Tableau de l'Index Glycémique pour Diabétiques

Glycaemic index ranks carbohydrate foods by how far they raise blood glucose relative to a reference, over two hours, gram for gram of available carbohydrate. That last clause is where most misuse begins: GI describes a fixed 50 gram carbohydrate portion, which for some foods is far more than anyone eats. Glycaemic load corrects for that, and is the more useful number in practice.

La formule

Glycaemic index = (blood glucose area under the curve for the test food / that for the reference food) x 100
Glycaemic load = GI x available carbohydrate per serving (g) / 100

• The reference food is glucose (GI 100) or white bread, and which one is used must be stated
• Available carbohydrate excludes fibre

Method as used in the international tables of glycaemic index and glycaemic load, maintained by the University of Sydney.

Categories and typical values

GI is conventionally banded as low, medium and high. The values below are typical published figures; individual foods vary considerably by variety, ripeness, processing and cooking, so treat them as approximate.

• Glycaemic load bands: 10 or less is low, 11 to 19 medium, 20 or more high per serving.
• Watermelon is the standard illustration of why GI alone misleads: high GI, but so little carbohydrate per serving that its glycaemic load is low.

What changes a food GI

GI is not a fixed property of a food type. Several factors change it substantially, which is why published values carry wide confidence intervals and why the same food can appear with different numbers in different tables.

• Ripeness: a green banana has a considerably lower GI than a fully ripe one, as starch converts to sugar.
• Cooking time: pasta cooked al dente has a lower GI than pasta cooked soft, because the starch is less gelatinised.
• Cooling: cooked and cooled potato, rice and pasta form resistant starch, lowering GI even if reheated.
• Processing: finer milling raises GI. Stone-ground and intact-grain products are lower than finely milled flour from the same grain.
• Meal composition: fat, protein and acid all slow gastric emptying and lower the glycaemic response of the whole meal.

How much GI matters in diabetes

Low-GI eating patterns produce modest but consistent improvements in glycaemic control in trials, with typical HbA1c reductions of a few tenths of a percentage point. That is real but small compared with total carbohydrate quantity, weight change and medication, which is why guidelines describe GI as a potentially useful refinement rather than a primary strategy.

The more important limitation is individual variability. Studies using continuous glucose monitoring have shown that the post-meal glucose response to the same food differs markedly between people, to the extent that population GI values predict an individual response only loosely. For anyone with a CGM, their own measured response to a specific meal is far more informative than any table.

• Total carbohydrate quantity affects blood glucose more than GI does. Carbohydrate counting remains the primary tool in type 1 diabetes.
• A low GI does not mean a food is healthy. Some high-fat foods have low GI precisely because fat slows absorption.

Limites

• GI is measured on a 50 gram available carbohydrate portion, which for some foods is much larger than a realistic serving. Glycaemic load is the more meaningful figure.
• Published values vary between tables and carry wide confidence intervals, because GI depends on variety, ripeness, processing and cooking.
• Individual glucose responses to the same food differ substantially between people, so population values predict any one person response only loosely.
• GI is measured on foods eaten alone. A mixed meal containing fat, protein and acid behaves differently from the sum of its parts.
• A low GI does not indicate a nutritious food, and some low-GI foods are low precisely because of high fat content.
• This is a reference chart. Diabetes management decisions, particularly insulin dosing, should follow the plan agreed with your diabetes team.

Questions fréquentes

What is a low glycaemic index?

55 or less on the glucose reference scale. Medium is 56 to 69 and high is 70 or more. For glycaemic load, which accounts for serving size, low is 10 or less and high is 20 or more.

What is the difference between glycaemic index and glycaemic load?

GI compares foods gram for gram of carbohydrate, using a fixed 50 gram portion. Glycaemic load multiplies GI by the carbohydrate actually in a serving. Watermelon has a high GI but a low glycaemic load, because a serving contains little carbohydrate.

Does cooking change the glycaemic index?

Yes, substantially. Pasta cooked al dente has a lower GI than pasta cooked soft, and cooking then cooling potato, rice or pasta forms resistant starch that lowers GI even after reheating.

Does eating low GI improve diabetes control?

Trials show modest, consistent improvements, typically a few tenths of a percentage point of HbA1c. That is real but small next to total carbohydrate intake, weight and medication, so guidelines treat GI as a refinement rather than a primary strategy.

Why does the same food affect me differently than the chart says?

Because individual glucose responses vary widely between people for the same food, as continuous glucose monitoring studies have shown. Population GI values are averages, and your own measured response is far more informative if you have a monitor.

Références

1. University of Sydney. Glycemic Index Research and GI News, international GI database.
2. National Institute of Diabetes and Digestive and Kidney Diseases. Diabetes Diet, Eating, and Physical Activity.
3. MedlinePlus. Carbohydrates.
4. MedlinePlus. Diabetic diet.