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" . My own opinion is that authorities who advocate cereals
in a prudent western diet largely do so for practical reasons .
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  which is an important
contributing cause of iron deficiency in third world countries and possibly
in the western world . 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 . He was made aware of the calcium-binding effect of
phytate  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 . McCance and Widdowson found adverse effects of bread
prepared from high-extraction wheat flour on retention of essential metals
by humans . They also showed that destruction of phytate improved
retention of calcium . 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 .
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 . 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.
Best regards to all of you,
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