Dr. Lulu Peters, who recommended that every woman count every morsel of food she eats and to eat no more than 1200 calories.

This was first proposed In 1918. It really goes back to late 19th-century Europe, and especially in Germany, they were doing a lot of work on calories and calorie counting. Even though Europeans remained to a certain extent dubious about the worth of calorie counting and dieting, it took off in America in a really big way. And while 1,200 calories isn’t necessarily enough for most adult bodies, it’s not like it’s a completely arbitrary number; it came from calculations during the late Victorian period, a measurement of calories in, calories out.

Sometimes, at first, you will lose weight on this very low-calorie diet…until your body decides enough is enough and slows your metabolism down so you’re not starving anymore. At that point, your weight plateaus and you might find it very easy to gain that weight back.

Peters book "Diet and Health: with keys to calories" came out around the end of World War I, and while rationing wasn’t law, for some it was important for Americans not to hoard food “in their own anatomy. It was one of the first modern diet books ever released. As the beauty ideals were changing from bosomy women with cinched waists in corsets to women with thin, slender frames in straight loose dresses, she suggested calorie counting as a way to lose weight. This book, a bestseller in both 1924 and 1925, helped popularize the diet that has in large part influenced calorie counting for nearly 100 years.

The 1200 calorie diet weight loss logic has since largely been debunked — there are so many other factors that come into play with weight loss, from hormones to how processed your food is.