40 adults were invited to watch a videotape and give some feedback when it was over. They were also given a complimentary bag of M&M s to eat while reviewing the video. Half were given a one-pound bag, the other half were given a half-pound bag. After the program, the researchers “weighed in” the results:

The results were dramatic. Those who were given a half-pound bag ate an average of 71 M&M’s. Those who were given the one-pound bag ate an average of 137 M&M’s, almost twice as many – 264 calories more. Sure, a person saves some money by buying the big bag, but if he decides to watch a hundred videos in the next year, it will also cost him nine pounds of extra weight.

(Brian Wansink, Mindless Eating)

The message here is simple: we eat more when given larger containers, regardless of the product. It doesn’t even matter whether it’s food. Shampoo, pet food, toothpaste – the more we’re given, the more we use. The only exception, interestingly, is bleach. This is probably due to our awareness of how powerful it is and how overdoing it can damage your clothes!

So why are we so easily led? Well, luckily, we’re all in the same group. Regardless of our weight, we tend to look for external cues to tell us how much to eat. A large bag of candy sends us a message that the amount is a “normal” to consume. We trust the size of the container as an indicator:

Although we may not finish the two-pound box of spaghetti when we make dinner for two, it makes us think it’s normal to take a few more bites than we would if it were a one-pound box. It bumps up our consumption norms and leads us to bump up how much we serve ourselves.

(Brian Wansink, Mindless Eating)

Maybe this will make us think twice when we buy anything that reads, “king size”!