What makes carrots orange, watermelon pink, corn yellow, or tomatoes deep red? Carotenoids! The colorful plant pigment family of the carotenoids can put a rainbow on your plate. The vivid carotenoids can do more than brighten up your dishes: different carotenoids have different health benefits. It is a good idea to include a healthy mix of carotenoid-rich foods in your diet, to extract the maximum goodness from each type of carotenoid.
Orange Carotenes as a Vitamin A Source
Three carotenoids have an essential role in the diet as a plant-based source of pro-vitamin A. These carotenoids are alpha-carotene, beta-carotene and beta-cryptoxanthin. Many orange and yellow fruits and vegetables get their intense coloring from alpha- and beta-carotene. Green leafy vegetables often contain both as well, but the color is masked by the presence of dark green chlorophyll. Few fruits and vegetables contain beta-cryptoxanthin, although it is found in some tropical fruits such as papaya and mango.1
In industrialized countries, one third of vitamin A requirements are estimated to be met by carotenoids, and this proportion is higher in vegetarians.2 The structure of alpha-carotene, beta-carotene and beta-cryptoxanthin means that they can be converted easily by the body to retinol, one of the active forms of vitamin A. Vitamin A has various diverse roles in the body: it is required for vision, normal immune function, and the growth and specialization of cells.3
Foods containing pro-vitamin A carotenoids are given a conversion factor that indicate how well they can be converted to retinol, called a Retinol Activity Equivalent. This estimates how much pro-vitamin A carotenoids are needed to produce a certain amount of retinol. In general, to get 1 microgram of retinol, 2 micrograms beta-carotene from a dietary supplement, 12 micrograms beta-carotene from foods or 24 micrograms alpha-carotene or beta-cryptoxanthin are needed. A medium orange carrot weighing 60 grams (2 oz) contains about 3,000 micrograms beta-carotene and 4,000 micrograms alpha-carotene, together providing around 400 micrograms of retinol.4 This is about half the vitamin A requirements of adult men and women.3
Yellow Xanthophylls for Eye Health
The xanthophylls get their name from the Greek word for yellow, and are found in many yellow, orange and green leafy vegetables such as sweet corn, yellow bell peppers and kale.5 Three xanthophylls, lutein, zeaxanthin and meso-zeaxanthin, are being studied for their possible role in eye health. Out of the hundreds of carotenoids that are found in nature, only 50 are absorbed from humans’ normal diet,6and these three are found in a very specific area of the eye that is responsible for detailed vision, and are prevalent throughout other parts of the eye. This has lead researchers to suggest that they may be important for normal visual function because they are selectively deposited in the eye.7
There are two ways that lutein and zeaxanthin are thought to support our vision. First of all, their yellow color means that they act as a yellow filter over the delicate vision cells at the back of the eye. Just as wearing glasses with yellow lenses blocks blue-colored light, the yellow xanthophylls lutein and zeaxanthin stop damaging blue light from reaching the retina.8 This can lead to improvements vision in bright light situations, as has been found in clinical trials.9,10 Like the other carotenoids, lutein and zeaxanthin are strong antioxidants. The process of vision in the eye results in oxidative stress, which antioxidants can protect against. As lutein and zeaxanthin are found throughout the eye, they are suggested to prevent damage and maintain vision during the aging process.7