Flax seed is said to contain about 23—33 g/kg of phytic acid, depending on the cultivar, location, and year of harvest (Oomah et al., 1996; Muir & Westcott, 2003). Phytic acid forms a complex with many important minerals, including iron, zinc, calcium, etc., thus making them less available. Antinutrients such as phytic acid are thought to have evolved as a defense mechanism so seeds such as flax can protect themselves from insect infestation. In any case, the phytic acid content in flax seed is lower or comparable to that of other oil seeds (Oomah et al., 1996; Morris, 2003).
Flax seed contains a vitamin B-6 antagonist, linatine, a cyclic hydroxylamine derivative (Klosterman et al., 1967). Linatine was found to adversely affect the growth of chickens fed linseed meal (Klosterman et al., 1967; Klosterman, 1974). As a result, in animal studies diets containing high levels of flax meal are supplemented with extra vitamin B-6. However, Ratnayake et al. (1992) and Dieken (1992) found that flax seed meal, when fed 50 g to humans, did not affect vitamin B-6 levels or metabolism.
Other antinutrients include trypsin inhibitors, oxalates, and cyanogenic glycosides, to mention a few. Cyanogenic glycosides, which are also present in flax, can be found in a number of plants, including cassava — for which it is known. In flax, however, the release of hydrogen cyanide is reported to be below the toxic or lethal dose (Toure & Xueming, 2010). The levels of cyanogenic glycoside released from 1—2 tablespoons of flax seed meal is said to be approximately 5—10 mg of hydrogen cyanide, which, according to Roseling (1994), is significantly lower than the acute toxic dose for an adult, which is between 50 and 60 mg. In fact, Zimmerman (1988) reported that the levels detected in blood were significantly lower than those of somebody smoking tobacco.
Although rare, allergic reactions to flax are not well documented. A few cases have been reported by Muthiah and colleagues (1995), who reported an anaphylactic reaction to the carbohydrate component of flax. Meanwhile, Alonso et al. (1996) also recorded a case of an anaphylactic reaction after the intake of flax oil (Muir & Westcott, 2003). One of the better known reactions, known as byssonosis, has been reported to occur from exposure to flax dust during the harvesting and processing of flax. Individuals coming into contact with the dust particles report incidences of asthma, pneumonia, and bronchitis.
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