As most people know, flamingos are actually a white bird. The orange feather colouration comes from the food they eat. The algae and crustaceans which make up a flamingo’s diet are rich in carotenoids. Carotenoids (as their name implies) are the orange pigments also found in carrots.
Flamingos are not the only animals to develop rich colours from carotene. Finches, koi carp, lobsters, prawns and even the distinctive pink flesh of salmon are coloured due to carotenoids eaten in the animal’s natural diet. Whether the colour is pink (as in flamingos) or orange (as in pumpkins) is a result of how oxygenated the carotene molecules are. Oxygenated carotene (canthaxanthin or astaxanthin) is pink, standard ß-carotene is orange.
If carotenoids can make a white bird turn bright pink, can they also change the colour of a human?
Carotene is fat soluble – that is it dissolves in oil but not water. This means that when you eat carrots, the colour can not be excreted in urine or sweated out. It is stored in body fat until it can be broken down. Thus if you eat an excess of carrot you will turn yellow or orange. It’s particularly obvious in the whites of the eyes (just look at the next person dieting exclusively on carrot sticks).
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Hill G.E., Inouye, C.Y., Montgomerie R. (2002) Dietary carotenoids predict plumage coloration in wild House Finches. Proceedings of the Royal Society of London, Series B 269: 1119-1124.