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Glycemic Index

The glycemic index (GI) compares the blood-glucose response to a fixed amount of available carbohydrate from a test food with the response to glucose. Glucose is assigned a value of 100. Values of 55 or less are conventionally classified as low, 56–69 as medium and 70 or more as high.1 GI does not state how many grams of carbohydrate are in a usual serving.

How is the glycemic index measured?​

In a standard test, participants consume a portion containing a fixed amount of available carbohydrate, commonly 50 g, and researchers compare the blood-glucose response over two hours with the same person's response to a glucose reference.1 The published value is an average. Cultivar, ripeness, processing, preparation and a mixed meal can change the response, so a table value is not a prediction for every serving or person.

High-GI vs low-GI foods — what's the difference?​

The categories describe the relative response observed in testing; they are not food-quality scores. A food can have a low GI yet supply substantial carbohydrate in a large serving, while a small serving of a high-GI food can contain little carbohydrate. GI values can also differ between varieties and preparation methods.

GI rangeConventional category
55 or lessLow
56–69Medium
70 or moreHigh

How does GI relate to insulin and glycemic load?​

GI records a glucose outcome, not an insulin measurement. Glycemic load adds the amount of available carbohydrate in a serving: GI × available-carbohydrate grams per serving ÷ 100. It can put a table value in serving context, but it remains an estimate built from an average GI rather than a personal glucose forecast.1

Does glycemic index matter on keto?​

GI and carbohydrate quantity answer different questions. A ketogenic plan must first define whether its target uses total, nonfiber or a specified label-based carbohydrate estimate; 20–50 g of nonfiber carbohydrate is a common research description, not a universal threshold. GI may provide additional context when comparing foods, but it cannot determine whether an individual will enter ketosis.

GI also cannot be converted into a gram-for-gram deduction for sugar alcohols (polyols). Individual polyols differ, and GI is neither an absorption percentage nor a regulator-defined net-carb formula.2 The net-carb explainer documents the separate US and EU/UK label arithmetic.

Frequently Asked Questions

Is glycemic index the same as net carbs?
No. GI compares the glucose response to a fixed amount of available carbohydrate under test conditions. Net carbs is an informal label-based estimate whose arithmetic depends on the label system and explicitly selected adjustments.
What do the GI categories mean?
Values of 55 or less are conventionally called low GI, 56 to 69 medium and 70 or more high, with glucose assigned a value of 100. The categories do not report serving size or overall food quality.
Can GI show whether a food will stop ketosis?
No. GI does not establish a personal carbohydrate threshold or predict a ketone response. A ketogenic plan still needs a clearly defined carbohydrate measure and target.
Is glycemic load the same as a glucose prediction?
No. Glycemic load combines a food's average GI with available carbohydrate per serving. It adds serving context, but individual responses and preparation can differ.

See also​

Works cited​

  1. International Tables of Glycemic Index and Glycemic Load Values: 2008 — Fiona S. Atkinson, Kaye Foster-Powell, and Jennie C. Brand-Miller, Diabetes Care, 2008 https://pubmed.ncbi.nlm.nih.gov/18835944/
  2. Health potential of polyols as sugar replacers, with emphasis on low glycaemic properties — Geoffrey Livesey, Nutrition Research Reviews, 2003 https://pubmed.ncbi.nlm.nih.gov/19087388/

Article history

  1. Revised GI limits and separated glycemic response from label-based net-carbohydrate arithmetic
  2. First published

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