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From foodconsumer.org H.eart & B.lood
The findings, resulting from Women's Health Initiative (WHI) project, are in contrary to the long-held notion that a low fat diet helps reduce the risk of heart disease and cancer, the first and second largest killers in the United States. One large randomized clinical trial of 2,437 women, who entered the trial with breast cancer surgery performed in the previous year, found that postmenopausal women who ate a low fat diet (20 percent energy from fat) were less likely to get a recurrence of breast cancer than those who ate a standard diet (40 percent of calories from fat), suggesting eating a low fat diet can help prevent breast cancer. The finding was presented at American Society of Clinical Oncology annual meeting, Orlando, Florida on May 16, 2005. Based on previous studies, the U.S. government and many health organizations including American Heart Association have long advocated for use of nutrition-balanced, healthy diets with low fat and high fruits/vegetables for prevention of heart disease and possibly some cancers. Some doctors quickly responded to the news saying that the evidence is there suggesting that reduction of dietary fat does not help risk of cardiovascular disease and cancer. "A concerted effort to reduce fat intake to 20 percent of total energy over an eight-year period did not reduce the incidence of breast or colorectal cancer in these women", Healthday News quoted Dr. Michael Thun, with the American Cancer Society as saying. Some are more cautious about the interpretation of the results suggesting that the study could not tell the whole story about the effect of the dietary fat on the cancer and heart disease risk and the results were unlikely the last word on the subject. "It's possible that a benefit for both breast and colorectal cancer will emerge over time," Dr. Jacques Rossouw, WHI project officer at the National Heart, Lung, Blood Institute (NHLBI). The studies were meant to evaluate a low-fat dietary pattern's effect on the risk of cancer. However, investigators also evaluated the data to review the effect on cardiovascular disease. The eight-year studies, funded by the NHLBI, involved about 48,000 post-menopausal women at an average age of 62, ranging from 50 to79, during the period of 1993-98. Forty percent of the subjects were asked to reduce their fat intake to 20 percent of total calories and increased consumption of fruits and vegetables (five or more servings) and grains (six servings) while the rest were allowed to continue following their typical Western diet containing about 35 percent of the total energy from fat. The studies found that those on the low fat diet had a 9 percent lower risk of breast cancer than those on the conventional high fat diet, but the risk reduction was not statistically significant although it might suggest a possibility. However, "study data indicate that women who started with the highest fat intake and who had greater changes in fat intake, show stronger evidence for reduction in their risk of breast cancer. Longer follow-up may be needed to show the effects of diet on cancer risk over time," said Leslie G. Ford, M.D., National Cancer Institute. A low fat diet did not seem to reduce the risk of colorectal cancer either, but those who used a low fat diet were associated with a 9 percent lower risk of polyps and adenomas, presumed precursors for the cancer, indicating that the benefit may show up in the future. A low fat diet was not linked with a reduced risk of heart disease and stroke, which kill nearly one million of Americans every year, according to the Centers for Disease Control and Prevention. This association seems to be understandable because the risk factors for heart disease such as triglycerides, low density lipoprotein (bad cholesterol) levels, and blood pressure were only slightly reduced in those on a low fat diet. Some experts suggest the fat reduction was not enough to have an effect. Subjects on the low fat diet could not continue using a low fat diet, and they ended up using a diet with 29 percent of energy from fat near the end of study. More importantly, Dr. Marcia Stefanick, Ph.D., professor of medicine at the Stanford Prevention Research Center and Chair of the WHI steering committee, said "Rather than trying to eat "low fat,' women should focus on reducing saturated fats and trans fats." The subjects in the studies were not asked to differentiate good fat such as found in fish, nuts, and vegetable oils from bad fats such as saturated fat and trans fat found in processed foods, meats, and some dairy products. The type of fat can make a huge difference. "While the participants' overall change in LDL "bad" cholesterol was small, we saw trends towards greater reductions in cholesterol and heart disease risk in women eating less saturated and trans fat," said Dr. Rossouw. Alberto Ascherio, Meir J. Stampfer, and Walter C. Willett from Departments of Nutrition and Epidemiology at Harvard School of Public Health estimated in a review article published on the University's web site that replacement of trans fat in the U.S. diet with natural vegetable oils would prevent approximately 30,000 premature coronary deaths per year, and epidemiologic evidence suggests this number is close to 100,000 premature deaths annually. http://www.hsph.harvard.edu/reviews/transfats.html The amount of dietary fat may be a less relevant issue than the type of fat when it comes to its effect on heart disease and cancer risk. Mediterranean diets contain quite high fat, but not as much saturated and trans fat as the Western high fat diet does, and "consuming a Mediterranean-style diet rich in olive oil, whole grains, fruits, vegetables, and nuts may reduce the risk of cardiovascular disease in patients with metabolic syndrome," says Mohsen Meydani, professor at the Friedman School of Nutrition Science and Policy at Tufts. "This (study) shows that you can't rely on using low-fat substitute to make a reduction," Dr. Stefanick said. "You really need to think about what kinds of fats you're eating and the foods that should be part of your diet, such as vegetables." Another possible explanation for the negative results from the studies was that the subjects may be too old for the studies and their dietary history was not surveyed. An early dietary habit may have a long-lasting effect on the heart disease and cancer risk. In addition, eight years is still not long enough to observe the effect of dietary change on these diseases, particularly, cancer. Simply switching to a low fat diet and sticking to it for a few years unlikely have a significant effect on heart disease and cancer prevention. These diseases usually take years, maybe decades in some cases to develop. Still another possibility is that the studies did not consider other risk factors such as lack of physical exercise and obesity that are now thought to be major risk factors. In addition, the studies relied on statistical analysis, which is subject to unintended errors and biases, introduced into the statistic models by the researchers. One positive finding, however, is that those following a high-carbohydrate, low-fat eating pattern did not increase body weight, triglycerides or indicators of increased risk of diabetes such as blood glucose or insulin levels. Breast cancer is diagnosed in 200,000 American women each year. Heart disease and stroke kill nearly 900,000 men and women in the U.S. each year. The current findings are the latest results from the WHI. Previous studies from the WHI have found that hormone therapy after menopause can raise the risk of cancer and heart disease. Results of a third clinical trial studying the effects of calcium and Vitamin D supplementation on osteoporosis-related bone fractures and on colorectal cancer will be published in February, according to NHLBI. Dr. Stefanick advised that women who want to maintain their health should follow a diet low in saturated and trans fats, and rich in vegetables and fiber – rather than to strive to eat "low-fat" foods. She also advised that attention should be paid to total caloric intake and regular exercise. "The results of this study do not change established recommendations on disease prevention. Women should continue to get regular mammograms and screenings for colorectal cancer, and work with their doctors to reduce their risks for heart disease including following a diet low in saturated fat, trans fat and cholesterol," said NHLBI Director Elizabeth G. Nabel, M.D. "The U.S. Dietary Guidelines for Americans recommend that adults keep total fat intake between 20 and 35 percent of calories, and saturated fats less than 10 percent of calories, with most fats coming from sources of polyunsaturated fats and monounsaturated fats, such as fish, nuts, and vegetable oils. For people with heart disease or at high risk for heart disease, targets for saturated fats may be further lowered." NHLBI states in response to the studies. © 2004-2005 by foodconsumer.org unless otherwise specified. |
