Glycemic index (low GI foods) vs sugar on food label?

Is the sugar value on the food label a good indicator of the glycemic level of the food?

On at least one glycemic index scale I've seen, cooked carrots are the food with highest value. More important in practice is the glycemic density, a lesser known measure. On such a scale potatoes would be high since they are almost purely starch, which is pure glucose although stuck together in long chains. During digestion, it all is converted, and rapidly, to glucose which is absorbed into the blood.

Sugar, at least in the form of pure glucose crystals, actually doesn't have a very high glycemic index at all. Complicating things is that there are several sugars, only one of which participates in the insulin level controlling blood glucose machinery. That's glucose, and prior to such things as high fructose corn syrup, it was the most common of the sugars in food (as itself or as part of a compound sugar like table sugar (1/2 glucose) or as starch). Some foods, such as some fruits (eg, oranges) have fructose not glucose, and of course lots of processed foods are now prepared with it (as "high fructose corn syrup") since it's the cheapest way to sweeten things when putting together a food product in large quantities.

The significant carbohydrates to blood glucose levels are those that contain glucose in one form or another. Other sugars (and other carbohydrates) are much less so. They still contain calories and can be used for fuel by cells, but they aren't managed by the insulin level/glucose level mechanisms. More and more today, calories excape that system since they're eaten in other forms.

In addition, the glycemic index is a bit misleading. The values were developed by feeding folks pure helpings of <whatever> and then watching their blood glucose levels. This is perfectly sensible as q lab technique, but neglects the real world. Foods interact with the digestive process, and real world results won't match the lab results all that welll. For instance, cooked carrots in a butter sauce will produce a much slower peak of blood glucose because of the fat in the butter. Fat/oil and protein eaten at the same time as plain carbohydrate slow down everything. Sweet potatoes (nearly all starch) have a much lower glyycemic index than white potatoes (also mostly starch), though no one knows why, but both are commonly eaten with sour cream or butter and so on. This will slow down carbohydrate absorption from either.


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The glycemic index is a measure of how fast glucose enters the blood, not a measure of how much/how fast -- that's glycemic density. Neither has much to do with real world circumstances since we rarely eat only a single thing at a time, and even in fussy kids who do there is a good bit of mixing internally. GI values are not so useful as they first appear.

not neccessarily, an apple and an orange are high in sugar compared to lentils or green vegetables or fish for example yet all score low on the GI index.