According to the British Thyroid Association (BTA), there is no evidence that people who have hypothyroidism need to completely avoid soyfoods. They do recommend waiting four hours after taking thyroid medication before consuming soy products, however. This is because soy protein can interfere with the absorption of the medication. The BTA also noted that the recommendation for soy is the same as it is for high-fiber foods, iron and calcium supplements, as well as antacids that contain aluminum or magnesium. All of these products also impair the body’s ability to absorb thyroid medication. Many drugs and herbs have similar effects. Thyroid medication is meant to be taken in the morning and on an empty stomach.