soy
4 interactions related to soy
levothyroxine + soy
Soy protein and isoflavones can bind to levothyroxine in the gut and reduce how much of the dose is absorbed, which can raise TSH and, in some people, increase the dose needed to stay in range. The effect is most relevant with large, variable soy intake taken close to the dose, and is best documented in infants fed soy formula.
tempeh + levothyroxine
Tempeh is a fermented soybean cake rich in soy protein, and soy protein binds levothyroxine in the gut and reduces how much of the thyroid hormone is absorbed. Fermentation lowers isoflavone bioavailability but leaves the soy protein intact, so the absorption interference remains. Taken consistently close to the dose, this can lower thyroid hormone levels enough to push TSH out of its target range.
edamame + levothyroxine
Edamame is whole young soybeans. Soy protein and isoflavones can bind levothyroxine in the gut and modestly reduce how much is absorbed if the two are taken close together. The evidence is limited and mixed: case reports and one pharmacokinetic study suggest a small reduction in absorption, while the only randomized crossover study found no significant effect. Any impact is best avoided simply by separating the dose from soy-rich meals.
tofu + levothyroxine
Tofu is one of the most concentrated sources of soy protein in the diet. Soy protein binds levothyroxine in the gut and reduces how much of the drug is absorbed, and case reports describe TSH rising when soy-heavy foods like tofu are added to a previously stable levothyroxine regimen. The effect is modest in most adults but clinically relevant in sensitive patients, and it is managed by timing.