In this month's Journal of the American Dietetic Association there's an elegant little paper that generates a none too surprising conclusion.
The paper details a randomized study whereby subjects were given a lunch meal which began with their being provided 0.5, 1.0 or 1.5 "portions" of pasta. They were then allowed to continue to eat as much pasta as they wanted following the preload consumption.
Being told you just ate 1.5 "portions" of pasta doesn't influence how much pasta you'll continue to eat afterwards or how full you'll feel.
According to the study subjects felt that the term "portion size" referred to the,
"standardised index of the nutritional content of a food/meal, rather than as an index by which to estimate personal food intake"So you mean people don't eat a third of a cookie if that's what the bag's "serving size" states?