|Left, sun tan; center, neutral; right, carotene-rich|
“Dr Ian Stephen, from the School of Psychology, University of Nottingham, Malaysia Campus, led the research as part of his PhD at the University of St Andrews and Bristol University. He said: "Most people think the best way to improve skin colour is to get a suntan, but our research shows that eating lots of fruit and vegetables is actually more effective.”
“Dr Stephen said: ‘We found that, given the choice between skin colour caused by suntan and skin colour caused by carotenoids, people preferred the carotenoid skin colour, so if you want a healthier and more attractive skin colour, you are better off eating a healthy diet with plenty of fruit and vegetables than lying in the sun.’
“Dr Stephen suggests that the study is important because evolution would favour individuals who choose to form alliances or mate with healthier individuals over unhealthy individuals.
“Professor David Perrett, who heads the Perception Lab, said: ‘This is something we share with many other species. For example, the bright yellow beaks and feathers of many birds can be thought of as adverts showing how healthy a male bird is. What's more, females of these species prefer to mate with brighter, more coloured males. But this is the first study in which this has been demonstrated in humans.’”
“Carotenoid supplementation is associated with improved development of the immune system in human children (Alexander et al. 1985), whereas individuals infected with HIV and malaria have reduced carotenoid levels (Friis et al. 2001). Carotenoid levels may also affect spermatogenesis in boars (Chew 1993), and women who failed to conceive during in vitro fertilization had unusually fluctuating carotenoid levels in their follicular fluid (Schweigert et al. 2003). Brightly colored carotenoid-based ornaments are displayed by many bird and fish species, the size and brightness of which reflect aspects of health and condition. Male greenfinches with brighter yellow breast feathers showed stronger humoral immune responses to a novel antigen (Saks et al. 2003). Male and female yellow-eyed penguins with more saturated yellow eye ornamentation produced more offspring per season (Massaro et al. 2003). Researchers have demonstrated mate choice based on the brightness of carotenoid ornaments in greenfinches (Eley 1991), yellow-eyed penguins (Massaro et al. 2003), and goldfinches (MacDougall and Montgomerie 2003).”
“It is not understood what determines the serum and tissue concentrations of carotenoids, but it is likely to be based in part on the quantitative and qualitative aspects of absorption and on the activity of an enzyme found predominantly in the intestinal mucosa cells, ß-carotene 15,15'-dioxygenase (39). This enzyme is responsible for initiating the conversion of carotene to retinol, and low levels would be expected in the longer-lived species.”Indeed, humans do show lower activity of this enzyme; see below. Continuing the quote from Cutler:
"Humans unselectively absorb both carotenes and xanthophylls into their tissues, whereas the shorter-lived species absorb only the carotenes (16-18). The amount of carotenoids in the diet would of course also play an important role in determining the amount of carotenoids that are absorbed, but not the qualitative aspects. Thus, although all carotenoids are derived from the diet, the amount and type that is absorbed in serum and other tissues is clearly a species-dependent characteristic. [italics added]
“During the evolution of increased MLSP in the mammalian species, and particularly in the primates (27, 40), carotenoid concentration in serum and tissues also may have increased. This may have been facilitated by an increased absorption of both the carotenoids and xanthophyll and a decrease in the activity of intestinal ß-carotene 15,15'-dioxygenase. Thus, the nonselective absorption of the carotenoids in humans may represent an end point to this evolutionary strategy; most of the carotenoid protection attainable through the diet is now being utilized.” [italics added]
- Carotenoids are fat-soluble so we must consume fats with carotenoid-rich foods to optimize carotenoid absorption. [p.136]
- Fiber present in fruits and vegetables reduces carotenoid absorption:
“Not only purified fibre, but also fruit and vegetables as sources of this fibre, cause reductions in carotenoid bioavailability. Dietary fibre, lignin, and resistant proteins found in green leafy vegetables inhibited the release of ß-carotene and lutein  and citrus pectin reduced the plasma ß-carotene responses .” [p.138]
- By rupturing plant cells in which carotenoids are stored, cooking and/or pureeing carotenoid-rich vegetables dramatically increases bioavailability of carotenoids.
“In healthy women, feeding heat-processed and pureed carrots and spinach cause serum ß-carotene to be three times higher than when the same dietary level of ß-carotene was consume in the raw food sources . In a population of women at risk for breast cancer, serum concentrations of lutein and a-carotene, but not of ß-carotene, ß-cryptoxanthin, or lycopene, were higher in women consuming vegetable juice, rather thatn cooked or raw vegetables .” [p.134]
- Fake-fats (sucrose-polyesters) inhibit carotenoid absorption. [p.136]
- Statin drugs and plant sterols reduce carotenoid absorption. [p.137]
- Duckett et al found that meat from grass-finished cattle contains 54% more ß-carotene than meat from corn-finished animals.
- Mother Earth News reported that pastured chickens produce eggs that contain 7 times as much ß-carotene as conventional eggs.
|Egg yolks: L, from grain-fed hen; R, from pastured hen.|
|Carotenoid-rich Primal Food: Beef with carrots, squash, and greens.|
Again, I suggest you to test this in your own experience. Dark green leafy vegetables and carrots have negligible carbohydrate content yet deliver large amounts of carotenoids. If you are sun sensitive, or want to see how increasing the carotenoid content of your skin affects your sun tan or untanned appearance, all you have to do is eat more high carotenoid foods to find out. It takes about 10 weeks of high carotenoid consumption to produce a change."In the old days we used to eat the guts of the buffalo, making a contest of it, two fellows getting hold of a long piece of intestines from opposite ends, starting chewing toward the middle, seeing who can get there first; that's eating. Those buffalo guts, full of half-fermented, half-digested grass and herbs, you did not need any pills and vitamins when you swallowed those."