Dr. Brian Wansink, well-known author of Mindless Eating, published an article on the effects of low-fat labeling on eating habits (“Can ‘Low-Fat’ Nutrition Labels Lead to Obesity?” Journal of Marketing Research, November 2006).  He argues that low-fat labeling increases consumption because the labels (1) suggest to us that the products have lower calorie density; (2) influence us to imagine that the serving sizes are larger than those of regular products; and (3) make us feel less guilty about eating the “low-fat” products.  The main source of support for his argument is a study conducted at a university open house in which incoming students and their families were invited to sample either regular or “low-fat” M&Ms (both samples were, in fact, regular M&Ms).  Dr. Wansink and his team measured how many M&Ms were consumed and how many calories the participants thought they consumed.  According to the results, participants who sampled the “low-fat” M&Ms consumed 28% more than those who ate the regular ones, suggesting that we over-consume “low-fat” labeled products.  The participants also grossly underestimated their calorie-intake by 48 percent; those participants who ate the “low-fat” M&Ms were worse at accurately measuring their consumption.

If we disregard the flaws in Dr. Wansink’s study (small sample size, self-reported weight, to name a couple), the results are quite troubling.  Are we really the clueless eating-machines that he makes us out to be?  I don’t think so.  Let’s consider an economic analysis of the eating choices available to Dr. Wansink’s participants who ate the “low-fat” M&Ms:  When consuming the “low-fat” M&Ms, the participants incurred a substitution effect by consuming a product that they believed had less fat density than the regular M&Ms.  When the participants realized the substitution, their guilt associated with eating the “low-fat” M&Ms decreased.  The decreased guilt led to increased consumption, otherwise known as a scale effect.  The decreased guilt also caused the “low-fat” M&M-eating participants to relax and, therefore, to pay less attention to their consumption levels.

A good way to understand the differing consumption levels of regular and “low-fat” M&Ms is to frame the participants as having lexicographic preferences.  A lexicographic preference structure means that, given a set of M&M characteristics (“low-fat”, calorie content, sugar content), the participants prefer them in an established order, where the first preference is preferred infinitely more than the second:  (1) “Low-Fat” (over regular), (2) Lower Calorie Content (over higher), and (3) Lower Sugar Content (over higher).   As long as the participants consider the decision to take “low-fat” over regular M&Ms as the first preference in their set, we can expect them to continue to consume excessive amounts of “low-fat” M&Ms.

Given the economic analysis above, the  solution to our over-consumption of “low-fat” products is simple:  We need to change the default M&M option from regular to “low-fat” if both options are available, thereby eliminating the first preference in our lexicographic preference set.  We are not irrational eaters, as Dr. Wansink describes us.  If we integrate healthier options into our preference structure, we can focus on the calorie content of our products and make better consumption choices.