Seafood
Moderate evidenceKelp
Koreans take three times more iodine from kelp broth than from kelp itself: 348 µg a day against 116 µg. Fishing the kelp back out does not take the iodine with it.
Clear kelp and tofu soup
The iodine stays in the broth, not in the piece you lift out. So the kelp goes in small, and comes out before the boil.
2 servings20 min
Ingredients
- Dried kelpone 5×5 cm piece (about 3 g)
- Firm tofuhalf a block (150 g)
- Garlic2 cloves
- Spinacha handful (70 g)
- Spring onionhalf a stalk
- Light soy sauce for soup1 tbsp
- Water3 cups (600 ml)
Method
Wipe the white powder on the kelp with a damp cloth — do not wash it off. It is mannitol, and it is flavour.
Put the kelp in 3 cups of cold water and leave it 30 minutes. The savour comes out without any heat.
Bring the pan up and lift the kelp out just before it boils. Boiled, it releases slime that clouds the broth — and more iodine.
Mince the garlic in and season with the soy sauce. Simmer one minute.
Slice the tofu thick, add it and give it three minutes, without stirring so it holds together.
Add the spinach and the sliced spring onion for 30 seconds. The moment the spinach wilts, turn off the heat.
Cooking note
The 5×5 cm piece is deliberate. Korea's food safety ministry measured dried kelp across the country at about 148,000 µg of iodine per 100 g — roughly seven times sea mustard. A 3 g piece is therefore about 4,400 µg, against an adult daily requirement of 150 µg.
Most of that iodine ends up in the broth. In the same survey, Koreans took an average of 116 µg a day from eating kelp and 348 µg a day from kelp broth. Three times as much. Lifting the piece out does not take it with you.
Which is why this is not an everyday soup. Two or three times a week is realistic. With thyroid disease, or on thyroid hormone, discuss the frequency with your clinician.
Pulling it before the boil serves two purposes. For flavour, it stops the alginate turning the broth slippery; for content, it stops more iodine leaching out. Both point the same way.
Do not stir after the tofu goes in. The protein has not set and it will break up. A gentle shake of the pan is enough.
Spinach gets the last 30 seconds. Longer and the folate and vitamin C leave for the broth while the leaves go stringy.
Ingredients used here
Grains & legumes
Strong evidenceTofu
Soy protein's LDL-lowering effect is confirmed across 43 randomised trials. The size of it is 3–4 %.
Vegetables
Moderate evidenceGarlic
The evidence for garlic points to a modest drop in blood pressure and cholesterol. The trick is to crush it and wait ten minutes before it hits the heat.
Vegetables
Moderate evidenceSpinach
"Spinach equals iron" is only half true. The real value sits in folate, vitamin K, and the lutein that accumulates in your eyes.