From: altar@beaufort.sfu.ca (Ted Wayn Altar)
Subject: Calcium: Dairy Products Good Sources?
Organization: Simon Fraser University, Burnaby, B.C., Canada
Date: Sat, 23 Jan 1993 21:13:54 GMT


IV.  ARE DAIRY PRODUCTS A GOOD SOURCE OF CALCIUM?

Remember, fat (and sodium) also decreases absorption, as mention
above,  decreasing again the calcium from whole diary products .

With respect to the influence of protein on calcium balance,
McDougall (ibid) summarizes 5 studies as follows:

initials           intake         balance with   balance with
of investigator    of calcium    low-protein      high-protein
                                  intake             intake
C.A.                 500             +31              -120
M.H.                 500             +24              -116
R.W.                 800             +12              -85
N.J.                1400             +10              -84
H.L.                1400             +20              -65

average              920              +19             -94

Defs.:   "low-protein intake"  =  47 to 50 grams of protein
        "high-protein intake"  =  141 to 151 grams of protein.
 Calcium balance figures are calculated for 24 hours and each of
 the studies used supplementary mixtures of proteins added to
 the normal diet in order to raise protein to higher levels.

The above high protein intakes are not unusual.  Remember, 50
grams of protein can be consume by eating only 6 ozs of chicken
without  skin, 7 ozs of broiled cod.  In contrast you would have
to eat 25 lbs of boiled potatoes or 11 cups of cooked rice.

If you are one high protein diet one needs to consume more
calcium but even with the large intakes of calcium used in 2 of
the studies above the calcium balance was still in the red.
There is no bodily adaptation of this balance to long-term high
protein diets.

In general, with each doubling of the amount of protein
one will lose by 50% the amount of calcium lost in urine.

Anyway, you might want to take at look at McDougall on this
issue as he provides a lot of good information and references
to other studies that indicate:
  a) in most experiments eating meat causes a negative
      calcium balance.
  b) Eskimos have an average of 10 to 15 % less bone than
      do comparable U.S. Caucasians, in spite of the fact
      that the Inuit exercise more.  The Inuit women lose
       10 -12% of their skeleton per decade as compared with
       a 9.5% loss estimated for U.S. white females.
   c)  Even a study funded by the National Dairy Council
       failed to support the use of adding dairy products to
       one's diet as significantly improving the calcium
       balance (unless one cuts out other sources of protein
       like meat or dairy!).

We should also note that plant protein does not have quite the
same inhibitory effect on calcium as does animal derived
protein, not only because there is less protein in plant
foods generally, but because they contain less of the sulfur
containing amino acids, like methionine, as is found
in meats.  These amino acids in particular have a calcium
losing effect on the kidneys (Zemel, J. "Role of the sulfur-
containing amino acids in protein-induced hypercalciurian in
men NUTRI., 1981, 111:545)

This seems to have been born out by an experimental study
(Breslau et al., J. C.IN. END., 1988, 66:140-6) which compared
the amounts of calcium excreted in the urine of 15 subjects who
followed experiemental diets for 12-day periods.  The diets
contained constant amounts of calcium (400mg/day) and protein
(75g/day), but differed with respect to 3 different protein
sources:

    Protein Source                  Ca Loss in Urine
    
    animal protein                  150mg/day
    vegetable & egg protein         121mg/day
    vegetable protein only.         103mg/day

This result suggests that diets higher in vegetable protein, as
opposed to meat protein, may better protect against bone loss,
hence osteoporosis.  In another experimental study using 12 post-
menopausal woman (ages 48 to 82) who for 167 days were carefully
feed a regulated diet supplemented with some minerals (including
calcium) so that they consumed 600mg of calcium.  This diet was
low in fruits and vegetables, hence low in boron.  With a
supplement of 3 mg of boron, calcium and magnesium loss in the
urine was reduced (serum oestrogen and testosterone also
increased, favouring bone calcium conservation).  The authors
concluded that a diet high in fruits and vegetables would thus
help prevent calcium loss and bone demineralization.  As we know,
vegetarians typically do eat more fruits and vegetables than is
found in the normal omnivore diet.

 
                                          ted
Newsgroups: rec.food.veg