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THURSDAY, Feb. 20, 2014 (HealthDay News) -- Obesity seems to increase the likelihood for developing precancerous growths called colorectal polyps, according to new research that offers fresh insight into colon cancer risk.
Specifically, the study links polyp risk to several key characteristics of obesity, including having elevated levels of the fat hormone leptin, having a higher body mass index (BMI) and having a larger waistline. BMI is a measurement of body fat taking height and weight into account.
However, investigators stressed that the current findings are not, as yet, definitive, and should not lead to any immediate revisions of current colorectal screening recommendations.
Co-author Jenifer Fenton said the study "cannot assume any cause, only association." Fenton is an assistant professor and researcher in the department of food science and human nutrition at Michigan State University, in East Lansing.
"In order to change the recommendations, which right now advise men to get screened starting at the age of 50, we'd have to find out if obese men are more likely to develop these polyps at an earlier age than their lean counterparts," Fenton explained.
"But we can't yet say that," she said. "For the moment, all we can say for sure is that obese men in this particular population were more likely to have polyps. We will need larger studies following a more generalized population over time to learn about timing."
The study, funded in part by the U.S. National Cancer Institute, was published recently in the journal PLoS One.
To explore a potential link between obesity and colon cancer risk, between mid-2009 and early 2011 the authors focused on 126 seemingly healthy men aged 48 to 65, all of whom were Michigan residents.
All the men underwent colonoscopies. In addition, the team noted BMI scores, waist measurements and leptin levels for all participants.
Roughly four in 10 of the men were found to be obese (with a BMI of 30 and up), with 78 percent falling into the category of either obese or overweight.
And when focusing on the overweight/obese group, the team found that 30 percent had more than one polyp.
After cross-referencing overall results, the investigators determined that men who were obese faced a 6.5 times greater risk for having three or more colorectal polyps than those who were lean (with a BMI under 25).
Obese men were also found to face an almost eight times greater risk than lean men for having at least one polyp, as opposed to none.
What's more, polyp risk seemed to rise incrementally with body fat status. Specifically, polyp risk was seen to rise by a factor of nearly three when lean men were compared to overweight men. And risk went up again by the same amount when comparing overweight men to obese men.
Importantly, the team also found that having higher levels of the fat hormone leptin was similarly associated with having a higher risk for developing polyps.
Fenton said that her previous work has already uncovered evidence for how the obesity-colon cancer connection might function.
"We found that precancer cells, like you find in a polyp, are very sensitive to leptin," she said. "And leptin increases with fat cell size and number. So in a laboratory setting and with animals we've seen that leptin makes these early cancer cells grow," Fenton explained.
"So while we can't yet add obesity to the risk profile for colon cancer, we do think we understand the mechanism behind this," Fenton noted. "And if this is confirmed in a larger population it could lead to a change in screening protocols."
Meanwhile, Lona Sandon, a registered dietitian and assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas, said that as far as she is concerned, it's never too early to start eating better and get weight under control.
"Obesity has been associated with several types of cancer, colon cancer just being one of them," Sandon said. "And so whatever the exact mechanism is behind why excess body fat seems to promote colon cancer risk, this work continues to demonstrate the importance of maintaining a healthy body weight and, therefore, eating a healthy diet."
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