Meteorology may be unique among the sciences in that it has a visible endpoint. Nutrition may be unique among the sciences in that it has got there. Is there really anything new to learn?

Well, some bacteria need vitamins all their own. Thiamine is supposed to be not a vitamin but a hormone in plants. In an old Merck Index, and you know how much I love old Merck Indices, there is mentioned a (human) vitamin T, named for the termites in which it was supposedly found. Nobody actually knows why pantothenic acid is everywhere. But we do know that iron's omnipresence is unavailing: its poor solubility makes it effectively very scarce, so much so that someone once said – speaking of algal nutrition – "Give me 300,000 tons of scrap iron and I will give you an ice age!" (I quote from memory and now cannot find the exact citation, but the general idea has certainly been bruited.)

For my own part, I think – based on the scantest of evidence – that xenon and deuterium will be found to have physiologically significant roles. But these aren't truly nutrients, and even if they were, everyone everywhere has always had the same amount of them. Indeed, you can do almost nothing to avoid them or stockpile them.

And yet the popularity of this field may never abate. The science itself will glide, not soar, and yet always captivate people. I taught it, or tried to, and was always taken aback by the diet-lore thrown at me. I was totally unprepared for it. I sought to forestall it by shifting to unexpected themes, like – as above – non-animal or monocellular nutrition, but nobody wanted to hear about that stuff. If you're in a nutrition course for the usual reason, namely to get out of a college science requirement, it's all about your digestive tube.

By now I've made the Merck Index sound like a pre-WWI edition of the Encyclopaedia Britannica, and if I haven't, here's another try: it had often struck me, as I whiled away happy hours in the lab leafing through the thing, that quite a lot of the substances listed were classified as purgatives. And they'd been so marked for a long time – I doubt any was the product of modern cutting-edge high-tech basic research. I think the classification was traditional, even medieval, based solely on the desperate actions of sick helpless people, people who felt, as we often still do, that something bad is inside of us and we might logically rid ourselves of it by egesting it. I imagine quite a lot of things will, if you swallow them, come right back out, one way or another, perhaps dragging a few demons with them.

The bad things are imagined to be, not in our brains or our blood, but in our bowels. And maybe good things can be there too. Wondering about one's gut is so human. Were I to teach nutrition again, I'd be a lot more sympathetic.

(1/16/13)