Decreased absorption and retention rates of magnesium in the rats fed on spinach-supplemented diets: possible explanations

Abstract

We studied the bioavailability of magnesium (Mg) in spinach after boiling with distilled water, using Mg-deficient growing male rats. The rats were fed a semipurified diet (Mg:0.063 per cent (w/w)) for 3 days. then a Mg-deficient diet (Mg:0.001 per cent (w/w)) for 5 days. They were then divided randomly into 7 groups of 6 rats each, and fed the semipurified diet (Mg: 0.063, 0.045 or 0.027 per cent (w/w)), or the spinach-supplemented diet (10 per cent (w/w) dried and powdered spinach after boiling with distilled water for 3 min at 100 degrees C). The Mg content of the diets supplemented with spinach grown on chemical nutrients, and on manure from pigs, cattle and fowl, was 0.069, 0.051, 0.043 and 0.036 per cent (w/w), respectively. Water intake and volumes of urine and faeces were significantly greater in the rats fed the spinach-supplemented diets than in those fed the semipurified diets. Apparent absorption of Mg, and urinary and faecal excretions of Mg were directly related to Mg intake: no significant difference was observed amongst the groups. Both the ratios of Mg absorption and retention were significantly lower in the rats fed diets supplemented with spinach than in those fed semipurified diets. The plasma Mg level was directly related to Mg intake in the rats fed the semipurified diets and the spinach-supplemented diets. However, the plasma Mg level in the rats fed spinach grown organically on manure from fowl tended to be higher than in the other groups. From these results, it was concluded that bound Mg in spinach was effectively utilized by Mg-deficient rats, however, the absorption and retention rates of Mg in rats fed diets supplemented with spinach were decreased. Possible explanations were discussed.