Effects of dietary protein, fat and beta-carotene levels on beta-carotene absorption in rats.

It is important that the factors influencing functional carotenoid absorption be made clear. The effect of rat diets containing different combinations of dietary protein, fat, and beta-carotene levels on beta-carotene absorption was evaluated. In the mid-level beta-carotene diet groups (1.8 mg beta-carotene/100 g diet), the retinol content in the liver and the ratio of the liver retinol content to the beta-carotene intake (namely, retinol accumulation rate) were both greater in the mid-level dietary protein groups (20 g protein/100 g diet) than in lower dietary protein groups (5 g protein/100 g diet), but were not affected by dietary fat level (10 g or 2 g fat/100 g diet). The liver beta-carotene content and its accumulation rate were lower in the mid-level dietary fat groups (10 g fat/100 g diet). beta-carotene 15,15'-dioxygenase (CDO) activity in the small intestine increased in the mid-level dietary protein groups, which resulted in an increase in the content of liver retinol converted from dietary beta-carotene. With respect to the mid-level dietary fat groups, the fecal beta-carotene excretion rate (%) increased. The low beta-carotene diet groups (0.006 mg beta-carotene/100 g diet) showed a higher serum retinol accumulation rate, CDO activity, and liver beta-carotene accumulation rate than the mid-level beta-carotene diet groups. These results suggest the marked effect of protein, fat, and beta-carotene level in diets on the absorption and metabolism of beta-carotene.