Why Doctors in 1911 Rejected Fasting (And What Changed)

When Upton Sinclair published The Fasting Cure in 1911, he expected curiosity. What he got instead was hostility. The medical establishment attacked him as a "shallow and unscrupulous sensationalist" — a phrase that appeared in the New York Times. His mail from readers who tried fasting and reported remarkable results ran to 600–800 letters. Of those, barely two came from physicians.

This collision between patient experience and medical orthodoxy is one of the more instructive episodes in the history of health — because the medical establishment was wrong, and the record of why they resisted tells us a great deal about how institutions respond to challenges they cannot profit from.

The Medical Landscape in 1911

To understand the hostility, you have to understand what medicine looked like at the turn of the twentieth century. Doctors in 1911 operated in a world before antibiotics, before randomised controlled trials, and before the germ theory of disease had fully reorganised clinical practice. Treatment largely meant prescribing medicines — often complex, expensive preparations — and recommending dietary or lifestyle changes that required ongoing physician supervision.

Sinclair, writing from the vantage point of someone who had spent roughly $15,000 over six to eight years on physicians, surgeons, druggists, and sanatoriums without lasting benefit, arrived at fasting through desperation. He had tried vegetarianism, raw food diets, and meat-only diets. He had visited specialists for his chronic nervousness, persistent headaches, and insomnia. Nothing held.

When fasting resolved the conditions that professional medicine had failed to address, Sinclair's conclusion was pointed: fasting is free. That was, in his view, precisely the problem.

Sinclair's Core Argument Against the Medical Profession

In The Fasting Cure, Sinclair argued that doctors' financial interests were structurally misaligned with the promotion of fasting. His logic was straightforward: a treatment that costs nothing, requires no prescription, and can be self-administered at home creates no revenue. Physicians who relied on ongoing patient visits and pharmaceutical prescriptions had little incentive to investigate or recommend it.

He drew a historical parallel that was deliberately provocative. He cited the case of Dr. Elliotson, a nineteenth-century physician who championed the stethoscope. The medical establishment of his day rejected the stethoscope so fiercely that Elliotson was effectively driven out of professional medicine. The stethoscope, of course, became indispensable within a generation. Sinclair invited readers to see fasting's rejection through the same lens: not a verdict on its effectiveness, but a reflex of institutional self-protection.

Of 600–800 reader letters Sinclair received after his original Cosmopolitan magazine article, 100 of 109 respondents reported clear benefit from fasting. Seventeen reported no benefit. Half of the non-benefiting cases were attributed to incorrectly breaking the fast — not to fasting itself. Sinclair found it telling that almost none of these letters came from people working within the medical system.

What Doctors Officially Said

The medical establishment's objections in 1911 were not entirely without logic, even if the conclusions drawn from them were wrong. Physicians raised two main concerns:

1. Fasting causes weakness and physical danger. This was the most common objection — the intuitive belief that withholding food would deprive the body of the energy it needed to function. Sinclair answered this at length with dozens of case reports of people who worked, walked, and even engaged in manual labour during fasts of 10 days or more.

2. Fasting is unscientific and anecdotal. This objection was harder to dismiss in 1911, because the mechanistic science to explain fasting had not yet been established. There were no controlled metabolic studies, no documentation of ketosis as a metabolic state, no measurement of HGH or autophagy or insulin pathways.

This second objection was actually fair in 1911 — and it was addressed with increasing rigour over the following decades. The same year Sinclair published his book, research laboratories were beginning to study prolonged fasting in controlled conditions. By 1915, Francis Gano Benedict and a team of Harvard and Carnegie scientists had completed a landmark 31-day supervised fast that documented metabolic changes with unprecedented precision. The science was catching up to the practice.

What Changed: The Science Arrived

The reversal of medical opinion on fasting has been gradual, uneven, and not yet complete — but it has been substantial.

The turning point came through several converging lines of research across the twentieth century:

Metabolic science. The documentation of ketosis as a physiologically normal and beneficial metabolic state — rather than a sign of starvation pathology — was central to rehabilitating fasting. Research established that the brain and heart preferentially use ketones when available, and that the liver produces ketones efficiently during fasting as a designed fuel system rather than an emergency response.

Hormonal research. The discovery that fasting triggers large increases in human growth hormone (HGH) — studies have shown increases of 300–500% during a 24-hour fast — reframed fasting as hormonally active and anabolically protective, not simply deprivational.

Autophagy. Perhaps no discovery has done more to legitimise fasting science than the Nobel Prize–winning work of Yoshinori Ohsumi on cellular autophagy, awarded in 2016. Autophagy — the process by which cells identify, dismantle, and recycle damaged components — is directly triggered by fasting. This process was effectively unknown when Sinclair was writing, but it provided the mechanistic bridge that the medical establishment in 1911 was asking for: a clear, cellular explanation of why fasting might produce the results people were reporting.

Clinical trials. From the 1980s onward, intermittent fasting protocols began appearing in peer-reviewed clinical literature. By 2014, Longo and Mattson published a comprehensive review in Cell Metabolism cataloguing the metabolic, neurological, and cellular benefits of fasting with full citations. Mainstream medicine could no longer dismiss the evidence base.

The Resistance That Remains

It would be too simple to say that medicine now embraces fasting uniformly. Many clinicians remain cautious, and some remain actively hostile — not out of financial interest, as Sinclair might have argued, but because the clinical guidance infrastructure moves slowly. Medical protocols change through guideline committees, institutional review, and decades of follow-up data. Individual clinicians trained in an era when fasting was considered dangerous or fringe do not update their views overnight.

There is also a legitimate concern that persists: fasting is not appropriate for everyone. Pregnant women, people with eating disorder histories, those on insulin or blood pressure medication, and people with specific metabolic conditions need careful guidance before fasting. The medical caution that existed in 1911 — stripped of its financial motivation — carries a reasonable residue that contemporary fasting advocates are right to acknowledge.

What Sinclair Got Right

With the benefit of more than a century of subsequent research, Sinclair's core claims have aged remarkably well:

Fasting gives the digestive system a complete rest, allowing repair — confirmed through modern gut microbiome and intestinal barrier research.
Fasting clears the body of what he called "morbid tissue" — a non-scientific term for what we now describe as cellular waste cleared through autophagy.
Mental clarity improves during fasting — documented in research on BDNF (brain-derived neurotrophic factor), which rises during fasting and supports neuronal health.
Hunger disappears after the first two to three days of a longer fast — confirmed by research showing ghrelin (the hunger hormone) normalises during extended fasting.

Sinclair had no cellular biology, no hormonal assays, no controlled metabolic chambers. He had observation, personal experience, and 277 reader case reports. That he got the fundamentals right is less a tribute to genius than a reminder that careful observation often outpaces institutional orthodoxy — especially when institutions have reasons not to look.

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Frequently Asked Questions

Why did the medical profession reject fasting in 1911? Primarily because fasting was free, self-administered, and required no physician involvement. There were also legitimate objections about lack of mechanistic science, which was eventually answered by twentieth-century research.

When did mainstream medicine start accepting fasting? Gradual acceptance began from the 1970s onward as metabolic research accumulated. The Nobel Prize awarded to Yoshinori Ohsumi for autophagy research in 2016 was a major turning point in public and clinical awareness.

Was Upton Sinclair a doctor? No. Sinclair was a journalist and author, best known for The Jungle. He wrote about fasting based on personal experience and reader case reports, not clinical training.

Is fasting accepted by mainstream medicine today? Many physicians now support intermittent fasting for weight loss and metabolic health. Major clinical bodies including the American Heart Association and the European Society of Cardiology have published position statements on time-restricted eating. Full clinical consensus is still evolving.

Did Sinclair's predictions about fasting come true? In broad terms, yes. The mechanisms he described — digestive rest, cellular clearing, mental clarity, hunger disappearance — have all been documented in subsequent scientific research, even though the vocabulary and frameworks he used were pre-scientific.

This article draws on historical research from 1911 and is for informational purposes only — not medical advice.

Sinclair, U. (1911). The Fasting Cure. Mitchell Kennerley.

Why Doctors in 1911 Rejected Fasting (And What Changed)