Recently, the glycemic index (GI) has attracted public attention and already is beginning to appear in GI values for food packaging. Then I explain what and how it affects our daily diet.
The GI concept emerged in the eighties when it was observed that different foods with the same amount of carbohydrates had different effects on the level of blood sugar. Thus, 30 g carbohydrate contained in bread may not have the same effect as 30 g of carbohydrates from the fruit or pasta. Indeed, the GI is a way of evaluating foods that contain carbohydrates according to the degree to which blood glucose rises after consumption. These are ranked on a scale of 0 to 100, where 100 is a reference food such as glucose or white bread. With the same level of carbohydrate foods with a high GI produce significant fluctuations in the level of blood sugar, while low GI foods cause a smaller increase of the same (1).
For many years, scientists have believed that the carbohydrates in the form of starch are digested and absorbed slowly, and that in the case of carbohydrates in the form of sugars, these processes were rapid. However, this is not true. Refreshments and mashed potatoes, for example, have a similar GI. What factors are involved then? The outer shape of a food processing mode, the type of fiber, starch or sugar in it and how to cook it are factors that influence the final GI.
In general, the structure of the food is as important as the type of carbohydrate it contains. For example, whole grains of wheat are relatively resistant to digestion, but once milled, and baked goods are easy to digest. For this reason, white bread and of fine texture have a high GI, while those with several grain breads.
Some foods like oats, apples and beans contain soluble fiber, which thickens and slows the passage of foods through the digestive tract. These foods are low GI. The type of sugar present in food is also relevant; glucose is the greatest impact on blood glucose, followed by sucrose (table sugar).
In practice, most foods with carbohydrates are not consumed individually but as part of an appetizer or a meal, and this has an effect on the glycemic profile. For example, bread can be eaten with butter or oil with meat and potatoes and vegetables. The combination of foods rich in fat and protein significantly slows the digestion of food and reduces the overall GI.
How to implement the IG to improve health?
Knowing the GI of foods can be useful for diabetics who must control their blood glucose. The consumption of foods with low GI can get the release of glucose in the blood occurring in a uniform manner throughout the day (2). The concept of MI can also be applied to the field of sports. Foods with a low GI helps to increase resistance, while food and beverages with a high GI allow replenish muscle glycogen after exercise (1).
Whenever there is more evidence that diets with a lower GI can be beneficial to prevent late onset of diabetes and coronary heart disease, possibly because they limit the demand for insulin and improve the level of blood cholesterol (2). The studies also point to the use of GI in relation to obesity and it has been suggested that diets with a low GI can lead to weight loss because they are very satiating (3). However, it is not known whether this is due to the GI or other foods that have a low GI. This will require reliable long-term leave doubts.
Diet management - the concept of glycemic load
The GI is not the only factor that determines to what extent the consumption of a food raises the level of sugar blood. If you eat the same amount in grams (g) of two similar GI foods (eg croissant and turnip), increased blood sugar level will be lower with the food that has a lower carbohydrate content (eg turnip, see table). If you eat two foods with similar GIs (eg Croissant and couscous), but whose usual rations are different, whose ration is smaller (eg Croissant, see table), will produce a smaller increase in the level of blood sugar. For this reason, we introduced the concept of glycemic load (GL), based on the concept of GI to provide a measure of total glycemic response to a food or meal (GL IG/100 = x grams of carbohydrate per serving). This makes it possible to directly compare the effects on sugar level two as the food consumed in the diet.
Combining foods with different GI for a low GL
The GI is a very useful tool to classify the impact of carbohydrates in the body. However, there is no point worrying too much by the relative values of food and IG separately, because the overall effect of a meal in the GI is difficult to predict. Probably the best solution for most people is to include a mix of nutritious foods with high GI and low in a healthy diet. Those who wish to reduce the CG of your diet should simply increase consumption of low GI foods such as legumes (beans, peas, lentils, etc..), Fruits, cereals based on oats, or substitute some foods with a high GI alternatives with a lower GI (for example, consuming breakfast with cereals based on oats, barley and bran bread and cereals, instead of white bread).
1. FAO / WHO (1998) Carbohydrates in Human Nutrition. Food and nutrition paper no.66 Rome, Italy.
2. Opperman AM, Venter CS, Oosthuizen W et al (2004) Meta-analysis of the health effects of using the glycaemic index in meal planning. British Journal of Nutrition - 92:367-381.
3. Brand-Miller J, Foster K Powell & McMillan P (2005) The Low GI Diet Revolution ISBN 1-56924-413-8 New York.
Flint A, Moller BK, Raben A, et al (2004) The use of glycaemic index tables to predict the glycaemic index of composite breakfast meals. British Journal of Nutrition 2004 91:979-89.