What are You Measuring?

We = (what we eat) – (what they eat) « Jon Udell:

We have traditionally measured the energy content of food by comparing input (the food we eat) and output (the feces we excrete). Burn both in a calorimeter, subtract, and the difference is the energy that was extracted from the food.

Yes, but extracted by whom? Or rather, by what? The energy that we humans take from our food has almost all been extracted by the time it reaches the end of the small intestine. But it has a long way to go yet. It must also pass through the large intestine, where dwell a myriad of gut flora. And they, Wrangham says, are hungry. If you eat a raw banana you only get some of its energy, and they get most of the remainder. If you eat a cooked banana, though, you get a lot more of its energy and leave less for them. The end result looks the same, but the internal distribution is quite different.

So you need to compare the energy in food entering the mouth to the energy remaining in the digestive products leaving the small intestine. Only then does the dramatic difference between the energies we get from raw versus cooked food become evident.

This is a great parable about instrumentation, measurement, knowledge, and epistemology. What other profound errors of basic understanding arise from misplaced instrumentation? And what might we learn by making simple — and in retrospect obvious — adjustments?

(Via kottke.org.)

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