In the last paleodiet post, Robert Crayhon discusses the issue of high
protein and bone loss in the diets of our hunter gatherer ancestors.
Three recent papers which also concern the topic of high dietary protein
intake and bone loss are:

        1.      Heaney RP.  Excess dietary protein may not adversely
affect bone. J. Nutr 1998; 128:1054-57.
        2.      Massey LK.  Does excess dietary protein adversely affect
bone? Symposium overview. J Nutr 1998;128:1048-50.
        3.      Barzel US, Massey LK. Excess dietary protein can
adversely affect bone. J Nutr 1998;128:1051-53.

        Heaney et al (1) concluded that if the calcium to protein ratio
(mg:g) is greater than or equal to 20, then there is probably adequate
protection for the skeleton.   Using an assumed plant:animal subsistence
ratio of 35:65, the Ca:protein ratio for modern diets based upon stone
age food categories (fruits, vegetables, and lean meats including fish,
poultry, shellfish, game meat and organ meats), would be about 2.47.
If one assumes a subsistence ratio exactly opposite (65% plant and 35%
animal), as my colleague Boyd Eaton has (4), and use his wild plant and
animal food data base, then the Ca:protein ratio would be 6.29 for stone
age humans.   The median Ca:protein ratio for 50-59 year old women as
shown using NHANES III data is 9.30 (1).
        From these data, it appears tha it would be virtually impossible
for stone age man, living in his native environment, eating wild plant
and animal foods to have come remotely close to a dietary Ca:protein
ratio equaling or exceeding 20.   Paradoxically, the fossil record shows
stone age man to have thick bones with large cortical cross sectional
areas (5).   Consequently, it is likely that the skeleton of stone age
man and woman would have been more robust and fracture resistant than
that of western, industrialized men and women (5,6).
        How could this apparent paradox be possible?  Stone age men and
women did not consume supplemental dietary sodium chloride, which like
protein can also cause an increased calciuresis (7) and loss of bone
mass (8).   Further, the Ca:Mg ratio was about 1:1 in pre-agricultural
diets, whereas in western diets it can be as high as 4:1 (9).  High
dietary calcium can can cause magnesium deficiencies, even when normal
levels of magnesium are ingested (10).   Because supplemental magnesium
appears to prevent bone fractures and can result in increased bone
density (11), it is possible that the high consumption of dairy
products, at the expense of magnesium rich fruits and vegetables may
unexpectantly result in a reduced bone mineral density.
        Additionally, bone mass is also dependent upon the relative
acid/alkaline dietary load (2,3).   Acid generated by the diet is
excreted in the urine and can cause calciuresis.   Meat and fish have a
high potential renal acid load (PRAL) whereas fruits and vegetables have
a negative PRAL, meaning they reduce acid excretion.   The human kidney
cannot excrete urine with a pH lower than 5; consequently  the acids
(mainly phosphate and sulfate) of acid producing foods such as meats,
fish and some cereals must be buffered partially by calcium  which is
ultimately derived from the skeleton (2,3).   Because  fruits and
vegetables can act as alkaline buffers for the acids derived from meats
and fish, they have been recently shown to decrease urinary calcium
excretion even when dietary protein and calcium were constant (12).
Thus, the high levels of fruits and vegetables that stone age people
consumed, may have partially counteracted the calciuretic efffects of
high protein diets.
        Finally, our stoneage ancestors would have likely had higher
plasma levels of vitamin D than modern man because of their greater
exposure to sunlight.   Vitamin D, synthesized in the dermis via
ultraviolet radiation enhances calcium absorption and can prevent bone
loss.   Lastly, because our ancestors were more active than modern man
(6), their increased activity levels may have also improved their bone
mass despite a high protein intake.

                                Cordially,


                                Loren Cordain, Ph.D.
                                ESS Dept
                                Colorado State University
                                Fort Collins, CO 80523



                                REFERENCES

        4.      Eaton SB et al.  Paleolithic nutrition. A consideration
of its nature and current implications. N Engl J Med 1985;312:283-89
        5.      Ruff CB et al.  Post cranial robusticity in Homo 1.
Temporal trends and mechanical interpretation. Am J Phys Anthrop
1993;91:21-53.
        6.      Cordain L et al.   Evolutionary aspects of exercise.
World Rev Nutr Diet 1997;81:49-60.
        7.      Nordin BEC et al.  The nature and significance of the
relationship between urinary sodium and urinary calcium in women. J Nutr
1993;123:1615-22.
        8.      Devine A et al.  A longitudinal study of the effect of
sodium and calcium intakes on regional bone density in postmenopausal
women. Am J Clin Nutr. 1995;62:740-5.
        9.      Varo P.  Mineral element balance and coronary heart
disease.  Int J Vit Nutr Res 1974;44:267-73.
        10.     Evans GH, Weaver CM et al.  Association of magnesium
deficiency with the blood-lowering effects of calcium. J Hypertension
1990;8:327-337.
        11.     Sojka JE, Weaver CM.  Magnesium supplementation and
osteoporosis. Nutr Rev 1995;53:71-74.
        12.     Appel LJ et al.  A clinical trial of the effects of
dietary patterns on blood pressure. N Engl J Med 1997; 336:1117-24.