What Is "The Fasting Cure"? Upton Sinclair's 1911 Guide to Fasting

Over a century before intermittent fasting became a mainstream health topic, a journalist and social reformer named Upton Sinclair documented his own extensive fasting experiments and collected 277 case reports from readers who had tried them. The result was The Fasting Cure, published in 1911 — a book that was mocked by the medical establishment at the time and is now, in surprising ways, a historical mirror of what modern research is confirming.

This is the story of that book, what it actually says, and why it still matters.

The Short Answer

The Fasting Cure (1911) is Upton Sinclair's firsthand account of using fasting to recover from years of chronic illness after conventional medicine had failed him, combined with 277 reader-reported cases documenting fasting's effects on conditions ranging from rheumatism and asthma to insomnia and kidney disease. It is not a medical textbook — it is a passionate personal record from a man who wanted to share something that had transformed his health. Read with appropriate historical context, it is a remarkable document: many of Sinclair's observations about fasting's effects on the body align closely with what peer-reviewed science now demonstrates.

Who Was Upton Sinclair?

Sinclair (1878–1968) is best remembered today for The Jungle (1906), his exposé of the US meatpacking industry that triggered the Pure Food and Drug Act. He was a prolific journalist, novelist, and social activist — not a physician. He had no medical training, and he was clear about this. His methodology was that of an investigative reporter: try it himself, collect testimonials from others, document what happened, and publish the results.

This context matters. The Fasting Cure is a primary source document from an era before clinical trials, systematic reviews, or evidence-based medicine as we now understand it. It should be read as such — with genuine curiosity and appropriate scepticism in equal measure.

How the Book Came to Be Written

By his early thirties, Sinclair had spent what he estimated at $15,000 — a substantial sum in 1911 — on physicians, surgeons, druggists, and sanatoriums. The result, he wrote, was continuous suffering: chronic nervousness, persistent headaches (he described himself as "never more than fifteen minutes ahead of a headache"), insomnia, and a general state of exhausted ill-health.

He had tried vegetarianism, raw food diets, and meat-only diets before encountering the idea of fasting through the physical culture movement — particularly through Bernarr Macfadden, a bodybuilder and health reformer whose institution in Chicago had conducted supervised fasts of unusual length. Sinclair decided to try a fast himself.

The article that resulted from his experiments was published in Cosmopolitan magazine and generated between 600 and 800 letters from readers who had tried fasting after reading it. Of those, 109 provided detailed accounts of 277 separate fasting episodes. Sinclair compiled these into The Fasting Cure.

Sinclair's Personal Fasting Experience

His first major fast lasted 12 days. The first four were difficult — physical weakness, dizziness on standing — but he reported remarkable mental clarity even in this early phase. He lost 15 pounds in the first four days, which he later interpreted as evidence of how burdened his body had been with excess waste and fluid. After those first days, the fast became easier: hunger disappeared almost entirely, his mind became active, and he described reading and writing more than he had in years.

He broke the fast carefully, beginning with orange juice and moving to a milk diet over several weeks. The recovery was, by his account, extraordinary — he gained 32 pounds in 24 days on the milk diet and described a state of mental and physical vitality he hadn't experienced in years.

His second 12-day fast, conducted some months later, was markedly different. There was almost no weakness. He walked four miles each morning and performed light gym work throughout. He described his mind as so active that he "read and wrote incessantly." The contrast between his first and second fast — the first hard and dramatic, the second almost effortless — became a central theme of the book.

The 277 Cases: What People Reported

The case reports Sinclair collected came from a wide cross-section of early twentieth-century America. Average fast length in the survey was six days. Of 109 respondents:

• 100 reported benefit from their fasting experience
• 17 reported no benefit
• Of those who didn't benefit, roughly half attributed the failure to breaking the fast incorrectly
• Of cases where health improvement wasn't permanent, the majority relapsed to previous eating patterns

The conditions reported as helped included rheumatism, chronic digestive trouble, asthma, catarrh (chronic throat and sinus inflammation), appendicitis, kidney disease, insomnia, skin conditions including eczema, headaches, nervous exhaustion, and influenza.

Some individual cases are striking. An elderly couple, both near 72, who had suffered from chronic conditions for forty years, undertook fasts of 28 and 31 days respectively. Sinclair's own wife recovered from serious stomach illness following three surgical operations. A railway accident victim, wasted to 119 pounds from 186, undertook a six-day fast and gained 27 pounds in recovery, eventually walking 442 miles in eleven days.

These are anecdotal reports from a self-selected group in a non-controlled setting. They cannot be taken as clinical evidence. What they do represent is a consistent pattern of subjective improvement across a diverse range of people and conditions — a pattern that modern fasting research has begun to explain mechanistically.

Sinclair's Theory of Why Fasting Works

Sinclair's explanatory framework was rooted in the concept of autointoxication — the idea that overeating causes nutrients to ferment in the digestive tract, producing toxins that the body's elimination systems cannot adequately clear. This fermentation, he argued, was the underlying cause of most chronic disease. Fasting, by removing the input of food entirely, allowed the digestive and assimilative systems to "go out of business" — redirecting the body's energy from digestion toward cleansing and repair.

He also proposed that during a fast, the body preferentially burns diseased and morbid tissue before healthy tissue — tumours, waste deposits, and degraded cells consumed first as the fast deepens.

By 1911 standards, this framework was plausible but speculative. The specific biochemical mechanisms were unknown. And yet, from a modern perspective, the observations Sinclair documented map remarkably well onto processes that science has since identified.

Where Sinclair Was Right: The Modern Science Connections

Several of Sinclair's core observations now have scientific explanations:

The body cleans damaged tissue during fasting — Sinclair's intuition that the body preferentially metabolises diseased or morbid material during a fast is consistent with what we now call autophagy: the cellular process by which damaged proteins, dysfunctional mitochondria, and misfolded molecules are broken down and recycled. Yoshinori Ohsumi's Nobel Prize-winning work (2016) established that fasting is one of the most reliable activators of autophagy. The body does, in a very literal sense, consume its own damaged components first.

Digestive rest enables healing — The idea that resting the digestive system has therapeutic value is supported by modern research on the gut microbiome and intestinal repair. Intermittent fasting has been shown to allow the gut epithelium time to repair, reduce intestinal permeability, and shift the microbiome toward more beneficial compositions. A 2014 review by Longo and Mattson in Cell Metabolism documented fasting's broad systemic effects, including gut-level repair mechanisms.

Mental clarity improves during fasting — Sinclair's repeated observations about mental acuity during fasts align with what we now know about ketones and brain function. After 14–16 hours without food, the brain begins using ketones as a fuel source. Ketones are a highly efficient fuel for neurons and are associated with improved concentration, reduced brain fog, and in some research, neuroprotective effects. Sinclair didn't know about ketones, but he documented the experience precisely.

Hunger disappears after the initial days — This observation, which Sinclair found remarkable and counterintuitive, is now explained by ghrelin regulation. Ghrelin (the hunger hormone) follows a pattern, not a continuous signal — and after the initial adaptation period, fasting-adapted individuals typically experience a significant reduction in ghrelin-driven hunger. This is a consistent finding in modern fasting research.

Where Sinclair's Claims Are Speculative or Unverified

In honesty, several elements of Sinclair's framework don't hold up to modern scrutiny:

Autointoxication as a comprehensive disease theory has been largely abandoned. The idea that intestinal fermentation causes systemic toxicity across the range of conditions Sinclair attributed to it is not supported by modern evidence. While gut dysbiosis and intestinal permeability are genuine research areas, they don't map directly onto Sinclair's 1911 model.

The tongue as a reliable detox indicator — Sinclair placed great emphasis on the state of the tongue as an index of cleansing progress (coated = still detoxing; clear = purified; hunger returning = complete). While tongue coating can reflect various digestive states, using it as a primary fasting progress indicator has no strong modern evidence base.

The very long fasts (40, 50, 90 days) referenced in the book are not recommended and cannot be contextualised within current safety frameworks. Sinclair himself acknowledged he never attempted a complete fast and never recommended them casually. Extended fasting beyond a few days carries genuine risks and should only be undertaken under medical supervision.

Why This Book Still Matters in 2026

The Fasting Cure is not a scientific text and should never be read as one. What it is — and what makes it worth reading today — is a detailed firsthand record of human fasting experience at a time when no one had financial incentive to document it. Sinclair wrote it, as he wrote The Jungle, because he believed something important was being suppressed and that ordinary people deserved to know about it.

The medical establishment in 1911 called him a "shallow and unscrupulous sensationalist" in the New York Times. The echoes of that dismissal — fasting as something fringe, dangerous, or unserious — persisted for most of the twentieth century. What has changed is that fasting research, now conducted in well-resourced academic settings with rigorous methodology, has consistently found mechanisms that explain observations Sinclair was documenting through personal report over a century ago.

He got a remarkable amount right, through nothing more sophisticated than careful attention to his own body and honest collection of others' experiences. That is worth something.

For more on the modern science of what happens in the body during a fast, see What happens to your body hour by hour when you fast. For the autophagy mechanisms Sinclair intuited, see How intermittent fasting promotes autophagy.

For the complete guide to intermittent fasting, get Intermittent Fasting in Practice on Amazon. Buy the book and claim 3 months free on our fasting app at https://www.fastinginpractice.com/redeem.

Frequently Asked Questions

Is The Fasting Cure by Upton Sinclair public domain? Yes. Published in 1911, it is fully in the public domain worldwide. It can be read, quoted, and republished freely.

Did Upton Sinclair have medical training? No. He was a journalist, novelist, and social reformer. He was explicit about this in the book. His observations are those of a careful self-experimenter and reporter, not a clinician — which is both a limitation and, in some ways, a strength. He documented what he actually experienced rather than filtering it through medical orthodoxy.

Was Sinclair's view of fasting accepted by doctors at the time? No. The medical profession in 1911 was largely hostile. The New York Times attacked him publicly. Of the 600–800 letters his Cosmopolitan article generated, only 2 came from physicians. Sinclair argued, pointedly, that fasting's low cost and self-administered nature gave it no natural commercial constituency within medicine.

What modern research best supports Sinclair's observations? The strongest modern support comes from autophagy research (Ohsumi, 2016 Nobel Prize), metabolic switching research (Longo & Mattson, Cell Metabolism, 2014), and gut health studies showing intestinal repair during fasting windows. The general principle — that periodic abstinence from food has therapeutic value — is one of the most robustly replicated findings in modern nutritional science.

Is The Fasting Cure relevant for everyday intermittent fasting practice today? As a practical guide, it is dated. As a historical document showing that fasting's effects were being carefully observed long before modern science caught up with the explanations, it is genuinely illuminating.

This article references historical accounts from "The Fasting Cure" by Upton Sinclair (1911) and is for informational purposes only. It does not constitute medical advice. Always consult a healthcare professional before making changes to your diet.