Can Fasting Help with Anxiety and Nervousness?

In 1911, Upton Sinclair described himself as a man who was "never more than fifteen minutes ahead of a headache" — chronically nervous, persistently exhausted, and spending thousands of dollars on physicians with little lasting relief. What changed everything for him, and for hundreds of readers who wrote to him after his Cosmopolitan article, was fasting.

The idea that restricting food intake could calm the nervous system sounds counterintuitive. But Sinclair's accounts, alongside a growing body of modern research, suggest this is exactly what can happen.

Historical Context: Sinclair's Theory on Fasting and Nerves

Framing Sinclair's work correctly matters: The Fasting Cure (Mitchell Kennerley, 1911) is a firsthand account and a collection of reader testimonials — not a clinical trial. But as historical evidence, it is rich, detailed, and worth examining carefully.

Sinclair believed that anxiety and nervous exhaustion in his era were largely driven by what he called autointoxication — a process in which fermenting, undigested food in the gut produced toxins that burdened the liver, kidneys, and nervous system. He argued that the modern diet of his time (heavy in starches, sugars, and excessive quantities of food) kept this process running continuously, producing a kind of background toxic load that manifested as nervousness, insomnia, headaches, and mental instability.

His solution was simple: stop eating and let the body clear itself out.

In his 277-case survey of readers who had tried fasting, nervous prostration and neurasthenia (the 1911 term for anxiety and nervous exhaustion) appeared repeatedly as conditions that responded to fasting. Cases described relief from chronic nervousness, sleeplessness, and mental agitation — often within the first week of a fast.

What Sinclair Observed in Himself

Sinclair's own account is particularly detailed about the mental dimension of fasting.

During his first 12-day fast, he noted that while the first four days brought physical lassitude and dizziness, his mental clarity was exceptional from the outset. He described reading and writing more than he had "dared to do for years before." The chronic nervousness that had plagued him — the background state of anxiety and near-headache — diminished substantially.

His second 12-day fast showed no weakness at all. He walked four miles every morning, read and wrote throughout, and produced work he considered some of his best.

Sinclair quoted a correspondent: "After a complete fast the body will come to its ideal weight" — and he observed the same principle applied to the nervous system. The body seemed to find its baseline when the constant burden of digestion and detoxification was lifted.

What Sinclair Said About Fear During Fasting

One of his most unusual and prescient observations concerned the role of mental state during fasting: "The first danger of fasting is fear."

He argued that nervous excitement, terror, or panic during a fast could cause genuine physical harm — and that this was why fasting with experienced, calm companions made such a difference. The psychological state during a fast wasn't incidental; it was central.

He compared earthquake survivors who died from what was labelled starvation — but who had, in fact, been near others who had survived just as long — with fasters who had gone far longer in controlled conditions without harm. His interpretation was that fear of hunger is often more harmful than hunger itself.

This maps onto something modern neuroscience has documented: the brain's stress response (the hypothalamic-pituitary-adrenal axis) responds to perceived threats, including feared starvation, by releasing cortisol and adrenaline — which worsen anxiety. A calm, informed, purposeful fast does not trigger the same alarm response.

Connection to Modern Science

While Sinclair's "autointoxication" theory has not survived intact into modern medicine, several mechanisms he intuited have found modern equivalents:

The gut-brain axis. Modern research has confirmed a bidirectional communication highway between the gut and the brain. An inflamed, dysbiotic gut does produce signalling molecules that affect mood and anxiety levels. Fasting has been shown to improve gut microbiome diversity and reduce intestinal inflammation — changes that may calm the nervous system over time.

Insulin and blood sugar stability. The blood sugar crashes that follow high-carbohydrate meals trigger adrenaline release as the body attempts to bring glucose back up. Chronic blood sugar volatility is a recognized driver of anxiety, irritability, and emotional instability. Fasting eliminates this volatility entirely during the fasting window.

BDNF (Brain-Derived Neurotrophic Factor). Fasting increases BDNF, a protein that supports neuron health and has been associated with reduced anxiety and improved mood regulation in clinical research.

A 2021 meta-analysis published in Nutrients (Berthelot et al., 2021, PMID 34836202) examined 11 studies involving 1,436 participants and found that fasting was associated with significant reductions in both anxiety (b = −0.508, p = 0.038) and depression scores compared to control conditions.

Practical Takeaways from Historical Evidence

Sinclair's detailed accounts and his survey of 277 cases suggest several practical patterns:

Nervousness and anxiety were among the most commonly reported conditions that responded to fasting — appearing in multiple cases across his survey.
The first 2–3 days were the hardest mentally, as the body adjusted and the habit of eating reasserted itself. But beyond that window, mental calm was commonly reported.
Water intake was critical. Sinclair identified insufficient water as a key cause of fasting failures — and chronic dehydration is a known aggravator of anxiety symptoms.
Breaking the fast correctly mattered enormously. Many cases where benefit did not persist were attributed to returning to the same diet that had caused the problem — specifically, starch-heavy, sugar-heavy eating.

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Frequently Asked Questions

Did Sinclair believe fasting could cure nervousness?

He did, within the framework of his autointoxication theory. He saw the nervous system as being burdened by the products of excessive, fermenting food intake, and fasting as the mechanism to clear that burden. His personal experience supported this, as did many of the 100 of 109 readers who reported benefit from fasting in his survey.

Is it safe to fast if I already have anxiety?

This article reflects historical accounts from 1911 and modern observational data — neither constitutes medical advice. People with diagnosed anxiety disorders should consult a healthcare professional before undertaking any significant dietary change, including fasting. Sinclair himself warned that fear and nervous tension during a fast could be harmful, suggesting that psychological readiness matters.

Does fasting always reduce anxiety, or can it make it worse?

Sinclair acknowledged that fasting could worsen anxiety in people who were afraid of it. The mental state going into a fast matters. Modern data also shows that overly aggressive fasting — especially in women — can raise cortisol and worsen anxiety in some individuals. Starting with shorter fasting windows and building gradually is the safer approach.

How long into a fast do people typically notice mental calming?

Based on Sinclair's accounts and modern testimonials, most people report a shift in mental clarity and reduced anxiety from around day 4–5 of sustained fasting. The first 2–3 days are typically the hardest, with hunger and mild nervousness peaking before settling.

What does modern research say about fasting and anxiety?

A 2021 meta-analysis of 11 studies found that fasting significantly reduced self-reported anxiety scores compared to control groups. Research on the gut-brain axis, insulin stabilization, and BDNF production offers mechanistic support for why this might occur. The evidence is promising but not yet conclusive — more large-scale RCTs are needed.

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.

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

Can Fasting Help with Anxiety and Nervousness?