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tell them that your doctor put you on a special diet that is just for you and is being over looked by a nutritionist (this is not technically a lie) tell them that you are on 5 small meals a day and plenty of liquid and since you need your proteins you have your liquid shakes to boost your protein and yeah you wish you could eat more but the diet is definately working and since it's coming from your doc and a nut then hey they can't be wrong...then jokingly ask "so I didn't know you guys completed your medical school....great job" Make them shut up a little bit. Everyone thinks they are an authority on diet and excercise because they watch doctor oz and the doctors......

Lol I love your reply