> There are no scientific findings based on human experiments as
> far as I am aware (rather than lab experiments in test tubes) which
> point to [oxalic acid] inhibiting calcium intake.

Am J Clin Nutr 1989 Oct;50(4):830-2
Oxalate: effect on calcium absorbability.
Heaney RP, Weaver CM
Creighton University, Omaha, NE 68178.

Absorption of calcium from intrinsically labeled Ca oxalate was
measured in 18 normal women and compared with absorption of Ca
from milk in these same subjects, both when the test substances were
ingested in separate meals and when ingested together. Fractional Ca
absorption from oxalate averaged 0.100 +/- 0.043 when ingested alone
and 0.140 +/- 0.063 when ingested together with milk. Absorption was,
as expected, substantially lower than absorption from milk (0.358 +/-
0.113). Nevertheless Ca oxalate absorbability in these women was higher
than we had previously found for spinach Ca. When milk and Ca oxalate
were ingested together, there was no interference of oxalate in milk Ca
absorption and no evidence of tracer exchange between the two labeled
Ca species.
----------------------
Am J Clin Nutr 1988 Apr;47(4):707-9
Calcium absorbability from spinach.
Heaney RP, Weaver CM, Recker RR
Department of Medicine, Creighton University, Omaha, NE 68178.

The absorbability of calcium from spinach was compared with the
absorbability of Ca from milk in 13 healthy adults in a randomized
cross-over design in which the test meal of either milk or spinach had
200 mg of Ca labeled with 45Ca. Absorption was measured by the
standard double-isotope method in which both the test food and the
miscible Ca pool are labeled with different Ca tracers. Measurement of
both Ca and oxalate in our test spinach revealed a very slight
stoichiometric excess of oxalate; hence it is likely that all of the spinach
Ca was effectively bound. Absorption was higher from milk in every
case, with the mean absorption from milk averaging 27.6% and from
spinach, 5.1%. The mean within-subject difference between Ca
absorption from milk and from spinach was 22.5 +/- 9.5% (P less than
0.0001). These results conclusively establish that spinach Ca is much less
readily available than milk Ca.

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J Nutr 1987 Nov;117(11):1903-6
Oxalic acid decreases calcium absorption in rats.
Weaver CM, Martin BR, Ebner JS, Krueger C
Department of Foods and Nutrition, Purdue University, West Lafayette,
IN 47907.

Calcium absorption from salts and foods intrinsically labeled with 45Ca
was determined in the rat model. Calcium bioavailability was nearly 10
times greater for low oxalate kale, CaCO3 and CaCl2 than from
CaC2O4 (calcium oxalate) and spinach (high in oxalates). Extrinsic and
intrinsic labeling techniques gave a similar assessment of calcium
bioavailability from kale but not from spinach.



--Jean-Louis Tu <[log in to unmask]>