Obesity and cancer: Increasing risks, complicating treatments

Even the thinnest person among us has fat on his or her body. Or, put another, more scientific way, adipose tissue, the connective tissue rich in fat cells, or adipocytes. Adipose tissue is important for storing energy and helps in the production of hormones. It also helps keep us warm, through a process called thermogenesis. But too much adipose tissue, like too much of many things, may lead to obesity, which in turn may raise the risk for many diseases, such as heart disease, diabetes, stroke and cancer.

Today, obesity is a national epidemic. The U.S. Centers for Disease Control and Prevention (CDC) estimates that more than 42 percent of Americans are obese. That’s up from 30.5 percent in 2000. The CDC estimates that 40 percent of all cancers in the United States are attributed to being overweight or obese. The organization, along with the International Agency for Research on Cancer, has linked these 13 cancer types to obesity:

The statistics are concerning because, even as incidence rates for cancers not linked to excess weight fell 13 percent from 2005 to 2014 in the United States, the number of new cases of 12 of the 13 weight-associated cancers rose 7 percent. The one exception in that group is colorectal cancer, whose incident rate declined during that time period, due to better screening and prevention, according to the CDC. However, colorectal cancer diagnoses have risen sharply among younger Americans in recent years.

How do you know if you’re overweight or obese?

Obesity develops when you consume more calories than you burn from doing normal daily activities and exercise. According to the CDC, a person is overweight or obese if his or her weight is “higher than what is considered as a healthy weight for a given height.”

Obesity is measured using the body-mass index (BMI), a calculation of a person’s height and weight. A person with a BMI of 30 or more is considered obese. Click here to calculate your BMI on the CDC’s body-mass index calculator.

The BMI index should not be your only measure of obesity, Dr. Perre says. BMI may overestimate the degree of adiposity in people who are overweight but very muscular. BMI may underestimate adiposity in older people due to loss of muscle mass associated with aging. Measuring waist circumference in those with a BMI 25-35 may provide additional information regarding a person’s risk of obesity related health issues, he says.

Cause and effect

Some major cancer risk factors, such as smoking, lack of exercise, alcohol abuse or poor diet, are tied to habits or lifestyle. Age and family history are other key cancer risk factors. Obesity typically develops from somewhat of a combination of several of these factors. Obesity may be a product of poor diet or a sedentary lifestyle. Inherited genes may also factor into the equation. And many of us know how hard it is to lose weight as we get older.

While some contributing lifestyle issues may also increase the risk of cancer, research suggests a direct cause-and-effect connection between obesity and cancer. For example

Chronic inflammation: Fat cells may create an environment in the body that causes low levels of chronic inflammation. Under normal circumstances, inflammation develops as a reaction to injury or disease and is often a sign that the body is healing itself. But, over time, chronic inflammation may damage cellular DNA, which may lead to uncontrolled cell growth and the formation of tumors.

“We know that many of the same factors that go hand in hand with obesity may also increase a person’s risk of cancer,” says Anthony Perre, MD, Vice Chief of Staff at Cancer Treatment Centers of America (CTCA), Philadelphia. “Part of the connection may be related to the adipose tissue itself. It may increase inflammation, and we know that inflammation plays an important role in the development of cancer.”

Hormone production: Obesity wreaks havoc on the production of hormones, especially estrogen and insulin, that raise cancer risk. Fat cells have a tendency to produce high levels of estrogen that may increase the risk of breast and gynecologic cancers. Some obese people also have higher levels of insulin, which may increase the risk for colorectal, kidney and other cancers.

Cell regulation: Fat cells may affect the inner workings of hormones or proteins that regulate cell growth and division. This may cause cells to divide and grow out of control, eventually forming tumors.

Immune suppression: New research suggests that obesity may weaken T-cells found near tumor cells by altering their metabolism. These changes alter the immune cells’ ability to attack and kill the cancer cells.

Affecting diagnosis and treatment

Obesity may not only increase cancer risk, but it may also complicate the diagnostic process, reduce the effectiveness of some cancer treatments and interfere with side effect management.

“Obesity may affect some of the diagnostic tests we use,” Dr. Perre says. “For instance, we may not get as good a picture from diagnostic imaging because of the excess adipose tissue. Obesity may also cause some technical challenges for radiation therapy. Surgery may be more complicated, and radiation has to pass through more tissue, potentially causing more collateral damage.”

A 2017 study by doctors and researchers in Southern California found that fat cells may absorb and break down common chemotherapy drugs, reducing their potency. “By absorbing and breaking down the drugs, the fat cells may be removing the drugs from the immediate environment around tumor cells in bone marrow or other areas of the body where fat cells are plentiful,” the study says. “This finding may help explain why obesity is linked to poorer outcomes in several types of cancer.”

Obesity may also lead to diabetes, a disease also frequently diagnosed in cancer patients.A 2010 report published by the American Diabetes Association (ADA) concluded: "Cancer and diabetes are diagnosed within the same individual more frequently than would be expected by chance."

Doctors may often be faced with treating diabetes and cancer at the same time, which may require a difficult balancing act. Steroids used as part of chemotherapy regimens may increase glucose levels in the blood, making it difficult to control blood sugar during cancer treatment. This may lead to poorer outcomes, delayed wound healing and increased risk of infection. High blood sugar may also exacerbate cancer-related fatigue, and the appetite loss caused by some cancer treatments makes it more difficult for some diabetic patients to eat well and maintain their blood-sugar levels.

Lower your cancer risk

Many Americans find that losing weight is a frustrating battle. Americans spend billions on gym memberships, diet plans and weight-loss products. Yet, the number of obese Americans continues to grow. But weight loss doesn’t need to be dramatic to make a difference.

Among postmenopausal women, losing even 5 percent of their body weight, or 10 pounds on average, may lead to a lower risk of breast cancer compared to those who don’t lose weight, one study found. Another study concluded that women who lost 5 percent or more of their body weight also had a lower risk of endometrial cancer.

Below are some tips that may help you lose weight, and, as a result, help reduce your risk of cancer, diabetes and other weight-associated conditions.

Know what your goals are. Are you ready to lose weight now that you have a better understanding of the risks involved? Plan to lose no more than a half-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. It typically takes 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. Logging your daily weight helps you keep track of your progress.

Track your activity. Try a fitness-tracking device.

Incorporate a healthy diet. Slowly incorporate healthy foods that you enjoy. Rather than cutting out all your favorite foods, consider first just cutting back on them.

Dr. Perre says diet is the primary factor in losing weight. But exercise can help keep the weight off. Both should be part of developing a weight-loss plan you’re better able to stick to.

“It’s tough to lose weight for a variety of reasons,” he says. “There are genetic reasons and social pressures. And those need to be addressed. But it’s important. Losing weight doesn’t just reduce your cancer risk; it may improve your overall health.”

Learn more about diabetes and cancer.