Most people are well aware there’s a strong link between excess body weight and chronic health issues like high blood pressure, heart disease, and diabetes. Perhaps less well known is that obesity and cancer risk are also strongly correlated. In fact, according to Dr. Bradley Sachs of The Toledo Clinic Cancer Centers, it’s estimated that approximately 20% of cancer cases in the US can be attributed to excess body weight. Furthermore, studies have shown that people who are overweight or obese generally have a higher risk of cancer recurrence and less favorable treatment outcomes.
Why is it so important to recognize the relationship between cancer and body weight? As Dr. Sachs explains, “When you consider that 70% of US adults age 20 or older are either overweight or obese, and that children and adolescents are getting heavier as well, it’s clear the problem of excess body weight has reached epidemic proportions, putting more and more people at increased risk of developing cancer in the future.”
The most accurate way to measure obesity is by using the body mass index (BMI) scale, along with measurements such as waist circumference and waist-to-hip ratio. On this scale, a BMI of 18.5 to 24.9 is considered normal, 25.0 to 29.9 is overweight, and 30.0 to 39.9 is obese (with a BMI of 40.0 or higher being severely obese).
Where fat is deposited on the body appears to influence cancer risk as well. “Belly fat, for instance, is more metabolically active, and there seems to be a correlation between having fat around the belly and having fat deposited within the organs, which has a greater effect on cancer risk,” states Dr. Sachs.
Research has shown that higher amounts of body fat are associated with an increased risk of several different types of cancer. For example, according to the NIH (www.cancer.gov):
- Women who are overweight or obese are two to four times more likely than normal-weight women to develop endometrial cancer.
- People who are overweight or obese are up to twice as likely as normal-weight people to develop liver cancer.
- People who are overweight or obese are about 1.5 times as likely to develop pancreatic cancer as normal-weight people.
- People who are overweight or obese are nearly twice as likely as normal-weight people to develop renal cell cancer, the most common form of kidney cancer.
- Many studies have shown that, in postmenopausal women, a higher BMI is associated with a modest increase in the risk of breast cancer. For example, a 5-unit increase in BMI is associated with a 12% increase in risk. Among postmenopausal women, those who are obese have a 20% to 40% increase in risk of developing breast cancer compared with normal-weight women.
- Compared with normal-weight people, people who are overweight have about a 20% increase in the risk of gallbladder cancer, and people who are obese have a 60% increase in risk.
- People who are obese are about 30% more likely to develop colorectal cancer than normal-weight people.
Exactly how excess body fat increases cancer risk is not known, though several theories have been suggested. “One is that adipose tissue—or fat—creates a chronic low level of inflammation, which over time damages the DNA. And we know that DNA damage is what ultimately causes cancer. We can correlate that to what we know about certain inflammatory diseases and cancer risk. For example, there’s a higher incidence of colon cancer among people with ulcerative colitis and Crohn’s disease, and a higher risk of esophageal and gastric cancer among people with GERD,” Dr. Sachs says.
Other factors that the NIH suggests could explain the link between obesity and cancer include (but aren’t limited to) the higher level of estrogen present in fatty tissue (linked to an increased risks of breast, endometrial, ovarian, and other cancers); the higher blood levels of insulin and insulin-like growth factor common in obese people (linked to an increased risk of colon, kidney, prostate, and endometrial cancers); certain hormones produced by fat cells, called adipokines, that are associated with cell proliferation; and the effects fat cells have on other cell growth regulators.
More studies are needed to determine whether losing weight helps reduce cancer risk in those who are overweight or obese, but evidence seems to be pointing in that direction. “For example, studies have shown that obese people who undergo bariatric surgery to lose weight are at lower risk of developing cancer than those who are obese but don’t have the surgery,” Dr. Sachs says. “Furthermore, there’s strong evidence showing that, regardless of weight, physical exercise lowers cancer risk.”❦