[jnordwick]

> cravings for things like addictive drugs also increase for a while as you withdraw.

This is in party because once you become a heavy user, your body stops producing various chemicals or becomes accustomed to larger amounts to meet its baseline (such as dopamine and other neurotransmitters). When you stop your body slowly start producing those again and has to become accustomed to the new baseline. That craving is exactly your body telling you that you are missing something.

Is there anything that shows vegetarian and vegan dieters increase the production of chemicals associated with what they are refraining from? Most drug addictions deals with chemicals the body can make itself, but it the substances lacking in a vegan diet would seem to be things we cannot produce.

There are large populations that have eaten that way their entire life. I wonder how their body chemistry is different than those that started veganism later in life. They don't have to adjust. If they started eating meat, what changed in iron or protein synthesis do they go through?