MONDAY, Sept. 22, 2003 (HealthDayNews) -- Researchers are questioning the conventional wisdom that a low-fat, high-fiber diet might reduce the risk of breast cancer.
But one critic contends their study is seriously flawed.
The study, published in the Nov. 1 issue of Cancer and available online Sept. 22, measured hormone levels in pre-menopausal women over the course of a year, to try and determine what effect a low-fat, high-fiber diet might have on breast cancer risk. There's much evidence to suggest that excess estrogen in postmenopausal women can contribute to certain types of breast cancer.
While those on the diet did experience a decrease in circulating estrogen, the researchers say the drop wasn't statistically significant.
However, New York University oncologist Dr. Julia Smith calls the study "inconsequential," and says it raises more questions than it answers.
"It's a fallacious presumption to think that you can look at these hormone levels and their effect on pre-menopausal women and translate that into having any meaning for the postmenopausal woman -- the group that is at greatest risk for breast cancer," Smith says.
Even if what the study has shown is true, Smith says, the data are totally unrelated to the conclusion.
"It is a troubling leap of faith to presume that what occurs in a pre-menopausal woman is going to have the same influence after menopause," Smith says.
Perhaps more important, she points out the study authors did not take into account any mitigating factors that could have easily influenced the rate of hormone production, including smoking, alcohol intake, exercise or even the use of certain medications, including birth control pills.
"Basically, this study used what seems to be some highly unreliable data, while ignoring important mitigating factors, to arrive at a conclusion concerning dietary intervention, that, in the end, isn't even applicable to the age group that is most at risk for breast cancer," Smith says.
The 15-month Northwestern University study involved 213 healthy women between the ages of 20 and 40. They were randomly assigned to one of two groups. Members of the first group followed their normal eating habits. The second group followed a low-calorie, high-fiber diet. Fat intake for the second group was limited to no more than 20 percent of daily caloric intake, and fiber levels had to equal at least 25 grams a day. The women in the second group were also told to eat at least eight servings of fruits and vegetables every day.
At the start of the study, blood tests revealed baseline levels of key sex hormones, including estrogen and progesterone. Levels were measured again after four menstrual cycles, and repeated once more after 12 cycles. To help ensure that blood tests were given at the same point in each woman's cycle, all the women used home ovulation test kits to track their menstrual cycles.
The result: Estrogen levels decreased by an average of 7.5 percent in the group following the dietary restrictions, compared to a drop of just 0.9 percent in the control group. There were no differences in the levels of other sex hormones measured during the study. In addition, age, body mass index or baseline hormone levels did not appear to influence the findings, nor did weight loss, which was only minimal in both groups.
While the study did show a decrease in circulating estrogen in the women who followed the low-fat, high-fiber diet, the authors conclude those changes were not statistically significant. Although they concede the small effects on estrogen might have a larger impact when viewed over a long period of time, the researchers also strongly suggest a low-fat, high-fiber diet may not have the same impact on the risk of breast cancer as previously believed.
Smith maintains it's impossible to draw that conclusion based on the study's findings.
"Even if they had designed this study in a way that we could say for sure that there was a drop in estradial (estrogen), which I'm not sure they actually did, we would still be left with the open question about whether this was in any way related to the postmenopausal increase in breast cancer. And I do not believe it is," Smith says.
More information
To learn more about links between diet and breast cancer, visit The American Cancer Society. For more on the link between estrogen levels and breast cancer, check with Cornell University.
