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New research suggests that losing weight may help reduce colorectal cancer risk in those who have overweight or obesity. Thomas Barwick/Getty Images
  • 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 weight change in adulthood influences the chance of colorectal adenomas — benign growths 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 among both men and women 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, Cancer Spectrum.

The PLCO study’s purpose was to determine how effective screening regimens are in reducing death from cancer. They enrolled 154,942 men and women 55 to 74 years old, from 1993 to 2001.

Participants were excluded if they had a personal history of colorectal polyps, colorectal cancer or other colon conditions. And, they were required to have a negative baseline test — a flexible sigmoidoscopy (FSG) — which visualizes the lower colon and rectum for growths.

Of the individuals meeting the above eligibility criteria, 17,629 received a repeat FSG test 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 one of the first to look at weight gain and loss over a lifetime in relation to the risk of colorectal adenoma. Dr. Kathryn Hughes Barry, Ph.D.,M.P.H., 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:

“We found that losing weight from early to late adulthood — at least 1 pound every 5 years — was associated with a 46% reduced risk of developing colorectal adenoma. Our study findings particularly support a benefit of weight loss for adults who are overweight or obese.”

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.

MNT asked Dr. Barry to explain why obesity influences adenoma growth.

She replied: “It is thought that increased weight and obesity may increase adenoma risk in part by increasing the chance of developing insulin resistance […]The body responds by making more insulin, and there may also be other biological changes such as an increase in insulin-like growth factor 1 (IGF1) signaling.”

“These changes,” Dr. Barry added, “can increase cell growth and reduce the chance of cell death, changes that are linked with increased chances of developing cancer. Insulin resistance may also lead to type 2 diabetes, which is considered an independent risk factor for colorectal cancer.”

MNT also asked surgical oncologist Dr. Anton Bilchik, Ph.D. what mechanisms he thought could be responsible for the increased risk of colorectal cancer.

According to Dr. Bilchik, Chief of Medicine & Professor of Surgery, St. Johns’ Cancer Institute, Providence St. Johns’ Health Center in Santa Monica, CA: “It’s very clear that there is a higher risk of adenomas and colorectal cancer in people who [have obesity], people who [eat] high amounts of red meat, processed food, don’t exercise, and have increased alcohol use.”

“What’s unclear is how much alcohol is too much — but there is a definite correlation in terms of risk factors and colorectal cancers […] Excessive use of wine or any other alcohol has deleterious effects and puts people at risk for colorectal cancer and cardiovascular disease as well.”

– Dr. Anton Bilchik, MD, Ph.D., FACS, MBA

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 and rectum.

MNT discussed this limitation of the study with Dr. Anton Bilchik:

“This is one of the limitations. Because, as we know, adenomas occur throughout the colon, and the inability to visualize the right colon really gives us no idea whether the pathogenesis of adenomas on the right side may be similar to the left, and, whether obesity plays a role in right-sided adenomas, as [it] does on left-sided adenomas.”

MNT also asked Dr. Bilchik about recent developments in colorectal cancer:

“One of the most interesting and concerning aspects of colorectal cancer is the massive increase in young people being diagnosed under age 50. It’s gone up more [t]han any other cancer in young people. The question really is ‘Why?’ And the majority of people being diagnosed are not obese, are not smokers. So, there clearly is another reason.

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.”

– Dr. Anton Bilchik, MD, Ph.D., FACS, MBA

“The other very interesting area right now,” Dr. Bilchik added, “is that there are some patients that have a favorable immune microenvironment [and] they don’t need chemotherapy, suggesting that some patients may be cured by surgery alone, that chemotherapy does not necessarily have a benefit, so the biology, the molecular make-up of the tumor, and the surrounding environment [is] where a lot of the research is going on, because, clearly, one size does not fit all.”

“We are really trying to figure out how to personalize colorectal care,” said Dr. Bilchik.

MNT queried Dr. Barry as to the team’s future research directions. Dr. Barry summarized,

“Our study is one of the first to investigate weight loss in adulthood in relation to the risk of colorectal adenoma; most previous studies of weight change and adenoma risk have focused on weight gain. Therefore, it is important to see if our finding for weight loss can be replicated in other studies.”