A recent review published in CA: A Cancer Journal for Clinicians summarizes the evidence that the global prevalence of excess body weight and the incidence of obesity-related cancers is on the rise.
Research shows having an excess of body weight increases a person’s risk for developing at least 12 types of cancer.
The global tide of overweight and obesity
Over the past four decades, the global prevalence of having excess body weight has roughly doubled, from 21 percent in men and 24 percent in women to 40 percent in both sexes.
The total number of adults having obesity has grown from 100 million to 671 million, a 600 percent increase since 1975. The number of children having overweight or obesity has increased, too, from 5 percent to 27 percent for boys, and from 6 percent to 24 percent for girls.
The cause of the global epidemic of overweight and obesity is multifactorial. “The obesity epidemic is driven largely by changes in the global food system, which promotes energy‐dense, nutrient‐poor foods, alongside reduced opportunities for physical activity,” says Sung.
Increase in obesity-related cancers
Accompanying the increase in the prevalence of overweight or obesity is an increase in obesity-related cancers.
In 2012, nearly 4 percent of all cancers worldwide were attributable to excess body weight.
The proportion of cancers attributable to body weight – called the population-attributable fraction, or PAF – varied according to cancer type, sex, and global region. For example, excess body fatness was a driving factor in approximately 31 percent of all endometrial cancers, but only 4 percent of all ovarian cancers.
Similarly, women who had overweight or obesity were more than twice as likely to develop an obesity-related cancer as men having overweight or obesity (368,500 cases in women, versus 114,800 cases in men).
High-income Western countries had the highest rates of obesity-related cancers overall, with nearly half of them attributable to excess body weight. “Excess body weight contributes to chronic inflammation and alterations in the hormonal system, which can cause DNA damage and uncontrolled cell growth, eventually leading to the development of cancer,” says Sung.
Altered hormone levels may increase risk of developing hormone-sensitive cancers, such as breast, endometrial, prostate, and colorectal cancers. In addition, excess body weight increases a person’s risk for developing diabetes, a known risk factor for cancer.
The global PAFs and cancer burden
The global PAFs (population-attributable fraction) are likely an underestimation of the total cancer burden, says Sung, due to the limitations of relying on BMI as a measure of body fatness.
Body weight is commonly reported and classified according to a person’s body mass index, or BMI. Health professionals calculate BMI by dividing a person’s weight in kilograms (kg) by their height in meters squared (m2). “BMI is easy to measure, which allows convenient comparisons of weight status within and across populations,” says Hyuna Sung, PhD, a principal scientist at the American Cancer Society and lead author of the study.
Although BMI is not a perfect measure – for example, it doesn’t differentiate between fat and lean body mass – scientific evidence indicates that it correlates well to densitometry (underwater weighing), the gold standard of measuring body composition, says Sung. A BMI greater than 25 kg/m2 is classified as overweight; greater than 30 kg/m2 is classified as having obesity.
Stemming the global tide of overweight and obesity and the associated cancer burden presents considerable challenges. “As the obesity epidemic is driven by environmental and societal factors, policy-led interventions are needed to reverse the trends,” says Sung. “These policy changes should address the production, distribution, and marketing of unhealthy foods, and changes in the built environment to promote adequate levels of physical activity.”
Weight loss may reduce risk of developing cancer, especially among women, the authors of the review noted, and may improve chances of survival. AICR recommends achieving and maintaining a healthy weight throughout adulthood to reduce cancer risk.