Scientists have long thought that limiting the calories a person consumes can prevent, or at least slow the progression of certain cancers. But researcher at UAB (University of Alabama at Birmingham) using mice suggests that body composition — whether a person is lean or obese — actually is key to reducing cancer risks.

How the body handles calories, these researchers say, is much more important to controlling cancer risks than how many or how few calories are consumed — a finding that could have strong implications for preventing and treating cancer in humans.

In findings published in the Jan. 1 issue of Cancer Research, the UAB team found that transgenic mice predisposed to prostate cancer that were lean had a much slower progression of cancer than did heavier mice.

“This study suggests that body composition, being lean as opposed to being obese, has a greater protective effect against cancer,” said Tim R. Nagy, Ph.D., UAB professor of nutrition sciences and study principal investigator. “Excess calorie retention, rather than consumption, confers cancer risk.”

Nagy’s team placed transgenic mice into two controlled environments, either 27 degrees centigrade or 22 degrees centigrade, and fed them equal amounts of food. The mice living at the cooler environment needed more energy to regulate their internal temperature and so burned more calories simply to stay warm. These mice lost weight and were leaner than the mice kept at the warmer temperature.

The mice kept at 27 degrees were heavier and had more fat mass. Cancer in these mice progressed at a much greater rate than in the lean mice. The heavier mice also had higher levels of leptin, a hormone associated with obesity that promotes cancer, and lower levels of adiponectin, a hormone that appears to protect against cancer.

“We believe this is the first study to show that the beneficial effect on cancer risk by reducing the number of calories in the diet is more closely related to leanness or obesity than previously thought, and not a factor of food intake or total calories ingested,” Nagy said.

Nagy’s team kept two other groups of transgenic mice in the 27 and 22 degree environments. These mice were allowed to eat as much food as they wished. The mice in the cooler environment ate 30 percent more food than the mice in the warmer environment, indicating they required the additional calories to maintain body temperature.

The body composition for both of these groups of mice remained the same; and both had the same level of cancer progression, indicating that the increased calorie intake from the cooler-temperature mice plays no role in cancer protection.

This research was supported by funding from the National Cancer Institute, part of the National Institutes of Health.