Is it true that eating walnuts or other nuts can interfere with levothyroxine absorption?

Yes regularly eating walnuts or certain high‑fiber foods close to your levothyroxine dose can reduce how much of the medicine your body absorbs. ^[1] Walnuts, soybean flour, cottonseed meal, and dietary fiber can bind levothyroxine in the gut, which may lower its bioavailability and potentially require dose adjustments. ^[2] Grapefruit juice can also delay absorption and reduce bioavailability, so timing matters with foods and drinks. ^[1]

Why nuts (especially walnuts) matter

Walnuts are specifically listed among foods that can bind levothyroxine and decrease absorption from the gastrointestinal tract. ^[2] This interaction is similar to what happens with high-fiber foods, which can trap the medication and keep it from being absorbed efficiently. ^[3] When absorption drops, the thyroid-stimulating hormone (TSH) can rise and become more variable, indicating your body is not getting a consistent amount of thyroid hormone. ^[4]

What the official guidance recommends

It’s recommended to take levothyroxine on an empty stomach, ideally in the morning, 30–60 minutes before breakfast. ^[5] If you routinely take levothyroxine within one hour of foods known to affect absorption (like walnuts or high-fiber foods), your dose may need to be reevaluated. ^[6] Separating levothyroxine from interfering substances by several hours helps maintain stable thyroid levels. ^[5]

Practical timing tips

• Take levothyroxine first thing in the morning with a full glass of water, then wait 30–60 minutes before eating. ^[7]
• If your routine includes walnuts, other nuts, or high‑fiber breakfast foods, consider having them later in the day to avoid the interaction window. ^[6]
• Be consistent with timing: non‑fasting regimens (with breakfast or at bedtime soon after eating) are associated with higher and more variable TSH levels compared to fasting intake. ^[4]

Other common absorption blockers

Beyond walnuts and fiber, several agents can reduce levothyroxine absorption. ^[1] Iron and calcium supplements, aluminum/magnesium/calcium antacids, sucralfate, and certain bile acid sequestrants should be taken at least 4 hours apart from levothyroxine. ^[5] Grapefruit juice may delay and reduce bioavailability, so it’s best not to take it near your dose. ^[1]

How to know if it’s affecting you

If your TSH has been climbing or fluctuating despite taking your medication, timing with food (including nuts or fiber) could be part of the reason. ^[4] Taking levothyroxine in a fasting state keeps TSH within the narrowest target range, which helps avoid under‑ or over‑replacement. ^[4]

Bottom line

Walnuts and some other foods can bind levothyroxine and lower its absorption, so take levothyroxine on an empty stomach and separate it from walnuts, high‑fiber foods, and grapefruit juice by at least 30–60 minutes (and from mineral supplements by 4 hours) to help keep your thyroid levels stable. ^{[2] [5]}