This month, Dr. Sydney Spiesel discusses the disappointing research on low-fat diets, whether chills cause colds, the newfound benefits of drinking the eggs of pig whipworms (truly), and why saw palmetto won't help your prostate. (Click here and here for the last two monthly columns.)
Low-fat diets: Don't give up yet.
State of the science: For many years, doctors were pretty sure that if people ate less fat and more fruits, vegetables, and grains, they would reduce their risk of cancer in general and of breast and colorectal cancer specifically. They believed this about colorectal cancer because in countries in which people on average consumed half the fat that Americans do, the risk of colorectal cancer is a third lower. Immigrants who come to the United States from such countries take on the higher cancer risk of their new home, suggesting that the difference is caused by an environmental factor, like diet, rather than simple genetics. The evidence for reduced risk of breast cancer came from experiments in which low-fat rodent diets decreased the risk of mammary tumors in rats and mice, as well as some (though by no means all) human epidemiological studies.
Just the thought that excess dietary fat might lead to colon or breast cancer generated many plausible hypotheses to explain how it was true. I even thought of some myself. So, I'm as disappointed as anyone about the published results of three studies by the Women's Health Initiative on whether decreasing dietary fat would decrease the risk of cardiovascular disease, breast cancer, and colon and rectum cancer.
Latest study: The Women's Health Initiative is an example of Big Science applied to medicine—large, carefully planned studies that attempt to resolve important questions affecting many lives. Begun in 1991 by the National Institutes of Health, the WHI studies on post-menopausal women have included more than 100,000 participants. Many are just now coming to fruition. (The past month also saw publication of a WHI study on calcium supplementation and bone loss; click here for my thoughts on that.)
In the low-fat studies, almost 50,000 post-menopausal women between the ages of 50 and 79 were randomly divided into two groups. One group (40 percent of the participants) underwent behavioral modification to decrease their dietary fat and to increase their intake of fruits, vegetables, and grains. The remaining 60 percent were given written dietary advice but not asked to make changes. Both groups were observed for an average of eight years (by people who didn't know anything about the group assignments). Researchers took note of actual changes in the diets of both groups and tracked rates of breast, colon, and rectum cancer. They had less success than they hoped at getting the research subjects to change their diets. But as a whole, the intervention group ate less fat than the women in the other group, reducing their contribution of energy from fat by about 10 percent (researchers had hoped for 20 percent). The differences were tracked by diet histories and confirmed by blood tests.
Results: Unfortunately, the lower-fat diet made virtually no difference in the risk for colorectal cancer and only a small change in the risk for developing invasive breast cancer. Extending the study longer may show that this improvement is genuine. Still, the results are disappointing (unless, of course, you've got a taste you can't shake for fatty foods) though we clearly need to be cautious about accepting them. We don't know whether these results for post-menopausal women also apply to younger people or to men. And we don't know whether a greater average reduction in dietary fat—perhaps at the level that the researchers originally hoped for—would have led to a significant decrease in cancer risk. For now, though, the WHI results remind us that early, plausible-seeming research doesn't always hold up when a question is re-examined on a larger scale with a really careful study design.
Cold feet and colds: dashed dreams.
State of the science: Like most people, I take great and perverse pleasure when common wisdom trumps science. So, as you can imagine, I felt a thrill of anticipation when I heard about a study showing that a chill can cause a cold. My grandmother always said so, but medical science insisted otherwise, based on some experiments in which chilled subjects were deliberately infected with cold viruses. So, who was right?
Latest research: In a new study, Claire Johnson and Ronald Eccles of Cardiff (Wales) University's Common Cold Centre intended to show that chilling the feet sometimes causes symptoms of the common cold. The experiment randomly divided 180 people into two groups. (So far, so good.) Half put their feet in a pot of cold water for 20 minutes, and the other half put their feet in an empty pot for 20 minutes. (Less good, since it would be no secret which group a subject was placed in.) Four or five days later, the participants were mechanically tested by a machine that measured stuffed-up-ness. (Good.)
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