Here is a summary of psychological research about why we eat more than we think. The details of the experiments can be found in “Mindless Eating” by Brian Wansink.
1) Larger portions make us eat more (even if we’re not aware of it).
2) If you give people a larger package of anything, they will pour more (chips, M&Ms, cereal, spaghetti, you name it!) The size of the package gives people a cue as to what/how much is acceptable to eat.
3) We don’t realise when we eat more – there was a great experiment done with soup, where some people had refillable bowls, and some people had normal bowls. Even though the people with refillable bowls ate 30-40% more, they thought they had had the same as people with normal bowls.
4) We eat less sweets when they are in an opaque bowl with a lid, than when they are in a clear bowl. Get cloudy bowls!
5) If you move the sweets further away from where you sit, you are less likely to eat them (it’s too much effort walking 6 paces to retrieve what you want).
6) If you want to encourage healthy eating/snacking, put bowls of carrot and celery out, they will get mindlessly eaten!
7) Willpower is not strong enough to constantly resist food; it’s better to get the environment to work for you.
8) If you buy bulk food, repack the food in smaller bags when you get home.
9) The perception of variety will make people eat more e.g., if there are different colours of the same food (e.g., m&ms), or lots of bowls of nibbles, people will eat more.
10) When supermarkets use signs like “Limit 12 per customer”, people buy more than if there is no sign. We are very suggestible to numbers, and tend to anchor our behaviour around this. For example, you might not buy 12 chip packets, but you might buy six, which is maybe three more than you were planning.