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Increasing Intake of Soybean Protein or Casein, but Not Cod Meal, Reduces Nephrocalcinosis in Female Rats¹

Xizhong Zhang^*,,2 and Anton C. Beynen^*,

^* Department of Laboratory Animal Science, State University, Utrecht, The Netherlands Department of Nutrition and Food Hygiene, Shanxi Medical College, Taiyuan, Shanxi, The People's Republic of China Department of Human Nutrition, Agricultural University, Wageningen, The Netherlands

Female weanling rats were fed diets with soybean protein, casein or cod meal at 171, 342 or 513 mmol nitrogen/100 g for 3 wk. The diets were isonitrogenous and balanced for fat, cholesterol, calcium, magnesium and phosphorus. Cod meal feeding at 171 and 342 mmol nitrogen/100 g diet produced lower kidney calcium concentrations than the feeding of either soybean protein or casein. Increasing protein intakes were associated with reduced kidney calcium concentrations in the rats fed either soybean protein or casein but not in those fed cod meal. The anti-nephrocalcinogenic effect of increasing intakes of soybean protein may relate to the lowering of urinary phosphorus concentration. Increasing intakes of casein probably inhibited nephrocalcinogenesis by lowering urinary pH and raising urinary magnesium concentration. Increasing cod meal concentrations in the diet lowered urinary pH and raised urinary magnesium and calcium concentrations, but the effects on nephrocalcinogenesis of these changes probably counteracted each other.

KEY WORDS: • dietary protein • calcium • magnesium • phosphorus • rats

¹ Xizhong Zhang was supported by a 1988–1990 scholarship of Shanxi Provincial Government, The People's Republic of China and by the Netherlands Foundation for Nutrition and Health Research.

² To whom correspondence should be addressed at: Department of Laboratory Animal Science, State University, P.O. Box 80.166, 3508 TD Utrecht, The Netherlands.

Manuscript received 14 February 1992. Revision accepted 7 July 1992.