Obesity is a serious health problem in the United States. Centers for Disease Control and Prevention (CDC) data from 2023 show that more than 35%, or more than 1 in 3, adults in 23 states have obesity. It’s a striking and scary statistic considering not a single state had an adult obesity prevalence at or above 35% before the year 2013.
It’s especially problematic because many adults with obesity have other serious chronic health conditions. For example, 58% have high blood pressure, a risk factor for heart disease, and 23% have diabetes.
Many adults with obesity are also at a higher risk for developing cancer. Obesity is considered a risk factor for at least 13 types of cancer, which make up 40% of all cancer cases diagnosed in the United States each year.
“We know that the lifetime risk for a number of cancers is very much influenced by weight and obesity,” says Maurie Markman, M.D., President of Medicine & Science at City of Hope® Cancer Centers Atlanta, Chicago and Phoenix. “One can only anticipate a wave of these cancers if we can’t attack this problem.”
Backed by new research, doctors and scientists are rethinking and redefining obesity to help distinguish between people who may be heavy, but healthy and those who are truly at risk for developing obesity-related diseases.
In this article, we’ll explore:
- What Is Obesity?
- Obesity and Cancer: What’s the Connection?
- Obesity-Related Cancers
- Does Any Extra Weight Increase Cancer Risk?
- Does Losing Weight Change Cancer Risk?
If you or a loved one has been diagnosed with cancer and are looking for a second opinion, call us 24/7 at 877-524-4673.
What Is Obesity?
According to the CDC, people are considered overweight or obese when they weigh more than what doctors consider a healthy weight for their height. Doctors commonly use body mass index (BMI) as a screening tool for overweight and obesity. For adults, a person with a BMI between 25 and 29.9 is overweight. Someone with a BMI of 30 or higher has obesity.
Although BMI has long been the sole determining factor for obesity, new beliefs and definitions are beginning to take hold.
For example, in 2023, the American Medical Association (AMA) described BMI as “an imperfect way to measure body fat in multiple groups given that it does not account for differences across race/ethnic groups, sexes, genders, and age-span.”
Anthony Perre, M.D., F.A.C.P., a new patient intake physician at City of Hope Cancer Center Atlanta, says BMI shouldn’t be the only measure of obesity, noting that it may overestimate the degree of adiposity (or fatty tissue in the body) in people who are overweight but very muscular. Similarly, he adds, BMI may underestimate adiposity in older people who experience age-related loss of muscle mass.
In another example, The Lancet Diabetes & Endocrinology Commission recently published an article seeking to establish objective criteria for clinical obesity — and to differentiate it from preclinical obesity.
According to the commission, a clinical obesity diagnosis requires one or both of the following:
- Evidence of reduced organ or tissue function (i.e., signs, symptoms or diagnostic tests that show abnormalities in the functioning of one or more tissues or organ systems)
- Substantial, age-adjusted limitations of daily activities reflecting the specific effect of obesity on mobility, other basic activities of daily living (like bathing, dressing and eating) or both
Preclinical obesity, on the other hand, means preserved function of tissues and organs, but a generally increased risk of developing clinical obesity and other diseases like type 2 diabetes, heart disease and certain types of cancer.
The commission stated BMI shouldn’t be used as an individual measure of health. Instead, it should only be used as a measure of health risk at a population level, for epidemiological purposes, or for screening purposes.
People with clinical obesity should receive treatment, the commission determined, but people with preclinical obesity should undergo health counseling and monitoring, as well as interventions to reduce their risk of disease as needed.
“Public health strategies to reduce the incidence and prevalence of obesity at population levels must be based on current scientific evidence,” the commission noted, “rather than unproven assumptions that blame individual responsibility for the development of obesity.”
Obesity and Cancer: What’s the Connection?
While smoking is still the leading cause of preventable cancer deaths in the United States — with a link to 20% of all cancers and 30% of all cancer deaths — obesity is associated with up to 8% of cancers.
The reason remains murky, but researchers believe overweight and obesity can cause long-lasting inflammation and higher-than-normal insulin levels, insulin-like growth factor and sex hormones like estrogen — changes that may lead to cancer.
“We know that many of the same factors that go hand in hand with obesity may also increase a person’s risk of cancer,” Dr. Perre says. “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.”
Obesity-Related Cancers
Not only is obesity linked to 13 types of cancer, but in some cases, the risk levels associated with obesity are significantly higher than in those who are at a healthy weight or even overweight.
For example:
- Endometrial cancer is seven times greater in women with severe obesity and up to four times greater in women who are overweight or have obesity
- Esophageal cancer is five times greater in people with severe obesity and up to three times greater in people with obesity
- Stomach (gastric) cancer is two times greater in people with obesity
- Liver cancer is two times greater in people who are overweight or have obesity
- Kidney cancer is two times greater in people who are overweight or have obesity
Other obesity-associated cancers include:
- Breast cancer
- Colorectal cancer
- Gallbladder cancer
- Head and neck
- Meningioma (a type of brain cancer)
- Multiple myeloma
- Pancreatic cancer
- Thyroid cancer
Does Any Extra Weight Increase Cancer Risk?
Being heavy, overweight or obese doesn’t mean you will cancer. Skinny people and those who maintain a normal weight get cancer, too.
But when it comes to your risk for developing cancer, researchers point to excess body weight, which includes being overweight or obese, as a major factor. Also, studies have found that the risk for developing cancer increases the more excess weight someone gains and the longer they’re overweight.
The timing of weight gain may also affect risk. Being overweight or having obesity as a child or young adult, as opposed to later in life, may make you more likely to develop certain cancers.
Does Losing Weight Change Cancer Risk?
Some studies have found decreased risks for developing breast, endometrial, colon and prostate cancers among people with obesity who lost weight. One large study of postmenopausal women, for example, found a lower risk of obesity-related cancers — especially endometrial — with intentional weight loss of more than 5% body weight.
Other research that examined people with obesity who underwent bariatric (or weight-loss) surgery found that women in particular had reduced risks for developing cancer overall.
Taking weight-loss drugs, such as GLP-1 medications, under a doctor’s supervision may also reduce the risk for obesity-related cancers.
Although it’s important to note that cancer risk doesn’t come down to weight alone, it’s equally important to remember that losing weight if you’re overweight or have obesity may help lower it.
Simple steps like eating healthy foods, cutting out or lowering alcohol use, and exercising regularly may reduce both your body weight and your risk of cancer.
These steps may also help people already diagnosed with cancer. That’s because obesity may affect both the effectiveness and toxicity of systemic cancer therapies, like chemotherapy, endocrine therapy, immunotherapy and targeted therapies.
Obesity may also complicate the diagnostic process and interfere with side effect management. In fact, research has found that obese patients have worse outcomes from cancer treatments than people who are not obese.
“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.”
As Stephen Lynch, M.D., vice chief of staff at City of Hope Cancer Center Phoenix, says: “Improving overall health is simply going to put a person in a better place physically and emotionally.”
If you or a loved one has been diagnosed with cancer and are looking for a second opinion, call us 24/7 at 877-524-4673.