You might know that being overweight or obese can negatively affect your heart health, energy levels, and even joints, but you may be shocked to learn that obesity also plays a role in cancerous growths. Within the last few years, the connection between obesity and cancer has become a hot topic among the general public, noted Neil Iyengar, MD, a specialist with the Breast Cancer Research Foundation and researcher at Memorial Sloan Kettering Cancer Center in New York City. Research has long supported the idea that obesity is a risk factor for cardiovascular disease and many other health concerns, but more recent findings suggest that being overweight is linked to developing certain types of cancer.
In the U.S. each year, around 28,000 men and 72,000 women are diagnosed with cancer associated with being overweight and obese, according to the National Cancer Institute (NCI). A report from the American Cancer Society suggests that excess body weight is responsible for over 544,000 cancer diagnoses, which is about 3.9% of all cancer diagnoses in the world.
Specifically, being overweight or obese has been connected to increased risk for developing 13 types of cancer, according to a 2016 study published by the International Agency for Research on Cancer. Obesity and weight-related diseases currently represent 40% of all cancers in the U.S., and ongoing studies indicate that fat centered around the waist is especially risky.
Unfortunately, the connection between body weight and cancer risk isn’t as simple as “lose weight, avoid disease” (nor does everyone who is overweight get diagnosed with cancer). The majority of studies on cancer and body weight don’t focus on individuals who lose weight but rather on people who can’t keep the weight off, so it’s difficult to determine exactly what your cancer risk would be if you started dropping weight. The best course of action is to avoid gaining any more weight, according to Graham Colditz, MD, Associate Director of the Institute for Public Health at Washington University in St. Louis. Still, losing a couple of extra pounds wouldn’t do any harm, either. Dr. Colditz noted that weight loss can reduce the risk of diabetes, heart disease, and stroke, so that may stand true for cancer as well, all of which is a compelling reason to get back into shape, balance a healthy diet with exercise, and avoid gaining more weight.
Below are 10 cancers that have been linked to obesity so far, as well as why those extra pounds might have an impact.
Breast Cancer
Obesity increases the risk of developing breast cancer in women and men. Particularly staggering is that data shows between postmenopausal women who are overweight are 20% to 40% more likely to develop breast cancer than their normal-weight counterparts, as indicated by the NCI. In fact, for every five-point increase in your BMI score, the risk for developing cancer increases by 12%. Fatty tissues rpduces estrogen, and after menopause, that fat becomes the main source of the hormone for women. Estrogen also has ties to breast cancer, so it makes sense that heavy excess body fat, and thus increased estrogen levels, may increase the likelihood of developing breast cancer.
Not to mention, fat tissue may become “unstable and inflamed” and any chronic inflammation in obese individuals could propel cancerous growths, according to Dr. Iyengar. Because breasts are primarily made of fatty tissue, it’s possible that some sort of “fat tissue dysfunction” is a key link between excess fat tissue and breast cancer risk.
Colon Cancer
People who are overweight are about 30% more likely to develop colorectal cancer than healthy weight individuals, according to the NCI. There are two leading theories on why bodyweight appears to influence colon cancer risk. Some study results have shown that insulin resistance, which is when the body can’t properly use insulin for regulating blood sugar, increases the risk of developing colon cancer. In turn, it’s not uncommon for overweight or obese individuals to develop insulin resistance.
Moreover, Dr. Iyengar noted that the colon is surrounded by fatty tissue, and when inflamed, that tissue may promote cancerous growths.
Endometrial Cancer
The endometrium, best understood as the mucous membrane that lines the uterus, may grow too rapidly which can produce endometrial tumors. According to the NCI, obese and overweight women are two to four times more likely than normal-weight women to develop endometrial cancer. Similarly to breast cancer, having excess fat may promote increased estrogen levels which in turn may propel cancerous growths in the endometrium. Additionally, this type of cancer has been linked to insulin resistance. According to Dr. Iyengar, both the hormonal and metabolic systems play a role in endometrial cancer.
Kidney Cancer
The risk of renal tumors, the leading type of kidney cancer, is nearly twice as high in overweight or obese individuals than their healthy weight counterparts, according to the NCI. Insulin resistance may increase the risk of kidney cancer, and this pre-diabetes condition is not uncommon among overweight individuals. The kidneys are surrounded by fat, Dr. Iyengar noted, and inflammation of fatty tissue can have a powerful impact on the kidney. Further research is needed to better understand the link between fatty tissue and kidney cancer.
Liver Cancer
The risk of liver disease is also twice as high among overweight or obese individuals than normal-weight individuals. Researchers have considered several reasons why fatty tissue promotes tumorous growths, according to Dr. Iyengar. We know that Hepatitis C, a viral disease of the liver, can develop into liver cancer, as can cirrhosis (scarring on the liver), which is normally caused by hepatitis or chronic alcoholism. Both diseases cause chronic inflammation, Dr. Iyengar noted, similarly to inflammation associated with being overweight or obese. In either case, that inflammation may initiate the growth of cancerous cells.
Meningioma
Meningioma is cancer that develops in the meninges, better known as the membranes that coat the inside of the skull, and it generally develops slowly over time. Meningioma risk is about 20% higher in overweight individuals, according to the NCI. However, there’s not much data explaining why obesity correlates with tumors in the meninges. Dr. Iyengar said that there’s still much to be explored and researched in this area.
Multiple Myeloma
Multiple myeloma, also known as Kahler’s disease, is a cancer of the plasma cells in bone marrow. According to the NCI, this type of cancer is about 10 to 20% more likely to develop in individuals who are obese or overweight than in people who are at a healthy weight. According to Dr. Iyengar, it is believed that inflammation-promoting chemicals produced by fatty cells likely enable multiple myeloma growth, as there are fat cells in bone marrow.
Stomach Cancer
People who are obese are two times as likely to develop stomach cancer than their healthy weight counterparts, according to the NCI. There’s very little evidence to fully understand the connection, noted Dr. Iyengar, but it’s possible that disruptions in the microbiome, or the balance of microorganisms that decompose nutrients in the gut, could play a role. Fat tissue surrounding the upper stomach may also be a key component.
Thyroid Cancer
A five-point increase in BMI is linked to a nearly 10% increase in the risk of thyroid cancer. The thyroid is a butterfly-shaped organ in the neck that helps control digestion. It produces hormones, but research indicates that thyroid cancer isn’t related to estrogen produced by fatty tissue, Dr. Iyengar said. According to the NCI, around 57,000 people are diagnosed with thyroid cancer in the U.S. each year. Ultimately, more research is needed to better understand how body weight relates to thyroid cancer risk.
