Pagophagia is an eating disorder where you chew a lot of ice. A friend of mine had it. After she discovered she loved crunching ice cubes, she started going through several trays of ice cubes per day. A trip to Russia, where ice cubes were unavailable, was highly unpleasant. Eventually my friend learned that pagophagia is caused by iron deficiency. When she started eating more iron, her ice craving went away.
Why do we work this way? The evolutionary reason, I think, is that in the ancient world where this tendency evolved, a desire to crunch something was usually satisfied by crunching bones. After you discovered how pleasant it was to crunch bones, you sought them out. Bone marrow is high in iron. Crunching those sought-out bones increased your iron intake.
The umami hypothesis says that we like umami tastes, sour tastes and complex flavors so that we will consume more harmless-bacteria-laden food (which keeps our immune system on its toes). In the ancient environment where these tendencies evolved, in other words, a desire to eat food with these characteristics led us to eat bacteria-laden food. At the Fancy Food Show, I met a maker of sparkling tea who was unable to get enough complexity without using bacteria.
Just as a person with pagophagia chews ice, most of us do one or more of these:
- add monosodium glutamate (e.g., Accent) for umami taste
- add vinegar for sourness (I put a few drops of vinegar in coffee-like drinks)
- add many spices for complexity
The result, I suspect, is that most of us have immune systems with plenty of room for improvement. I stopped getting easy-to-notice colds when I started sleeping better so the high frequency of reported colds (the average American adult gets about three per year) may be a sign that this is true.
I suspect that that human preferences were fairly well optimized to guide pre-civilization humans toward good health. If humans need Y for optimal health, we would expect natural selection to have developed preferences that led to sufficient Y intake.
One such preference might be a taste for Y, itself. Given that Y might be expensive for the body to measure directly, however, selection-based optimization would likely have found some easy-to-measure X to serve as a reliable marker for Y. If you consider a similar optimization process to have been performed for all the myriad Ys that our bodies need, it’s reasonable to conclude that we humans crave a lot of related Xs as a result.
Fast forward to today. With agriculture, we have introduced many “new” foods, some of which do not preserve the traditional X-and-Y relationships our pre-civilization bodies expect. Further, with modern food science, we can figure out what any particular X is, manufacture it in isolation, and sprinkle it into all sorts of unrelated foods. All of a sudden, those foods become a whole lot more crave-worthy, but our bodies’ natural preferences become a whole lot less reliable (or a whole lot more manipulable, depending on your cynicism level).
It’s an interesting situation, this X for Y thing, one that raises some fascinating research questions. For example, can market research lead us to better eating? Go to the supermarket, buy popular junk food, and examine the ingredients for possible X markers. If we consider those Xs to be the most-strongly craved (as revealed by marketing and sales optimization), they might point to the Ys we most strongly need. For each potential X, figure out what Y it indicated in pre-civilization times, and eat more of that.
That’s interesting stuff. I think you’re on to something here, Seth.
This disconnect between marker X and required nutrient Y reminds me of work showing how rats (and mice) with an electrode placed in their hypothalamus will work to exhaustion to press a lever that results in a delivery of stimulation of the hypothalamus. This is called brain reward stimulation.