What Doctors Thought About Fasting in 1911 vs. What They Think Now

When Upton Sinclair published The Fasting Cure in 1911, he wasn't just describing a personal health experiment — he was picking a fight with the entire medical establishment of his day. More than a century later, fasting has quietly moved from "quackery" to a legitimate subject of clinical research. The gap between those two reactions says a lot about how medicine changes its mind.

A Hostile Reception in 1911

Sinclair's book grew out of a magazine article in Cosmopolitan that generated 600 to 800 letters from readers who had tried fasting after reading it. Of all those letters, only two came from physicians. The rest of the medical profession, by Sinclair's account, treated the idea with open contempt — the New York Times went so far as to call him a "shallow and unscrupulous sensationalist."

Sinclair had his own theory about why doctors resisted so strongly: fasting was free, self-administered, and required no drugs, surgery, or ongoing office visits. He compared the reaction to the historical resistance doctors once showed toward the stethoscope, when the physician Elliotson was treated as a professional outcast simply for adopting a new diagnostic tool. In Sinclair's telling, medicine had a financial as well as an intellectual reason to dismiss fasting.

The most dramatic illustration of this hostility was what he called the Rader Case: a man fasting under supervision in Seattle was forcibly interrupted by health officials who attempted to have him declared insane. He died shortly afterward, and Sinclair argued it was the shock of the intervention — not the fast itself — that killed him. Whether or not that causal claim holds up, it captures how far the establishment was willing to go to stop the practice.

Sinclair's Case for Fasting

Sinclair wasn't a doctor; he was a journalist who had spent roughly $15,000 over six to eight years chasing relief from chronic nervousness, insomnia, and headaches through physicians, surgeons, and sanatoriums, with little to show for it. A 12-day fast, followed by a gradual milk-based refeeding period, left him feeling better than any conventional treatment had.

He went on to collect 277 fasting episodes from 109 readers. A hundred of them reported benefit, ranging from rheumatism and chronic headaches to insomnia and stomach trouble. Sinclair's explanation was that overeating produced fermentation and toxins that clogged the body's organs, and that fasting gave the system a chance to "clean house" — a theory of autointoxication that was already falling out of favor with mainstream physiology even in his own era.

What Modern Medicine Actually Thinks

A century on, doctors are no longer dismissing fasting outright — but they aren't endorsing Sinclair's specific theory either. The autointoxication idea, that undigested food rots and poisons the bloodstream, has not held up as the mechanism behind fasting's effects. What has held up, in a very different form, is the broader observation that giving the digestive system extended rest produces measurable physiological change.

Modern research on time-restricted eating and prolonged fasting points to processes Sinclair had no vocabulary for: autophagy, the cellular "clean-up" process in which cells break down and recycle damaged components, and metabolic switching, where the body shifts from burning glucose to burning fat and producing ketones. These mechanisms offer a modern, evidence-based explanation for some of what Sinclair's letter-writers described — improved mental clarity, reduced inflammation-related symptoms, and a sense of physical reset — without requiring his toxin theory to be true.

In other words: Sinclair's data points were often real, even where his explanation for them was wrong. That's a useful lesson in reading any historical health text — take the observations seriously, and let modern science supply the mechanism.

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Frequently Asked Questions

Did any doctors support Sinclair's fasting claims in 1911?

Sinclair noted that of the 600–800 letters generated by his original magazine article, only two came from physicians, reflecting how isolated pro-fasting voices were within the medical profession at the time.

What was the medical establishment's main objection to fasting?

Beyond skepticism about the science, Sinclair argued doctors had a financial incentive to prefer ongoing paid treatment over a free, self-administered method — though mainstream physicians of the era also had genuine physiological objections rooted in prevailing nutritional theory.

Is the autointoxication theory Sinclair relied on still accepted today?

No. The idea that undigested food ferments into systemic poisons has not been supported by modern physiology. Contemporary explanations for fasting's effects center on autophagy and metabolic switching instead.

Why does fasting research look different today than it did in 1911?

Modern studies use controlled trials, blood biomarkers, and imaging to measure what Sinclair could only observe anecdotally through reader letters — giving today's conclusions a firmer evidentiary basis, even when they echo his original observations.

Has fasting gone from rejected to mainstream in medicine?

It's more accurate to say it's gone from rejected to studied. Time-restricted eating and therapeutic fasting are active areas of clinical research today, though they remain one tool among many rather than a universal cure.

This article draws on historical research from 1911 and is for informational purposes only — not medical advice. Always consult a qualified healthcare professional before making any dietary changes.

What Doctors Thought About Fasting in 1911 vs. What They Think Now