What is a natural experiment?
A natural experiment is a change nobody designed that still splits the world into comparable groups. When Christiaan Eijkman’s laboratory chickens were switched from polished white rice to cheaper unpolished rice, they recovered from a beriberi-like paralysis. That accident pointed to something essential in the rice’s outer layers, and led to the idea of vitamins.
Last time's quick check: you can farm a field only one way at a time, so one of its two potential outcomes always stays hidden. Today, three detective stories from food. In the 1880s, beriberi was crippling the Japanese navy. Sailors' legs weakened and swelled, and some died of heart failure.
A naval surgeon, Takaki Kanehiro, noticed it struck sailors on white-rice diets far more than officers who ate more varied food. In 1884 he tested it. The training ship Tsukuba sailed the route the Ryūjō had sailed shortly before, when 169 of its 376 crew fell ill with beriberi and 25 died. This time the crew ate more barley, meat, milk and vegetables. Fourteen men fell ill, and none died.
It was a before-and-after comparison on the same route: weaker than Lind's side-by-side test, but the difference was enormous. Takaki thought the cause was a shortage of protein. He was wrong about why, and right about what to do. A few years later, in the Dutch East Indies, an army doctor called Christiaan Eijkman was hunting for a germ that caused beriberi. His laboratory chickens developed a similar paralysis. Then, mysteriously, they recovered.
The explanation was a change nobody had planned. For a while, the chickens had been fed polished white rice left over from the military hospital. When a new administrator stopped military rice going to civilian chickens, the birds were switched to cheaper unpolished rice, with its outer layers intact. They got better.
An accidental change like that is called a natural experiment: something nobody designed that still splits the world into comparable groups. Eijkman followed the clue with deliberate feeding tests, and his colleague Gerrit Grijns proposed that the rice's outer layers held something essential. That idea led to vitamins, and Eijkman shared a Nobel Prize in 1929.
Across the American South in the early 1900s, pellagra was killing thousands: a rash, diarrhoea, confusion. Most doctors thought it was an infection. In 1914 the US Public Health Service sent Joseph Goldberger to investigate. Goldberger noticed that in orphanages and asylums the staff never caught it, only the inmates. An infection wouldn't choose like that; a diet would.
He changed the food in some institutions, adding milk, eggs and meat, and pellagra disappeared. To show it wasn't catching, he and his volunteers even swallowed material from patients. None fell ill. With the economist Edgar Sydenstricker, he traced it back to poverty: families in the South's cotton economy living on cornmeal, fatback and molasses.
Maize was the staple, but not as it had been eaten in Mexico and Central America for thousands of years, cooked with an alkali that frees its niacin. The missing vitamin, niacin, was identified in 1937. Three diseases, one thread. In each case, how food was grown, milled or cooked decided whether it nourished.
Polishing rice, swapping lemons for limes, cooking maize without alkali: small changes in the chain from farm to plate, with large effects on health. That chain is what this series is ultimately about. Next: back to the farm, and the wheat field where the modern experiment was born.
He noticed that in orphanages and asylums the staff never caught it, only the inmates: an infection wouldn’t choose like that, but a diet would. He added milk, eggs and meat to the food in some institutions and pellagra disappeared, and he and his volunteers even swallowed material from patients without falling ill.
It was a before-and-after comparison on the same route, not a side-by-side test. The Tsukuba’s crew ate more barley, meat, milk and vegetables than the Ryūjō’s had, and the difference was enormous. But it compared two voyages rather than two groups at the same time, and Takaki was wrong about why the diet worked.
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