Sunday, December 12, 2010

A sampling of dietary science

Doctors and scientists are frequently lambasted by the public and the press for changing our minds about what is healthy and what is not. One day we say eggs are good for you and another they are bad. Fat is bad for you unless you are doing Atkins. Carbs are bad for you unless they are whole grains. And so on. I share the frustration, but want to explore one reason for this phenomenon and then go over a couple of recent diet studies.

Research can be hard enough to conduct even when you have strict control over all the variables. Therefore research becomes that much more complex when you are trying to measure the effect of variables that are moving targets such as "diet". I put this term in quotes because it can and does have a variety of meanings. In this case I intend it to mean what a subject eats on a day to day basis. Think for a moment about what you ate yesterday and the day before. Was it the same? Were any two meals the same? Now extrapolate that variability over the years and years it takes for someone's "diet" to impact their health. How can you really compare one diet to another? Well, we have to try to do it anyway and hope that people's diets with average out and give us some ideas about what is healthy and what is not.

So, getting to the science I wanted to share:

First, from Circulation is a paper by Micha et al which looked at red meat vs. processed meat in the risk of diabetes, stroke, and heart disease. The authors reviewed results from 20 studies totaling 1.2 million people. They found that while processed meats increased the risk of diabetes by 19% and heart disease by 42%, red meat did not increase either risk. Neither type of meat increased the risk of stroke. One important take home point I took from this however, is that the "dose" of meat they studied was 100 grams, or 3.5 ounces. If you did not know, the recommended portion of meat at a given meal is only four ounces and NOT the 18 oz Porterhouse you might find at your local steakhouse. So while beef jerky might be worse for you than a hamburger, everything should be taken in moderation.

Second, Sun et al published their findings in the Archives of Internal Medicine from a cohort study of nearly 200,000 people comparing consumption of brown rice with white rice and the risk of diabetes. They found that replacing 50g/d of white rice with brown reduced the risk of diabetes by 16%. While some people say that carbs are carbs, I tend to disagree, as this research would suggest.

Third and lastly, some science that is a little more robust. This time we have a randomized trial where, for two years, 307 received either a low-carb or low-fat diet and were followed for weight loss, as reported by Foster et al. As with many such trials, subjects were motivated at first but the dropout rate was high. An initial weight loss of 11 kg was similar in both groups, but then weight returned to be down only 7 kg after 2 years. To me, the take home message here is that weight loss can be accomplished in a variety of "diets", especially in the short term, but the effects are not likely to last unless crucial changes to overall lifestyle accompany the diet. I recently heard someone say that you should never go on a diet you don't want to follow for the rest of your life, and I would agree because otherwise you are almost certain to revert to the prior behaviors which resulted in weight gain in the first place.

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