Impact of dietary lipids and meal patterns on carotenoid bioavailability from raw vegetables

Shellen Goltz, Purdue University

Abstract

The role of dietary carotenoids as nutritive and disease preventative plant pigments has stimulated interest in methods to enhance the bioavailability of these compounds. Considering the fat-soluble nature of carotenoids and the role of triacylglycerols (TAG) in several steps of carotenoid intestinal absorption, it is recognized that co-consumption of lipid in the form of TAG is one of the most effective stimulators of carotenoid absorption in vivo. However, the amount and source of commonly consumed dietary lipids required to optimize bioavailability has not been systematically evaluated. Further, in response to the 2010 Dietary Guidelines recommending an overall reduction in fat intake, strategies to enhance carotenoid absorption when consumed with a low to moderate amount of dietary lipids should also be investigated. Given that carotenoid absorption is a saturable process, the bioavailability of these plant pigments may be promoted by consuming multiple, small carotenoid-rich meals in place of one large daily dose. The objective of these studies was to evaluate the impact of dietary lipids and meal patterns on the bioavailability of carotenoids from raw vegetables in vivo. The first study examined the impact of both amount and source of TAG on the postprandial absorption of carotenoids from vegetable salads. Twenty-nine healthy subjects consumed three identical salads with 3, 8, or 20g of canola oil, soybean oil, or butter as assigned by treatment groups in a Latin square design. Postprandial carotenoid absorption was measured by isolating triacylglycerol rich fractions (TRL) of blood collected from 0-10h. Carotenoid contents of TRL fractions were analyzed by HPLC-DAD. While both amount and source of co-consumed lipid impacted carotenoid bioavailability from these salads, amount exerted a stronger effect. Considering all lipid sources, 20g of lipid promoted higher absorption compared to 3g and 8g for all carotenoid species (p<0.05), except for alpha-carotene (P=0.07). Pooling results from all lipid amounts, canola oil promoted the greatest absorption followed by soybean oil and butter, respectively, however these results were not statistically significant. The second study evaluated whether dividing one large carotenoid dose into two smaller doses, in the form of salad vegetables from the first study, would further enhance carotenoid absorption when consumed with a relatively low amount of canola oil. Six healthy subjects consumed equal amounts of fat-free "chef's salad" ingredients at two meals representing lunch and dinner, along with raw salad vegetables and 8g canola oil split between meals in the following patterns: 100 and 0%; 75 and 25%; and 50 and 50%. Postprandial carotenoid absorption was determined by isolating TRL fractions from blood samples collected between 0-12h. TRL carotenoid concentrations were analyzed by HPLC-DAD. For the apolar carotenes and for combined carotenoids, absorption was greatest when 75% or more of the vegetables were consumed in the first meal (P<0.05). For the relatively polar xanthophylls, consumption of all vegetables in the first meal seemingly improved absorption compared to 75% or less at one time. However, these results were not statistically significant. Taken together, these data suggest that dietary lipid is a key potentiator of carotenoid absorption from common salad vegetables. Further, when fat intake is reduced, carotenoid absorption may be the greatest when consumed in one meal instead of several lower fat and carotenoid meals. Future research focused on dietary lipids should systematically evaluate the impact of lipid amount and source on carotenoid intestinal uptake and transport using a coupled in vitro digestion and Caco-2 human intestinal cell culture model to better understand factors that may potentiate carotenoid bioavailability in vivo. Regarding meal patterns, a larger-scale, longer-term study providing the upper limit of allowable lipids under the 2010 Dietary guidelines should be completed to better evaluate how meal patterns impact carotenoid absorption over time.

Degree

Ph.D.

Advisors

Ferruzzi, Purdue University.

Subject Area

Food Science|Nutrition

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