Carotenoids are phytochemicals found in high concentrations in photosynthetic organisms. Here the role of carotenoids is to aid photosynthesis by acting as light harvesting elements during time of low light exposure. In addition, carotenoids may act as antioxidants through the scavenging of singlet oxygen at times of high light exposure. When animals eat carotenoid containing foods, the carotenoids are absorbed and can accumulate in the tissues where they have antioxidant effects. Common dietary carotenoids include lycopene, α-carotene and β-carotene, mostly from red, orange and yellow coloured vegetables and fruits such as carrots, tomatoes and peppers. Dietary carotenoids are associated with a number of health effects and in particular may decrease the risk of cancer, possibly because they act as antioxidants in animals tissue, where they are particularly effective at scavenging singlet oxygen. Carotenoids possess a similar structure to vitamin A, and this structure makes the carotenoids lipid soluble.
Carotenoids and vitamin A are absorbed along with dietary fat from the gut. Dietary fatty acids from saturated, polyunsaturated and monounsaturated fats form fat globules called micelles in the small intestine, and these are transported across the enterocytes to the lymphatic system where they enter the circulation in the subclavian vein. Most dietary lipids present in the diet are transported in this way and the absorption of lipids in general is more efficient if there is enough dietary fat to cause the formation of suitable fat globules. The absorption of carotenoids may therefore be enhanced by the presence of lipids in the diet. A number of studies have investigated the absorption of lipid soluble vitamins and phytochemicals and generally the presence of dietary fat is required for their efficient absorption. For example in one study, the presence of cooked eggs in a carotenoid meal was effective at increasing the absorption of a number of carotenoids, which were detected in the blood lipoproteins of the subjects following consumption of the food.
In particular, the presence of eggs in the meals increased the absorption of lutein and zeaxanthin by 4 to 5 fold over control meals containing low amounts of cooked egg. But lutein and zeathanthin are present in eggs and so the increased concentration of these carotenoids in the blood may have been due to the inclusion of the eggs. However, following the egg meal, there was also a significant 3 to 8 fold increase in blood lipoprotein for the carotenoids lycopene, α-carotene and β-carotene. Because these carotenoids are not present in eggs it suggests that the eggs increased the carotenoid absorption from the other foods in the meal. Eggs therefore appear to be a food that are effective at increasing the absorption of carotenoids from other foods, and this likely related to the lipids in eggs. The meals consumed by the subjects included accompanying salad, and this likely contained a number of carotenoids including the lycopene, α-carotene and β-carotene detected in their blood lipoproteins.
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