By Sara Bondell
Excess body fat has already been recognized as an important cause of cancer, but new research suggests obesity is far worse for a person’s cancer risk than anyone previously guessed.
The study, published in the International Journal of Epidemiology, found the effect of being overweight on cancer risk is at least twice as large as past estimates. Researchers used a method called Mendelian randomization, which uses measured variation in genes to examine the cause-and-effect relationships on disease in observational studies, and looked at eight different types of cancer often linked to obesity.
“Obesity may be as important as smoking as a contributor to overall mortality and cancer, and may even surpass it,” said Moffitt Cancer Center epidemiologist Dr. Kathleen Egan. “Obesity, particularly visceral fat, leads to physiological changes and a range of effects, including insulin resistance, chronic inflammation and an unhealthy gut microbiome, that contribute to cancer.”
The study says that while researchers previously estimated obesity is responsible for around 6% of cancers, it is in fact substantially higher.
While smoking prevalence has decreased, obesity is on the rise, and researchers expect to see an increased number of cancer cases attributed to excess weight gain in the coming years. Egan says things like a sedentary lifestyle, unhealthy diet and excessive alcohol intake can contribute to cancer risk at least in part because they promote obesity. She points out that while informative, the study is based on genetic correlates of obesity whereas the gold standard in research is measured body weight.
According to the National Health and Examination Surveys, 70 percent of U.S. adults over the age of 20 are either overweight or obese. Obesity has been linked to many gastrointestinal malignancies including stomach, esophageal, liver, colorectal and pancreas cancer.