Poison in your food

The breathless Should we worry about soya in our food? warns us away from soybeans. One of the people it cites is the owner of a brand of organic soy sauces.

He lived in Japan for 18 years and his Japanese wife, Setsuko, is a cookery teacher. "I never saw soy beans on the table in Japan - they're indigestible."

In Japan they eat soybeans they call edamame and in Taiwan and China, they call them máodòu 毛豆.

I'm skeptical about the dangers of the soybean. Lots of vegetables are dangerous. Consider the following, based on information from the New Zealand Food Safety Authority and the Food Toxicology chapter of Prevention and Therapy of Cancer and Other Common Diseases: Alternative and Traditional Approaches:

• Almonds, fruit pits (apple, apricot, cherry, peach, pear, plum), lima beans, flax seed and cassava or manioc are among the highest sources of amygdalin, which can turn into hydrogen cyanide in the stomach causing discomfort, illness and sometimes death.
• Edible foods containing furocoumarins include celery, parsley, parsnips, citrus fruits, figs and some spices. Normal levels of furocoumarin are low in celery, while markedly increased concentrations are found following fungal invasion or following exposure to cold, chemicals or UV radiations. The highest concentrations are found in edible parts of roots of celery, parsnips and parsley. One of the toxins can cause stomach ache and may also cause a painful skin reaction when contact with the plant is combined with UV rays from sunlight.
• All potatoes contain natural toxins called glycoalkaloids. The levels are usually low but higher levels are found in sprouts, and the peel of potatoes that taste bitter. Severe stomach ache and even death from glycoalkaloid poisoning has been reported overseas, but is very unusual.
• Lectins have been found at comparatively high levels in legume seeds, beans, potatoes and wheat germ. As few as four or five raw kidney beans can cause severe stomach ache, vomiting and diarrhoea.
• Plants like spinach, rhubarb, beet leaves, tea and cocoa contain oxalic acid. The bioavailability of oxalate was greatest for peanuts and beet roots and somewhat less for rhubarb and spinach. Oxalic acid poisoning can cause muscle twitching, cramps, decreased breathing and heart action, vomiting, pain, headache, convulsions and coma.
• Zucchini may occasionally contain a family of natural toxins called cucurbitacins. Bitter zucchinis have caused people to experience vomiting, stomach cramps, diarrhoea and collapse.
• Raw or unprocessed cassava, bamboo shoots, flax and lima beans contain a toxin called cyanogenic glycosides. This can lead to exposure to hydrogen cyanide and its related toxicity.
• Consumption of divicine found in fava beans (Vicia faba) or inhalation of its pollen can produce a disease syndrome termed favism. Favism is characterized by hemolytic anemia, hemoglobinuria and shock.
• Marine fish, especially squid, is the major dietary source of dimethylamine. Dimethylamine is a precursor of N-nitrosodimethylamine, a potent carcinogen in a wide variety of animals. Consumers of large amounts of marine fish have an increased risk of stomach cancer.

The "Alternative" in Prevention and Therapy of Cancer and Other Common Diseases: Alternative and Traditional Approaches sounds a little unscientific to me, but it's packed with references, and the author also sounds a couple of caveats:

[A]ll plant materials contain natural pesticides, alkaloids and other chemicals that are as mutagenic as industrial chemicals. Furthermore, food processing and preparation added considerably amounts of mutagens to the diet. Ames estimated that each day the average American consumed 1,500 mg of natural pesticides compared to less than 0.1 mg of synthetic pesticides. Many of the vitamins are beneficial at low doses but toxic at high doses. Ultraviolet radiation in sunshine activates vitamin D and prevents rickets but in high doses causes skin cancer.

Concern has been expressed about synthetic or naturally-occurring chemicals in foods as causative agents in human cancer.... However, the toxicity of these chemicals may often be minimized by natural defense systems in food, such as metabolism and DNA repair. A holistic view of toxic factors provides a more meaningful risk assessment of dietary toxins and carcinogens. Food additives prevent food spoilage and poisoning from pathogens and protect nutritional quality of foods. No evidence has been found that these compounds in current use in industrialized countries significantly contributes to the overall cancer risk. They do, however, substantially reduce the risk of pathogen related food poisoning, which far outweighs any unproven risk of increased cancer.