You’ve probably run across someone chronicling a juice cleanse or fast on social media—perhaps insisting that the demanding practice is bringing them more energy and a clearer mind. This idea, that skipping meals is a path toward health and productivity, emerged around the turn of the twentieth century, as R. Marie Griffith explains.

Griffith writes that early Christians and Medieval saints fasted to curb sexual desire, express humility, and experience communion with God. Later, Martin Luther prescribed fasts “to subdue and control the body.” But by the mid-nineteenth century, few American Protestants saw fasting as part of their spiritual toolkit.

The practice came back into vogue among the white, Protestant majority starting in the 1890s not as a means of mortification but as a path to a stronger body and more cheerful spirit. Edward Hooker Dewey, a respected doctor and former Civil War field surgeon, wrote a series of books advocating skipping breakfast and avoiding overeating. Dewey blamed heavy eating for crime, disease, and all kinds of social ills.

He and his followers believed fasting would make men and women kinder, more reasonable, and more productive. In 1899, one businessman reported that, while fasting, he got to the office an hour earlier, stayed an hour later, and skipped his hour-long lunch break. “I sat there at my desk and put in a long, hard day’s work,” he wrote. “My mind was clear, my eye was sharper than usually, and all the functions were in excellent working order.”

Griffith writes that Bernarr Macfadden took things a step further. Mcfadden’s books on fasting featured naked photos of his own lean and muscular physique. He recommended a seven-day fast as a tool for not just health but pleasure. Spending a week without food would restore male virility, and, after a fast, eating would be far more enjoyable. He wrote, “No need of aggravating the sickness of dyseptics by mentioning the ‘duty of self-denial,’ and evok[ing] visions of spiritual advisers helping themselves to the assets of world-renouncing idiots.”

This materialist focus extended to an intense absorption with bodily functions, according to Griffith. Writers chronicled their hunger pains, changes in weight, urine color, and tongue coatings. Over the course of a fast, construction engineer Robert Baille Pearson extensively detailed the quality of his excrement, which he claimed eventually became “perfectly odorless.”

Not all turn-of-the-century fasters ignored the more ethereal aspects of fasting. Wallace D. Wattles, a member of the New Thought movement, insisted that the body had no real need for food at all, instead living through the “mysterious power” of God. But what they had in common with each other, and with many fasters today, is the intense focus on personal, individual improvement with rewards in the here and now.

The ultimate lesson, Griffith writes, is that, “purged, regulated, and self-contained, he who fasted would reap extraordinary fortune.”