When their usual portion size were increased, participants increased their calorie intake by 26%.
Context and priming information can significantly affect our behaviour
See the full study here :
Ello-Martin, J. A., Ledikwe, J. H., & Rolls, B. J. (2005). The influence of food portion size and energy density on energy intake: implications for weight management–. The American journal of clinical nutrition, 82(1), 236S-241S, https://doi.org/10.1093/ajcn/82.1.236S