The glycemic index (also called glycemic index) is used to assess the ability of glucose contained in food to enter the bloodstream. In other words, it corresponds to the speed at which carbohydrates are transformed into glucose to reach the blood system.
The glycemic index (GI) is commonly used to define the ability of a food to increase blood sugar levels. Thus, the GI of each food is classified according to three categories (low, moderate, high) on a scale of 0 to 100.
The higher the GI value, the greater its power to increase blood sugar levels. The glycemic index of 100 corresponds to that of pure glucose.
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Some reminders to understand the issues of GI
Like many parameters of the human body (temperature, pH, etc.) blood sugar is maintained constant (around 1 g/L) throughout the day. Sugar is used by the body's cells to produce energy (ATP) through glycolysis.
The pancreas releases insulin, a hypoglycemic hormone, to lower the amount of sugar in the blood. This is made possible by the ability of insulin to bring sugar into cells. To put this into perspective, we can say that insulin is a key that opens the cell door for nutrients to enter.
Part of the sugar will therefore be able to enter the cells of the muscles and the liver, organs capable of storing a small quantity of sugar in the form of glycogen (assembly of glucose molecules). But if too much glucose is present in the blood, the excess will be converted into fat to be stored in adipocytes (cells that store fat in reserve).
The pancreas releases glucagon, a hyperglycemic hormone that raises blood sugar levels. Glucagon therefore plays the opposite role of insulin: it is the key that opens the door of the cells in order to release nutrients.
Reactions of the body depending on the GI
The higher the glycemic index, the more quickly the quantity of glucose present in the food is found in the blood, thus causing a rise in blood sugar.
Therefore, if we consume a food with a low glycemic index, the blood sugar level will slowly increase, giving the pancreas time to adjust the blood sugar level.
In the case of a sudden increase in blood sugar (following the intake of a large quantity of a food with a high glycemic index), insulin secretion is released “emergency” through the pancreas. This secretion has two consequences on the body.
Firstly, we observe a strong variation in blood sugar levels. Indeed, in a short time, the body goes from hyperglycemia to reactive hypoglycemia (reaction).
This type of hypoglycemia is triggered when the amount of insulin released is too large.
Remember, insulin is the little key that gets sugar (among other things) into cells. If blood sugar levels rise too high, the pancreas can release a slight excess of insulin, causing the blood sugar level to drop slightly below the “normal value”. This is what we call “reactive hypoglycemia” (which is paradoxically caused by an excessive increase in the quantity of sugar in the blood).
This reactive hypoglycemia sends a chemical message to the brain to stimulate feelings of hunger, so that blood sugar levels can be restored. During this period of hypoglycemia, the symptoms encountered are as follows:
- Sudden drop in energy;
- Irritability;
- Sweats;
- Headaches (headaches);
- Palpitations;
- Increased feeling of hunger;
- Dizziness, drowsiness.
Secondly, it is proven that insulin is a hormone promoting weight gain. Indeed, in order to regulate blood sugar, insulin causes excess glucose to be stored in the form of triglycerides within adipose tissues. You read correctly: it transforms excess sugar into “fat”. In the brain, insulin inhibits the transmission of nerve impulses, suppressing the feeling of fullness. Consuming too much sugar with a high glycemic index is therefore problematic, because it leads to an endless cycle of hunger... In other words: “sugar begets sugar”.
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Conversely, consuming low GI foods allows blood sugar to remain stable, limits insulin secretion and therefore limits cravings.
What factors affect the glycemic index?
The glycemic index of the same food may vary depending on different factors. A fruit can therefore have a glycemic index of 30. And the same fruit consumed in compote will have a glycemic index of 50.
In fact, blending and cooking the fruit acts as a kind of “pre-digestion”. Once consumed, a compote will therefore take less time to be assimilated than a raw apple.
The table below shows that certain processing of a food affects its glycemic index.
Here are the factors likely to vary the glycemic index of a food:
- Transformations : the more a food is mixed, crushed, pressed, the higher its glycemic index. This phenomenon is explained in particular by the disappearance or degradation of fibers, thus leading to faster absorption of carbohydrates.
- The composition : complete and semi-complete starchy foods still with their shell have a lower GI than so-called “white” starchy foods. Indeed, this envelope contains many minerals and vitamins, but above all a significant quantity of fiber.
- The cooking : the more a food is cooked, the higher its GI due to an acceleration in the gelatinization of the starch. Gelatinized starch converts more quickly into glucose.
- The food matrix : in addition to fiber, a food rich in lipids and proteins helps reduce the GI. This point is discussed in this article.
- Aging (or maturation) leads to an increase in GI through the phenomenon of starch gelatinization.
We often recommend never consuming sugary products in isolation to avoid this hyperglycemia.
Therefore, the ideal is to combine a dairy product or a whole starch with a sweet product so as to limit the “total glycemic index” of the snack.
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Why does fiber influence GI?
Fibers are carbohydrates that are indigestible by the body. As a result, they do not provide energy. Their role lies elsewhere.
There are two types of fiber: soluble fiber and insoluble fiber
Fiber therefore has a significant impact on the glycemic index. This is the reason why wholemeal bread has become fashionable again, to the detriment of white bread devoid of dietary fiber.
Be careful, if a daily intake of fiber is important, too much ingestion can have some negative effects including bloating, diarrhea or constipation, etc.
What is glycemic load?
The glycemic load is a measurement that is both qualitative and above all quantitative. It therefore measures the ability of a food to raise blood sugar levels by taking into account the actual quantity of the portion ingested.
Glycemic load = [GI x amount of carbohydrates in a serving of food (g)] / 100
- Zero: no glycemic load;
- Low: glycemic load of 10 or less;
- Moderate: glycemic load of 11 to 19;
- Strong: glycemic load of 20 and above.
Thus, it is more and more common to find the concept of glycemic load rather than glycemic index because it allows us to really realize the impact in terms of the quantity ingested. In conclusion, the glycemic index is an important factor in regulating our blood sugar levels. It is preferable to favor foods with a low GI, especially for a diabetic person.
Why are the glycemic index and load important?
Since the last century, our diet has changed considerably, moving from a natural diet based on very little processed products, to an increasingly industrial diet with ultra-processed products rich in added sugars.
For example, we consumed 1 kg of sugar per person per year in 1850 compared to 35 kg today. Another telling figure: an 8-year-old child has already eaten more sugar than his grandfather ate in his entire life.
Alas! We now know that consuming an excessive amount of sugar (which directly contributes to increasing the glycemic index or load) for several years could deplete/disorganize the pancreas and lead to a diabetic sugar type II(1).
An American study(2) based on data collected between 1909 and 1997 showed that increased consumption of refined carbohydrates in the form of corn syrup, coupled with decreased consumption of dietary fiber, correlated with increased prevalence of diabetes type II.
Despite this study (and many others), it should be noted that there is currently no international consensus regarding the usefulness of the glycemic index in the dietary prevention and management of diabetes. Indeed, if in Europe we seem to agree on the harms of consuming meals with a high glycemic load(3) ; on the other side of the Atlantic, we continue to advocate that the total quantity of carbohydrates is more important than the source or type(4).
This diet consists of giving priority in your diet to foods with a low glycemic index. This diet can therefore be of interest to people with diabetes and those trying to lose weight.
What you must remember
Apart from the risks of type II diabetes, the explosion in the consumption of refined sugar (with a very high glycemic index) in recent decades is also linked to greater risks of overweight and obesity.(5), cardiovascular diseases(6), and inflammation(7)(8), itself responsible for many cancers(9), joint degeneration(10) (osteoarthritis), or even neurodegenerative diseases(11) (Alzheimer's disease and other dementias).
If your health is important to you, it is not a bad idea to contact a dietitian nutritionist to take stock of your diet.
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