Dean asked for references to the notion that phytic acid in cereal grains causes calcium depletion. In 1992 Professor Harold H. Sandsted, who is Interim Editor-in-Chief of the American Journal of Clinical Nutrition, the most important journal of nutrition, noted that "the evidence seems overwhelming that high intakes of fiber sources that are also rich in phytate can have adverse effects on mineral nutrition of humans" and that, "in view of the [reviewed] data, it appears that some health promoters who suggest that U.S. adults should consume 30-35 g dietary fiber daily either have not done their homework or have simply ignored carefully done research on this topic" [1]. My own opinion is that authorities who advocate cereals in a prudent western diet largely do so for practical reasons [2].
So let's look do the homework. Whole meal cereals and other seeds have in their shells phytic acid which strongly binds to minerals like calcium, iron, zinc and magnesium to form insoluble salts, phytates [1, 3-7]. It is well known that whole meal cereals by this mechanism decrease the absorption of such minerals [1, 3-7]. There is apparently no adaptation to a habitual high intake of phytic acid [8] which is an important contributing cause of iron deficiency in third world countries and possibly in the western world [9]. It is also an important cause of mineral deficiency in vegetarians [10-12]. The most commonly studied minerals are bound to phytic acid possibly in the following decreasing order: calcium > iron > zinc > magnesium (Fredlund K, personal communication).
Mellanby found back in the 30s that young dogs got rickets when they were fed oatmeal [13]. He was made aware of the calcium-binding effect of phytate [14] and showed that phytate was the dietary factor responsible for inhibition of calcium absorption by oatmeal as well as the induction of rickets in dogs [15]. McCance and Widdowson found adverse effects of bread prepared from high-extraction wheat flour on retention of essential metals by humans [16]. They also showed that destruction of phytate improved retention of calcium [17]. Substantial evidence have later firmly established this negative impact of phytate [1, 3-7]. Not even rats seem to be fully adapted to graminivorous diets since phytate adversely affects mineral absorption in them as well [18].
In the archaeological record, rickets is rare or absent in preagricultural human skeletons, while the prevalence increases during medieval urbanization and then explodes during industrialism [19]. In the year 1900, an estimated 80-90 per cent of Northern European children were affected [20, 21]. This can hardly be explained only in terms of decreasing exposure to sunlight and descreased length of breast-feeding. An additional possible cause is a secular trend of increasing intake of phytate since cereal intake increased during the Middle Ages (Morell M, personal communication) and since old methods of reducing the phytate content such as malting, soaking, scalding, fermentation, germination and sourdough baking may have been lost during the agrarian revolution and industrialism by the emergence of large-scale cereal processing. The mentioned methods reduce the amount of phytic acid by use of phytases, enzymes which are also present in cereals [22-26]. These enzymes are easily destroyed during industrial cereal processing [27, 28].
It should be noted that dietary fiber alone has no impact on mineral absorption [5, 29] why a high intake of fiber from fruits and tubers can safely be recommended, at least from this point of view.
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