Atwater’s most unsettling discovery—to himself as much as to the world at large—was that alcohol was an especially rich source of calories, and thus an efficient fuel. As the son of a clergyman and a teetotaler himself, he was appalled to report it, but as a diligent scientist he felt his first duty was to the truth, however awkward. In consequence, he was swiftly disowned by his own, devoutly Methodist university and its already scornful president.
Before the controversy could be resolved, fate intervened. In 1904, Atwater suffered a massive stroke. He lingered for three years without recovering his faculties and died aged sixty-three, but his long efforts secured the calorie’s place at the heart of nutrition science, evidently for all time.
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As a measure of dietary intake, the calorie has a number of failings. For one thing, it gives no indication of whether a food is actually good for you or not. The concept of “empty” calories was quite unknown in the early twentieth century. Nor does conventional calorie measurement account for how foods are absorbed as they pass through the body. A great many nuts, for instance, are less completely digested than other foods, which means that they leave behind fewer calories than are consumed. You may eat 170 calories’ worth of almonds, but keep only 130 of them. The other 40 sluice through without, as it were, touching the sides.
By whatever means you measure it, we are pretty good at extracting energy from food, not because we have an especially dynamic metabolism but because of a trick we learned a very long time ago: cooking. No one knows even approximately when humans first began cooking food. We have good evidence that our ancestors were utilizing fire 300,000 years ago, but Richard Wrangham of Harvard, who has devoted much of his career to studying the matter, believes that our ancestors mastered fire a million and a half years before that—which is to say long before we were properly human.
Cooking confers all kinds of benefits. It kills toxins, improves taste, makes tough substances chewable, greatly broadens the range of what we can eat, and above all vastly boosts the amount of calories humans can derive from what they eat. It is widely believed now that cooked food gave us the energy to grow big brains and the leisure to put them to use.
But in order to cook food, you also need to be able to gather and prepare it efficiently, and that is what Daniel Lieberman of Harvard believes is at the heart of our becoming modern. “You can’t possibly have a large brain unless you’ve got the energy to fuel it,” he told me when we met in the autumn of 2018. “And in order to fuel it, you need to master hunting and gathering. That’s more challenging than people realize. It’s not just a question of picking berries or digging up tubers; it is a matter of processing foods—making them easier to eat and digest, and safer to eat—and that involves toolmaking and communication and cooperation. That is the essence of what drove the shift from primitive to modern humans.”
In nature, we actually starve pretty easily. We are incapable of deriving nutrition from most parts of most plants. In particular we cannot make use of cellulose, which is what plants primarily consist of. The few plants that we can eat are the ones we know as vegetables. Otherwise we are limited to eating a few botanical end products, such as seeds and fruits, and even many of those are poisonous to us. But we can benefit from a lot more foods by cooking them. A cooked potato, for instance, is about twenty times more digestible than a raw one.
Cooking frees up a lot of time for us. Other primates spend as many as seven hours a day just chewing. We don’t need to eat constantly to ensure our survival. Our tragedy, of course, is that we eat more or less constantly anyway.
The fundamental components of the human diet—the macronutrients: water, carbohydrates, fat, and protein—were recognized nearly two hundred years ago by an English chemist named William Prout, but it was even then clear that some other, more elusive elements were needed to produce a fully healthy diet. No one knew for the longest time exactly what these elements were, but it was evident that in their absence people were likely to suffer a deficiency disease like beriberi or scurvy.
We now know them, of course, as vitamins and minerals. Vitamins are simply organic chemicals—that is, from things that are or were once alive, like plants and animals—while minerals are inorganic and come from soil or water. Altogether there are about forty of these little particles that we must get from our foods because we cannot manufacture them for ourselves.
Vitamins are a surprisingly recent concept. A little over four years after Wilbur Atwater died, a Polish émigré chemist in London, Casimir Funk, came up with the notion of vitamins, though he called them “vitamines,” a contraction of “vital” and “amines” (amines being a type of organic compound). As it turned out, only some vitamins are amines, so the name was later shortened. (Other names were also tried, among them nutramines, food hormones, and accessory food factors, but failed to catch on.) Funk didn’t discover vitamins but merely speculated, correctly, as to their existence. But because no one could produce these strange elements, many authorities refused to accept their reality. Sir James Barr, president of the British Medical Association, dismissed them as “a figment of the imagination.”
The discovery and naming of vitamins didn’t begin until almost the 1920s and has been a checkered affair, to put it mildly. In the beginning, vitamins were named in more or less strict alphabetical order—A, B, C, D, and so on—but then the system began to fall apart. Vitamin B was discovered to be not one vitamin but several, and these were renamed B1, B2, B3, and so on up to B12. Then it was decided that the B vitamins weren’t so diverse after all, so some were eliminated and others reclassified, so that today we are left with six semi-sequential B vitamins: B1, B2, B3, B5, B6, and B12. Other vitamins came and went, so that the scientific literature is filled with a lot of what might be called ghost vitamins—M, P, PP, S, U, and several others. In 1935, a researcher in Copenhagen, Henrik Dam, discovered a vitamin that was central to blood coagulation and called it vitamin K (for the Danish koagulere). The next year, some other researchers came up with vitamin P (for “permeability”). The process hasn’t entirely settled down yet. Biotin, for instance, was for a time called vitamin H, but then became B7. Today it is mostly just called biotin.
Although Funk coined the term “vitamines,” and is thus often given credit for their discovery, most of the real work of determining the chemical nature of vitamins was done by others, in particular Sir Frederick Hopkins, who was awarded the Nobel Prize for his work in 1929—a fact that left Funk permanently in one.
Even today vitamins are an ill-defined entity. The term describes thirteen chemical oddments that we need to function smoothly but are unable to manufacture for ourselves. Though we tend to think of them as closely related, they mostly have little in common apart from being useful to us. They are sometimes described as “hormones made outside the body,” which is a pretty good definition except that it is only partly true. Vitamin D, one of the most vital of all vitamins, can both be made in the body (where it really is a hormone) or be ingested (which makes it a vitamin again).