Study puta bowl of M&Ms at the entrance of a building and invited people to scoop as many as they wanted.
Participants ate more candy when served with a large spoon than when served with a small spoon.
One unit of something feels like an optimal amount
See the full study here :
Geier, A. B., Rozin, P., & Doros, G. (2006). Unit bias: A new heuristic that helps explain the effect of portion size on food intake. Psychological Science, 17(6), 521-525.https://doi.org/10.1111/j.1467-9280.2006.01738.