NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/rec/food/veg/12448

Text File | 1993-01-24 | 8.2 KB | 173 lines

Newsgroups: rec.food.veg
Path: sparky!uunet!paladin.american.edu!howland.reston.ans.net!usc!rpi!newsserver.pixel.kodak.com!sasquatch!young
From: [e-mail] (Rich Young)
Subject: Re: Milk and calcium (here we go again)
Message-ID: <[e-mail]>
Originator: young@sasquatch
Sender: [e-mail]
Reply-To: [e-mail]
Organization: Clinical Diagnostics Division, Eastman Kodak Company
References: <[e-mail]>
Date: Sat, 23 Jan 93 17:41:54 GMT
Lines: 159

In article <[e-mail]> [e-mail] (Michele Coleman) writes:

[...]

>    What about all those places in the world where people don't drink
>milk at all, like parts of Africa and Asia?  How do women there fare?

    Generally, they have a lower incidence of osteoporosis, but it's
    dangerous to automatically assume that this is completely attributable
    to diet.  Blacks, for instance, are known to have bone densities
    which are as much as 10 percent greater than Orientals or Caucasians.
    This is genetic, not environmental.  Another confounding factor is
    exercise: strenuous physical activity is known to strengthen bones,
    regardless of diet, and Asians may be getting much more exercise
    than the typical American.  There are other factors which tend to
    cast some doubt on epidemiological studies which rely on fracture
    rates to evaluate bone strength: for example, Western society
    uses the automobile far more often than most African and Asian
    societies, which means more accidents, which in turn means more
    fractures.

    It may be possible to correct for these factors in a well-run
    epidemiological evaluation, but it is incumbent upon the reader
    to verify that such factors as these have, in fact, been taken into
    account in any data presented.  Another point to keep in the
    very front of one's mind is the fact that "correlation" does not
    necessarily mean "causation."  A perfect example is a chart
    presented by Dr. John McDougall in "McDougall's Medicine" which
    shows hip fractures per 100,000 population for a group of varied
    populations.  He claims a high correlation between consumption
    of animal protein and hip fractures...he neglects to mention that
    the correlation is almost identical with life expectancy at birth.
    So, which causes the hip fractures: consumption of animal protein or
    old age?

>Does this osteoperosis thing appear in other mammels--that would be
>interesting to know.  Elephants and moose seem like they have an awful
>lot of bone--so where does all that calcium come from?  The soil must be
>chalk (sorry) full of it.

    One must be very cautious in drawing conclusions about humans
    from observation of other mammals.  Diets differ significantly,
    digestion often differs markedly, and living habits may be
    completely at odds with human practices.

    Bears, for example, experience no net loss of bone minerals while
    they undergo extended periods of inactivity during their winter
    sleep, but humans lose significant bone mass in just a few days
    in outer space.  Elephants and moose eat twigs and bark (among
    other things), both of which are utterly indigestible to humans.
    Interestingly, both of these animals, especially elephants, are
    known to travel some distance to reach "mineral licks" at which
    they supplement their diets by licking and eating exposed mineral
    salt deposits, which often include calcium salts.

>How about when I have a baby--from conception
>to weaning that child grows lots of bone--does it all come from mine
>(yikes!) if I'm not drinking my milk?

    Yes.  It all comes from your body, but the source is not only
    your bones, but your diet as well.  Milk is probably not an
    absolute requirement, but it is an easy source of calcium.  What's
    really important, however, is that you get plenty of calcium,
    regardless of source.  Failure to do this may jeopardize your
    health and that of your baby.

>If protein leaches calcium from
>the bones, is that true of all protein, or just animal protein?

    Protein does not, in and of itself, "leach calcium from the bones."
    High protein intake tends to increase calcium excretion in the urine.
    This excreted calcium is taken from the blood.   The body requires
    a fairly delicate balance of calcium which is transported by the
    blood.  If the blood level of the mineral is too low, the body will
    draw upon its reserve stores, the bones, and seek to raise the blood
    levels.  When all is well, both removal and deposition of calcium
    are ongoing processes.  It is only when removal outpaces deposition
    that there is a potential problem; and if blood calcium is high in
    the first place, perhaps due to increased consumption, then one
    might reasonably expect a similar rise in urinary calcium, regardless
    of diet.  It should be noted that this deposition and removal
    process is mediated by a variety of chemicals and hormones, one of
    which is vitamin D.

    Excessive intake of phosphorus can also cause increased urinary
    excretion, so limiting intake of such items as carbonated soft
    drinks can have a beneficial effect as well.

    It is not clear that excessive consumption of vegetable protein
    would not cause increased urinary excretion, but this is difficult
    to test, since excessive consumption of protein from vegetable
    sources is much less likely due to the decreased nutrient density
    of most plant sources.  There is, however, at least one study which
    implicates cereal grains in bone loss, and another which mentions
    soy protein.  My own opinion is that excessive protein consumption,
    regardless of source, will increase urinary excretion of calcium.

>How
>much protein is too much?  I mean, how much rice and beans and tofu can
>I eat each day before I have to get worried?

    If protein consumption is limited to levels recommended by the
    RDA, there should be little concern.  The problem with the American
    diet is that protein consumption often exceeds the RDA by a factor
    of two or three, especially for those whose diet is heavily meat-
    based.

>If I already have a full
>set of bones, why do I have to keep getting more calcium?  Why can't I
>just keep the bones I've got?

    As noted above, removal and deposition of calcium in the bones is
    a normal process, as is excretion of calcium in the urine.  Sufficient
    calcium must be consumed to compensate for the normal excretion.

>Am I just doomed if I don't eat kale?  [...]

    Hardly.  Calcium is a fairly common mineral and is found in many,
    many foods, although concentrations and availability for absorption
    vary widely.  Remember that ingestion isn't the only thing which
    affects the degree of mineralization in bones...exercise also has
    a notable effect, and absorption of calcium from food may be increased
    as exercise level increases.  Also, one large stalk of broccoli
    (now politically correct since Bush left office) contains abnout
    10 percent of the adult RDA.

>What about those multivitamin pills--is the
>calcium there at all worthwhile?

    Well, yes, it does get absorbed, but there's so little of it that
    it probably won't be a big factor.  This is not a conspiracy on the
    part of vitamin manufacturers, but rather a simple, pragmatic
    reality: a single day's supply of calcium in pill form would be
    more than could reasonably contained in one swallowable tablet or
    capsule.


>Since there are an awful lot of
>vertebrates in the world, there's an awful lot of bone, so it seems to
>me that calcium must be everywhere, in all the plants we eat.  After all,
>all the vertebrates and even some other critters always seem to find it.

    Yes, it's a fairly common mineral.

>So why are we worried at all?  Is it all dairy products that are harmful,
>or only fatty ones; i.e., how about skim milk?

    It is not at all clear that anything except the fat content of
    dairy products is 'harmful" to adults and children older than
    one year.  Skim milk is an excellent source of calcium, and the
    bugaboo regarding protein is a red herring, since it is total
    protein consumption which is the key factor in urinary calcium
    excretion.  If you're worried, eat fewer beans when you drink milk.
    Thinking of milk as a "food," rather than a "beverage," may help.

    I hope this helps answer some of your questions.


-Rich Young (These are not Kodak's opinions.)