If I eat a lot of iodine based foods before my nuclear scan, will it harm the results?

Depends on… …what type of scan you will be having. Those involving the thyroid gland may be affected by dietary iodine, but the majority of other scans use a different radiopharmaceutical. Contact the nuclear medicine department where your scan will be done for further information. They usually provide preparation info prior to a scan if any special prep is required.
Iodine... If you are having a thyroid scan and uptake with iodine-123 or a scan with iodine-131 then yes. Dietary iodine can compete with radioactive iodine. The uptake of radioactive iodine may be falsely low if you eat a lot of iodine before you have a thyroid scan.
Maybe. If you are having a radioactive iodine thyroid scan ...Yes. The iodine in the foods will compete and even block the radioactive iodine from entering your thyroid. If you are having a technetium thyroid scan the answer is ..No it won't .