Performance difference between game difficulty settings?

Played a dozen games at normal difficulty, just started a game on casual and it was a lot smoother. Granted there are differences between world locations that cause some sort of variance in workload, but this has been continuous better frame rate for a while.

The most obvious difference is no food bar or hunger processing, but that doesn't seem like it would be a major drain on resources. What other differences are there between the difficulty settings?