How long do I have to be on a low iodine diet for thyroid nuclear scan?

2 weeks. A low-iodine diet should usually be followed for 2 weeks prior to a thyroid whole-body scan. The rationale behind this is to reduce the chances of non-radiactive iodine (in food and table salt) to compete with the radioactive active iodine use for diagnosis (i-123) and treatment (i-131).
7days. Patient s should be on low iodine diet for one week before the the scan.