Do you feel sick because you're eating too much in one sitting, or for some other reason?
Well, quantity is a factor but not the only one. How hard it is to digest is a bigger factor.
For example, if I ate a tiny piece of meat for dinner tonight, I would be fine. If, however, I ate a bigger piece of meat, my stomach would go insane and I would be feeling sick the whole evening. Probably would have an hard night as well because it is so hard to digest. I could eat a plat of salad twice bigger and I would have no problem at all. (But, my stomach shrunk after eating so little for so long so "big" is probably smaller for me than for most.)