New at this..needing help with my diet history

I have to fill out a diet history...Just what are they looking for here. I never had much luck with diets...lost very little and if any gained it all back. I want to make sure I do this correctly..I do not want denied..anyone know specifically what they are looking for here? Is it ok to say that I did not lose any weight on a diet? Or that I gained it all back. Also another question..I take levothyroxine it is a thyroid supplement. I have taken this for years. Could this small thing keep me from getting surgery? Thanks any input welcome Sherri