They had people go into a movie theatre with either fresh or stale popcorn and were told to either eat with their dominant or non dominant hand.
The first thing the study uncovered is those that consumed popcorn on a normal basis at the movie theatre were more likely to eat more regardless of the popcorn being fresh or stale. Those that were not regular popcorn eaters ate less of the stale one.
This demonstrated that environment has a huge impact. If we associate food with a certain scenario, such as movies and popcorn, our brain can become hard wired to expect it.
The most interesting part of the study was the hands though. Just this subtle change helped participants slow down their consumption, especially with the stale popcorn.
This makes perfect sense to me. 1) You are changing the environment in which you associate the food with and 2) It takes a lot more work to eat with your bad hand.
I can think of a personal example of how this works. When I was in university my friends really liked going out for different ethnic foods. Some of these cultures involved eating with chop sticks. I was never raised with chop sticks so I didn't have a clue how to use them. Rather than look foolish in front of my friends, I bought a pair and attempted to eat my dinners every night for a month with them.
You know what I found?
I ate a whole lot less. I did get better over time, but just having to focus more on my food in order to eat it and being forced to slow down allowed me to recognize when I was full and end the meal sooner.
So if you are a fast eater or prone to over eating, try eating with your weak hand or pick up a pair of chop sticks. You might be surprised by how much less you eat!