On Sat, 18 Jul 1998, Susan Carmack wrote:

> You were asking what is wrong with legumes...Legumes contain phytic acid.
> I was talking to Ron Hoggan about it the other day. He explained:
>
> >Phytic acid forms a chemical bond with Calcium, magnesium, and some
> >other minerals that may be in our diet (and we want to absorb). The
> >resulting phytates cannot be cleaved in the human gut, so these minerals
> >are wasted, rather than absorbed. This results in low levels of calcium in
> >the blood, which stimulates the parathyroid to produce PTH (parathormone),
> >which liberates calcium from the bones.

Susan, thank you.  I was aware of the phytic acid issue, and I
agree that it is a concern, especially if large quantities of
legumes are used as a primary protein source.  I think it was
Elzi Volk, however, who recently pointed out that these
properties of phytic acid are largely prevented by vitamin C.
Boyd Eaton suggests that ancient diets were fairly high in C.  I
am thinking, therefore, that the moderate and intermittent use of
legumes would not pose a calcium deficit problem.

The use of legumes and grains *instead* of animal proteins would
be expected to cause problems, I guess, although it didn't seem
to bother my grandmother, who live on beans and rice primarily
until she was 93.

The issue of the lectins in legumes is more potentially serious.
Of course, lectins are present in high concentrations in many
foods, not just legumes.  The paleodiet is by no means a
lectin-free diet.  This is where the blood type theory becomes
potentially relevant, since lectins have different effects on
different blood types.  This fact is beyond dispute.  What is far
less clear is the health consequences of it.  Ray calls "foreign"
all lectins not eaten until the neolithic period, and thus he
assigns all legumes to this category.  But peanuts are edible
raw, so they should be an exception.  Other legumes are edible
after soaking or cooking, which indicates that may have been
eaten in modest amounts for 800,000 years or so.  At least, it's
hard to see why they wouldn't have been eaten.  The fact that
peanut agglutinin agglutinates O blood but not A blood, and
boosts immune system function in type As but not Os seems
significant to me.  It looks very much like an adaptation to this
protein, but only in part of the population.

Returning to the phytate issue, Gary Ditta's recent excellent
post on Paleodiet about hereditary hemochromatosis suggests
another adaptation to extensive dietary phytate.  In this
instance, the adaptation consists of a heightened retention of
iron, which is also blocked by phytates.  In a diet low in meats
and high in grains and legumes, hemochromatosis is an advantage,
since it allows for maximum retention of a scare resource: iron.
In a diet low in phytates (because of the use of refined instead
of whole grains) and high in red meats, hemochromatosis is a
*disease*, usually leading to premature death by cardiovascular
complications.  Neanderthin, in the meat-intensive variation
usually favored here, would be deadly for a person with
hemochromatosis.

Well, hemochromatosis is not that common, although it is the most
common inherited disease among white males.  There is, however, a
lack of confidence in estimates of its frequency in the general
population because it is so often undiagnosed.  I'm not
suggesting that it should be a general cause for concern, but it
is interesting that the difference between cardiovascular risk
between men and women in general becomes insignificant under two
circumstances:  If the woman has ceased menstruating or if the
man is a frequent blood donor.

Hemochromatosis may be another name for either "phytate
tolerance" or "maladptation to a meat-based diet".  If this could
happen with phytates it presumably could have happened with other
supposed anti-nutrients.

We need not only more information, but we need to understand what
we already have.

Todd Moody
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