Glycemic Index (GI) talks about how fast glucose is released from the food (meaning carbohydrate stores in the food) into the blood (compared to consuming pure glucose that does not need to be cleaved). In essence, it is about how quickly the appropriate form of carbohydrates is digested – that is, breaks down, overcomes various obstacles and flows in the form of glucose into the blood, where it is ready for use.
Take, for example, kiwifruit with a GI of around 50. When we eat one large kiwi (100g) with about 10g of carbohydrates (not counting fiber), these 10g carbohydrates get into the blood twice as slowly (50%) as if we drank 10g pure glucose mixed in water. Conversely, kiwi energy will be available twice as long in the blood – very roughly speaking (more accurately – half the amount of energy will be released into the blood within 2 hours compared to glucose).
GI of a particular food depends on:
- carbohydrate type (glucose, fructose, lactose, starch, etc., except fiber)
- how densely the carbohydrates are distributed in the food (less concentration is digested more slowly)
- fat, protein and fiber content in foods (mechanical barriers, slowing down digestion)
- plant maturity (the more mature, the more concentrated carbohydrates)
- thermal processing – cooking, baking (“predigesting” and thus easier digestion of carbohydrates)
- industrial processing (processed foods tend to have high GI)
- mechanical processing (eg blending, whipping – easier digestion)
- what combination of foods is eaten (the whole meal has to be taken into account regarding digestion)
According to GI, foods are divided into:
- low GI foods (55 or less) – slow carbohydrates
- medium GI foods (56 to 69)
- high GI foods (over 70) – fast carbohydrates
Sometimes the index is calculated as compared to white bread that has a GI (based on glucose) of about 70. In this case, GI of white bread is taken as 100 and all other indices are recalculated accordingly. For example, said kiwi has an index of 71 compared to bread. However, on this website we will always use GI in relation to glucose.
In general, it is better not to overdo it with high GI foods because energy from such food may not be consumed effectively. Since glucose gets into the blood quickly, if there is a lot of it (ie high GL, see below) and we are not doing physical activity, the body will not be able to use energy (for its operation) and save the part (first into glycogen and then) into fat stores. And as the energy is running out quickly this way, the body asks for another (hunger). In essence, the body is forced to overeat, although man does not feel it.
Another problem (after long-term overeating as described above) may be a decrease in insulin sensitivity (the body cannot effectively use the produced insulin because the blood glucose level (glycemia) is too often too high), leading to insulin resistance, diabetes, etc.
In addition to GI, we also know the insulin index, which talks about the insulin response to a given food. Basically, it overlaps with GI (the one based on bread), but unlike GI, it can be applied not only to carbohydrates but also to other foods. In that case it measures the insulin response to blood glucose increases, for example, after a portion of the received proteins (eg meat) is transformed into glucose. It is based on the caloric value of the food.
We often encounter glycemic load (GL), which is the weight of carbohydrates consumed in grams, multiplied by GI/100 (that is, GI indicates how much% of their weight will be GL). For example, our 100g kiwi with 10g carbohydrate has a GL equal to 50% (half) of 10 = 5. GL says that how many grams of carbohydrate (ie, energy) actually gets to the body in the near future (specifically at a time when all the energy from pure glucose was used). In practice, it is good to be aware of the GI of the individual food, and to take GL into account when consuming it (high GL is 20 or more, low 10 or less).
Back: Carbohydrates