Does Soy foods Affect Iodine?

Amount or timing may matter

The short answer

Soy isoflavones (genistein) inhibit thyroid peroxidase, the enzyme that uses iodine to synthesize thyroid hormones, reducing iodine utilization.

How to arrange timing

Take iodine supplements at least 4 hours apart from soy foods, especially if you have thyroid concerns.

Reference

Reference noted for this food and supplement combination: NIH ODS 2024; Messina & Redmond, Thyroid 2006

Important context

The effect can also change with food amount, supplement dose, product formulation, health conditions, and medication use. Ask a doctor or pharmacist first if you take medication, are pregnant or breastfeeding, or have a chronic condition.