Iron king no more: Nutrition table revision leaves hijiki in the dust
SHOTARO TANI, Nikkei staff writer
TOKYO -- Hijiki, a type of edible dark algae, is causing a stir in the Japanese culinary world. Consumed in Japan for centuries and a vital part of the traditional Japanese diet, hijiki has a reputation for being rich in iron. But a recent revision of the government's nutrition tables has revealed that the popular food's iron content has changed considerably.
In December 2015, the Ministry of Education, Culture, Sports, Science and Technology (MEXT) published the 7th edition of its standard tables of food composition in Japan, the first review in five years. Reflecting the changes in the Japanese diet over the years, the revised edition has increased the number of foods it covered for the first time in 15 years, and a more detailed breakdown of cooking methods.
But what drew widespread attention was the change in hijiki's reported nutrients.
The dark algae, mostly found growing on rocky coastlines, is the go-to food for many people who suffer from anemia. The Ministry of Health, Labor and Welfare recommends that adult men consume 7-7.5 mg of iron per day; past editions of the table listed hijiki as containing 55.0 mg of iron per 100 g. It ranked sixth in overall iron content in 2010, behind the likes of ground basil and nori seaweed. However, the revised edition shows that hijiki now contains only 6.2 mg of iron per 100g, one-ninth of what it had been.
"This is due to a difference in production methods," explained Ryoko Kawai, director at office for resources in MEXT. Hijiki, when processed after gathered, is boiled and steamed before being dried and eventually lined up in supermarkets. It was common for the boil/steam process to be done using steel pots, but "we understand that most domestic hijiki production is now done using stainless steel pots," she said.
When cooked in steel pots, hijiki absorbs iron from the pot, whereas with the stainless pots it cannot, hence the drastic drop in the iron content number. The new food table also contains nutrient information for hijiki cooked in steel pots; iron content is 58.2 mg per 100 g.
Hijiki is not the only food to take a hit in its iron content. Kiriboshi-daikon, cut and dried radish root, contains 3.1 mg of iron per 100 g in the new table, but in the previous edition, it contained 9.7 mg. The story is similar with hijiki: stainless knives are replacing steel knives in production, meaning less iron is absorbed.
The composition table is used by school nutritionists for menu planning for school meals, as well as nutritional guidance in many other areas. Hijiki is a popular menu item in school and hospital meals, so will the drop in iron content prompt nutritionists to look for alternatives?
"Hijiki is rich in other nutrients, so it is hard to see it being taken off lunch menus just because it doesn't contain as much iron as was thought," said Kawai from MEXT. "But it is possible that our revision might prompt the makers of hijiki to state whether their product is made using steel or stainless pots."