The psychology part is very interesting. Just having someone tell you that you look bigger can make you bigger. It's a huge mind game.
Telling someone they look bigger makes them think more about it, which will (perhaps) make them want to live up to what you have told them. This said, they work harder and
can become bigger.
There was a study done with maids at hotels that involved something of the sort. One group of maids were told that their work (cleaning the bedrooms, bathrooms, etc...) had a healthy impact on their health, while the other group was told nothing. The group that was told about their healthy work actually became more healthy and started to lose weight, unlike the other group.
It's an interesting read about the placebo effect --->
Placebo Effect and Maids.