The Korean custom of feeding new mothers seaweed soup has a nutritional basis. Wakame is rich in iodine and calcium, and iodine requirements rise sharply after birth for thyroid hormone production and milk supply.
The same fact cuts the other way. Average iodine intake in Korea is already among the highest in the world, and for anyone with thyroid disease, excess seaweed can be a problem.
Key benefits
Iodine is the raw material for thyroid hormone
Thyroid hormone cannot be made without iodine. During pregnancy and lactation, requirements rise to about 1.5 times normal, and adequacy is tied directly to fetal brain development. That is the background to seaweed soup as postpartum food.
It supplies calcium and magnesium together
150 mg of calcium and 107 mg of magnesium per 100 g fresh. In diets low in dairy, seaweed acts as a genuine calcium source.
Alginate acts as soluble fibre
The viscous alginate in wakame forms a gel in the gut that slows absorption of sugars and fats. Some studies find a flatter post-meal glucose rise.
Extremely low in calories
Rehydrated wakame is mostly water, so it contributes almost no energy for its volume. It is an easy way to add bulk to soups and salads.
How to eat it well
- Soak dried wakame for about ten minutes, no longer. Over-soaking turns it soft and leaches water-soluble components.
- For soup, sauté it in sesame oil first, then add water — better for absorbing fat-soluble compounds.
- Salt the soup at the end. Wakame retains salt of its own, so seasoning early makes it too salty.
- Two or three times a week beats daily, given the accumulation of iodine.
- Dressing it with vinegar, as in a cold salad, favours calcium absorption.
What to watch out for
- Very high in iodine. With hyperthyroidism (Graves') or Hashimoto's thyroiditis, discuss frequency with your clinician.
- Before thyroid testing or radioactive iodine treatment, seaweed must be restricted; it affects accuracy.
- Seaweeds can accumulate heavy metals such as arsenic, so sourcing matters. Hijiki in particular is high in inorganic arsenic.
- On warfarin, account for wakame's vitamin K.
- If you restrict potassium for kidney disease, check your intake.
Nutrition
Approximate values per 100 g of fresh wakame. Dried wakame expands more than tenfold when soaked.
- Calories
- 45 kcal
- Carbohydrates
- 9.1 g
- Fiber
- 0.5 g
- Protein
- 3.0 g
- Iodine
- ~1,600 µg
- Calcium
- 150 mg
- Magnesium
- 107 mg
- Folate
- 196 µg
Key nutrients
- Iodine
- Calcium
- Fiber
- Magnesium
- Folate