Calcium and zinc balances of premenopausal women consuming spinach- compared to cheese-containing diets

Abstract

A cross-over design was used to assess the effects of alternate 3-wk feedings of identical diets containing either 453 g spinach or 93 g of cheese on calcium and zinc balance, oxalate excretion, and urinary hydroxyproline in 7 premenopausal women. The daily servings of cheese and spinach each accounted for approximately 77% of the calcium and 30% of the zinc provided by the experimental diets. Mean fecal (p<0.05) and urinary oxalate (p<0.01) were significantly greater on the spinach (high oxalate) compared to the cheese (low oxalate) diet. Mean calcium and zinc balances (−55 and −0.4 mg/day) during the cheese consumption period were not significantly different from those obtained during spinach consumption (−168 and −0.8 mg/day). Mean urinary calcium was greater (p<0.01) during cheese relative to spinach ingestion. The finding that subjects maintained a less negative calcium balance in spite of higher urinary calcium levels during the cheese compared to the spinach experimental periods suggested that the high oxalate and/or fiber load provided by 453 g of spinach decreased the overall calcium availability of the diet. This contention was supported by the higher urinary hydroxyproline (p<0.01) and hydroxyproline/creatinine ratio (p<0.05) observed during ingestion of the spinach-containing diet.