"I must explain," broke off Sir Henry, "that Miss Clark, alarmed at her increasing stoutness, was doing a course of what is popularly known as 'banting'." -- from The Tuesday Night Club, Agatha Christie, 1927
If you're American, as I am, you read "increasing stoutness" and "banting," and mentally converted it "dieting," perhaps thinking "British author." But there's real history behind it: William Banting, who, under a doctor's supervision, went on something very similar to a keto diet around 1860. Banting and his doctor disagreed on how the diet, supposedly designed to prevent diabetes, actually worked. Banting published a "Letter on Corpulence, Addressed to the Public" that can still be found in print and on the internet.