Reconstruction
In March 1981, David Jenkins, Thomas Wolever, and colleagues published a deceptively simple challenge to conventional carbohydrate advice. Diabetic exchange lists generally grouped foods by how much available carbohydrate they contained. The researchers argued that equal carbohydrate portions did not necessarily produce equal rises in blood glucose. They proposed supplementing chemical composition tables with a physiological measurement: the “glycemic index,” or GI.
The investigators tested 62 commonly eaten foods and sugars in groups of five to ten healthy, fasting volunteers drawn from a pool of 34 people. Most portions supplied 50 grams of carbohydrate; six bulky foods were tested at 25 grams. Grains, legumes, and vegetables were boiled in minimal salted water, while breakfast cereals were served with milk. Finger-prick blood samples were taken before eating and at intervals through two hours. The area under each food’s blood-glucose response curve was expressed as a percentage of the response to an equivalent carbohydrate dose of glucose.
The rankings disrupted easy assumptions about “simple” and “complex” carbohydrates. Dried legumes generally produced relatively small responses: lentils scored 29 and soybeans 15 on the study’s glucose-based scale. Wholemeal spaghetti scored 42, whereas cornflakes and instant potato each scored 80. Preparation, physical structure, starch characteristics, and the presence of fat or protein could matter alongside carbohydrate quantity. The experiment did not prove that every low-GI food was nutritious or that every high-GI food was undesirable; it measured one specific physiological response under controlled conditions.
Later researchers refined the method. Modern protocols generally use available-carbohydrate portions, repeated reference tests, incremental rather than total area under the curve, and sufficient participant numbers to address day-to-day variation. Glucose and white bread have both served as reference foods, so values must be converted before tables using different scales are compared. Glycemic load, introduced in nutritional epidemiology in 1997, added portion size by combining GI with the amount of available carbohydrate consumed.
The index eventually entered international reports, standardized testing methods, food databases, labeling programs in some countries, and debates about diabetes management and chronic disease. Its limitations remain important: variety, ripeness, grinding, cooking, cooling, meal composition, and individual physiology can change responses. Contemporary diabetes guidance therefore treats GI as a possible aid rather than a complete diet score. Its lasting contribution is methodological. The 1981 paper shifted discussion from what carbohydrate foods contain to what tested foods actually do after they are eaten, creating a durable bridge between the laboratory, the clinic, and everyday meals.
Historical context
Diabetic exchange lists had guided food planning for more than three decades, commonly treating foods with similar carbohydrate quantities as interchangeable. The GI study appeared sixty years after the University of Toronto’s 1921 insulin research and reflected the city’s continuing importance in diabetes science. Its controlled comparison of 62 foods in a pool of 34 volunteers belonged to a broader late-20th-century movement toward evaluating foods through measured physiological outcomes, not composition alone.
Evidence
Written sources
StrongThe original peer-reviewed paper documents the authors, experimental design, participating institutions, foods tested, measurements, results, and definition of the glycemic index.
Dating
StrongThe introducing paper was published in the March 1981 issue of The American Journal of Clinical Nutrition.
Food identification
StrongThe original paper names and reports results for 62 foods and sugars, including breads, grains, pasta, legumes, vegetables, fruits, dairy products, cereals, biscuits, and prepared foods.
Preparation method
StrongThe study directly reports portion calculations, boiling procedures, accompaniments, fasting conditions, meal timing, blood-sampling intervals, glucose analysis, and response-curve calculations.
Geographic attribution
ModerateToronto is defensible as the lead institutional location and address of the corresponding author, but the paper also lists collaborators affiliated with the University Laboratory of Physiology in Oxford and Central Middlesex Hospital in London.
Historical interpretation
StrongThe paper explicitly defines the measured value as the glycemic index and proposes it as physiological information to supplement carbohydrate exchange tables. Claims about its later influence are supported by subsequent FAO/WHO guidance, ISO standardization, clinical literature, and international tables.
Sources
- 1.David J. A. Jenkins, Thomas M. S. Wolever, Rodney H. Taylor, et al. (1981). Glycemic index of foods: a physiological basis for carbohydrate exchange. The American Journal of Clinical Nutrition 34(3): 362–366. doi:10.1093/ajcn/34.3.362Scientific literature
- 2.FAO/WHO Expert Consultation (1998). Carbohydrates in Human Nutrition. FAO Food and Nutrition Paper 66. www.fao.org/4/w8079e/w8079e00.htmModern synthesis
- 3.International Organization for Standardization (2010). ISO 26642:2010 Food products — Determination of the glycaemic index (GI) and recommendation for food classification. International Standard. www.iso.org/standard/43633.htmlModern synthesis
- 4.Fiona S. Atkinson, Jennie C. Brand-Miller, Kaye Foster-Powell, et al. (2021). International tables of glycemic index and glycemic load values 2021: a systematic review. The American Journal of Clinical Nutrition 114(5): 1625–1632. doi:10.1093/ajcn/nqab233Scientific literature
- 5.Jorge Salmerón, JoAnn E. Manson, Meir J. Stampfer, et al. (1997). Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. JAMA 277(6): 472–477. doi:10.1001/jama.1997.03540300040031Scientific literature
- 6.Alison B. Evert, Michelle Dennison, Christopher D. Gardner, et al. (2019). Nutrition Therapy for Adults With Diabetes or Prediabetes: A Consensus Report. Diabetes Care 42(5): 731–754. doi:10.2337/dci19-0014Modern synthesis
- 7.University of Toronto Libraries (2021). The Discovery and Early Development of Insulin. University of Toronto Libraries Digital Collections. collections.library.utoronto.ca/explore/insulin/Modern synthesis
Limitations
- moderatedescription
The phrase “historical and archaeological synthesis” is inaccurate for this event. The glycemic index is documented by a 1981 clinical nutrition paper and subsequent scientific and institutional literature; archaeology does not substantively support the attribution.
- minorlocation
Toronto is an appropriate lead location because the corresponding author and Department of Nutrition and Food Science were at the University of Toronto, but the original paper also lists Oxford and London institutional affiliations, so Toronto should not be interpreted as the study’s only institutional setting.
