Amount of Dietary Fat and Type of Soluble Fiber Independently Modulate Postabsorptive Conversion of β-Carotene to Vitamin A in Mongolian Gerbils

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Abstract
Current dietary guidelines recommend a decrease in fat intake and an increase in fiber consumption. Decreased bioavailability (BV) of carotenoids is thought to be associated with both of these recommendations. A 2 × 4 factorial design was used to test the effects of dietary fat level at 10 or 30% of total energy and fiber type using no fiber, silica, citrus pectin or oat gum (7 g/100 g) on β-carotene (βC) BV in 4- to 5-wk-old Mongolian gerbils. We assessed BV as both accumulation of βC and bioconversion of βC to vitamin A (VA) in tissues. A VA- and βC-deficient diet was fed for 1 wk followed by one of eight isocaloric, semipurified diets supplemented with carrot powder [∼1 μg βC, 0.5 μg α-carotene (αC)/kJ diet] for 2 wk (n = 12/group). Increasing dietary fat resulted in higher VA (P = 0.074) and lower βC (P = 0.0001) stores in the liver, suggesting that consumption of high fat diets enhances conversion of βC to VA. The effect of soluble fiber on hepatic VA storage was dependent on fiber type. Consumption of citrus pectin resulted in lower hepatic VA stores and higher hepatic βC stores compared with all other groups, suggesting less conversion of βC to VA. In contrast, consumption of oat gum resulted in hepatic VA and βC stores that were higher (P = 0.012) and lower (P = 0.022), respectively, than those of citrus pectin–fed gerbils. The level of dietary fat consumed with soluble fiber had no interactive effects on hepatic VA, βC or αC stores. Results demonstrate that βC BV is independently affected by dietary fat level and type of soluble fiber, and suggest that these dietary components modulate postabsorptive conversion of βC to VA. This study confirms the negative effects of citrus pectin on βC BV, and suggests that oat gum does not adversely affect βC BV.