Just tell them you are on a diet, and trying to eat healthier food choices and watching your portion sizes. They should respect you for those decisions. I don't think you need to delve into your personal medical history to justify what you want or are able to eat; nor do they need any further information beyond a polite comment to that effect. Or just say you've lost your appetite as of late, and that you feel better eating lighter meals.
I rarely go out to eat, but if I do, I do not explain myself to anyone when ordering, unless I feel like humoring them. Then I might tell them I am a surgically altered freak.
moms2big reacted to labwalker in What are your excuses?