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Arranging and completing large scale, long term research trials to study people’s lifestyle is a complex task. There are so many considerations to adjust for including variables such as age, gender, race, family history of health problems, smoking, income, and on and on. Also, finding an accurate cross sample of the population is key to any research. Even after all of this is accomplished there is always the question of whether the participants actually made a significant modification in their lifestyle during the study.
Three research papers were published recently reporting the data from the Women’s Health Initiative Dietary Modification Trial. This was a trial with almost 50,000 women who were studied over eight years. One paper reported on whether there was a reduced risk of heart disease and stroke in those who ate a lower fat diet (JAMA 2006; 295:655-666). The other papers were concerned with the effect of a lower fat diet on breast cancer (JAMA 2006; 295:629-642) and colon cancer (JAMA 2006; 295:643-654). At first glance, the research doesn’t appear to show much difference between a low-fat diet and a conventional diet.
There has been criticism amongst scientists that this study wasn’t long enough to show significant change.
There were, however, many other difficulties encountered by the researchers during this trial.
The first flaw is that the participants in the study did not mirror what the typical American eats. In 2003 we ate, on average, 2,757 calories and 106 grams of fat per day. Interestingly, this represents a 63% increase in fat from 1970, when we ate 65 grams of fat per person per day. In 1970, 65 grams of fat represented only 26% of our diet, and we now eat 35% of our calories as fat.
At the beginning of the study, participants ate about 1800 calories per day (much less than a typical American). Of this, 37% was fat, or about 74 grams of fat (again, much less than the typical American). At the end of the study the women in the group eating a low-fat diet were consuming 46 grams of fat while the comparison group was eating 64 grams of fat.
So both groups ate healthier than the typical American at the beginning of the study and both ate healthier at the end of the study. Because there was a reduction in calories and fat consumed in both groups, the results of the study are questionable.
Secondly, there was not much of an increase in fruits and vegetables in the study group. We now know that this is critical to a healthy diet and to reducing heart disease.
A third consideration is that the goal of the study was to reduce fat to 20% of calories. This target was, however, not met. We have very good data that supports a low-fat diet as being effective in preventing heart disease and the goal set by researchers was a good one. Since this wasn’t met the study conclusions are uncertain.
There are other considerations about the results that don’t allow us to draw good conclusions from the information. The women were all over fifty and, while there is research that shows it’s never too late to make lifestyle changes, the follow up time may be to short to show changes in this group significant enough to prevent cardiovascular disease or cancer.
Most importantly, the study wasn’t designed to modify different types of fat. Between the time the study was started and now, we have come a long way in understanding that it is more than just reducing total fat that is important. We know that the type of fat one eats is a critical factor in improving health.
There is good news to be found in the study. When you look at those women who ate the least amount of saturated fat, trans fats and more fruits and vegetables, there was a reduction in the risk of heart attack. Those who ate less than 8.5% of their calories as saturated fat had significantly lower incidence of colon cancer. Likewise, the risk of a heart attack was reduced in those who ate lower amounts of saturated fat, trans fats, and more fruits and vegetables.
The imperfections experienced by scientists with this research don’t cancel out the fact that we have many excellent studies that prove eating fewer calories, less saturated fat, very little trans fats, more Omega-3 fats, more whole grains and more fruits and vegetables helps you live longer and live better.
Eat well, eat healthy, enjoy life!
February 20, 2006
Last updated: 02/20/06