Obesity: History and Discovery
The story of obesity is not the story of a single discovery on a single day. It is the much longer story of how a particular state of the human body — one that has existed since the Ice Age, carved into Paleolithic figurines tens of thousands of years ago — was understood, judged, measured, and only recently recognized as a medical condition with deep biological roots. For most of recorded history the body in question was read through a moral lens, as evidence of gluttony or sloth. The scientific reframing came late and in stages: a Belgian statistician's height-and-weight ratio in 1832, the naming of the “body mass index” in 1972, the discovery in 1994 that fat tissue is itself a hormone-secreting organ, and the American Medical Association's formal classification of obesity as a disease in 2013. This page traces that arc with care, distinguishing the long-standing bodily state from its modern recognition as a disease, and treating the people it describes with dignity rather than blame.
Table of Contents
- The Word: Obesus and Its Roots
- Prehistory and the Venus Figurines
- Antiquity: Hippocrates and Early Observation
- Centuries of a Moral Framing
- Quetelet, the Index, and the Birth of BMI
- Leptin (1994) and Fat as an Endocrine Organ
- 2013: Recognized as a Disease
- The GLP-1 Era and a Changing Picture
- The Body-Positivity and Disease-Status Debate
- Research Papers and References
- Connections
The Word: Obesus and Its Roots
The English word obesity descends from the Latin obesitas (“fatness, corpulence”), which in turn comes from obesus. The adjective obesus is the past participle of the verb obedere — built from ob- (“over, completely”) and edere (“to eat”) — and is usually glossed as “having eaten oneself fat” or simply “fattened.” Curiously, the same Latin form could also be read passively as “eaten away, wasted, lean,” a reminder that ancient usage was less fixed than the modern medical term suggests.
The word entered English relatively late. Lexicographers trace the first recorded English use of “obesity” to Randle Cotgrave's 1611 dictionary, and the Oxford English Dictionary notes the term was rare before the nineteenth century. This linguistic timing is itself revealing: a precise, neutral, technical vocabulary for the condition arrived only as European medicine began, slowly, to treat body size as a measurable physiological matter rather than purely a question of character. The etymology — literally “to eat over” — also helps explain why the word carried a built-in implication of overindulgence long before any physiology was understood, a bias examined later on this page.
Prehistory and the Venus Figurines
The bodily state we now call obesity is not a modern invention; it is at least as old as the human capacity to store fat. The most striking prehistoric evidence comes from the “Venus” figurines of the Upper Paleolithic — small carved statuettes, found across Europe, that depict women with pronounced corpulence. The best known is the Venus of Willendorf, an oolitic-limestone figure about 11 centimeters tall, discovered in 1908 near Willendorf, Austria, and dated to roughly 24,000–22,000 years before present. Many of these figures emphasize precisely the anatomical regions associated with female fat storage, rendered with enough accuracy that the sculptors plainly modeled them on real bodies.
What these objects meant to the people who made them is genuinely unknown, and honest history should say so. Proposals have ranged from fertility or fortune symbols, to idealized images of abundance, to self-portraits, to — in one 2021 hypothesis — markers tied to nutrition and climate stress, with figurines found nearer the glaciers tending to be more corpulent. That climate-and-nutrition reading is a hypothesis, not established fact, and is flagged here as such. What can be said with confidence is narrower and more important: bodies with substantial fat existed in the Paleolithic, and human beings noticed and represented them. The condition long predates agriculture, industry, and processed food.
Antiquity: Hippocrates and Early Observation
Among the earliest written medical observations linking body size to health are those attributed to Hippocrates of Cos (c. 460–370 BCE) and his school. The Aphorisms contain the much-quoted line, “Sudden death is more common in those who are naturally fat than in the lean,” alongside a related observation that very fat persons tend to die earlier than slender ones. These are remarkable as early clinical generalizations — an ancient physician noticing, without any concept of arteries furring or blood pressure, an association between corpulence and abrupt mortality that modern cardiology would eventually explain.
It is worth being careful here, for two reasons. First, the Hippocratic corpus is a collection assembled by many hands, so these are best described as observations from the Hippocratic tradition rather than the certain words of one man. Second, such ancient lines are easily wrenched out of context to moralize about weight today; the original aphorism is a terse mortality observation, not a verdict on character. Other classical writers — Galen among them — also discussed corpulence and recommended diet and exercise, showing that antiquity could approach the subject practically. But the dominant cultural reading, in antiquity and long after, would lean elsewhere: toward judgment.
Centuries of a Moral Framing
For most of the two millennia between Hippocrates and modern endocrinology, corpulence in the West was understood chiefly through a moral and religious lens rather than a medical one. In medieval Christian thought, gluttony (gula) was numbered among the seven deadly sins, and sloth (acedia) among them too; a large body could be read as the visible residue of both. The condition was treated less as something that happened to a person and more as something a person had done — a failure of will, appetite, or discipline.
This framing had real and lasting consequences. It located the cause of the condition entirely within individual behavior, which made stigma feel justified and made any biological explanation seem unnecessary. Even as some early-modern physicians — such as the seventeenth-century English doctor Thomas Short, who wrote one of the first English treatises on corpulency in 1727, and Malcolm Flemyng, who lectured on it in 1760 — began to treat excess weight as a medical problem with diverse causes, the older moral story remained culturally dominant. Recovering this history matters because the moralizing reflex did not vanish with the rise of science; it persists today and continues to shape how people with obesity are treated, a point the disease-status debate below takes up directly.
Quetelet, the Index, and the Birth of BMI
The first durable step toward measuring rather than merely judging body size came from a man who was not a physician at all. The Belgian astronomer, mathematician, and statistician Adolphe Quetelet (1796–1874), in work published in 1832, observed that across adults of normal build, body weight tended to scale roughly with the square of height. The resulting weight-divided-by-height-squared ratio became known as the Quetelet Index — the direct mathematical ancestor of today's BMI.
A crucial caveat belongs right here, because it is routinely forgotten. Quetelet was building a science of l'homme moyen, the “average man,” as a tool of social statistics. He never intended his index as a measure of individual health or fatness, and it carried no diagnostic meaning in his hands. That diagnostic use came much later. In a paper published in the July 1972 issue of the Journal of Chronic Diseases, the American physiologist Ancel Keys and colleagues evaluated several relative-weight indices, judged Quetelet's the best simple proxy for body fatness in populations, and gave it the name we use today: the Body Mass Index.
So the modern metric has a split origin worth stating plainly: the formula is Quetelet's, from 1832; the name “Body Mass Index” is Keys's, from 1972. BMI's enduring usefulness is that it is cheap, fast, and population-scalable; its enduring limitation — acknowledged by Keys himself — is that it cannot distinguish muscle from fat or describe where fat sits on the body, which is why it works far better as a population screening tool than as an individual diagnosis.
Leptin (1994) and Fat as an Endocrine Organ
If any single discovery transformed obesity from a presumed character flaw into a problem of biology, it was the identification of leptin. Working at The Rockefeller University, the molecular geneticist Jeffrey M. Friedman and his laboratory spent roughly eight years using the then-new technique of positional cloning to hunt for the gene mutated in a strain of profoundly obese mice. In 1994 they succeeded, cloning the mouse ob gene and its human counterpart; in 1995 the gene's protein product was characterized and named leptin (from the Greek leptos, “thin”).
The finding was a conceptual earthquake. Leptin is secreted by fat cells in proportion to fat mass and acts on the hypothalamus to signal satiety — meaning that adipose tissue is not inert padding but an endocrine organ that talks to the brain and helps govern appetite and metabolism. Obesity, in other words, sits inside a genuine physiological feedback system that can be disrupted. A small number of people with rare congenital leptin deficiency became dramatically less hungry and lost weight when given the hormone, proving the loop is real in humans.
Honesty requires noting what leptin did not do. It was not the hoped-for cure for common obesity: most people with obesity have plenty of leptin and a degree of leptin resistance, so injecting more does little. The lasting significance is conceptual rather than therapeutic — leptin established, at the level of molecules, that body weight is biologically regulated, and it opened the modern field of obesity as endocrinology. That shift in understanding is part of what later made formal recognition of obesity as a disease scientifically defensible.
2013: Recognized as a Disease
On June 18, 2013, the American Medical Association's House of Delegates voted to adopt policy recognizing obesity as a disease — specifically, a “disease state with multiple pathophysiological aspects requiring a range of interventions.” The vote was not unanimous or uncontested: it passed with roughly 60 percent support and ran against the recommendation of the AMA's own Council on Science and Public Health, which had cautioned that BMI is an imperfect basis for defining a disease. It was backed by bodies including the American Association of Clinical Endocrinologists and others.
Two points keep this milestone accurate. First, the AMA was not the first organization to classify obesity as a disease — other groups, including some specialty societies and an earlier internal Social Security/IRS-era recognition, had moved in that direction — but because the AMA is the most influential physician body in the United States, its 2013 vote became the symbolic tipping point most often cited. Second, the AMA's action is policy, not biology: it did not change anyone's body, but it aimed to change how the medical system, insurers, and the public regard the condition.
Supporters argued the classification would reduce stigma, expand insurance coverage for treatment, and accelerate research and physician training. Critics worried it could medicalize a vast range of body sizes, lean on the blunt instrument of BMI, and inadvertently increase stigma by labeling tens of millions of people as diseased. Both concerns were sincere, and a decade of subsequent analysis found the resolution's promise only partly realized — which is exactly why this remains a live debate rather than a settled question.
The GLP-1 Era and a Changing Picture
The 2020s brought the most consequential therapeutic shift in the history of obesity treatment: highly effective medications based on gut hormones. GLP-1 receptor agonists — drugs that mimic glucagon-like peptide-1, a hormone the intestine releases after eating that promotes satiety and slows stomach emptying — were first developed for type 2 diabetes, then found to drive substantial weight loss. Semaglutide, marketed for weight management as Wegovy, received U.S. Food and Drug Administration approval for chronic weight management on June 4, 2021, with trial participants losing on average around 15 percent of body weight.
A second milestone followed when tirzepatide (Zepbound), a dual agonist acting on both the GLP-1 and GIP receptors, was approved by the FDA for chronic weight management on November 8, 2023, with even larger average weight reductions reported in trials. For the first time, medicine had non-surgical treatments that approached the results once seen only with bariatric surgery.
The historical significance runs deeper than the numbers. These drugs work precisely because obesity is biologically regulated — they act on the same hormone-and-brain appetite circuitry that the leptin discovery first revealed. Their effectiveness is, in a sense, the clearest practical vindication of the biological reframing of obesity, and a strong argument against the old purely-moral account: if appetite can be turned down by a molecule, then appetite was never simply a matter of willpower. At the same time, these are recent medications with real costs, side effects, access barriers, and the open question of what happens when treatment stops; their long-term place in care is still being worked out, and nothing here should be read as individual medical advice.
The Body-Positivity and Disease-Status Debate
Running alongside the science is a genuine and unresolved public debate about how obesity should be named and regarded — a debate this page presents factually rather than taking sides in. On one side, much of the medical community holds that classifying obesity as a disease is appropriate and humane: it acknowledges the biology, justifies treatment and insurance coverage, funds research, and helps move blame away from the individual. On this view, calling obesity a disease is itself an anti-stigma move, because diseases are things that happen to people rather than moral failings.
On the other side, many people — including clinicians, ethicists, and advocates in the body-positivity, fat-acceptance, and Health at Every Size movements — argue that defining a body size as a disease can do harm: it can pathologize natural human diversity, rely on the crude BMI cutoff, frame larger bodies as inherently sick regardless of actual health markers, and deepen the very weight stigma it claims to fight. Some emphasize that health behaviors and metabolic markers, not size alone, are what matter, and that weight-based discrimination in healthcare, employment, and daily life is itself a measurable harm.
The most useful way to hold this debate is to keep two distinctions in view, both of which this page has tried to honor. The first is between a bodily state (having a high proportion of body fat, which has existed since prehistory) and the decision to recognize that state as a disease (a modern, contested, value-laden act of classification). The second is between describing a condition and judging a person. History shows what happens when those are collapsed: centuries of moralizing that helped no one. Whatever one concludes about the label, the humane constants are clear — accuracy over stereotype, dignity over blame, and respect for the people the word describes.
Research Papers and References
The references below combine peer-reviewed historical and scientific literature with curated PubMed topic-search links covering the etymology, the Quetelet/Keys lineage of BMI, the discovery of leptin, the 2013 disease classification, and the modern GLP-1 medications. Where a stable identifier could be confirmed, a DOI or repository link is given; otherwise a PubMed topic search is provided. Each external link opens in a new tab.
- Eknoyan G. Adolphe Quetelet (1796–1874) — the average man and indices of obesity. Nephrology Dialysis Transplantation. 2008;23(1):47–51. — doi:10.1093/ndt/gfm517
- Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. Indices of relative weight and obesity. Journal of Chronic Diseases. 1972;25(6):329–343. — doi:10.1016/0021-9681(72)90027-6
- Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM. Positional cloning of the mouse obese gene and its human homologue. Nature. 1994;372(6505):425–432. — doi:10.1038/372425a0
- Friedman JM, Halaas JL. Leptin and the regulation of body weight in mammals. Nature. 1998;395(6704):763–770. — doi:10.1038/27376
- Kyle TK, Dhurandhar EJ, Allison DB. Regarding obesity as a disease: evolving policies and their implications. Endocrinology and Metabolism Clinics of North America. 2016;45(3):511–520. — doi:10.1016/j.ecl.2016.04.004
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). New England Journal of Medicine. 2021;384(11):989–1002. — doi:10.1056/NEJMoa2032183
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). New England Journal of Medicine. 2022;387(3):205–216. — doi:10.1056/NEJMoa2206038
- Johnson VR, et al. Promise and unrealized potential: 10 years of the American Medical Association classifying obesity as a disease. Frontiers in Public Health. 2023;11:1205880. — doi:10.3389/fpubh.2023.1205880
- Etymology and early history of the word “obesity” / Latin obesus — Online Etymology Dictionary: obesity
- History of obesity as a medical concept (concept history, framing, and classification) — PubMed: history of obesity as a medical concept
- Body mass index — history, validity, and limitations — PubMed: BMI history and limitations
- Leptin — 30 years since discovery; physiology and resistance — PubMed: leptin discovery and physiology
- Weight stigma and the disease-classification debate — PubMed: weight stigma and obesity as a disease
- GLP-1 receptor agonists for obesity — semaglutide and tirzepatide — PubMed: GLP-1 agonists for obesity