Dietary factors that affect carotenoid bioavailability

Carotenoids are thought to contribute to the beneficial effects of increased vegetable consumption. To better understand the potential benefits of carotenoids, we investigated the bioavailability of carotenoids from vegetables and dietary factors which might influence carotenoid bioavailability.In a four weeks intervention trial, we found that the increases in plasma concentrations ofβ-carotene and lutein after consumption of a high vegetable diet were 14% and 67%, respectively, of those after consumption of the same amount of carotenoids, supplied in their purified form. In another study, it appeared that the bioavailability ofβ-carotene was particularly low from spinach. Broccoli and green peas were more effective in enhancing plasma concentrations ofβ-carotene after four days consumption (relative bioavailability ca. 3%, 74% and 96% for spinach, broccoli and green peas, respectively). Disruption of the vegetable matrix by mechanical homogenisation significantly improved the bioavailability of lutein from spinach by 14% and of lycopene from tomatoes by 20 to 60%. One hour additional heating of the tomatoes (100°C) also enhanced the bioavailability of lycopene but this effect lacked significance.Carotenoids are absorbed in association with dietary fat and therefore the presence of dietary fat is thought crucial for carotenoid absorption. Four weeks consumption of a full-fat margarine (80% fat), supplemented withα-carotene andβ-carotene, effectively enhanced blood concentrations of these carotenoids. In a further study, we found that in healthy adult volunteers, only a small amount of fat (i.e. 3-5 g per meal) was sufficient to ensure uptake ofα-carotene andβ-carotene. For lutein supplied as lutein esters, however, the amount of fat required for optimal uptake was greater. Daily consumption of an unabsorbable fat replacer, sucrose polyester, with the main meal for four weeks, significantly reduced the bioavailability of carotenoids. Plasma concentrations ofβ-carotene and lycopene were reduced by 20% and 38% if 3 g/d sucrose polyester was consumed.Interaction among carotenoids appeared to interfere with carotenoid bioavailability in some but not all cases. Simultaneous ingestion ofα-carotene andβ-carotene did not affect the bioavailability ofβ-carotene whereas four weeks supplementation withβ-carotene and lutein significantly reduced the plasma concentration of lycopene by 39%.In conclusion, the type of food matrix in which carotenoids are located largely determines their bioavailability. Processing, such as mechanical homogenisation or heat treatment, has the potential to enhance the bioavailability of carotenoids from vegetables. The amount of dietary fat needed to ensure carotenoid absorption seems low, although it depends on the physico-chemical characteristics of the carotenoids ingested. Unabsorbable, fat-soluble compounds reduce carotenoid absorption and interaction among carotenoids may also result in a reduced carotenoid bioavailability.Research into the functional benefits of carotenoids should consider the fact that the bioavailability ofβ-carotene in particular is one order of magnitude higher when provided as pure compound added to foods than when naturally present in foods.