AFTER SAN FRANCISCO POLITICIANS Harvey Milk and George Moscone were gunned down in City Hall by their colleague Dan White in 1978, the murder trial launched a pre-Internet meme about moral accountability. White’s lawyers claimed that his capacity for judgment was diminished at the time of the killings. A sign of White’s mental impairment was his abnormal diet, especially an increased consumption of Coca-Cola and the sickly sweet, cream-filled cakes known as Twinkies: an American edible icon, concocted of not much more than sugar, calories and commercial ingenuity. The precise legal claims were, first, that Twinkie-eating was an indication of the defendant’s pathological mental state, not its cause, and second, that “there is a minority opinion in psychiatric fields that sugar-rich diets might exacerbate existing mood-swings.” But excitable journalists preferred a simpler version: Twinkies were the snack that drove men mad. “The Twinkie defense” entered American pop culture — and eventually the Oxford English Dictionary — as a tag for any number of obviously ridiculous but expert-endorsed claims about dietary causes of disturbed psychic states. 

The Twinkie defense is just tenable enough to be offered up as an accountability waiver — a seriously pathological version of its more benign kin, the “sugar rush” or “sugar high” — but also ludicrous enough to be officially disallowed. It’s a modern absurdity, but one that has a long and sinuous cultural history. Go back several hundred years and one finds that the general form of the Twinkie defense was central to medical thought and practice. The idea that diet might shape mental states was commonly accepted; the open question concerned what foods had what effects on the mind. 

The medical-physiological system handed down from Antiquity took what we now call psychosomaticism as a matter of course. Everything in the world was marked by its characteristic possession of the four “qualities” of heat, cold, moistness and dryness, and this included the human body and its aliment. According to which bodily “humor” was naturally dominant in you, your “temperament” — of mind as well as body — was sanguine (blood dominant; warm and moist), choleric (warm and dry), melancholic (cold and dry), or phlegmatic (cold and moist). That temperament dictated what sorts of foods tended to “agree with” you — on the general grounds that you should consume aliment whose qualities matched your own — and what you should eat when your humors became unbalanced (that is, when you were ill.) Then, you should “correct” imbalance by eating things whose opposing qualities might restore you to your own normal state. 

There was another traditional vocabulary for framing the food-body-mind nexus and this involved the notion of spirits. The animating principles of the human body were considered to be three types of almost, but not quite, immaterial spirit — natural, animal and vital — the last of which was elaborated in the brain and diffused throughout the body by the nerves, where it was the proximate cause of volitional action. Different items of aliment were made up of different proportions of “earthy residues” and of “spirituous matter,” which could be transferred to the blood and...