancer can be linked,” Dr. Hansra says. “The key message here is that people need to start eating right and exercising right away because obesity is preventable.” Research into obesity’s role in cancer is still in the beginning stages, but it’s known that being overweight or obese not only increases your risk of certain cancers but also your risk of cancer recurrence.

Excess weight may also reduce the effectiveness of your treatment while increasing your risk of treatment-related complications, cancer recurrence and mortality. The effect of weight loss post diagnosis is less clear but based on available research there seems to be positive benefits for losing weight. For example, one study found that overweight or obese breast cancer survivors may reduce their risk of cancer recurrence by losing about 5 percent of their weight. The weight loss led to changes in biological markers, including a 30 percent reduction in C-reactive protein, a marker of inflammation that’s associated with breast cancer mortality.

“We also see the insulin pathways within the breast tissue change in ways that we know are linked to lower cancer risk and mortality,” Melinda Irwin, study author and professor of epidemiology from Yale University, says in a press release. Where you carry your weight may also matter, with research published in the British Journal of Cancer suggesting that excess weight around your mid-section or hips may be particularly problematic for certain cancers.

An 11 centimeter (cm) increase in your waistline may be associated with a 13 percent increase in risk of obesity-related cancers, while an 8-cm increase in hip size may boost bowel cancer risk by 15 percent. So in addition to BMI, it’s possible that waist circumference, hip circumference and also your waist-to-hip ratio may also play a role in cancer risk.

Why Excess Weight Raises Cancer Risk

“There is still active investigation as to why obesity can increase a person’s risk of cancer,” Dr. Hansra says, “but there are several leading theories, including how obesity is a chronic inflammatory disease … and numerous inflammatory pathways have been linked to cancer development.” It’s known, for instance, that chronic inflammation plays a role in both cancer and obesity. “Obesity-induced inflammation confers additional cancer risk beyond obesity itself,” researchers write in Annual Review of Pathology, noting that “[m]ultiple mechanisms facilitate this strong association between cancer and obesity.”

Fat tissue secretes several hormones that play a role in tumor behavior, for example, as well as inflammation. Estrogen, for instance, is produced in excess by fat tissue, which may increase your risk of breast, endometrial and ovarian cancers. Obesity can also result in dysregulated metabolism, including insulin resistance, high blood sugar and high cholesterol and triglyceride levels, which can further affect tumor growth and development.

In addition to inflammation and hormones, Dr. Hansra notes, growth factors such as insulin-like growth factor-1 (IGF-1), which is often elevated in people with obesity, are also linked to the development of colon, kidney, prostate and endometrial cancers. Other growth regulators, such as mammalian target of rapamycin (mTOR) and AMP-activated protein kinase, may also be affected by fat cells and play a role in cancer development. “Local mechanisms,” such as increased inflammation in fat tissue, are another main factor linking obesity to cancer, according to Dr. Hansra. For example, obesity may induce fatty deposits in the liver leading to chronic steatohepatitis which increases liver cancer risk.

Losing Weight Can Lower Your Cancer Risk

The bright side to all of this is that losing weight can lead to a number of beneficial changes in your body that lower your cancer risk, from resolving metabolic dysfunction to lowering inflammation throughout your body. Further, it needn’t be a dramatic weight reduction to make a difference. Among postmenopausal women, losing even 5 percent of their body weight, or 10 pounds on average, led to a lower risk of breast cancer compared to those who did not lose weight.

Obese women who lost 5 percent or more of their body weight also had a lower risk of endometrial cancer in a separate study. If you’d like to lose weight, Dr. Hansra suggests getting help, as weight loss can be difficult on your own. Meeting with a doctor, registered dietitian, physical therapist and/or mind-body therapist can all be helpful on your weight-loss journey. “In addition, I recommend the following,” Dr. Hansra says:

  • Know what your goals are: Are you ready to lose weight and aware of any risks involved? You should plan to lose no more than 1/2 pound a week for lasting results. Know what your ideal weight should be and how many calories per day you should be consuming.
  • Start right away, as it will take time to gear up to lose weight.
  • Keep a log of your calories: pay attention to how quickly calories can add up from afternoon snacks like coffee with cream and sugar.
  • Weigh yourself daily. “It’s like using a debit card versus using cash every day,” Dr. Hansra says. “You tend to spend less when using cash because it’s easier to track. When you log your calories and weigh yourself, you hold yourself accountable.”
  • Track your activity using a fitness-tracking device.
  • Incorporate a healthy diet. Slowly incorporate healthy foods that you enjoy as a lifestyle change. Diets do not work and they are not reasonable in the long term. Don’t cut out any of your favorite foods. “Everything in moderation,” he says. For example, it is ok to have an occasional cheeseburger or milkshake as long as it is not a daily habit.

Finally, remembering that weight loss is a lifestyle change, not a diet, will help you stay on track, Dr. Hansra says. And take comfort in the fact that not everyone loses weight on the same schedule. “It’s easier for some to lose weight and others to gain — everyone’s body is different.” Further, if you’re a cancer patient on hormonal medicine, it may make you more likely to gain weight.

“For patients on hormonal medications, I recommend that they don’t lose hope and just are more vigilant and stricter about lifestyle changes,” Dr. Hansra says. “The key is to track your progress regularly by measuring your calories and progress.” And for anyone who’s considering weight loss, remember that lowering your cancer risk is but one benefit. “Even if you’re not diagnosed with an obesity-related cancer, you should still focus on weight loss,” according to Dr. Hansra. “You’re still at risk of other diseases, such as heart disease, stroke and diabetes. There are a lot of benefits to weight loss,” and along with lowering your risk of serious chronic diseases, you’ll likely feel better, too.