Writing a Novel While Fasting: Fasting and Creative Work

Upton Sinclair, best known for The Jungle, wrote some of his most productive work while fasting. During his two 12-day fasts in the early 1900s, he described reading and writing "more than he had dared to do for years." A friend who tried the same approach planned and wrote two-thirds of a play during a single extended fast.

This wasn't coincidence. Something about fasting — confirmed now by neuroscience over a century later — genuinely sharpens the mind for creative and intellectual work.

The Historical Account

In his 1911 book The Fasting Cure, Sinclair documented his own experience of fasting and mental clarity in striking terms. His first major fast lasted 12 days. The first four days involved physical weakness and dizziness on arising. But the mind, he noted, remained remarkably clear throughout.

From day five onward, the mental shift became unmistakable. He wrote more, read more, and reported a sense of creative sharpness he had not experienced during his years of eating normally. He also noted that a female correspondent shared a similar report: she had planned and written two-thirds of a play during her own 12-day fast, describing the higher faculties as being "in a peculiarly sensitive condition."

Sinclair attributed this partly to the removal of what he called "digestive burden" — the significant energy the body normally directs toward processing food — and partly to the clearing of toxins he believed accumulated from overeating.

His framework was speculative by 1911 standards. But it pointed toward something real.

What Modern Science Explains

We now have a clearer biological picture of why fasting affects creative and intellectual output.

BDNF (Brain-Derived Neurotrophic Factor) is one of the primary reasons. BDNF is sometimes called "fertiliser for the brain" — it promotes the growth of new neurons, strengthens existing neural connections, and is directly linked to improved learning, focus, and creative thinking. Fasting is one of the most reliable ways known to increase BDNF levels. Studies have shown BDNF rises significantly during caloric restriction and fasting periods.

Ketones as a cleaner fuel source is another major factor. After roughly 14–16 hours of fasting, the brain begins to use ketones — molecules produced from fat breakdown — as its primary energy source. Ketones provide more efficient energy to brain cells than glucose does. Unlike glucose, ketones don't cause the energy spikes and crashes associated with eating carbohydrates. The result is stable, sustained mental energy with none of the post-meal cognitive dip many people recognise as the afternoon slump.

Reduced inflammation also plays a role. Chronic low-grade inflammation affects cognitive function over time. Fasting reliably reduces inflammatory markers in the body, and this appears to have a positive effect on mental performance.

Why Creative Work Specifically Benefits

For sustained creative work — writing, composing, problem-solving, designing — three conditions are particularly helpful: focus, sustained energy, and access to ideas without mental fog.

Fasting tends to provide all three.

Sinclair himself was clear on this: he didn't simply feel vaguely better while fasting. He produced work he considered excellent. The author of Intermittent Fasting in Practice, Mehrdad Jamshidi, makes the same observation from his own experience — the entire book was written while fasting. He describes the state as one of "clean, stable energy" with no post-lunch crashes and concentration that lasts longer than it would after eating.

This isn't a performance boost through caffeine or stimulation. It's the natural cognitive state of a body running on ketones and freed from the digestive load of processing food.

When the Cognitive Benefits Appear

The timing matters. The first day or two of any significant fast — or the early adaptation period when someone is new to fasting — can feel foggy or headache-prone as the body transitions fuel sources. This is temporary.

Sinclair described the first four days of his initial fast as physically difficult, with dizziness on arising, even while noting mental clarity. By the second fast (which came after his body had adapted), there was no weakness at all. He walked four miles every morning and worked throughout.

For daily intermittent fasting (16:8 or OMAD), the cognitive sharpness typically becomes noticeable after the first 10 days, as the body adapts and insulin stabilises. Most practitioners report that their best focus and creative output happens in the final hours of the fasting window — when ketone production is at its peak — rather than immediately after eating.

Practical Lessons from 1911 and Today

Sinclair's advice on working while fasting was practical and grounded:

• Intellectual work is compatible with fasting from day 2–3 onward. The initial adaptation period is the hardest. Push past it.
• Heavy physical labour is not advisable during extended fasts. Creative and clerical work is well-suited; hard physical exertion is not.
• The mind often works better than usual once the digestive system goes quiet. What feels like a distraction (the absence of food) often becomes an advantage after a few days.
• Water intake is essential. Dehydration amplifies any cognitive fog during fasting. Drink consistently.

For those doing standard 16:8 or 18:6 fasting today, the practical application is simple: schedule your most demanding creative or intellectual work during the final hours of your fasting window or the early hours after waking. This is when ketones are highest and insulin is lowest — and when the Sinclair-observed mental sharpening is most pronounced.

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Frequently Asked Questions

Did Upton Sinclair really write while fasting?

Yes. In The Fasting Cure (1911), Sinclair documented writing and reading prolifically during both of his 12-day fasts, describing the mental output as equal to or better than his usual work. His second fast involved no physical weakness at all, with walks and writing throughout.

Why does fasting improve focus for creative work?

The main mechanisms are: increased BDNF (which supports neural connections and learning), ketones replacing glucose as brain fuel (providing stable, crash-free energy), and reduced post-meal cognitive dip. Removing the digestive load also frees energy that would otherwise be directed to the gut.

When do the cognitive benefits of fasting kick in?

For daily intermittent fasting, most people report noticeable mental clarity after 10 or more days of consistent practice. For extended fasts, Sinclair reported clarity from the early days even when experiencing physical weakness. The post-adaptation experience is typically described as significantly better than normal cognitive function.

Can I do creative work during the fasting window?

Yes — many people find the final hours of the fasting window their most productive. This is when ketone levels are highest, insulin is lowest, and the fuel shift to fat burning is most complete.

Is this backed by modern science?

Yes. The role of BDNF in fasting and cognitive function has been well-documented since the 1990s. Research on ketones as brain fuel and fasting's anti-inflammatory effects provides a solid scientific basis for what Sinclair observed anecdotally in 1911.

Related Articles

• Intermittent fasting and brain health: the neuroscience
• Does fasting improve brain function and focus?
• Why fasting improves mental clarity: from Sinclair to modern neuroscience

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.