Note: In a western-style diet, absorbed calcium matches urinary and skin calcium at an intake of 840 mg as in Figure 14. Reducing animal protein intakes by 40 g reduces the intercept value and requirement to 600 mg. Reducing both sodium and protein reduces the intercept value to 450 mg.
FAO/WHO and other Nutritionists...verbatim.
Protein
Hegsted, M. & Linkswiler, H.M. 1981. Long-term effects of level of protein intake on calcium metabolism in young adult women. J. Nutr., 111: 244-251.
Margen, S., Chu, J-Y., Kaufmann, N.A. & Callow, D.H. 1974. Studies in calcium metabolism. I. The calciuretic effect of dietary protein. Am. J. Clin. Nutr., 27:584-589.
Linkswiler, H.M., Zemel, M.B., Hegsted, M. & Schuette, S. 1981. Protein induced hypercalciuria. Federation Proc., 40: 2429-2433.
The positive effect of dietary protein – particularly animal protein – on urinary calcium has also been known at least since the 1960s.
Heaney, R.P. 1993. Protein intake and the calcium economy. J. Am. Diet. Assoc., 93:1259-1260.
Kerstetter, J.E. & Allen, L.H. 1989. Dietary protein increases urinary calcium. J. Nutr., 120: 134-136.
Nordin, B.E.C., Morris, H.A., Need, A.G. & Horowitz M. 1993. Dietary calcium and osteoporosis. Second WHO Symposium on Health Issues for the 21st Century: Nutrition and Quality of Life. Kobe.
One study found that 0.85 mg of calcium was lost for each gram of protein in the diet. A meta-analysis of 16 studies in 154 adult humans on protein intakes up to 200 g found that 1.2 mg of calcium was lost in the urine for every 1g rise in dietary protein. A small but more focussed study showed a rise of 40mg in urinary calcium when dietary animal protein was raised from 40 to 80 g (i.e., within the physiological range).
This ratio of urinary calcium to dietary protein ratio (1 mg to 1 g) is a representative value, which we have adopted. This means that a 40 g reduction in animal protein intake from 60 to 20 g (or from the developed to the developing world [Table 30])would reduce calcium requirement by the same amount as a 2.3 g reduction in dietary sodium,i.e. from 840 to 600 mg. (Figure 18).
Margen, S., Chu, J-Y., Kaufmann, N.A. & Callow, D.H. 1974. Studies in calcium metabolism. I. The calciuretic effect of dietary protein. Am. J. Clin. Nutr., 27:584-589.
Schuette, S.A., Zemel, M.B. & Linkswiler, H.M. 1980. Studies on the mechanism of protein-induced hypercalciuria in older men and women. J. Nutr., 110: 305-315.
Schuette, S.A., Hegsted, M., Zemel, M.B. & Linkswiler, H.M. 1981. Renal acid, urinary cyclic AMP, and hydroxyproline excretion as affected by level of protein, sulfur amino acid, and phosphorus intake. J. Nutr., 111: 2106-2116.
How animal protein exerts its effect on calcium excretion is not fully understood. A rise in glomerular filtration rate in response to protein has been suggested as one factor but this is unlikely to be important in the steady state. The major mechanisms are thought to be the effect of the acid load contained in animal proteins and the complexing of calcium in the renal tubules by sulphate and phosphate ions released by protein metabolism.
Nordin, B.E.C. & Polley, K.J. 1987. Metabolic consequences of the menopause. A crosssectional, longitudinal, and intervention study on 557 normal postmenopausal women.
Calcif. Tissue Int., 41: S1-S60.
Need, A.G., Horowitz, M. & Nordin, B.E.C. 1998. Is the effect of dietary protein on urine calcium due to its phosphate content? Bone, 23(Suppl):SA344.
Urinary calcium is significantly related to urinary phosphate (as well as to urinary sodium),particularly in subjects on restricted calcium intakes or in the fasting state, and most of the phosphorus in the urine of people on Western-style diets comes from animal protein in the diet. Similar considerations apply to urinary sulphate but it is probably less important than the phosphate ion because the association constant for calcium sulphate is lower than that for calcium phosphate.
The empirical observation that each 1 g of protein results in 1 mg of calcium in the urine agrees very well with the phosphorus content of animal protein(about 1 percent by weight) and the observed relationship between calcium and phosphate in the urine.
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