The History of Fasting as Medicine: From 1911 to Today

When Upton Sinclair published The Fasting Cure in 1911, the medical establishment called him a "shallow and unscrupulous sensationalist." The New York Times was particularly unsparing. Within decades, much of what he described — digestive rest, cellular renewal, metabolic switching — would be validated by research that eventually won a Nobel Prize. The journey from Victorian fringe medicine to peer-reviewed science is not just a historical curiosity. It tells us something important about how fasting works, and why it took so long for medicine to accept it.

Fasting Before Sinclair: A Practice as Old as Medicine Itself

Fasting was not Sinclair's invention. Hippocrates, widely considered the father of western medicine, observed that many diseases improved with abstinence from food and wrote that the body needed to be emptied of its excesses before it could heal. Paracelsus, the sixteenth-century Swiss physician, called fasting "the greatest remedy — the physician within." Religious fasting across Christianity, Islam, Judaism, Buddhism, and Hinduism had embedded periodic abstinence from food into human culture for millennia before anyone attempted to study it clinically.

What made the early twentieth century different was the attempt to systematise therapeutic fasting — to observe it, document it, and argue for it on scientific grounds rather than spiritual or moral ones. Bernarr Macfadden, a physical culture promoter, ran sanatoriums in Chicago where extended fasts of 30 days or more were supervised and recorded. Dr. Linda Burfield Hazzard in Seattle treated hundreds of patients with fasting protocols. These were not mainstream physicians — they operated at the fringe of medicine — but they generated the case literature that Sinclair drew upon in assembling his argument.

Upton Sinclair and the 277 Cases

In 1910, Sinclair — already famous for The Jungle, his exposé of the meatpacking industry — published an article in Cosmopolitan magazine describing his own fasting experiences and inviting readers to write to him with their results. He received 600–800 letters. From 109 people who provided structured responses, he collected reports on 277 separate fasting episodes.

The conditions his correspondents reported improving ranged from rheumatism and asthma to chronic headaches, nervous prostration, kidney disease, skin conditions, and digestive disorders. Of the 109 people, 100 reported benefit; 9 reported no benefit. Sinclair tabulated these cases and published them alongside accounts of his own two 12-day fasts, arguing that the medical establishment was ignoring a free and powerful healing tool precisely because it had no financial interest in promoting it.

His theory of how fasting worked was pre-scientific but striking in retrospect. He believed overfeeding caused "fermentation" in the digestive tract — a process that produced toxins faster than the elimination organs could clear them. Fasting halted this fermentation, gave the body a chance to expel accumulated waste, and redirected energy from digestion toward repair. In 1911, Sinclair had no language for autophagy, ketosis, or the gut microbiome. But what he was describing in experiential terms maps, with some adjustment, onto processes modern research has now characterised in molecular detail. For a deeper look at how these processes play out, see how intermittent fasting promotes autophagy.

Where Sinclair's Observations Meet Modern Science

The parallels between Sinclair's 1911 descriptions and current research are more than coincidental.

Gut rest and mucosal repair. Sinclair argued that the digestive system needed a complete rest to recover from years of overwork. Modern research confirms this. A 2018 study in Cell Stem Cell (Mihaylova et al.) found that fasting dramatically increased the regenerative capacity of intestinal stem cells. The gut's epithelial lining repairs itself most effectively when not engaged in active digestion. What Sinclair observed as "giving the gut a rest" is, at the cellular level, exactly that.

Metabolic switching. Sinclair noticed that once initial hunger disappeared around days two to three of a fast, a qualitative change occurred — energy improved, mental clarity intensified, and the body seemed to enter a fundamentally different state. The modern explanation is metabolic switching: the shift from glucose metabolism to ketone metabolism that occurs when liver glycogen is depleted. Ketones are not only an alternative fuel source — they are signalling molecules that activate pathways related to cellular repair, inflammation reduction, and brain function. What Sinclair described experientially, we can now map biochemically.

Autophagy. The most significant modern validation of fasting as cellular medicine came in 2016, when Yoshinori Ohsumi was awarded the Nobel Prize in Physiology or Medicine for his work on autophagy — the process by which cells identify, break down, and recycle their own damaged or dysfunctional components. Fasting is one of the most reliable triggers for this process. When Sinclair wrote that the body "metabolises disease tissue before healthy tissue" during a fast, he was describing, in the language available to him, something functionally similar to what autophagy researchers now study at the molecular level.

Inflammation. Sinclair believed fasting reduced what he called "autointoxication" — chronic low-grade poisoning from fermented gut contents. Modern research frames this as chronic low-grade inflammation, driven in part by gut permeability, dietary patterns, and metabolic dysfunction. Fasting has been shown in multiple peer-reviewed studies to reduce inflammatory biomarkers including interleukin-6, TNF-alpha, and C-reactive protein — consistent with what Sinclair's correspondents described reporting subjectively.

For a detailed look at what happens hour by hour as these processes unfold, see what happens to your body hour by hour when you fast.

What Sinclair Got Wrong — And Why It Matters

Honest appraisal of the history requires acknowledging where the early fasting literature overreached.

Sinclair's readers reported improvements in conditions that modern evidence does not support fasting as a treatment for — including active tuberculosis. Fasting worsens prognosis in TB patients, who are already underweight and energy-depleted. His collection method — a voluntary survey of enthusiastic readers — created extreme survivorship bias. People who had terrible experiences were unlikely to write to him to report them. The 100 who reported benefit were a self-selected group; the 9 who reported no benefit were almost certainly an underrepresentation of the total who struggled.

He was also wrong about the specific mechanism in some respects. The "toxins" of autointoxication as he imagined them — diffuse systemic poisons from gut fermentation — were not literally accurate as described. But the underlying observation that the gut produces metabolically active compounds affecting systemic health when chronically overburdened has found support in the modern literature on intestinal permeability, the gut-liver axis, and the microbiome.

The lesson is not that Sinclair was a quack — it's that he was a careful observer working without the tools to explain what he was seeing. The same observations look different when viewed through molecular biology.

The Long Road Back to Respectability

Between the 1930s and 1990s, fasting largely disappeared from mainstream medical practice. The rise of pharmaceutical medicine, the development of nutrition science focused on daily micronutrient needs, and cultural norms around regular eating ("three meals a day is essential") all pushed fasting into the territory of alternative medicine.

The revival began with animal studies in the 1990s and 2000s demonstrating that caloric restriction extended lifespan across multiple species. By the early 2010s, human clinical trials of intermittent fasting were producing results for metabolic health, weight loss, inflammation, and brain function. Mark Mattson's work at the National Institute on Aging, Valter Longo's research on fasting-mimicking diets, and the tsunami of longevity research following the 2016 autophagy Nobel Prize transformed fasting from folk remedy to legitimate research subject.

Today, intermittent fasting protocols — 16:8, 5:2, time-restricted eating — are studied in clinical trials across dozens of conditions. The evidence base is not yet complete, but the direction of travel is clear: periodic abstinence from food produces measurable biological effects that are difficult to replicate by other means.

What Remains Unchanged Since 1911

Some of Sinclair's practical advice has held up remarkably well over 115 years.

His insistence on drinking large amounts of water throughout a fast — now understood in the context of electrolyte balance, kidney health, and the clearance of metabolic waste products. His warning that breaking the fast incorrectly was "the most dangerous moment" — now validated by the science of refeeding syndrome in the context of extended fasting. His observation that the first two to three days are the hardest — consistent with what we know about the lag time before metabolic switching completes and ketone production stabilises.

And his core philosophical argument: that the body has a profound capacity for self-repair when given the space to carry it out — remains the central thesis of modern fasting research.

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FAQ

Q: Was Upton Sinclair's "The Fasting Cure" based on scientific evidence? A: It was based on personal experience and 277 reader-reported cases — anecdotal by modern standards, but unusually systematic for 1911. Many of his core observations align with what modern research has since confirmed at the molecular level.

Q: When did fasting become scientifically accepted? A: The modern evidence base developed significantly from the 2000s onward, accelerating after the 2016 Nobel Prize for autophagy research and multiple large human clinical trials in the 2010s showing benefits for metabolic health.

Q: Was Sinclair's "autointoxication" theory accurate? A: Directionally correct — the gut does produce metabolically active compounds that affect systemic health when chronically burdened — but not literally accurate in the specific mechanism he described. The modern equivalents are intestinal permeability, dysbiosis, and the gut-liver axis.

Q: What did Sinclair observe that modern science has most clearly confirmed? A: Mental clarity during fasting (now linked to ketone metabolism and BDNF elevation), hunger disappearing after day 2–3 (metabolic switching), cellular repair during fasting (autophagy), gut mucosal repair during digestive rest, and measurable reductions in inflammation markers.

Q: Is extended fasting safe today? A: Short-term intermittent fasting (16–24 hours) has a strong safety profile for healthy adults. Extended fasts (72 hours or more) require more careful preparation and ideally medical supervision — consistent with what Sinclair himself recommended for very long fasts in 1911.

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.