Introduction
L'index glicemico (IG) is a parameter that, referring to food, meals or the diet in general, it evaluates its ability to increase glycemia (amount of glucose in the blood).
The function of the glycemic index would be that of predict the short-term metabolic impact of energy nutrients, or of one or more foods, making it possible to draw up a nutritional program that takes under control glycemic fluctuations and their consequences for the body.
"In theory", all this would allow:
- decrease the "hunger crisis" or the sense of weakness due to the ipoglycemia reflected;
- lower thehyperglycemia chronic in sick subjects (type 2 diabetes mellitus) and its consequences (such as protein glycation);
- facilitate the slimming (in overweight subjects, especially insulin resistant).
As we will see, however, that of the glycemic index is a parameter less relevant than one might believe, even if the logic in support of a possible therapeutic utility would seem not to make a turn (apparently).
Let's go into detail.
Glycemic index
What is the glycemic index?
The concept of the glycemic index was introduced in 1981, after which it has been corrected and arranged several times.
The glycemic index (GI) of a nutrient, food or meal identifies:
>.
* Blood glucose concentration measurable in mg / dL or mmol / L.
This index is expressed in a percentage (%), which refers to a specific one food test, which is assigned a value of 100%.
The measurement is carried out by administering a portion of food containing it same amount of carbohydrates of the test - therefore, DON'T the same portion of the test.
there the two distinct equations, both available in the literature, different from each other because they are based on different test foods.
The most used one uses a solution of water and 50 g of glucose. The other instead, 50 g of White bread.
As glucose in solution is 1,37 times faster than white bread, to convert from one index to another simply multiply or divide the value of the second or first scale by 1,37.
The glycemic trend, which graphically would draw a curve to bell, is observed for a period of time equal to 120 ' (2 hours).
For example, a food with a glycemic index of 10 (%) is capable of increasing blood sugar at a rate equal to 1/10 compared to the glucose solution.
According to the logic of the glycemic index, foods can be divided into 4 categories:
- A very low IG fino a 40;
- A bass IG from 41 to 55;
- A medium GI between 56 and 69;
- Ad high > 70.
Critical issues
Some criticalities of the glycemic index
First of all, there are numerous factors that affect the glycemic index of foods; some are: individual responses and nutritional composition - also influenced by other characteristics which we will discuss below.
Subjective criticalities of the glycemic index
The individual response is the variable that most undermines the practical use of this criterion.
It could also be argued that "the glycemic index is designed to track large numbers by averaging a large sample."
Certainly, but dietetic "work" is still applicable to the individual and not to the community (for which the famous "guidelines" are more suitable).
Observing different people "apparently similar" in terms of build and habits, the glycemic index of a single food can also change significantly. This is mainly due to the differences "digestive"- exocrine secretions (saliva, pancreas), motility of the digestive tract, state of the mucosa, enzyme density, absorption capacity, etc.
Even the metabolic state in acute can give very flexible values. First of all, the same subject who is being tested many times, also allowing glycemic normalization, before and after offers different numbers between them. This, of course, respecting identical procedural crimes. This is due to subtle extra- and intracellular mechanisms of "sensitivity" which, deducibly, require a longer time to normalize than the glycaemia.
Regarding the metabolic set in acute, it must be said that the glycemic trend - remember having an observation of 2 hours - of a subject "emptied"from his stocks di glycogen muscular and hepatic, with a high post-workout oxygen debt, which participates in opening a large metabolic window, is completely different when observed in conditions of general homeostasis.
Instead discussing metabolism in the chronic, the same subject with one body composition different (perhaps observed at different moments in life) will give inconsistent results. When sedentary and overweight (probably insulin resistant), vice versa normal weight, muscular and active, the subject will have a totally different metabolic management of glucose.
Nutritional problems of the glycemic index
The glycemic index is affected by overall nutritional composition food or meal.
In fact, if a test such as the glucose water solution disregards any other aspect of composition, it is not so simple for foods.
- Dietary Fiber, grassi e protein reduce the glycemic index;
- La maturity of fruits increases the glycemic index;
- Type of carbohydrate in question; glucose has the highest glycemic index, while fructose the lowest. Raw starch (polysaccharide) is indigestible and all starches have one structure different from each other, with different glycemic indexes. The starch resistant has a very low glycemic index;
- State of hydration, since "dry" carbohydrates are poorly digestible, hydrating them increases the glycemic index. Too much, however, can have the effect opposite to;
- La cooking of carbohydrates hydrolyzes them, making them more easily digestible and quickly absorbed, increasing the glycemic index. However, if the composition is mixed, factors of reduction of protein digestibility, glycation etc can take over;
- La cooking fiber makes them more soluble, therefore less indigestible but more capable of gelling the digestive content. The impact is controversial.
That of the meals
What does the glycemic index of meals depend on?
The glycemic index of the diet depends above all on the chemical composition of single foods. Increase if the meal is composed only of foods with a high glycemic index, in particular glucose or short polymers of the same - such as maltodextrins.
It decreases instead if the meal also contains a lot of fat, protein, fiber, too much or too little water. Among sugars, fructose and galactose have a glycemic index lower - the same goes for their digestible polymers - as they must first be converted by the liver into glucose.
Paradoxically, a very large meal can have a glycemic index lower than a medium-small one.
But how could this be an advantage? It is not. This makes us understand the senselessness of taking the glycemic index as a reference when what really matters is the caloric amount of the diet - given by the glycemic load of all meals, but also by the amount of protein and fat. The metabolic impact, on the other hand, referring above all to the release of insulin (index and insulin load), deserves a separate discussion and will not be dealt with in this short article.
The glycemic index increases and with a cooking deep, although parallel factors such as water absorption, protein glycation, etc. can take over. AND lower on the other hand, in the case of starch, if it remains raw or if it undergoes inversion (resistant starch).
Warning! The factors that increase or decrease the glycemic index must be appropriately contextualized, in the sense that while having an impact, they may not do so in a significant or decisive way.
High GI Carbohydrates
What Are High Glycemic Index Carbohydrates?
High glycemic index (JIA) carbohydrates are those capable of raising the concentration of glucose in the blood suddenly, an event which - associated with a high glycemic load - overactivates insulin secretion which, in turn, creates different effects on metabolism; In summary:
- Promotes glycogenosynthesis (accumulation of glycogen, a reserve sugar) in the liver and muscles;
- Depresses the consumption of fats (lipolysis) and neoglucogenetic amino acids (neoglucogenesis);
- It promotes liposynthesis (synthesis of fatty acids and triglycerides) starting from the excess of carbohydrates and dietary proteins, and the deposition of fats in adipose tissue;
- In conditions of muscle fatigue, it promotes the regeneration of damaged fibers;
- Inhibits the action of glucagon;
- It stimulates the secretion of leptin by the adipose tissue - which promotes the feeling of satiety.
Regardless of the glycemic index, what drastically increases blood sugar and insulinemia is the excess of carbohydrates, therefore of glycemic load.
Additionally, JIA carbohydrates can find a very useful use in sports. For example, after a very intense and prolonged activity, which favors the depletion of glycogen stores, the body needs a certain amount of carbohydrates to restore (replenish) muscle and liver reserves. High glycemic index carbohydrates are especially helpful in replenishing these supplies as efficiently and quickly as possible.
| Foods with High Glycemic Index and High Caloric Density | Foods with Medium and High Glycemic Index | Foods with a Low Clicemic Index |
| sugar | White bread | All fruit and vegetables (excluding exceptions) |
| Certain refined grains (puffed rice, bag fries, wafers, cornflakes) | Biscuits | Milk and yogurt |
| Sweets and cakes | Potatoes | Fructose |
| Sweetened drinks (carbonated drinks, "summer" drinks, iced tea, etc.) | Croissant | Whole grains (especially oats and barley) |
| Foods containing "sugar" or "glucose syrup" in the ingredients | Raisins | Pasta cooked al dente |
| Certain types of fruit and vegetables (carrot, melon, pumpkin, etc.) |
What is it for
What is the point of understanding the glycemic index of the diet?
Since hyperglycemia is one of the most widespread and harmful metabolic disorders, also for the resulting hyperinsulinemia, the evaluation of the GI aims to understand e evaluate which foods can be considered "recommendable" and which ones are not.
On the other hand, it is now known that blood sugar "spikes" more, rather than in response to the intake of high GI foods, after consuming a high glycemic load (CG). This other parameter corresponds to the quantity of glucose that a food, in a standard portion, is capable of pouring into the plasma - an aspect which, not surprisingly, is also related to the caloric density of the product.
It must also be said that the glycemic load should be evaluated in the complex; moreover, what matters are, on balance, the total calories.
While considering suitable the daily breakdown of energy into several meals (for various reasons), absurdly, if our daily requirement were 2000 kcal and we took only 1800 kcal with a single meal, we would lose more weight than by making 5, the sum of which reaches a total of 2000 kcal.
Also on the glycemic load of the single meal, there would be a separate chapter to open. Will it really be wrong to drastically increase or decrease that of a single meal? It depends, above all, on what has been done before and what will be done after this meal.
In fact, if we were talking about unhealthy people, therefore insulin resistant and obese, we could say that it is always It is advisable to moderate the glycemic and insulin index (when possible of course), giving priority to the glycemic load and total calories.
Conversely, considering an endurance athlete, we could also find it profitable to create a maxi-glycemic load to be administered immediately after the performance, or even add up the entire carbohydrate quota by spreading it over the 2 hours of pre-intra- and post-workout.
It's not over. Thanks to the process of neoglucogenesis, even foods containing mainly are able to increase blood sugar protein (amino acids neoglucogenic) is triglycerides (glycerol).
What is more, amino acids and fatty acids also have properties of insulin stimulation. This means that not only carbohydrate-rich foods, but others as well, can increase insulin, both in a manner employee from glycemia, both in way independent.
Variability
In 2003, on the "International table of glycemic index and glycemic load values" (Foster-Powell K, Holt SH, Brand-Miller JC. HumanNutrition Unit, School of Molecular and Microbial Biosciences, University of Sydney, NSW, Australia - Am J Clin Nutr. 2003 Apr; 77 (4): 994) a new and updated glycemic index table was published.
The novelty of this publication was the introduction of the concept of variability. In fact, it was discovered that the glycemic index of a food can vary based on:
- Varieties (for example, different varieties of a fruit have different glycemic indexes)
- Degree of ripeness (an unripe fruit has a different glycemic index than a very ripe fruit)
- Geographical area of ​​production (for example an apple grown in Denmark or in your country)
- Production methods (for example the various "industrial" products)
- Fat and protein content (e.g. ice cream)
- Fiber content (for example, real corn flakes, rich in fiber, vs. the higher calorie corn flakes much more like cookies)
- Storage and drying
- Cooking method (for example boiling or baking changes the glycemic index)
- Duration of cooking (for example pasta al dente or slightly overcooked)
- Other ingredients of the recipe (pasta with pesto will have a different glycemic index than pasta with tomato sauce).
Click on the image to view the GLYCEMIC INDEX TABLE.
Conclusions
How to consider the glycemic index of the diet?
Setting an entire food pattern on the glycemic index is conceptually mistaken.
Comparing the GI between foods makes sense only if the difference is clear and, even in this case, it is subject to other criteria.
For the purposes of a healthy and balanced diet, the GI assumes an altogether marginal role. On the other hand, it is essential to carefully evaluate the caloric amount and, possibly in sick or obese subjects, the insulin index (II) and the insulin load (CI) - which as we have said also concern foods without carbohydrates - to establish the most adequate portions of foods rich in carbohydrates such as pasta, bread and sweet fruit.
Preferring pasta to rice or potatoes unnecessarily restricts our possibilities of variation, pushing us towards theorthorexia. Orthorexia is a real obsession with healthy eating, comparable with anorexia and bulimia with the difference that these two diseases are related to quantity, orthorexia to the quality of food.
Those who already follow a balanced diet, integrating the concept of glycemic index, would not add anything useful to their eating behavior. In fact, in a healthy diet, the breakdown of macronutrients is calculated as a percentage of the subject's caloric needs. A normal-calorie diet consisting of about 55-60% carbohydrates, 25-30% fats and the remainder in proteins, appropriately distributed throughout the day, does not require anything.
The concepts of glycemic index and glycemic load, related to the resulting insulin load and index, are particularly important in diseases such as type 2 diabetes mellitus and related complications, the consequent hypertriglyceridemia and obesity.
In fact, by compromising the functionality of LDL (cholesterol transport lipoproteins), chronic hyperglycemia increases cholesterolemia and promotes the atherosclerotic process - responsible for serious cardiovascular events. It can also damage nerve and eye tissue. If that weren't enough, by decompensating insulin production and function, it promotes overweight, leads to impaired glucose tolerance due to insulin resistance, etc.
Common sense and good nutrition education remain the most useful precautions. Eating everything but in moderation is in fact an optimal way to keep the glycemic index, the glycemic load, the insulin index and the insulin load of the diet under control.
Overweight and metabolic pathologies are not caused by the occasional transgression, but by bad daily habits. A healthy person can indulge in a small dessert at the end of each meal as part of a healthy diet, as long as a neutral calorie balance is respected.
However, it would be a good idea to reduce the use of sugar to sweeten drinks, limit the consumption of sugary drinks (caca cola, fruit juices and so on) by drinking more water instead. To this it is advisable to associate an appropriate protocol of motor physical activity, which allows you to better control weight and above all to optimize the metabolism of dietary carbohydrates.
