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Protein / Soy Consumption & Osteoporosis
Protein consumption has anabolic effects on cell growth in general. (1) Protein also increases bone-formation (2)
Extra calcium, on the average, also increases bone-formation, so might the effects of extra protein be similar to those of extra calcium?
Like calcium intake, protein intake also positively correlates with both bone-mineral density (3) and hip-fracture incidence; (4) the higher the average calcium / protein consumption, the more calcium the bones will hold, on the average, but also the higher the hip-fracture incidence. And solely because consuming more protein (in combination with high calcium) may lead to a higher bone mass, a high protein (and high calcium) diet is advised to prevent osteoporosis, simply ignoring the accelerating effect on the aging process.
No matter what the diet, the bones always contain less calcium at the age of 70 than at the age of 30. And since the bones obviously ‘refuse’ to structurally hold on to redundant calcium, an increased bone-formation rate leads to increased bone-turnover too. More importantly, an increased bone-formation rate leads to exhaustion of osteoblast reproductivity.
Some people argue that protein even has direct catabolic effects on bone, due to increased endogenous acid production, and they point to increased urine calcium levels after animal protein consumption. (5) Another study however showed that there were not any correlations between extremely high protein intake (1.26 g / kg bodyweight) and calcium excretion rate. (6)
Since osteoporosis only occurs as a lifetime effect, and since the bones try not to hold on to redundant calcium, the direct effects of protein on bone-metabolism most likely does not affect per saldo bone mineral density (BMD). That is why no correlation between BMD and protein intake was found (7). So, in the same way that an increased calcium intake does not necessarily increase BMD (8) (since the body tries to sufficiently decrease its calcium absorption rate), a higher dietary protein intake does not necessarily have any effect on calcium / bone-metabolism. (9)
Statistically, calcium consumption very strongly correlates with hip-fracture incidence. (see main page) How strong is the correlation between protein intake and hip-fracture incidence?
Less strong. Obviously, calcium intake increases osteoblast and calcium turnover more strongly than protein does.
For example: Protein consumption in Greece is highest, but incidence of hip fractures in Greece is not very high (10), and far lower than in Italy, (11) Switzerland, (12) Sweden, (13) etc.
Another example: Swiss protein consumption is even lower than Japanese protein consumption, but osteoporosis incidence in Switzerland is far higher. (14)
Another example: Kuwait protein consumption is quite low, but osteoporosis incidence is comparable to osteoporosis incidence in Italy and France. (15)
Protein consumption in gram / day; 1998
117 Greece 115 USA 115 France 111 Italy 110 Spain 107 Australia 106 Netherlands 105 Denmark 104 Norway 104 Finland 104 Austria 103 New Zealand 101 Sweden 99 Poland 99 Canada 98 Australia 96 UK 95 Kuwait 94 Japan 89 Switzerland 82 China 61 Togo 54 Laos 53 Gambia 51 Ghana 50 Guinea 48 Cambodia 46 Congo 36 Liberia 27 Dem. Rep. Congo
Can consuming soy-protein instead of animal protein be protective?
Animal protein consumption is believed to increase endogenous acid level due to relatively high sulfur amino acid contents (methionine and cystine). this is speculated to increase bone-resorption. Soy protein, indeed, contains less sulfur amino acids (and the soy-protein-quality is therefore lower) and might therefore decrease bone resorption. Some studies showed that in comparison with animal protein, soy protein decreases calcium excretion. (16) Other studies showed no differences in bone-turnover / calcium excretion. (17)
Moreover, the disease osteoporosis is not due to an increased bone-resorption which decreases bone-mineral density. A low BMD is not equal to osteoporosis. If that would be the case, osteoporosis could be easily cured by increasing BMD. But in osteoporosis the osteoblast reproductivity is irreversibly decreased with an inability to repair microfractures. (See main page) So, soy-protein can only be protective if consumption of soy-protein does not increase bone-formation (and thus not accelerate aging of osteoblasts). Unfortunately, soy-protein (like other protein) does increase bone-formation. (18)
More importantly, soy contains high levels of phyto-estrogens (19); Lifetime adequate estrogen levels are known to be protective against osteoporosis; osteoporosis risk in women is far higher than in men because estrogen levels are decreased in women every four weeks and are permanently decreased after menopause.
These phyto-estrogens, however, are 'weak' estrogens and can replace common (powerful) estrogens. (20) Consuming soymilk for only three months can already decrease estradiol level 27%. (21) Consuming phyto-estrogens can, therefore, even cause infertility (22).
If this decrease in estrogen level would be compensated for by an increase in phyto-estrogens that act the same as estrogens, this would be without consequence, but:
Estrogen inhibits activity of osteoblasts (23) and thus inhibits uptake of calcium into the bones, (24) slowing down the ageing process. Genisteine, however, (the main soy-phyto-estrogen) increases activity of osteoblasts (25) and thus increases uptake of calcium into the bones, (26) accelerating the aging process. This partly due to a genisteine-induced increased intestinal calcium absorption. (27)
Estrogen, furthermore, also decreases deportation of calcium from the bones but phyto-estrogens certainly do not inhibit bone-resorption more than natural estrogens do. (28) In fact, where administration of estrogen decreased bone-turnover in rats, a soybean diet did not. (29)
Conclusion Soy consumption may hasten osteoporosis. The degenerative effects of calcium are, however, far greater, since osteoporosis incidence is lower in Asia than in Europe and the US.
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Back to Excessive Calcium Causes Osteoporosis
Sources Abstract of these sources can be found at the National Library of Medicine
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