Glycemic Index

Glycemic index (GI) compares the incremental blood-glucose response after a food providing a fixed amount of available carbohydrate with the response to a reference food.¹ It is a measurement, not a verdict on a food — and the longer glycemic index and keto discussion builds on the boundaries below.

Glycemic index

A standardized comparison of group-average glucose responses.

• Term
• Measure
• Context

How GI is measured

Standard protocols commonly use 50 g of available carbohydrate, with 25 g available as an option for low-carbohydrate-density foods. Results are usually reported with glucose as the reference at 100, and published GI values are group averages.¹

Two misconceptions to drop at the door: GI is not simply a digestion-speed ranking, and it is not a personal prediction. Food variety, ripeness, processing, preparation, lab method, and variation within and between people can all move results. A GI value cannot show the response to an ordinary mixed meal or guarantee any individual's response.

What the categories mean

With glucose as reference 100, the conventional bands are low at or below 55, medium from 56 to 69, and high at 70 or above. These are descriptive categories — not food-quality grades and not safety grades.

GI, glycemic load, and net carbs

Glycemic load (GL) multiplies GI by the grams of available carbohydrate in a stated serving, then divides by 100. It adds portion context that GI alone lacks, but it remains an estimate.

Net carbs is informal label arithmetic, not an FDA-defined nutrient.² GI cannot be converted into a fiber, polyol, or allulose deduction, and straight carbohydrate grams answer yet another question. None of these — GI, GL, carbohydrate grams, or label arithmetic — determines whether a person enters ketosis. For that separate carb-budget question, see how many carbs on keto.

What GI cannot predict

Because published values are group averages shaped by variety, ripeness, processing, preparation, lab method, and person-to-person variation, GI cannot predict an individual's response or the effect of a mixed meal. The categories say nothing about food quality or safety. And for diabetes, GI and GL can add context, but they do not replace a clinical eating plan, glucose monitoring, or medication guidance.

FAQ

Frequently Asked Questions

Does a low GI mean a food is keto-friendly?

No. GI is not a food-quality grade, and it does not determine whether a person enters ketosis. Carbohydrate grams and label arithmetic answer different questions entirely.

Is GI just a measure of how fast a food digests?

No. GI compares incremental blood-glucose responses against a reference food under a standard protocol.^{[1](#footnote-1)}

How is glycemic load different from GI?

GL multiplies GI by the available-carbohydrate grams in a stated serving and divides by 100. It adds portion context but remains an estimate.

Can I convert a food's GI into net carbs?

No. Net carbs is informal label arithmetic, not an FDA-defined nutrient, and GI cannot be converted into a fiber, polyol, or allulose deduction.^{[2](#footnote-2)}

Is a high-GI food unsafe?

The categories are descriptive, not safety grades. For diabetes, GI and GL can add context but do not replace a clinical eating plan, glucose monitoring, or medication guidance. For related vocabulary, see [insulin](/supporting/resources/glossary/insulin).

Will a food's GI predict my own glucose response?

Not reliably. Published values are group averages, and variety, ripeness, preparation, lab method, and within- and between-person variation all affect results, so GI cannot guarantee an individual's response to a mixed meal.

Works cited

1. International Tables of Glycemic Index and Glycemic Load Values 2021: A Systematic Review — American Journal of Clinical Nutrition, 2021 https://pubmed.ncbi.nlm.nih.gov/34258626/
2. Get to Know Carbs — American Diabetes Association https://diabetes.org/food-nutrition/understanding-carbs/get-to-know-carbs