The effect of high intakes of casein and casein phosphopeptide on calcium absorption in the rat

The effect of the level or source of dietary protein or protein-derived pep tides on Ca absorption is not well understood. We determined, therefore, th e influence of habitual dietary casein level, meal casein and meal casein p hosphopeptide (CPP) on Ca absorption in the rat. True fractional Ca absorpt ion was investigated in male 7-week-old rats, Wistar strain, in three separ ate studies using a faecal Sc-47:Ca-47 ratio method. In studies A and C, ra ts (n 8 per group) were fed on a purified diet containing 200 g casein/kg f or 2 weeks. Rats were then given a Ca-47-labelled meal (10 g) containing (p er kg) either 0, 100, 200, or 300 g casein (study A) or 0, 100, 200, 350 or 500 g CPP (study C). In study B, rats (n 24 per group) were fed on a purif ied diet containing (per kg) either 200, 350 or 500 g casein for 2 weeks. E ach group was then further randomized into three groups (n 8 per group) and given a 47Ca-labelled meal (10 g of the same diet) containing (per kg) eit her 200, 350 or 500 g casein. Ca absorption from a meal was unaffected by i ncreasing meal casein concentration from 0 to 300 g/kg (study A), but was i ncreased with a meal casein content of 500 g/kg (study B). Fractional Ca ab sorption decreased with increasing usual dietary casein intake in the range 200-500 g/kg (study B), suggesting intestinal adaptation. Ca absorption wa s unaffected by inclusion of 100 g CPP/kg in a single meal but was signific antly (P < 0.001) reduced by 200, 350 and 500 g CPP/kg meal, with no eviden t dose-relationship. Thus, while Ca absorption was enhanced by high-casein meals, the mechanism remains unclear.