I looked up the section in The Six Week Cure for the Middle Aged Middle, they ran an Iodine load test and they found that despite eating what they believed to be a diet that contained a fair amount of natural iodine from dried kelp, sea vegetables, salty foods and iodized salt - one retained 50 percent and one 60 percent of the iodine load. They corrected this with an iodine supplementation and switched to naturally harvested sea salt. They didn't state which supplement that they switched to.