Mother Nature gave us the perfect tools to measure our food: our hands. Each person is different and each person's food needs are different. One handful is the perfect size for protein in a meal. Two hands are your salad/veggie portion. One thumb measures off your fats/sweets.
Of course, I do get jealous at my 6?4? friend who can eat huge portions. I could match him, but I shouldn?t! Hopefully, my stomach will shrink to its proper size.