This month, researchers Ebneter et al published the results of a study that explored 4 outcomes related to labeling and calorie disclosure.  I am only going to tell you about 2 of the outcomes. One is the amount of calories consumed and the other is the amount of calories the people 'guessed' were in a serving size.  Outcomes 3 and 4 are not a research interest of mine.  For your information, they were 'taste perception' and 'perception of healthiness.'
   The study was an experiment that took place outside of a natural setting.  The people involved in the study were all undergraduate female college students attending a Hawaiian university.  I tell you this so you can consider how much you are like the people who were in the study.
   For the experiment, the researchers placed the women in one of 4 rooms.  Each room had a bowl of uniquely colored M&Ms.  The women were told that they were taking part in a taste test.  A card was set next to each bowl of M&Ms. One card said Low Fat M&Ms and nothing more.  One card said Low Fat M&Ms and one serving (~55 pieces) has 240 calories.  A third card said Regular M&Ms and nothing more and the last card said Regular M&Ms and gave the same calorie information.  (There was no actual difference in the M&Ms).
   The researchers weighed the bowl before and after each of the 175 women went into a room (one woman at a time per room). They gave the women 15 minutes to do the taste test and then removed the items. When the items were gone, the researchers asked the women to estimate the number of calories in a serving of the M&Ms they had tasted. 
   Here is what they learned. (NOTE: the differences might have been by chance alone, i.e., there was not a statistically significant difference between the numbers).
   People with a low fat label ate more calories than those in the regular label group. People without a calorie label in the low fat condition guessed the calories per serving lower than 240.  People without a calorie label in the regular label condition guessed the calories too high (more than 240).
   I will let you think about that.  My concern is the focus on high and low fat when the problem (in general) is consuming too many calories.  I am especially concerned that people mistakenly think low fat is low calorie AND that people do not know how many calories is low or high.  I believe that this study doesn't support the use of low fat labels as much as it supports the use of a traffic light label.  With a traffic light label we can put a big red circle around the fat grams and the calories.
    Here is a nutrition facts panel for a bag of M&Ms - I don't think they make 'low fat' ones.  M&Ms are high in fat - but have 3 times as much sugar as fat!
   There are several labels out there, but according to Mars, the maker of M&Ms, a package this size has 240 calories, 10 grams of fat and 30 grams of sugar.

Here is the study citation.

Ebneter, D. S., Latner, J. D., & Nigg, C. R. (2013). Is less always more? The effects of low-fat labeling and caloric information on food intake, calorie estimates, taste preference, and health attributions. Appetite, 68(0), 92-97. doi: 10.1016/j.appet.2013.04.023