We have already looked at the glycemic index (GI) and which factors influence it, in order to try and “predict” the speed with which a food might raise our blood glucose levels. However, we can consider that the GI is only a theoretical value and has a fairly limited practical use.
Yet, most foods we eat are complex. That is, they are not only composed of carbohydrates; they also contain fibre, water, proteins, vitamins… And we often tend to combine them with other foods.
For this reason, we are going to see another reference value much more complete than the GI: the glycemic load (GL).
What the glycemic load (GL) is?
GL quantifies the speed at which the carbohydrates (CH) will arrive as glucose to the blood. The main difference with GI is that GL not only takes into account the rate of food-absorption, but also considers how much CH an average portion of food contains.
The GL is calculated by using the following formula:
GL = GI · CH (g) per regular portion / 100
Let’s see some examples to better understand…
Cooked carrots have a very high GI (92), but the GL of a portion of two cooked carrots is low (6.4).
GL cooked carrot = 92 (GI) · 7 (grams of CH in a two-carrots portion) / 100
(GL = 644 / 100 = 6.4)
This happens because a carrot contains a lot of fibre yet actually only contains 3-4 g of carbohydrates per unit. In other words: so that cooked carrots raise glycemia in the same way that pure glucose does, a portion of 15 cooked-carrots should be eaten. However, eating 15 carrots would be very unappetizing in one meal!
Watermelon has a high GI (75), but the GL of a normal portion of 150 g is low (7.13).
GL watermelon = 75 (GI) · 9.5 (CH grams in a 150 g of watermelon-portion) / 100
(GL = 712.5 / 100 = 7.13)
That is, so that watermelon raise our glycemia in the same way that pure glucose, it would be necessary to eat more than 1 kg! Again, eating this amount in one meal would be very difficult!
White bread has a GI of 70. If we calculate the GL of a slice:
GL of 1 white-bread slice = 70 (GI) · 20 (CH grams) / 100 = 1400 / 100 = 14 (GL)
If we eat two slices, the glycemic load will double:
GL of 2 white-bread slices = 70 (GI) · 40 (CH grams) / 100 = 2800 / 100 = 28 (GL)
As you can see, the amount we ingest also influences the glycemic response that a certain food is going to have. Therefore, if you exceed a “normal” portion, the GL will also be higher and, consequently, blood glucose will also raise more.
Here you have a chart where you can see the differences between GIs and GLs of different foods, based on the amounts we usually consume:
How foods are classified according to their GL?
HIGH GL: 20 or more.
MEDIUM GL: From 11 to 19.
LOW GL: 0 to 10.
Therefore, the lower a foods glycemic load; the slower it will raise blood glucose levels.
It is also important to know the total GL of a meal. In other words: to know exactly the GL of a meal, we should add together everything we eat or drink. Thus we can calculate its influence on our glucose levels. In advance, we can say that meals with reduced GL might help us to stabilize our blood glucose.
Final considerations on GL
- The GL uses the GI value as a reference, so it is also a limited concept. Not only because of the inaccuracy of the GI, but because it also influenced by the intake of other nutrients in the same meal, such as fat or fibre.
- There are many foods that have a low GI (and a low GL) because they are rich in saturated or trans-fats, but they are not recommended. Keep this in mind, because our food must be as heart-healthy as possible.
- To obtain the maximum benefits of glucose control through GL, we should consume more carbohydrates in vegetables and whole-grain cereals, as well as limiting the intake of processed foods, industrial pastries, processed cereals, preserves, soft drinks, etc.
- The way of food-cooking also influences the GI. Consequently, cooking also has an impact on GL. For example, “soft” pasta will have a greater GL than “al dente” pasta, because its GI is also higher.
If you are just starting to control glycemia through feeding, it will surely seem that all this is a mess. Don’t despair, practice makes perfect. Being patient, you will be able to know almost by instinct which foods are better for maintaining blood glucose levels stable.
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