Why a bigger plate makes you eat more
Put a normal portion on a large dinner plate and it looks meagre. Put the same portion on a small plate and it looks like plenty. Nothing about the food changed. Your judgement of how much you are eating did.
This is an old visual illusion with a name, and it has a very practical consequence: people served on bigger plates take more, eat more, and report feeling no fuller. The eye estimates the portion against the rim, and the rim lies.
The effect is not large per meal. It is large across a year, because it happens at every meal, and because the correction goes only one way. A small plate never makes you feel you have overeaten.
I like this example because the usual advice about eating is about willpower, and this has nothing to do with willpower. It is a fact about perception, and you can change the plate instead of trying to change yourself. That is the general shape of a good nudge: alter the environment so that the easy choice and the better choice are the same one, and leave the person’s freedom exactly where it was.
If you want to eat a bit less, do not buy a book. Buy smaller plates.
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