May 17, 2001 -- Watching how much and what kind of fat you eat may have an unexpected benefit, according to a report in the May issue of Metabolism. Meals low in fat may actually decrease levels of testosterone, a male sex hormone that may increase risk of prostate cancer.
"This was only a preliminary, short-term study," says researcher Madeleine J. Ball, MD, a professor of biomedical sciences at the University of Tasmania in Australia. "It aims to alert other researchers to consider the short-term effects of meals on hormones."
Ball and coauthor Raymundo C. Habito studied 15 healthy men 2-6 hours after eating four different types of meals under similar conditions. All meals contained the same number of calories, but differed in type of protein and in quantity and type of fat.
After low-fat meals of tofu or lean meat, but not after meals high in animal fat, testosterone and another index of male hormone levels dropped. Adding unsaturated vegetable oil to the lean meat meal didn't change the effect on lowering male hormones.
"We are accustomed to thinking that the potential effects of diet on sex hormone levels are gradual and long-term," says Gann, who was not involved with the study.
Possible mechanisms that Gann suggests might allow sex hormone levels to change so quickly after meals are insulin levels rising after eating, or shifting of male hormones from one body tissue, such as fat or blood, to another.
While earlier studies did not show major differences in male hormones after eating relative to fasting, Gann says this does not rule out an effect from specific types of meals.
"Our findings require further research," Ball says. "But they fit with other concerns about the adverse effects of high saturated fat diets on a number of diseases."
She suggests that decreasing dietary fats, especially animal fats, may protect against prostate cancer and other diseases sensitive to hormones, and that soy protein and safflower oil may be good substitutes for animal fats. Lower sex hormones after meals low in animal fat may provide long-term benefits in reducing the risk of these diseases.
"Societies consuming a low-fat vegetable diet have low rates of prostate cancer," Stephen Barnes, PhD, a professor of pharmacology and environmental health sciences at University of Alabama in Birmingham, tells WebMD when asked for objective commentary. "When those people come to the U.S.A. to our fat- and protein-rich diets, their prostate cancer risk shoots up rapidly."
"Extreme changes in dietary intake can have widespread effects on sex hormones, and so can extreme levels of physical activity. Small to moderate differences in meal composition are probably not all that important," Richard N. Baumgartner, PhD, tells WebMD when asked for independent comment.
"While a diet extremely low in animal fats could theoretically reduce chances of prostate cancer, the effect is not that well studied," says Baumgartner, an epidemiologist in the clinical nutrition program of the University of New Mexico in Albuquerque. "Genetic and other influences are probably more important."
Renato Pasquali, MD, a professor of endocrinology at the S. Orsola-Malpighi Hospital in Bologna, Italy, cautions that "lower [index of male hormone] levels have been linked to risk of heart disease and type 2 diabetes."