Calorie Restriction Lowers Breast Cancer Risk
Study Offers Clues About the Role of Early Diet in Disease
By Salynn Boyles
March 10, 2004 -- New research shows that restricting calories early in life can help decrease breast cancer risk later on.
Animal studies have long linked severe calorie restriction to a decrease in cancers and other diseases, and the new study is one of the first to indicate that the same may be true for humans. The findings may also help explain why malnourished women in developing countries have less breast cancer.
Researcher Karin Michels, ScD, from Boston's Brigham and Women's Hospital and Anders Ekbom, MD, PhD, from Stockholm's Karolinska Institute tested the theory by comparing breast cancer frequency among women who had a history of anorexia nervosa with women with no history of the potentially life-threatening eating disorder.
The women who had been treated for the eating disorder developed half as many breast cancers, and the reduction in breast cancer risk was even greater for women who went on to have a child. The study is reported in the March 10 issue of The Journal of the American Medical Association.
Early Diet Appears Important
The researchers say their findings show that early diet -- around puberty and young adulthood -- can play an important role in later breast cancer risk. But they are quick to point out that the findings do not mean that starvation diets are healthy for young women or anyone else.
"Anorexia nervosa is a very serious condition that is potentially life threatening," Michels tells WebMD. "It has been linked to an increased risk for osteoporosis and other health problems, and we are definitely not advocating starvation diets to lower breast cancer risk."
Being overweight, especially after menopause, is strongly associated with an increase in breast cancer risk. Newly published research shows that women can lower that risk by maintaining a healthy body weight throughout their lives, American Cancer Society spokesman Len Lichtenfeld, MD, tells WebMD.
"The message we need to be sending to young women is to watch their diets, exercise, and maintain a healthy body weight," Lichtenfeld says. "But the message is the same for older women and men. We now know that obesity increases the risk of many different cancers, including breast cancer."
One limitation to the study, Lichtenfeld says, is that it says little about the impact of early diet on breast cancer risk among the largest group of women -- those who develop the disease after menopause. Most of the women in the study were diagnosed before they reached menopause.
Study Findings
Michels says she chose women with a history of anorexia for her study because the group represented a unique human model of extreme, prolonged calorie restriction early in life.
The researchers are not recommending anorexia as a means of preventing breast cancer. About 6% of people with severe anorexia die from their disease, according to the National Association of Anorexia Nervosa and Associated Disorders.
Researchers identified more than 7,300 women in Sweden who had been hospitalized for anorexia prior to age 40 over a three-decade period. A comprehensive national cancer registry was used to compare breast cancer frequency among the former anorexia patients to that of the population at large.
Women with a history of the eating disorder were 53% less likely to get breast cancer than the general female population.
This jumped to a 76% reduction in breast cancer risk in those women who had also given birth. Pregnancy has long been linked to reduced breast cancer risk.
Possible reasons for the observed reduction in breast cancer risk include decreased levels of estrogen and other growth hormones among women on extremely low calorie diets and the restrictive impact that such diets have on cell division.
"Very low calorie intake and low body weight are associated with low estrogen levels, and low estrogen levels have been linked to a lower risk of breast cancer," says Brigham and Women's Hospital chief of obstetrics and gynecology Robert Barbieri, MD.
Another possible reason for the association, Barbieri says, is that people on very low calorie diets have lower levels of human growth hormones such as insulin-like growth factor type 1 (IGF-1). Animal studies show that IGF-1 can promote tumor growth. Barbieri was not involved in the study.
"In worms, growth hormones have been directly linked to life expectancy, and people are wondering if this might be another way in which calorie intake could regulate cancer risk," he tells WebMD.
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SOURCES: Michels. K. Journal of the American Medical Association, March 10, 2004; vol 291: pp 1226-1230. Karin B. Michels, ScD, MSc, MPH, Obstetrics and Gynecology Epidemiology Center, Brigham and Women's Hospital; associate professor, Harvard Medical School, Boston. Robert Barbieri, chief, obstetrics and gynecology, Brigham and Women's Hospital, Boston. Len Lichtenfeld, MD, deputy chief medical officer, American Cancer Society. National Association of Anorexia Nervosa and Associated Disorders
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