Can Fasting Help with Anxiety and Nervousness?

Anxiety and nervousness were among the first conditions Upton Sinclair described being helped by fasting — both in his own case and in the hundreds of reader reports he collected in his 1911 book The Fasting Cure. Over a century later, modern neuroscience is beginning to understand why.

The Direct Answer

Fasting can reduce anxiety for many people, particularly anxiety driven by blood sugar instability, gut dysfunction, or chronic inflammation. The historical record from 1911 is striking: Sinclair himself suffered from persistent nervousness and chronic exhaustion before discovering fasting, and his transformation was dramatic. Many of his readers reported the same.

Modern research adds a biological framework: fasting appears to reduce inflammatory markers, stabilise blood sugar, support gut health, and boost BDNF (brain-derived neurotrophic factor) — all of which influence anxiety levels.

Historical Context: What Sinclair's 1911 Cases Showed

In The Fasting Cure (Mitchell Kennerley, 1911), Upton Sinclair documented not just his own nervous system recovery but also collected accounts from 277 fasting episodes reported by 109 readers. Among the most consistently reported benefits were improvements in what he called "nervous prostration" and "neurasthenia" — the Victorian-era terms for what we would today recognise as chronic anxiety, nervous exhaustion, and burnout.

Sinclair himself was a compelling case study. By his own account, he spent years and roughly $15,000 in today's equivalent money on physicians, sanatoriums, and medicines trying to resolve his persistent headaches and nerve-based exhaustion. Nothing worked reliably. Then he tried fasting.

His first 12-day fast produced something he hadn't experienced in years: clarity of mind, improved sleep, and a significant reduction in what he described as chronic nervousness. He noted that from around day five onward, his mental state became unusually calm and productive — he wrote prolifically during that period.

Sinclair (1911) made a key observation: "The first danger of fasting is fear." He believed that mental composure during a fast was not just a comfort — it was biologically important. Nervous terror during a fast, he argued, could create genuine physical harm. Conversely, calm fasting seemed to restore the nervous system.

The Modern Science: Why Fasting Might Ease Anxiety

Modern research has identified several mechanisms that could explain what Sinclair observed.

Blood sugar stability. Many anxiety symptoms — racing heart, irritability, difficulty concentrating, impending doom feelings — overlap significantly with hypoglycaemic (low blood sugar) symptoms. When people eat a high-carbohydrate diet, blood sugar swings frequently produce these anxiety-like states. Fasting and switching to fat as a fuel source stabilises blood sugar, which can dramatically reduce these pseudo-anxiety episodes. Read more in our article on intermittent fasting and brain health.

BDNF (Brain-Derived Neurotrophic Factor). Fasting boosts BDNF, a protein that supports neuronal growth and repair. Low BDNF is consistently linked to anxiety and depression in the research literature. Higher BDNF levels appear to buffer stress responses and improve emotional resilience.

Inflammation. Chronic low-grade inflammation is increasingly recognised as a driver of anxiety and mood disorders. Fasting has been shown to reduce several inflammatory markers including CRP, IL-6, and TNF-α. Lower inflammation supports calmer neurological function. See our article on intermittent fasting and inflammation for the full picture.

Gut-brain axis. The gut produces approximately 90% of the body's serotonin. A disrupted gut microbiome is associated with heightened anxiety. Fasting provides the gut with rest, promotes microbial diversity, and may help restore the gut-brain signalling that influences mood. Sinclair's fermentation theory — that overfeeding causes toxic buildup in the digestive tract — anticipated this gut-brain connection by over a century.

Cortisol and the stress response. Fasting, when done correctly, can modulate cortisol patterns. However, this is a nuanced point: aggressive or prolonged fasting can temporarily raise cortisol, which is counterproductive for anxiety. Short daily fasting windows (14–16 hours) appear to be the most beneficial for mood stability without stressing the HPA axis.

What "Correct" Fasting Looks Like for Anxiety

Not all fasting helps anxiety equally. A few distinctions matter:

Food quality first. If you're fasting but still eating sugar and processed carbohydrates in your eating window, the blood sugar swings continue. Sinclair would have called this "partial eating keeping hunger alive." Modern physiology would call it maintaining insulin resistance. Either way, the anxiety-driving mechanism remains.

Start with shorter windows. A 16-hour fast is very different from a 36-hour fast in terms of cortisol response. People prone to anxiety should start with 13–15 hours and build gradually. Extended fasting (24h+) can temporarily elevate cortisol, which may worsen anxiety in some individuals.

Mental composure matters. This is Sinclair's most interesting observation, and one that modern stress research supports. The anxious anticipation of hunger can be more biologically disruptive than hunger itself. Learning to distinguish between habitual hunger and true hunger — and approaching fasting with calm curiosity rather than fear — changes the physiological response.

Electrolytes. Low magnesium, in particular, is strongly linked to anxiety and irritability. When insulin drops during fasting, the kidneys flush electrolytes. Supplementing with magnesium (or eating magnesium-rich foods like dark leafy greens and avocados) addresses this directly.

What Fasting Will Not Fix

Fasting is not a substitute for mental health treatment. Severe anxiety disorders, panic disorders, PTSD, and generalised anxiety disorder require professional support. Fasting may complement treatment, but it should not replace it.

Similarly, if fasting is causing anxiety — if you're experiencing heart palpitations, a sense of dread, or worsening symptoms — that's a signal to shorten the fasting window, eat more in the eating window, and consult a healthcare professional.

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

FAQ

Does fasting reduce anxiety or make it worse?

For many people, fasting reduces anxiety — particularly anxiety linked to blood sugar instability, inflammation, or gut dysfunction. However, very aggressive or prolonged fasting can raise cortisol and temporarily worsen anxiety in some individuals. Starting with a modest window (14–16 hours) is the safest approach.

How long before fasting reduces anxiety symptoms?

Improvements in mood and anxiety are commonly reported within one to three weeks of consistent fasting, particularly when food quality is also addressed. Blood sugar stabilisation — which is a major driver of anxiety reduction — typically takes seven to fourteen days.

Can fasting help with panic attacks?

There is no direct clinical evidence that fasting prevents panic attacks. However, the blood sugar and inflammatory factors that fasting addresses do contribute to anxiety generally. Some people report fewer panic episodes after establishing a consistent fasting routine and cleaning up their diet.

What did Upton Sinclair say about nervousness and fasting?

In The Fasting Cure (1911), Sinclair documented that his own chronic nervousness resolved during his first extended fast. He collected reports from readers showing similar improvements in "nervous prostration" and neurasthenia. He also warned that nervous fear during a fast could cause genuine harm — mental composure was, in his view, as important as the fast itself.

Is fasting safe for people with anxiety disorders?

Many people with anxiety do fast safely and report benefit. That said, anyone with a diagnosed anxiety disorder should consult a healthcare professional before starting a fasting protocol, particularly if they are on medication, as fasting can affect medication absorption and blood sugar levels.

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.

Can Fasting Help with Anxiety and Nervousness? What History and Science Both Say