MONDAY, June 10, 2002 (HealthDayNews) -- The higher the fiber intake of young girls, the more likely their periods will occur later than average.
That's the finding of a new study by researchers at the University of Toronto.
And later periods, in turn, reduce the risk of getting breast cancer later in life, previous research suggests.
"This is the first study to actually focus on fiber and components of fiber [and its effect on the onset of menstruation]," says Malcolm Koo, assistant professor of public health sciences at the University of Toronto, who led the study, published in the journal Public Health Nutrition.
Other studies have evaluated fiber and other dietary components, body weight, a mother's age of first menstruation and additional factors to predict when a girl's periods will start.
Koo's team evaluated 589 girls, ages 6 to 14, taking into account their weight, physical activity and mother's first menstruation. The researchers also asked the girls about their dietary fiber intake. The age of menstruation onset varied from 8.5 to 15.6 years, with a median of 13.6. In the United States, the average age of menstruation onset is 12 or 13 years.
Least likely to menstruate at younger ages were those girls who ate the most fiber. Those who ate about 25.5 grams a day were half as likely to have early menstruation as those in the lower intake group, who averaged 18.2 grams daily.
The fiber lowers the body's estrogen levels, Koo says, and that delays the onset of menstruation.
"Dietary fiber can bind with free estrogens in the intestinal tract, increasing the elimination of estrogen from the body," he says. "The more estrogen circulating in the bloodstream, the earlier menstruation starts. By keeping the concentration of estrogen in the body low, you delay the onset of menstruation."
In his study, Koo also found that girls who eat high amounts of monounsaturated fats, such as olive and canola oils, also have later onset of menstruation.
"Some previous studies have shown that a high-fat diet leads to early onset of periods because of higher body fat [from eating a lot of fat]," Koo says. But he found that did not apply to the monounsaturated fats.
Although there is no formal recommendation for dietary fiber intake i the United States, most experts recommend adults take in between 20 grams and 35 grams a day. According to Koo, the general guideline for children is the child's age plus 5 to 10 grams. A girl aged 10, for instance, could take in about 20 grams of fiber a day. A one-cup serving of raisin bran cereal has four grams, for instance, and a raw unpeeled apple has about three grams.
Another expert has praise for the study, but says it still doesn't completely answer the question of timing of onset of menstruation.
"I think that the conclusions are pretty good," says Dr. Donna Shoupe, a professor of obstetrics and gynecology at the Keck School of Medicine at the University of Southern California, Los Angeles.
But she wonders if the fiber deserves all the credit.
"It has long been known that a critical body weight seems to trigger pubertal events; the problem is that no one really knows why. I think that those who eat lots of fiber tend to be those who also eat less fat and carbs (carbohydrates) and are more slender."
But Koo is convinced it's the fiber. "I adjusted for body weight, so that consideration is taken care of," he says.
"It's important to know your daughter's dietary fiber intake," Koo tells parents of young girls. Increasing the fiber just slightly, he says, could delay onset of menstruation and reduce the risk of breast and other cancers later in life.
Even if the fiber doesn't succeed in delaying menstruation onset, he says, there are other benefits to hefty amounts of fiber.
"It helps prevent chronic diseases, such as high blood cholesterol, [and] reduces the risk of colon cancer," he says.
And, of course, it's good for promoting regularity.
What To Do
For information on how birth weight affects menstruation onset, see the American Academy of Pediatrics. For more information on fiber, visit the International Food Information Council Foundation.
