Absorption of calcium from a leafy vegetable rich in oxalates

Abstract

1. Plant foods, especially green leafy vegetables, are the cheapest and richest source of calcium in developing countries and are recommended in balanced diets. Hence it was worth while obtaining further information about the availability of Ca from these commonly-consumed green leaves.2. The green leafy vegetable belonging toAmaranthusspp. was taken as a suitable experimental model because it is not only commonly-consumed, but is also rich in Ca and oxalates. In the first experiment, each of the eight adult male subjects was given a basal diet containing negligible Ca, a milk diet and an‘Amaranthus’diet, both containing the same amount of Ca. These diets were given on 3 consecutive days and the urinary Ca excreted in a 6 h period after the test diet was considered an approximate index of Ca absorbed in that period. The second experiment was designed to study the influence ofAmaranthusspp. on the availability of milk Ca. Each of the ten adult male subjects were given a basal diet, a milk diet and a diet containing the same amount of milk withAmaranthusspp. added to it. Urinary Ca excreted in a period of 6 h was estimated.3. While availability of Ca from milk was good, that fromAmaranthusleaves was low. The ingestion ofAmaranthusleaves together with milk adversely affected the absorption of milk Ca.4. In view of these findings, recommendation of green leaves as a regular source of Ca to the vulnerable section of the Indian Community should be considered with caution. Since green leaves are a main source of other nutrients, especially β-carotene, their consumption cannot be discouraged and hence leaves low in oxalates should be recommended.