The study took place in the UK, and though the researchers did what they could to mask the experiment (i.e., they told people that they were assessing how emotion affects taste), it was still unnatural (i.e., 1) they knew they were in a study and that researchers were going to collect the popcorn buckets at the end, and 2) they had to fill out a questionnaire at 3 time points during their stay at the cinema). Nonetheless, and taken with a little popcorn salt, the findings were interesting.
First, the use of labels in general, a RED high fat or a GREEN low fat did not change consumption. Whether a person got a bucket of popcorn with no label, a red label or a green, they ate on average 549 calories if it was toffee flavored and 242 calories if it was salt flavored (from this I am guessing butter was not involved!). There was not an interaction between label and BMI or label and weight concern. So for the basic question of whether labeling led to a difference in the amount of calories consumed, segmenting people based on BMI or weight concern didn’t change the outcome - there was no effect.
However, when looking at 3 way interactions, the researchers found some interesting paradoxes ~ though not necessarily new ones. SES does seem to matter when you also consider weight concern. Interestingly, a person who was concerned about their weight and was more affluent ate more popcorn when they had a low fat label than a similar person who was not concerned about their weight. The higher SES person who was concerned about their weight ate MORE with a low fat label; on the other hand, a low SES person who was concerned about their weight ate less popcorn whether the label said low fat or high fat. In other words, when they had a popcorn with a label on it, they ate LESS than if they had a popcorn without a label. The researchers expect that the label is a prompt - a reminder that calories matter.
What does all this mean? Well, you have to answer that question for yourself and do read the study if you are so inclined, because I am not sure that I interpreted everything correctly. My thought, much in line with the researchers, is that nutrition labeling can work, but we need to understand more about how it works and for whom. I also think that the type of label is of utmost importance. I did not like these because low or high fat doesn't tell you anything about calories.
Crockett, R. A., Jebb, S. A., Hankins, M.,& Marteau, T. M. (2014). The impact of nutritional labels and socioeconomicstatus on energy intake: an experimental field study. Appetite.