If we don't count the Diet of Worms in 1521, which sounds like it would certainly induce weight loss but in fact has nothing to do with food (or creepy-crawlies), the modern conception of dieting can probably be traced to the 19th century. This was when a formerly portly London undertaker, William Banting, published a pamphlet called Letter on Corpulence, Addressed to the Public. This Richard Simmons prototype described the ailments he attributed to his former fatness, including "failing sight and hearing, an umbilical rupture requiring a truss , bandages for weak knees and ankles." In language that is strikingly similar to today's fad diet pitches, he promised that "by proper diet alone, the evils of corpulence may be removed without the addition of those active exercises."
His recommendations, also reminiscent of contemporary diet advice, were to abstain from or greatly reduce consumption of bread, butter, milk, sugar, beer and potatoes. Instead, he ate mostly meat, vegetables and wine. The pamphlet sold tens of thousands of copies around the world, and was translated into several other languages.
In 1918, California doctor Lulu Hunt Peters introduced the concept of calories to the general public in a pithy book called Diet and Health with Key to the Calories. She offered advice for both those who wished to lose weight and those who wished to gain, although, she wrote, "How any one can want to be anything but thin is beyond my intelligence."
Written in a chatty, let-me-give-it-to-you-straight-sister style (accompanied by stick-figure illustrations drawn by her nephew), Peters set forth a formula for determining ideal weight, amount of calories necessary for maintaining, losing or gaining weight, and a list of the caloric values of foods—in other words, exactly the same sort of thing you'll find on diet Web sites today.
Countless similar diet books, usually targeted at women, filled bookstores in the following decades, especially the second half of the 20th century. A few in particular became hugely successful. The Scarsdale Diet—which offered a ridiculously low 1,000-calorie-a-day plan with strict proportions of protein, fat and carbohydrates—was a big hit in the 1970s. The Atkins Diet, which continues to be popular, also debuted in the 1970s.
The advice sometimes varied—in 1966, Martinis & Whipped Cream claimed you could eat as much as you wanted if you cut carbohydrates, while a volume from the following year promised weight loss through self-hypnotism—but the books almost invariably had the same message: thin is in, stout is out.