Why Does Nutrition Advice Always Seem to Be Changing?
It can be hard to keep up with ever-changing guidelines. Marion Nestle shares a few principles to help steer you right.
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Everyone eats. Everyone can claim firsthand experience and expertise. Whose experience and expertise should you trust? “Mine, of course,” is my standard (slightly facetious) answer. I can understand why people trust celebrities more than scientists or nutritionists; they feel like friends, even if the relationship is unreal. It doesn’t help that nutritionists have impenetrably confusing credentials, ranging from none beyond personal experience to years of graduate and post-graduate study.
It also doesn’t help that nutrition science is so extraordinarily difficult to do. Just think of what it would take to show whether eggs, the largest dietary source of cholesterol, raise the risk of heart disease. To achieve definitive results, you would need to put large numbers of people matched in age, gender, and risk on one of two defined diets, the same except for whether eggs are included. To make sure your study subjects stick to the diet, you would have to confine them under close supervision for expensively long periods to see whether eggs induced symptoms.
Humans are not lab rats. We make terrible experimental animals. This forces nutrition scientists to resort to indirect measures, such as blood cholesterol levels, that do not always relate clearly to disease risk.
I’ve long said that the most intellectually challenging problem in nutrition is to figure out what people eat. Diets vary from day to day, and yours differs from mine. Scientists ask us to write down everything we ate yesterday (24-hour recall), or to keep track of what we eat in a day (24-hour dietary record), or to fill out a survey of how often we ate a given food in the last week, month, or year (food-frequency questionnaire). The accuracy of these methods depends on how well we remember what we ate. They are, to say the least, imprecise. At the moment, better methods are too expensive and difficult to use with large numbers of people, leaving researchers to do the best they can with whatever information they can get.
Humans are not lab rats. We make terrible…
