In Defense of Food: An Eater's Manifesto

by Michael Pollan

The zero-sum fallacy of nutrition science poses another obstacle to nailing down the effect of a single nutrient. As Gary Taubes points out, it’s difficult to design a dietary trial of something like saturated fat because as soon as you remove it from the trial diet, either you have dramatically reduced the calories in that diet or you have replaced the saturated fat with something else: other fats (but which ones?), or carbohydrates (but what kind?), or protein. Whatever you do, you’ve introduced a second variable into the experiment, so you will not be able to attribute any observed effect strictly to the absence of saturated fat. It could just as easily be due to the reduction in calories or the addition of carbohydrates or polyunsaturated fats. For every diet hypothesis you test, you can construct an alternative hypothesis based on the presence or absence of the substitute nutrient. It gets messy.