Mono-sodium glutamate (MSG) is a flavor enhancer, much like salt, but tastes better (because salt is flat salty), also you need less amount of it than salt in adding flavor to meals. I have no idea if it has an effect on getting full faster, but it did become controversial a few years back when studies showed that msg couldn't be fully metabolized, and it remains in the body system. Some even suspected that it might be the cause of Alzheimer's Disease, but who knows. :).
Does it cause people to get fuller faster? I've noticed a lot of buffets use MSG.
MSG is a salt, really a food enhancer and it adds flavor to meals.
It's also addictive.