The Carnegie Nutrition Laboratory: Where Fasting Science Was Born

When people talk about intermittent fasting today, they cite modern researchers — Valter Longo, Mark Mattson, Yoshinori Ohsumi. But the foundational scientific work that established what actually happens inside a human body during prolonged fasting was conducted over a century ago, inside a purpose-built laboratory in Boston funded by one of history's greatest philanthropic institutions: the Carnegie Institution of Washington.

Understanding the Carnegie Nutrition Laboratory — its mission, its methods, and the landmark study it produced — is essential context for anyone who wants to understand where fasting science began.

The Carnegie Institution and the Science of Nutrition

In the early 20th century, the Carnegie Institution of Washington was directing funds into the most pressing scientific questions of the era. Nutrition was one of them. The study of how the human body uses food — and what happens when food is withheld — was considered not just medically important but socially vital. Poverty, disease, and poor nutrition were public health crises in industrialising America, and understanding the body's metabolic needs was a prerequisite for addressing them.

Francis Gano Benedict was appointed director of the Carnegie Nutrition Laboratory in Boston, Massachusetts. He was a methodical, technically exacting scientist — the kind of researcher who built his own instruments when existing ones were insufficiently precise. His laboratory became one of the most sophisticated metabolic research facilities in the world.

The Respiration Calorimeter: The Heart of the Laboratory

The defining instrument of the Carnegie Nutrition Laboratory was the respiration calorimeter — a device that Benedict designed and built to measure the human body's heat production with exceptional accuracy. A person entered the calorimeter and spent the night (or extended periods) inside while the machine measured the heat they produced, the oxygen they consumed, and the carbon dioxide they exhaled.

This direct heat measurement — called calorimetry — gave Benedict something that no researcher before him had achieved with such precision: a real-time, continuous measurement of the body's energy expenditure during fasting. He could answer, with scientific confidence, the question: exactly how does the body's energy use change when it has no food?

The calorimeter was paired with a separate respiration apparatus for daytime measurements of gaseous exchange — oxygen consumed and carbon dioxide produced — which allowed calculation of the respiratory quotient. This ratio reveals which fuel the body is burning: carbohydrates produce a respiratory quotient near 1.0; fats produce a quotient near 0.70. During the 31-day fast studied in 1915, Benedict watched the respiratory quotient fall from near 1.0 in the first days to below 0.72 in the middle and later weeks — direct, objective evidence of the body's shift from carbohydrate to fat as its primary fuel.

The 1912 Experiment: A 31-Day Complete Fast

The culmination of Benedict's early fasting work was a controlled experiment conducted in April–May 1912 on a Maltese subject named Agostino Levanzin, published in 1915 as A Study of Prolonged Fasting — Carnegie Institution of Washington, Publication No. 203.

Levanzin was 40 years old at the start of the fast. He had previous fasting experience — including a 37-day self-directed fast in Malta — and had spent the year before the experiment eating only one meal a day. He was physically healthy and mentally capable. He arrived at the laboratory on April 10, 1912, underwent three days of baseline measurement, and then began a complete fast on April 14, drinking only distilled water for 31 consecutive days.

The choice of distilled water was deliberate. Any mineral content in tap water would have affected the urine analysis, which was one of the most critical components of the study. By controlling water intake precisely — beginning at 750 millilitres per day and adjusted by medical recommendation as the fast progressed — Benedict could track with confidence exactly what the body was excreting and what that meant about its internal chemistry.

What Was Measured and Why

The scientific breadth of the Carnegie study was extraordinary for its time. Every day during the 31-day fast, Levanzin was subjected to:

Physical measurements: Weight (taken each morning after urination and before dressing), rectal temperature, pulse rate, blood pressure, abdominal girth, and clinical examination of the heart, lungs, liver, and abdomen by the laboratory physician.

Respiratory measurements: Morning sessions in the respiration apparatus measuring oxygen consumed and CO2 produced, giving the respiratory quotient and therefore the fuel mix being burned.

Nightly calorimetry: Levanzin spent nights in the respiration calorimeter, which measured total heat production and provided the most precise data on basal metabolic rate.

Urine analysis: Total urine was collected daily. Constituents measured included: nitrogen (the proxy for protein catabolism), creatinine, uric acid, phosphorus, calcium, magnesium, sodium, chloride, and total acidity including ketone bodies (beta-hydroxybutyric acid and acetone). This was one of the first systematic documentations of nutritional ketosis in human fasting.

Psychological testing: Daily tests of memory (10 one-syllable words recalled after a delay), reaction time (speed of response to a stimulus), word association (speed and type of verbal response), and visual acuity. Grip strength was measured with a dynamometer.

Blood analysis: Periodic blood samples measuring red blood cell count, haemoglobin, and later in the study, white blood cell differentials.

This multi-disciplinary approach — covering metabolism, physiology, biochemistry, and psychology simultaneously — produced a dataset that remains scientifically valuable over a century later.

Key Scientific Findings from the Carnegie Study

The 1915 publication by Benedict yielded several findings that connect directly to modern fasting science:

Glycogen depletion timeline. Carbohydrate combustion peaked at 68.8 grams on the first day of the fast and fell to approximately 4 grams per day by days 10–13. After day 13, carbohydrate combustion had effectively ceased — the body had fully depleted its glycogen stores. Modern estimates for glycogen depletion in typical people are shorter (12–48 hours), but Levanzin had been eating one meal a day for a year, giving him unusual baseline metabolic flexibility (Cahill, G.F., 2006, Annual Review of Nutrition).

Metabolic adaptation. Total heat production fell from approximately 836 calories on day 3 to a minimum of approximately 625 calories on night 21 — a reduction of roughly 25% in basal metabolic rate. This mirrors what modern research describes as metabolic adaptation during caloric restriction (Leibel et al., 1995, New England Journal of Medicine).

Protein sparing. Nitrogen excretion — the measure of protein catabolism — peaked on day 4 and then fell progressively, reaching its lowest values in the final days of the fast. This demonstrated that the body shifts aggressively away from burning protein once fat catabolism is established, a process now understood through the protein-sparing effects of ketosis (Longo & Mattson, 2014, Cell Metabolism).

Nutritional ketosis. Beta-hydroxybutyric acid and acetone bodies were detected systematically in the urine throughout the fast — one of the earliest controlled scientific documentations of nutritional ketosis in human fasting. The acidosis was moderate and the body's buffering systems compensated throughout, with no dangerous acid-base derangement.

Cardiovascular adaptation. Pulse rate declined from early-fast highs to a low of 73 beats per minute on day 23. Blood pressure also declined. These findings are consistent with what modern therapeutic fasting research describes as beneficial reductions in cardiac workload (Wilhelmi de Toledo et al., 2019, Nutrients).

Cognitive resilience. Despite 31 days without food, Levanzin showed no severe cognitive collapse. His word association responses remained coherent and sophisticated throughout. On day 29, he wrote detailed, multi-page autobiographical notes — a demonstration of preserved high-level cognitive function near the end of a month-long complete fast. His mental performance varied day to day, with mental attitude identified as the single most significant variable in cognitive test results (Mattson et al., 2018, Nature Reviews Neuroscience).

The Breaking of the Fast: A Critical Lesson

The most dangerous moment of the entire experiment occurred not during the fast but immediately after it. On day 31, the fast was broken with lemons (eaten whole), oranges, honey, and grape juice. The sudden reintroduction of food caused severe intestinal colic — Levanzin required brief hospitalisation.

This episode, documented in the 1915 study, prefigures what was only formally named and described after World War II: refeeding syndrome. The physiological mechanism — the sudden restoration of carbohydrate driving rapid cellular uptake of phosphate, potassium, and magnesium, creating dangerous imbalances — was observed in action at the Carnegie laboratory in 1912, decades before it had a clinical name (Mehanna et al., 2008, BMJ).

The lesson embedded in this data remains as relevant today as it was in 1912: the longer the fast, the more carefully and gradually the fast must be broken.

Why the Carnegie Study Still Matters

A Study of Prolonged Fasting remains relevant for several reasons. It is the most scientifically controlled study of complete prolonged fasting conducted on a human subject up to its time. Its methodology — daily physiological measurement, controlled water intake, respiratory calorimetry, psychological testing — established a template for rigorous fasting research that modern scientists still recognise.

It also demonstrated, with scientific precision rather than anecdote, that a human being could undergo a complete 31-day fast under controlled conditions and emerge cognitively intact, physically capable (Levanzin climbed stairs on day 31, photographed for documentation), and metabolically explicable. The body's extraordinary adaptability — its ability to shift fuel sources, conserve protein, reduce heat production, and maintain essential function — was laid out in data for the first time.

Modern fasting science builds on this foundation. Every paper on metabolic switching, ketosis, protein sparing, or fasting-induced metabolic adaptation owes something to what Benedict and his team measured and documented in that Boston laboratory over a century ago.

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Frequently Asked Questions

Who ran the Carnegie Nutrition Laboratory? Francis Gano Benedict, a leading American physiologist and nutritional scientist, directed the laboratory. He had a team of Harvard and Carnegie scientists working alongside him, including physicians, chemists, psychologists, and physiologists.

Who was the subject of the 1912 fasting experiment? Agostino Levanzin, a 40-year-old Maltese polymath — pharmacist, linguist, and experienced faster. He had previously conducted a 37-day self-directed fast and was medically cleared for the experiment.

How long was the study fast? 31 consecutive days of complete fasting, drinking only distilled water. Preliminary measurements began April 10, 1912; the fast ran April 14 to May 14.

What was the respiration calorimeter? A purpose-built chamber that measured the heat produced by a person's body during rest, allowing direct calculation of basal metabolic rate. It was one of the most precise metabolic measurement instruments of its era.

Where can I read the original study? The full text of A Study of Prolonged Fasting (1915) is in the public domain and can be accessed through digital archives including the Internet Archive.

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.

The Carnegie Nutrition Laboratory: Where Fasting Science Was Born