Nori (Dried Seaweed)
Food · Vegetable · Food, Typed Supps
2,200 mcg of iodine per hundred grams, against a daily upper limit of 1,100.
Stage by stage
- A sheet is 3 g (The pack): Which is what makes the 2,200 mcg per 100 g figure liveable — one sheet is around 66 mcg.
- Iodine (Thyroid): Fifteen times the daily requirement per 100 g, against an upper limit of 1,100 mcg.
- Protein (Muscle): 46.7 g per 100 g by dry weight — higher than beef or soybeans.
- Fibre (Gut): 34.3 g per 100 g, alongside 1,400 mcg folate and 290 mg vitamin C.
What the evidence supports
- Supplying dietary iodine — strong evidence. At 2,200 mcg/100 g it is the densest food source in existence, and a 3 g sushi sheet delivers around 44% of the adult daily requirement.
- Evidence that it causes Thyroid dysfunction from excess seaweed intake — moderate evidence. Real and documented. The adult upper level is 1,100 mcg/day, which 50 g of nori exceeds. Case reports cluster with kelp supplements and kombu rather than sushi-quantity nori.
Timing
No timing. The variable is which seaweed and how much: nori sheets are safe at any realistic intake, kelp and kombu are not.
Time to effect
- Per sheet: About 66 mcg of iodine — 44% of a day, well inside the limit.
- Weeks: How quickly excess iodine can disturb thyroid function.
Allergens
None of the fourteen major allergens. May contain: Sulphites. Derived from what this food is, not from a product label.
Eating patterns
Fits: Vegan, Vegetarian, Pescatarian, Halal, Kosher, Keto, Gluten-free. Depends on the product: Low-FODMAP.
Satiety
Not scored: the satiety index is measured on 240 kcal servings, and nobody eats a 240 kcal serving of this. The question does not apply rather than the answer being unknown.
Environmental footprint
0.5 kg CO2e and 108 litres of freshwater per kg, matched to "Other vegetables" in Poore & Nemecek (2018), Science 360.
Cost band
Cheap — roughly £2.5 per kg, as a band midpoint rather than a price.
Key nutrients
Nutrition per 100g
- Calories: 303
- Protein: 46.7g
- Carbohydrate: 2.3g
- of which sugars: 0.3g
- Fat: 4.3g
- of which saturated: 0.9g
- Fibre: 34.3g
- Sodium: 470mg
Food vs. supplement
Kelp supplements are the reason iodine excess appears in case reports at all — they concentrate the same nutrient without the serving-size constraint that makes a 3 g nori sheet self-limiting.
Kitchen tip
Nori sheets are the safe form. Kelp supplements and kombu broth are where the iodine problems actually come from.
Common myth
“Seaweed is a superfood — you can’t have too much.” In reality: You can, and it is the one food where that is genuinely easy. Nori carries 2,200 mcg of iodine per 100 g against an adult upper limit of 1,100 mcg a day. A sushi sheet is 3 g and entirely safe; kelp supplements and kombu broth are where the case reports of iodine-induced thyroid disease come from. Too much iodine causes thyroid disease just as too little does.
Recipes that use it
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In the glossary
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