Responding to news reports of a large US study published in JAMA, which showed that women who began eating a lower-fat diet at over age 50 were not significantly protected from cancer and heart disease, Sarah Keating M.D., a Canadian doctor, wrote to the Toronto Star to say these women’s diets were not strict enough:
The latest study on low-fat diets is further indication that only truly significant changes to our eating habits can reduce our risk of disease.
As a physician, I know that eliminating meat and other animal products from the diet — a step the low-fat dieters in this study did not take — is proven to reduce the risk of heart disease, obesity, and some forms of cancer.
The China Healthy study and other research on populations around the world have already shown that people on plant-based diets have strikingly low cancer rates. This is because vegetarians typically eat less saturated fat, more fibre and are, on average, slimmer than meat eaters. A 2003 study showed that a vegetarian diet lowers serum cholesterol concentrations about as effectively as cholesterol-lowering statin drugs, a key to preventing heart disease.
By choosing a meatless diet rich in naturally low-fat foods, such as beans, whole grains, fruits, and vegetables, we can significantly reduce our intake of artery-clogging saturated fat and protect ourselves from a number of chronic illnesses.
Toronto Star, Letters, Feb 10, 2006
Although headlines claim that the study has shown no benefit for women on the lower-fat diet, comments from some of the researchers themselves indicate that despite the size and cost of this study, the results are far from definitive.
Why? The women switched to a low fat diet relatively late in life. At 8 years out, the study has not run long enough. By today’s standards, the women received inadequate guidance on types of fat to avoid (especially, they were not advised to avoid trans fats). And many of the women on the supposedly “low-fat” diet drifted away from the relatively moderate target levels of fat back to close to a normal US diet. Even so,the women on the low-fat diet actually did develop less cancer. As reported by The Baltimore Sun,
[The study recruited] 48,835 healthy women with an average age of 62 were enrolled. Forty percent of them were given what is descriobed as intensive counseling to help them reduce their fat intake, while the remainder continued with their normal diet.
Even with the counseling, most women were not able to reduce fat consumption from the average of 35 percent of their calories at the beginning of the study to the target of 20 percent.
At the end of the first year, their fat consumption was 24 percent of calories; by the sixth year it had inched back up to 29 percent.
That lower adherence to the diet than planned was, in part, “why we don’t have definitive results yet,” said biostatistician Ross Prentice of the Fred Hutchinson Cancer Research Center in Seattle.
The study did not differentiate between different types of fat.
Prentice cautioned that the subjects were all “very healthy women who were already following most of the [government’s] dietary guidelines,” so their ability to decrease risk by lowering fat might have been low.
“Unhealthy women may gain more benefit.”
The Mercury News presents a Q&A with one of the study leaders, Marcia Stefanick of Women’s Health Initiative:
Best bet: Eat more fruits, veggies
Q What did the Women’s Health Initiative diet study find?
A The study of 48,835 women found that a low-fat diet alone does not prevent breast cancer, colorectal cancer or heart disease in women over 50. However, there were some signs that a low-fat diet might improve health.
Q What were those signs?
A Women who dramatically lowered the amount of fat they ate and increased their consumption of fruits and vegetables had lower rates of breast cancer than women in a comparison group who did not change their diets. Fewer polyps, a potential sign of colon cancer, were found in women who ate a low-fat diet. Women who ate less saturated fat or trans fats and more fruits and vegetables appeared to have a lower risk of cardiovascular disease.
Q Does this mean that I should abandon my low-fat diet?
A Not necessarily. The women in the low-fat group did not reduce their fat intake as much as researchers had hoped. As a result, they say more study of a truly low-fat diet is needed to determine whether it can prevent cancer. More benefits of a low-fat diet may emerge as the women are studied for another five years. In addition, reducing saturated fat and trans fats have been shown to help improve heart health.
Q If a low-fat diet isn’t going to help, what else can I do to prevent heart disease and cancer?
A Researcher Marcia Stefanick of Stanford University recommends following a diet that’s low in saturated and trans fats, and rich in vegetables and fiber, rather than a generic “low-fat'’ diet. Pay attention to total calories and strive to get your weight to a healthy level. Exercise regularly. Women should also get routine mammograms and screenings for colorectal cancer and heart disease risk. Routinely check your cholesterol profile, blood pressure, blood sugar and body weight.
