George Carlin once famously asked, “Why is there no blue food? I can’t find the flavor of blue!” Some, even back in the mid-seventies when he first asked this question, brought up blueberries as an example of blue food, but they were dismissed as actually being more purple than blue. No one back then talked about blue cheese, though (I guess that it was a simpler time!).
A number of people on the Internet have taken up the “no blue food” challenge and have posted rich, very blue pictures of a number of types of berries, crustaceans (both crayfish (as pictured below!) and lobsters, apparently, come in blue!), and mushrooms. But to me, their protest really does prove Carlin’s point: there are not very many kinds of foods that are blue! There are lots of green and brown and white and yellow and purple and orange and red foods, but very few blue foods!
A number of questions and pathways of discussion open up here: Why are so few foods blue? What makes a food blue in color? Are there any dietary or health benefits of eating foods rich in these coloring chemicals? And, why is this topic being discussed in the final winter ecology blog of the year?
I’ll answer the last question first: we ALL think about food in the winter! The winter, by necessity, is a time for eating!
Now let’s tackle these other questions in order.
Why are so few foods blue?
Cecil Adams in the on-line Washington City newspaper (December 9, 2011) deals with this important question. He begins by noting that fruits and vegetables are instruments that plants make in order to attract animals. The animals eat the fruits and vegetables and then disperse the plant’s seeds. By riding around in and passing through (and out of) the intestines of a bird or mammal (or reptile or amphibian or arthropod or any other mobile heterotroph) the plant gains wings and legs and many other possible type of locomotory organs and is thus able to distribute its potential progeny sometimes over vast geographic areas! To better attract animals to their fruits and vegetables, the plant must come up with ways to make these seed bearing organs stand out and be noticed. One very easy way to do this is to color them in a way that stands out against the often dense surrounding “sea” of green leaves (the color green, by the way, represents the reflected (non-absorbed) wavelengths of light that bounce off of the plants’ key photosynthetic pigment, chlorophyll).
The color that stands out most sharply against green is red. This basic concept of nature was “discovered” by a wide range of scientists and artists (including Isaac Newton, Johann Wolfgang von Goethe (who seemed to be involved in everything!), J.M.W.Turner, Claude Monet, Paul Cezanne, Vincent Van Gogh, and many, many more!). Boutet’s color wheel (developed in 1708) and Chevreul’s color wheel of 1828 (which greatly impressed the Impressionist’s in the later part of the Nineteenth Century!) illustrates the idea of “opposite colors” (those colors directly across from each other on the wheel). These opposite colors when placed side by side evoke the greatest contrast even to the point of generating on a flat surface the illusion of three dimensions! Not surprisingly, the color on the opposite side of the Chevreul Color Wheel from green is red!
Plants can make red pigments from two basic types of chemicals: carotenoids and anthocyanins. Carotenoids are fat soluble pigments found in the chloroplasts and chromoplasts of a plant cell. They function either as photo-accessory pigments (capturing a wider array of wavelengths of light than chlorophyll alone) or they help to reflect any excessive levels of incoming light (“photo-protection”). Carotenoids can be yellow, orange, or red. Anthocyanins, on the other hand, are water soluble pigments typically found in the large, central vacuole of a plant cell. These pigments may also function as photo-protectors but are possibly even more important to the plant in their roles of attracting (and directing) pollinators and seed dispersing heterotrophs! Anthocyanins can be blue, or purple, or red. We see, then, that red is common color in both of these plant-based pallets!
And here is the essence of the case against “blue foods:” red is a very abundant and widely used pigment in both the carotenoid and anthocyanin color arrays. If a plant also makes a blue anthocyanin pigment it will most frequently be mixed with red! If you remember your Art 101 class, blue mixed with red makes purple! Not surprisingly, there are many fruits and vegetables that are purple!
So to see a truly blue food, we must exclude red! And, as the brilliant George Carlin so astutely pointed out, that doesn’t occur very often.
Question #2: Are consuming these blue pigments good for you?
The Linus Pauling Institute at Oregon State University has a wonderful web site that explores dietary anthocyanins. These chemicals are part of a nutritional group of chemicals called the “flavonoids.” Flavonoids act as anti-oxidants in in vitro (“test tube”) studies, and they are proposed to function in a similar way inside an organism (although direct evidence is somewhat lacking since the chemical structure of these flavonoids are greatly changed by the time they get digested and absorbed into the blood stream (and possibly even processed and chopped up in the liver!)). Anti-oxidants reduce levels of free radicals (again, in “test tube” studies) and thus may play a role in reducing inflammation, cell and tissue damage (and maybe even programmed cell death (“apoptosis”)). These impacts could reduce the incidence and progression of heart disease, atherosclerosis, cancer, neurodegenerative diseases like Alzheimer’s or Parkinson’s disease, and maybe even be able to counteract the cellular wear and tear of aging. Again, though, clinical trials have not really shown that these antioxidant benefits are realized from the consumption of foods rich in these flavonoid molecules!
So, eat blueberries and drink red wine and dark beer because they taste good! If there is an extended benefit from them, so much the better!
Adams finishes up his 2011 Washington City Paper article with an interesting speculation: what if chlorophyll had not become the key pigment in photosynthetic energy transduction in plants? There are other pigments that can capture the energy from wavelengths of light: retinol, for example. Retinol reflects not the green wavelengths like chlorophyll, but, instead, the purple. Plants, then, in our hypothetical world of retinol-based photosynthesis would be purple instead of green! Looking at the Chevreul Wheel of color for the opposing color to purple we find a mix of green and yellow! In this retinol world, then, most fruit and vegetables would be chartreus! (a very unsettling proposition!)