Interactions of lactose with calcium, magnesium and zinc in rats.

The effects of lactose on utilization of calcium, magnesium and zinc were examined in two studies. In study 1, weanling male rats were fed either nonfat dry milk or CaHPO4, dolomite or a calcium chelate with supplemental lactose or sucrose for 27 d. In study 2, weanling male rats were fed diets based on milk or lactose-hydrolyzed milk for 28 d or in one meal labeled with 45Ca. Rats fed the lactose-hydrolyzed milk rather than the untreated milk digested their diet more completely, apparently absorbed total calcium and 45Ca less efficiently, and lost more calcium in urine but retained similar amounts of total calcium and 45Ca in bone. The effect of lactose hydrolysis on the absorption of 45Ca was similar whether rats were fed only one meal of the milk-based diets or were fed the diets chronically. The rats fed supplemental lactose (study 1) or unhydrolyzed milk (study 2) retained more magnesium and zinc in bone.