It's possible. I questioned her several times as to whether that was really the only thing, because I too had difficulty believing it, and she insisted that was the reason. But it's certainly possible that there was simply something else that she didn't feel able or willing to explain. Though, after it intially became clear that it was a major problem for her I tried to force myself to eat more things, and there was a period of reconciliation where the relationship got better again for a couple weeks before the multi-day dish that I couldn't stomach and the resulting renewal of blowing-uppedness.