Fasting and Asthma: Historical Evidence and Modern Insights

Asthma is, at its core, an inflammatory disease. The airways become hypersensitive, inflamed, and reactive — which raises an obvious question: could reducing whole-body inflammation through fasting have any effect on asthma?

Over a century ago, Upton Sinclair was asking exactly the same question, and his readers were sending him their answers.

The Historical Context

In 1911, journalist and social reformer Upton Sinclair published The Fasting Cure, a book based on his personal fasting experiments and 277 case reports collected from readers who had tried fasting for various conditions. Among the conditions Sinclair documented as responding to fasting was asthma — alongside rheumatism, digestive disorders, nervous exhaustion, chronic headaches, and skin conditions.

Sinclair was not a physician, and he was careful (by the standards of the day) to present these as personal accounts, not clinical proof. But the consistency of reports about respiratory conditions improved enough to include them prominently in his book.

One case stands out in particular: a man with both asthma and dropsy (severe fluid retention), weighing 220 pounds with legs described as "like sacks of water." After seven days of fasting followed by four weeks on a light diet, this man returned to farm work — chopping wood and pitching hay. Sinclair included this case as evidence that fasting could produce dramatic recoveries even in conditions that had become debilitating.

Sinclair's Theory: Why He Thought Fasting Helped

To understand Sinclair's enthusiasm, you need to understand his core theory of disease, which he drew from both his own experience and the work of physicians of his era.

His argument went roughly as follows: chronic overfeeding causes surplus nutrients to ferment in the digestive tract. This fermentation produces toxins faster than the body's elimination organs (liver, kidneys, skin) can clear them. The result — which he called autointoxication — is a state of chronic, low-grade toxicity that manifests as inflammation throughout the body.

In this model, asthma was not primarily a lung disease but a systemic inflammatory condition rooted in the gut. Giving the digestive system a complete rest through fasting allowed the body to redirect its energy toward clearing this toxic load. Once the backlog cleared, inflammation in the airways — as elsewhere — would subside.

Sinclair had no way to measure this scientifically. But he was describing, in the language of 1911, something that modern science would come to understand through entirely different mechanisms.

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

What Modern Science Says About Fasting and Inflammation

Modern research has confirmed that fasting — particularly intermittent fasting and time-restricted eating — does reduce systemic inflammation. Studies measuring inflammatory markers such as C-reactive protein (CRP), interleukin-6 (IL-6), and tumour necrosis factor alpha (TNF-α) have found meaningful reductions with various fasting protocols.

This matters for asthma because airway inflammation is driven by many of the same cytokines and immune pathways affected by systemic inflammation. When the body's overall inflammatory burden decreases, there is good reason to expect that locally manifested conditions — including reactive airways — may improve alongside it.

A 2019 study published in Cell examined the effects of Ramadan fasting on immune cell populations and found notable shifts in monocyte populations and inflammatory markers. A separate 2021 study found that gut microbiome diversity improved with fasting, which is relevant because the gut-immune-lung axis is increasingly recognised as a driver of asthma severity.

However, it is important to be clear: there are no large clinical trials specifically examining intermittent fasting as a treatment for asthma in humans. The evidence is mechanistically plausible but not clinically proven.

The Gut-Lung Axis: A Modern Lens on Sinclair's Theory

Sinclair's fermentation theory sounds archaic, but it maps surprisingly well onto what researchers now call the gut-lung axis — the bidirectional relationship between gut microbiome health and respiratory function.

Research published in the last decade has established that:

• Gut microbiome diversity correlates with asthma severity, with lower diversity associated with worse outcomes
• Leaky gut (increased intestinal permeability) allows bacterial products to enter the bloodstream, driving systemic inflammation that affects the lungs
• Dietary patterns that reduce gut fermentation of refined carbohydrates appear to improve asthma control in observational studies

Sinclair's insight — that digestive dysfunction underlies chronic inflammatory conditions including respiratory ones — turns out to have been pointing at something real. He was wrong about the mechanism (fermentation in his era meant something different from the gut microbiome science we have today), but directionally correct that the gut and respiratory system are linked.

What This Means in Practice

If you have asthma and you're considering intermittent fasting, a few things are worth keeping in mind:

Fasting may reduce the inflammatory load that worsens asthma. By lowering insulin, clearing inflammatory cytokines, and giving the gut time to repair, intermittent fasting addresses several upstream drivers of airway inflammation.

Food quality matters as much as timing. Eliminating sugar, refined grains, and seed oils removes the primary dietary drivers of inflammation. Many people with asthma who start fasting also change what they eat — and it's often hard to separate which change is driving improvement.

The first week may feel worse before better. Any detoxification or adaptation period involves transient symptoms. If your asthma is well-controlled with medication, do not adjust your medication without medical guidance during a fasting transition.

Weight loss may independently improve asthma. Obesity is one of the strongest independent risk factors for asthma severity. If fasting helps achieve and maintain a healthier weight, the indirect benefit for asthma control may be significant regardless of any direct anti-inflammatory effect.

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Frequently Asked Questions

Can fasting cure asthma?

There is no clinical evidence that fasting cures asthma. What the evidence does suggest is that reducing systemic inflammation through fasting — and the dietary changes that accompany it — may improve asthma control in some people. This is not a substitute for prescribed medication or medical oversight.

Is it safe to fast if I use an inhaler?

For most people using reliever inhalers, fasting poses no specific interaction risk. Preventer inhalers (corticosteroids) are generally safe to continue during a fast. If you take oral corticosteroids or other systemic medications for asthma, consult your doctor before changing your eating pattern.

Did Sinclair report any cases where fasting made asthma worse?

Sinclair did not document cases of asthma worsening with fasting, though he acknowledged that not all conditions responded. His survey reported 17 out of 109 respondents found no benefit. He attributed most non-responses to breaking the fast incorrectly rather than fasting making the condition worse.

How long should I fast to potentially see any effect on inflammation?

Research on inflammatory markers generally shows measurable changes after two to four weeks of consistent intermittent fasting (16–18 hours daily). Significant changes in gut microbiome composition take longer — typically six to eight weeks of consistent practice. Shorter, occasional fasts are unlikely to produce meaningful inflammatory changes.

What dietary changes alongside fasting might benefit asthma?

The dietary changes most consistently associated with reduced asthma severity include: eliminating refined sugars and seed oils, increasing omega-3 fatty acids (oily fish, flaxseed), eating fermented foods for gut diversity, and reducing ultra-processed foods. These align well with the food approach recommended alongside intermittent fasting.

Related Articles

• Does intermittent fasting reduce inflammation?
• Intermittent fasting and inflammation: the research explained
• How fasting clears toxins from your body

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.