Reducing Weight to Reduce Risk
A team of international researchers led by Dr. Paola Pisani of the International Agency for Research on Cancer in Lyon, France has just published a study linking excess body weight to an increased risk of breast, colon and other cancers.
Writing in the International Journal of Cancer, Pisani's team reported on their analysis of demographic cancer incidences in the European Union. They specifically focused on kidney, endometrial, colon, prostate, gallbladder and breast cancers, which have all been linked with obesity.
By comparing cancer incidence with an individual patient's body mass, they concluded that excess weight accounted for about 5 percent of all cancers in the European Union: 3 percent in men and 6 percent in women.
"Reduction in body mass would have its greatest effects on endometrial, breast and colon cancers," they wrote.
They added that their findings "have considerable public health relevance, since they suggest that it is possible to prevent an appreciable proportion of cancer cases by maintaining a healthy body weight." They estimated that "some 36,000 cases [of cancer] could be avoided by halving the prevalence of overweight and obese people in Europe."
And yet, an earlier article published in the Journal of Clinical Oncology somewhat muddled the theory that excessive dietary fat is linked to greater cancer risk, at least for breast cancer.
Dr. Michelle Holes of Harvard Medical School and Brigham and Women's Hospital in Boston and colleagues studied hormone levels from 381 healthy postmenopausal women in 1989 and 1990. They measured their fat intake through food-frequency questionnaires that the participants previously completed in 1986 and then again in 1990.
They observed that a high-fat diet did not lead to higher plasma levels of estrogen. (High estrogen levels have been associated with an increased risk of breast cancer.) "This result is inconsistent with the hypothesis that fat intake predisposes to breast cancer risk by raising endogenous estrogen levels," they wrote. Even without adjusting for obesity, they noted, the association between dietary fat and estrogen was not significant.
Still, numerous other studies have linked a high fat diet with an increased cancer risk. For example, a report that received widespread publicity last year concluded that "waist circumference," i.e., abdominal fat, was a risk factor for breast cancer, particularly in postmenopausal women who have never taken hormone replacement therapy.
Writing in the American Journal of Epidemiology, Dr. Zhiping Huang of the Harvard School of Public Health and colleagues examined the association between waist circumference and breast cancer risk in 47,382 women involved in the Nurses' Health Study. Waist and hip measurements were taken in 1986 and the group was followed through 1994.
During the study period, 197 premenopausal women developed breast cancer and 840 postmenopausal women developed the disease. In premenopausal women, the researchers found that "both waist circumference and the waist/hip ratio were positively but not significantly related to risk of premenopausal breast cancer."
However, they found that waist circumference, hip circumference and the waist/hip ratio were "moderately associated" with an increase in breast cancer risk in the postmenopausal women. This association was strongest for postmenopausal women who had never taken hormone replacement therapy.
Huang's team wrote that "abdominal obesity" appears to be associated with increased estradiol, an estrogen which has been linked to increased breast cancer risk.
Similarly, a study led by Dr. Ingrid Hall of the University of North Carolina, Chapel Hill, found a link between waist-to-hip ratio and breast cancer risk in both African-American and Caucasian women.
Writing in the American Journal of Epidemiology, Hall and her colleagues concluded that despite higher general obesity rates for African-American women compared with Caucasian women, overall body size does not appear to increase their relative risk of breast cancer. However, there does seem to be a specific link between an increasing waist-to-hip ratio and a greater risk for the disease.
Hall's team studied the association between numerous physical factors-including waist-to-hip ratio-and the risk of breast cancer. They compared 350 African-American breast cancer survivors with 353 African-American women without the disease, and 523 Caucasian breast cancer survivors with 471 Caucasian women without the disease. All of the women were participants in the population-based Carolina Breast Cancer Study.
After adjusting for body mass index, they found a positive association between breast cancer risk and the waist-to-hip ratio in both premenopausal and postmenopausal women of both races. They wrote that their findings suggest " central fat distribution ... may be an adverse risk factor for breast cancer."
Many studies have suggested that diet can play a major role in cancer prevention. It is estimated that the incidence of 50 percent of certain cancers (including breast, prostate, pancreas, ovary, endometrium, and colon)-and 35 percent of deaths from these cancers-can be directly associated with Western dietary habits.
In general, the typical diet in the United States provides only about half the recommended fiber intake and is far too high in calories, especially those which come from fat (certain kinds of which have been shown to enhance the development of cancerous tumors).
To achieve any meaningful risk reductions for breast and certain other cancers, caloric intake must be reduced, nutritionists warn, especially the fat component. The latter should be 20 percent or less of total caloric intake. In addition, fiber should be increased to 25-35 grams per day for adults, especially fiber derived from grains, vegetables, legumes, and fruits.
Such dietary improvements would not only reduce risk levels for cancers and other chronic diseases, but would dramatically throttle the ballooning cost of medical care in the United States.
SOURCES:
International Journal of Cancer, February 1, 2001; 91:421-430
Journal of Clinical Oncology, November 1, 2000; 18:3668-3676
American Journal of Epidemiology, December 1999; 150:1316-1324
American Journal of Epidemiology, April 2000; 151:754-764
American Obesity Association (http://www.obesity.org)
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