The effect of lactose and fermentation products on paracellular calcium absorption and femur biomechanics in rats

The paracellular absorption and subsequent utilization of calcium was examined in male Wistar rats fed diets containing a skim milk protein concentrate (SMPC), SMPC + 20% lactose (ML) SMPC + 50% lactose (HL) and yogurt powder concentrate (Y), respectively. Animals fed the HL diet exhibited a lower (p ≤ 0.05) food intake resulting in decreased calcium intake and body weight gain to SMPC, ML and Y fed animals. Plasma α-amino nitrogen and triglyceride levels were significantly (p ≤ 0.05) lower in HL fed animals than SMPC and ML fed animals, indicating nutrient malabsorption in these animals. Intestinal absorption and femur deposition of 45Ca were not different in SMPC, ML and Y fed animals, but significantly (p ≤ 0.05) enhanced in HL fed animals. Femur ash weight and mineral composition were not affected by dietary treatment, but femur weight and biomechanical bone hardness were significantly (p ≤ 0.05) lower in HL fed animals. Our results indicate that lactose enhancement of calcium absorption occurs at a critical intestinal concentration of lactose and is not seen when substituted with lactose fermentation products. There was no evidence indicating a difference between calcium bioavailability from milk and yogurt dairy sources. The reduced bone strength in HL fed animals could not be attributed to reduced femur mineralization. A greater effect associated with other forms of nutrient malabsorption is suspected.