Obesity is on the rise worldwide. In 2016, the World Health Organization tallied 650 million adults with obesity globally.
Many people are aware that obesity is a risk factor for diabetes, stroke, and cardiovascular disease, but fewer may realize that obesity also increases one’s lifetime risk for developing cancers.
A recent study addresses how long-standing obesity adds risk for developing colorectal adenomas— a benign growth that may lead to colorectal cancer.
The study also shows that losing weight may reduce the risk for people who have overweight or obesity.
Colorectal adenomas that persist and grow for long periods can be a stepping-stone to colorectal cancer, the third leading cause of cancer death in adults in the United States.
In a concerning new trend, colon cancer is on the rise in people below 55, at a rate of 1% per year from 2005 until 2016.
Leveraging data from a large, multi-center cancer risk study called the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, the scientists assessed how weight changes affect people’s risk of developing colorectal adenomas.
The findings appear in the Journal of the National Cancer Institute Spectrum.
Weight loss tied to 46% reduction in risk
The PLCO study’s purpose was to determine how effective screening regimens are in reducing death from cancer. They clinically followed 154,942 men and women 55 to 74 years old, from 1993 to 2001.
Participants were rejected if they had any prior risk for colon cancer. And, they were required to have a negative baseline test — a flexible sigmoidoscopy (FSG) — which visualizes the lower colon for growths.
The remaining 18,588 individuals received a repeat FSG study at 3 or 5 years. The scientists matched the participants’ FSG results with their self-reported weights at 20 years, 50 years, and the time of the study.
This study is the first to look at weight gain and loss over a lifetime. Dr. Kathryn Hughes Barry, Ph.D., corresponding author of the study and assistant professor in the Department of Epidemiology and Public Health at the University of Maryland School of Medicine, MD, told Medical News Today:
Mechanisms that may explain the results
Men who lost weight from early to late adulthood exhibited a significant decrease in the risk of developing adenomas. Conversely, the more the participants gained weight, the higher their risk of developing adenomas.
Men benefited more from weight loss than women. Why men derived more benefit than women is not clear, but the scientists hypothesize that men may have a higher proportion of mid-abdominal weight, which increases their risk and therefore benefit more from weight loss.
Study limitations
Dr. Barry and colleagues acknowledge limitations in the study. The researchers note that the study participants were largely non-Hispanic white people, uncovering a diversity gap in their study.
Also, the PLCO study’s colorectal screening relied on a procedure called “flexible sigmoidoscopy,” which is limited to the lower colon.
A lot of work is being done trying to understand the microbiome and its relationship to the immune system in terms of understanding the pathogenesis of colon cancer and also identifying potential targets for treatment.