Loaded with nutrients not available from land-based vegetables, sea vegetables add new dimensions to your diet with the added benefit that they may protect against cancer.

Q: I’ve heard that sea vegetables are highly nutritious. Should I include them in my diet?

No matter how conscientious you are about eating your five servings of vegies every day, chances are you’re not including the variety that offers the greatest nutritional punch gram for gram. And no, for once it’s not cabbage or broccoli or something equally unloved; instead, it’s that delicious stuff that holds your sushi ingredients in place.

In certain parts of the world, sea vegetables have a long history of use as a medicine: Asian cultures, for example, have used them for millennia to treat cancer. And as so often happens, modern research is uncovering plenty of scientific evidence to support traditional healing methods. Scientists increasingly attribute the low rate of cancer in Japan to the frequent consumption of sea vegetables.

Results from test-tube and laboratory animal studies indicate that sea vegetables suppress colon cancer and boost the immune system. Japanese researchers have investigated the effects of extracts from eight different kinds of sea vegetables on cells treated with potent cancer-inducing chemicals. Strong evidence exists that these extracts have the power to knock out tumours, although the reason for this is not clear. It may be the antioxidant beta carotene (the same substance that colours carrots and kumara); it may be the high levels of cancer-fighting phytoestrogens called lignans; or it may also be compounds such as sodium alginate not found in land-bound vegies.

However, while the source of the healing powers of seaweed is open to debate – at least until further research identifies the mechanism – there’s no question about its nutrient content. Seaweeds are rich in minerals such as potassium, calcium, magnesium, and iron, and loaded with vitamins: 30 grams of nori, for example, contains 11 milligrams of vitamin C and 1500 IU vitamin A. Seaweed is also one of the few non-meat sources of vitamin B12, and for this reason should form a part of a vegetarian or vegan diet: vegans who regularly eat sea vegetables have higher blood levels of this important vitamin than people who don’t eat them.

Sea vegetables are rich in iodine, which is beneficial in the right quantities – 150 micrograms a day – but potentially harmful in excess. The thyroid gland utilises iodine to make hormones that regulate the body’s metabolism; however, iodine intake of more than 1000 micrograms a day can cause the thyroid to work less efficiently. Iodine is also necessary for processing protein and carbohydrates. If you have any concerns at all about iodine intake, consult a naturopath or nutritionist before adding seaweeds to your diet to ensure intake is acceptable.

Sodium chloride (salt) is the other potential troublemaker: one-half a cup of raw wakame contains a whopping 900 milligrams of sodium. Get rid of excess with a light rinse: while soaking loses more, it also reduces the iodine content.

You need only a small quantity of dried sea vegetables to benefit from them: around 10 grams a day is enough to make a difference. Add small pieces to stir fries, grain and pasta dishes, salads, and stews and soups. In fact, the best way to retain maximum nutritional value is to make a stock as some of the minerals are released into the broth: use 15 grams of crumbled, dried sea vegetables to one litre of water and simmer for 30 minutes. And be sure to eat the seaweed – don’t strain it away!

Another delicious way to get your daily seaweed serving is to make cheater’s sushi whenever you are eating rice or quinoa or any grain, or grated or finely slivered land vegetables: cut a sheet of nori into strips, then wrap up a bite-sized morsel of grain and/or vegetable. Or simply eat lunch at your local sushi bar as often as possible: after all, it can’t be considered an indulgence when it’s so good for you!