Why Scientists Studied a 31-Day Complete Fast in 1912

In April 1912, a multilingual Maltese pharmacist named Agostino Levanzin arrived at the Carnegie Institution's Nutrition Laboratory in Boston and began a 31-day complete fast — consuming nothing but distilled water for the entire period. A team of Harvard and Carnegie scientists surrounded him with equipment: a respiration calorimeter, blood analysis instruments, daily urine collection, grip strength tests, reaction time measures, and psychological examinations. Every day, for more than a month, they measured what happened to the human body when food stopped completely.

The resulting study — A Study of Prolonged Fasting, published by Francis Gano Benedict in 1915 — remains one of the most comprehensive investigations of human fasting physiology ever conducted. But what motivated this unusual experiment? And what were scientists hoping to learn?

The Scientific Questions Driving the Study

By the early twentieth century, fasting had a long history in popular health culture. Figures like Upton Sinclair had written enthusiastically about its benefits. Professional fasters — men who fasted for weeks on public stages — had attracted scientific attention throughout the 1880s and 1890s. Giovanni Succi, the most famous of these professional fasters, had been studied repeatedly in Paris, Turin, and Berlin.

But the scientific study of prolonged fasting was still fragmentary. Researchers had measured some aspects of metabolism during shorter fasts or in less controlled settings. What the field lacked was a single, comprehensive, rigorously documented account of what happens to every measurable aspect of the body — metabolism, weight, blood chemistry, psychology, cardiovascular function, kidney output — across a complete fast of maximum length.

Benedict's motivations were multiple:

Understanding the body's fuel hierarchy. Scientists knew that the body used glucose as its primary fuel. But it was not yet fully understood in systematic terms how quickly carbohydrate stores (glycogen) depleted during fasting, what happened next, how much protein the body broke down compared to fat, and how efficiently it learned to conserve protein over time. The 31-day fast offered a chance to map the full arc of metabolic adaptation.

Documenting ketosis scientifically. The existence of acidic compounds in the urine of fasting subjects — what we now call ketone bodies — had been noted by earlier researchers but not systematically documented across a prolonged fast from start to finish. Benedict's team measured these daily, producing one of the first controlled scientific records of nutritional ketosis in a human subject.

Settling the question of whether prolonged fasting was dangerous. Popular accounts of extended fasting had created both enthusiastic advocates and alarmed critics. The medical establishment generally viewed prolonged fasting with suspicion. A rigorous, monitored experiment with daily physician examination could answer, with scientific data, whether a person could fast for thirty-one days without dangerous organ damage — and what the measurable risk markers looked like.

Testing cognitive and physical performance during fasting. One of the claims made by fasting advocates was that mental clarity and physical ability were not merely maintained but sometimes enhanced during fasting. Benedict's team designed a battery of daily psychological and physical tests — word memory, reaction time, word association, visual acuity, grip strength — specifically to measure this scientifically rather than relying on subjective reports.

Why Agostino Levanzin?

The choice of subject was deliberate. Levanzin, born in Malta in 1872, was not an ordinary participant. He had a pharmacist's training, had studied medicine and law, spoke six languages fluently, and had a demonstrated history of prolonged fasting — including a 37-day fast in Malta during which he had gone from 171 pounds to 134 pounds.

More importantly, he had come to fasting through his own chronic illness. He described a history of overfeeding-induced neurasthenia — a state of nervous exhaustion from eating too much, too frequently. Fasting had restored his health when conventional medicine had not. In the year before the experiment, he had already been eating one meal per day.

This meant Levanzin was physiologically adapted to intermittent food restriction, which made him an unusually suitable subject for studying the full arc of a prolonged fast. A person with no prior fasting experience would likely have struggled with the early days in ways that might have compromised the later scientific measurements. Levanzin had the rare combination of scientific credibility, established fasting history, and genuine personal motivation — he described himself as happy to undergo the experiment "for the benefit of humanity."

He also arrived with a cooperative relationship toward measurement, despite having strong opinions and a contentious personality. He understood what was being done and why, and he submitted to daily blood draws, urine collection, caliper measurements, clinical examinations, and psychological testing throughout the thirty-one days.

The Experimental Setup

The Carnegie Nutrition Laboratory in Boston was equipped with a respiration calorimeter — an airtight chamber that could measure the heat a person produced while sleeping, providing a direct measurement of metabolic rate. This was cutting-edge equipment in 1912, and Benedict's laboratory was one of the few facilities in the world capable of running such measurements continuously.

Alongside the calorimeter, the team collected:

Daily weight measurements (taken each morning after urinating, before dressing)
Blood samples analysed for composition, specific gravity, and cellular changes
Daily urine collection measuring nitrogen (proxy for protein catabolism), ketone bodies, creatinine, uric acid, and mineral excretion
Pulse and blood pressure taken multiple times daily
Rectal temperature to track core body temperature changes
Alveolar air samples (air from deep in the lungs) providing an index of acid-base balance
Daily acetone breath tests to monitor ketosis
Daily psychological tests conducted at standardised times
Grip strength measurements using a hand dynamometer
Physician clinical examination every alternate day

The subject drank only distilled water — a controlled choice that eliminated any mineral content from water, allowing more precise measurement of what minerals came specifically from tissue catabolism.

The preliminary period of three days before the fast established baseline measurements for comparison. Levanzin arrived on April 10, 1912; the fast began April 14 and continued to May 14.

What the Scientists Found

The findings mapped what happens in the body more precisely than any previous investigation:

Glycogen depletion took longer than expected. Carbohydrate combustion peaked at 68.8 grams on the first day of fasting and declined progressively, reaching approximately 4 grams per day by days 10–13. After day 13, carbohydrate combustion effectively ceased — the body had fully depleted its glycogen stores. This 13-day timeline for complete glycogen depletion was longer than modern estimates, likely because Levanzin had been eating only one meal per day before the fast, which may have affected how he stored glycogen.

Fat became the dominant fuel source. After the glycogen transition point, the respiratory quotient (a ratio of CO2 produced to O2 consumed) fell to values of 0.71–0.76 — indicating fat dominance. This is consistent with what modern fasting research describes as the shift to fat oxidation and ketosis.

Protein catabolism decreased over time. Nitrogen excretion — the proxy for how much protein the body is breaking down — peaked on day 4 and then fell progressively. By the later weeks of the fast, the daily nitrogen loss per kilogram of body weight had dropped to approximately 0.143 grams — well below the early-fast peak of 0.207 grams. This protein-sparing adaptation is now understood as a core feature of ketosis, confirmed by later researchers including Cahill (2006, Annual Review of Nutrition) and Longo & Mattson (2014, Cell Metabolism).

Metabolic rate dropped significantly. Heat production fell throughout the fast, reaching a minimum of approximately 625 calories per 24 hours on the twenty-first night — down from roughly 836 calories on day 3. This represents approximately a 25% reduction in basal metabolic rate, consistent with the metabolic adaptation documented in the Minnesota Starvation Experiment (Keys et al., 1950) and in modern caloric restriction research (Leibel et al., 1995, NEJM).

Cognitive performance held up. Despite thirty-one days without food, Levanzin showed no severe cognitive deterioration. His word association responses remained coherent; he climbed stairs without unsteadiness on day 31 (photographed as documentation). On day 29, he wrote multi-page autobiographical notes. Performance varied day to day, often correlated with mood — on days when his mental attitude was cheerful, test results were markedly better.

Breaking the fast caused the most dangerous moment. When the fast ended on May 14 with lemons, oranges, honey, and grape juice, Levanzin experienced severe intestinal colic and had to be briefly hospitalised. This confirmed the critical importance of reintroducing food gradually — what would later be described clinically as refeeding syndrome (Mehanna et al., 2008, BMJ) was present and documented in this 1912 experiment, decades before the formal clinical description.

Why This Study Still Matters

Benedict's Study of Prolonged Fasting is still cited in modern research on fasting metabolism, protein catabolism, and refeeding safety. The fundamental findings — protein sparing during ketosis, metabolic rate reduction, the safety of extended fasting under monitoring, the criticality of careful refeeding — have all been confirmed by subsequent research using technologies Benedict did not have access to.

For fasting researchers, the 1912 experiment provided an unusually thorough baseline. For anyone curious about the history of fasting science, it demonstrates that systematic, rigorous inquiry into fasting has been underway for more than a century — long before the current wave of interest in intermittent fasting made it a subject of widespread scientific and popular attention.

For the complete guide, get Intermittent Fasting in Practice on Amazon — and claim 3 months free on our fasting app at fastinginpractice.com/redeem.

FAQ

Who was Francis Gano Benedict? Benedict was Director of the Nutrition Laboratory at the Carnegie Institution of Washington in Boston. He was one of the leading nutrition scientists of the early twentieth century, responsible for developing the respiration calorimeter used in this and many other experiments.

Why did Levanzin agree to fast for 31 days? Levanzin had a personal history with fasting — he had fasted multiple times before and credited the practice with restoring his health. He described himself as motivated by the opportunity to contribute to scientific knowledge. He was also intellectually engaged with the measurements being taken throughout the study.

Is a 31-day fast safe? Based on Benedict's study and subsequent research, a prolonged fast of this length can be physiologically survivable under continuous medical supervision for a healthy individual. It is not something to undertake without expert guidance, close monitoring, and careful refeeding afterward. The 1912 study was conducted precisely because such safety questions needed answering under controlled conditions.

What happened to Levanzin after the study? After the fast ended, he experienced a difficult refeeding period with intestinal distress and was briefly hospitalised. He later became difficult to manage during recovery. His longer-term fate is not well documented in the scientific record.

How does the 1912 study relate to modern intermittent fasting? The 1912 study examined complete starvation over 31 days — which is different from the 12–24 hour fasting windows used in modern intermittent fasting protocols. However, the fundamental metabolic mechanisms — glycogen depletion, ketosis, protein sparing, metabolic adaptation — are the same processes, just observed at an extreme that clarifies the underlying biology.

This article draws on historical scientific research from 1915 and is for informational purposes only — not medical advice. Always consult a qualified healthcare provider before undertaking any prolonged fast.

Benedict, F.G. (1915). A Study of Prolonged Fasting. Carnegie Institution of Washington, Publication No. 203.

Why Scientists Studied a 31-Day Complete Fast in 1912