I agree with the part about calories. However, her theory about volume does
not hold water. (pun intended)

In an experiment where test subjects ate a liquid shake from a spout, the
volume they ate varied with calories. It took about two weeks for the test
subjects to adjust the volume they ate after experimenters changed the
calorie density. This two week delay explains why the idiot doctor finds
people eating the same volume, when she switches them to foods with a higher
calorie density. She would have to feed the high calorie food to her test
subjects for at least two weeks and then measure the volume of the eating.
She would find that they would eat tiny portions.

Stomach size has nothing to do with it.