Like any other food, eating excessive amounts of flax seeds can be harmful to your health. Raw flax seeds naturally contain cyanogenic glycosides-such as linamarin, linustatin, and neolinustatin. These cyanogenic glycosides can release cyanates that can be combined with sulfur molecules in our body to form thiocyanates. Excessive amounts of thiocyanates can sometimes be a problematic for our thyroid function and, for this reason, flax seeds are considered goitrogenic. These cyanogenic glycosides are not exclusive to flaxseed and are found in brassica vegetables and cassava, with many of the health concerns regarding cyanogenic glycosides stemming from studies showing that cassava was toxic to animals and humans (McMahon and others 1995). Cassava contains significantly more cyanogenic glycosides than flaxseed.
In addition to cyanogenic glycosides, trypsin inhibitor, linatine, and phytic acid are other antinutrients contained in flaxseed. Trypsin inhibitor activity (TIA) in flaxseed is lower than those in soybean and canola seeds.
Other anti-nutritional compound present in flax seeds is linatine, an antipyridoxine factor. Although linatine is a problem in chicks, flaxseed has not been associated with a vitamin B6 deficiency in humans. In fact, no effect on serum pyridoxine levels in subjects consuming 45 grams of flaxseed per day over 5 wk has been observed (Dieken 1992). These data suggests that linatine is not of a concern as long as we eat less than 45 g of flax seeds a day.
Daun and others (2003) reported that a person would have to consume 8 cups (1 kg) of ground flaxseed to achieve acute cyanide toxicity. At the recommend daily intake of about 1 to 2 tablespoons, approximately 5 – 10 mg of hydrogen cyanide is released from flaxseed, which is well below the estimated acute toxic dose for an adult of 50 to 60 mg inorganic cyanide and below the 30 to 100 mg/d humans can routinely detoxify (Roseling 1994)
Eating excessive amounts of flax seeds too quickly can cause mild digestive problems in some people. This means flax seeds take some getting used to. We suggest: start out with a teaspoon daily and work your way up to a tablespoon. In a balanced diet that already provides omega-3 fatty acids from other foods, one tablespoon (eight grams) of flaxseed daily will often provide enough alpha-linolenic acid (ALA) to meet person’s omega-3 dietary needs.