Human Lycopene and Beta-cryptoxanthin Absorption From Citrus Fruit

Lycopene and beta-cryptoxanthin are carotenoids found in a small number of foods. Unlike lycopene, beta-cryptoxanthin is among the 10% of carotenoids that can form vitamin A. Lycopene is primarily found in tomatoes and tomato-based products, but also in pink grapefruit and pink guava. Beta-cryptoxanthin is primarily found in tangerines, oranges, pumpkin, peaches, and papayas. Tomatoes and tomato products contain very high concentrations of lycopene, but beta-cryptoxanthin is present in modest amounts, of about 2 to 3 mg per serving, even in its primary food sources. Lycopene is typically the most abundant carotenoid in the diet and in the blood. Despite its scarcity in foods, beta-cryptoxanthin is the third or fourth most abundant carotenoid in blood.

This suggests that beta-cryptoxanthin absorption and metabolism may be quite different from the absorption and metabolism of lycopene and other carotenoids. Specifically, it suggests either that beta-cryptoxanthin itself is absorbed unusually well or that the citrus fruits that are the primary food sources of beta-cryptoxanthin in the diet are much more bioavailable than the tomato products that are the major source of lycopene. The investigators hypothesize that adults absorb a significantly greater amount of beta-cryptoxanthin than lycopene even when both carotenoids are supplied in comparable amounts in a similar matrix.

Subjects will be given a list of foods that are good sources of lycopene and beta-cryptoxanthin and asked to avoid them. Both carotenoids are found in limited numbers of foods, and can be avoided by limiting intakes of tomatoes, red and orange peppers, pumpkin, watermelon, pink guava, pink grapefruit, tangerines, oranges, papayas and mangos. The investigators will feed citrus fruit to volunteers in a randomized crossover design. On study days 14 and 28, subjects will receive either tangerines, or pink grapefruit in a randomized fashion so that each subject gets both treatments during the study. Each subject will serve as his/her own control, and will be fed both treatments at different times, separated by a two-week washout period.

On days 14 and 28, subjects will arrive at the Western Human Nutrition Research Center at approximately 10:30 AM. After a baseline blood draw, subjects will be fed their carotenoid-containing fruit with a controlled meal (low carotenoid, 30-35% fat). Subjects will be given a controlled, low carotenoid, 30-35% kcal from fat dinner at about 6:30 PM on treatment days (days 14 and 28) and a controlled low carotenoid, 30 - 35% kcals from fat breakfast at about 8 AM on study days 15 and 29. Investigators will collect 25 mL of blood per collection, by venipuncture of an arm vein at the following time points, 0, 3, 5, 7, 9, 21, and 24hr following the fruit containing meal. Blood will be collected into heparinized vacutainer tubes and placed on ice in a covered ice bucket.