I think it's rather common to downplay things in fear of judgement, reaction, or consequence. I have a lot of fear of all three sometimes and I have a hard time with it, even being honest with myself about symptoms and issues. In fact, just today I chronicled some of the problematic behavior I have done and realized it's far beyond what I initially realized. I play down my (hypo)manic moments a lot, and say they aren't an issue when I realize now, they are extensive and hard to not see them for what they are.

My point is, I think part of it is natural to feel the way you do -- but maybe you could try baby stepping your way to being a bit more honest. Perhaps you can say "I'm putting in effort to eat well, but I am having a hard time because of [insert reason here]. I feel I am ok (if you do), but I'm trying (if you are-- or just say you're having a hard time justifying the effort)". I think there are nuanced ways to express yourself more honestly and not have such a harsh reaction. Try anticipating questions and writing out a response. If you know they are going to ask about your eating habits, have something prepared.

That's just a suggestion. I know it is hard to open up to people especially when they are in control of your care. I'm sorry you have such a hard time about opening up with them.