Is seaweed really a superfood? I certainly hoped it was true. Recently I had a bad flu that turned into pneumonia. As soon as I left the hospital, I started to research super foods that could promote healing. Seaweed was at the top of almost healthy food list and its powers seemed endless. I found claims that seaweed could:
- Cure cancer
- Prevent Alzheimer’s
- Lower blood pressure
- Reduce risk of stroke
- Detox the body
- Lower risk of breast cancer
- Clear the lungs
- Soothe a hangover
There are more than three main types and 10,000 varieties of seaweed, all with varying nutritional profiles. Brown seaweed like Kombu and Wakame are used in soups and stir fry dishes; red seaweed like nori is pressed into shees and rolled into sushi; and green seaweed like hijiki is often eaten as a salad.
All forms of sea vegetables contain minerals and a whole alphabet of vitamins. This widely available food contains vitamins A, C, E, as well as potassium, magnesium and in fact its one of the few vegetable sources of vitamin B12 and calcium. But if something sounds too good to be true, it probably is. The list of nutrients is somewhat misleading. Sea vegetables are eaten in small servings ( one tablespoon to 1/2 cup). The average 2 oz portion has less than 4% of the RDA of any of the vitamins. By contrast a small serving of broccoli has 40% of necessary vitamin A and 155%o of vitamin C– and at less than 30 mg of sodium. Seaweed is widely touted as a great source of calcium, but the real numbers tell a different story. A 2 oz serving has 30 mg of calcium while a half cup of milk has 100 mg of calcium. Even more troubling, its not clear how much of the calcum in seaweed is actually absorbed.
The Dark Side of Seaweed
Most types of sea vegetables tend to be high in sodium, really really high. For example, a scant 1/2 cup of wakeme has 660 mg of sodium By comparison, 1/2 cup of most vegetables have less than 40 mg of sodium. Other forms of seaweed can clock in at 34 times the amount of potassium as the same size serving of bananas. At this level, potassium can cause irregular heartbeat and kidney problems.
But wait there is more bad news. One half cup of kombu and hijiki have 3000% the recommended daily allowance (RDA) of iodine. This mineral is necesessary for thyroid health but too much can increase risk of thyroid cancer. In fact the higher rates of thyroid cancer in Japan has been linked to the iodine in their sea vegetables. Iodine can also trigger acne like acne eruptions. I was stunned to read that the link between acne and dairy is now thought to be due to the iodine in cows milk ( they get the iodine from the grass they munch on). And in addition to excess iodine and potassium, sea vegetables pick up chemicals from the sea including toxic heavy metals and even arsenic. Yikes.
Bottom line– Bite for bite you will get better nutrition at less risk from less exotic vegetables like sweet potatoes, kale and blueberries. Given the high levels of sodium, potassium, iodine and possibly arsenic, conventional wisdom limits seaweed servings to 1-2 small servings per week. You can sprinkle one tablespoon crushed Nori over traditional salads or add Wakame to soups or stir fry dishes for flavor and texture. But look to other foods for nutritional payloads.
Coming up soon– Seaweed in skin care