The glycemic index (GI) is a pivotal point for many diets, including the Zone diet, the South Beach diet, and the Montignac method.
What is the Glycemic Index?
The glycemic index (GI) is a numerical classification system used to measure the rate of digestion and absorption of foods containing carbohydrates and their subsequent effect on blood glucose levels, i.e. the levels of glucose in the blood.
Michael & Mary Dan Eades on the glycemic index, apples and glucose
After the studies of Dr. Jenkins at the beginning of the ’80s, he was increasingly rooted in the idea that foods with low glycemic index were good, while those with high glycemic index were harmful.
The problem with this theory is that the glycemic index does not compare apples with apples, but a comparison of apples with glucose. Apples contain a complex mixture of pectin, lignin, cellulose and other fibers, in addition to pure carbohydrates. The fibers slow down the absorption of pure carbohydrates, causing a low glycemic response and probably also other independent effects on the levels of sugar and insulin. The glycemic index of the apple is not a function of the carbohydrates it contains, but the actions of the rest of the apple on these carbs.
Nora Gedgaudas- glycemic index/load
For example, there are two different ways in which a food may be considered a low glycemic index.
- It may consist of fiber, so it does not contain sugar or converts to sugar once ingested.
- May contain fructose, which does not have particular effects on insulin, but it’s of extreme glycation, which can be extremely detrimental to the arteries. In fact, fructose is of 20 to 30 times more “glycation” (therefore more harmful) than glucose.
One thing that the glycemic index does not take into account is that other foods are eaten together, which can affect the glycemic effects of a particular food. In addition, the glycemic index is based on a time window of 3 hours and does not take into account certain foods such as sugar or alcohol that have a glycemic effect and impact on the levels of delayed blood sugar (something that had not been included until a short time ago).
The glycemic index in certain cases may therefore be misleading. There is, however, perhaps another more useful way to calculate the carbohydrate content in foods- the glycemic load. The glycemic load takes into account, however, the glycemic index, but it is based on standard portion and is calculated by taking the glycemic index assigned, divided by 100 and then multiplied by the actual content of carbohydrates in a given serving. This is not a perfect method, but definitely better than the glycemic index.
Ron Rosedale on the glycemic index and fructose
The glycemic index is definitely a good tool but certainly not perfect. For economic issues and time, most of the experiments to determine the impact of a particular food on the levels of sugar in the blood does not last more than 3 hours after administration.
Although fructose has a low glycemic index, it can cause serious health problems, primarily by promoting insulin resistance and fat accumulation. In fact, it causes more damage in the body from the glucose. Some researchers have administered fructose to laboratory rats to induce insulin resistance, creating a diabetic state to test the effectiveness of anti-diabetic medicines.
Gary Taubes on the glycemic index, saturated fat, and diabetes
In the ’80s, the studies of Jenkins and Wolever on the glycemic index as a tool to control blood sugar triggered a lively debate among diabetes experts.
Dr. Reaven, a researcher at Stanford University, argued that the concept of the glycemic index made no sense and it was downright dangerous: the saturated fats have no glycemic index, and saturated fat added to sugar and other carbs reduces their glycemic index, making this mix of foods “benign”, although it is not so.
Reaven also discredited the glycemic index as an element on which the clinic is based on the levels of sugar in the blood, when it considered insulin, and insulin resistance, the most important thing on which to focus. The focal point is that the glycemic index of sucrose is lower than the glycemic index of flour (bread) and starch (potatoes), and the reason is in fructose. Carbohydrates are broken down into starch during digestion, first into maltose and then into glucose, which moves directly from the small intestine to the bloodstream. This results in an immediate increase in blood sugar and then the glycemic index.
A tablet of sugar (e.g. sucrose) is composed of both glucose and fructose. Glucose moves in the blood and increases the levels of sugar, as if it came from a starch, but fructose can only be metabolized in the liver. Much of the fructose consumed is directed from the small intestine directly to the liver. As a result, fructose has an immediate effect on the minimum levels of sugar in the blood, and thus, only half of the glucose sugar is reflected by the glycemic index. And since fructose is detected by the glycemic index with difficulty, it seemed that it was the ideal sweetener for diabetics.
By defining carbohydrates as good or bad depending on glycemic index, diabetologists have actually wrongly diagnosed the impact of fructose on health. The point is the influence of glucose and fructose on blood sugar but not on the liver. Glucose arrives directly in the blood and is stored by the tissues and organs as a source of energy; only 30-40% passes through the liver. The fructose instead goes directly from the liver, where it is metabolized almost entirely. As a result, according to Dr. Eleazar Shafrif, “fructose is a metabolic burden to the liver, and the liver responds by converting it into triglycerides – fat.”
Vegetarian diets and glycemic index
The restriction of carbohydrates is often associated with an increase of products of animal origin. The reason is simple: if you eat primarily or exclusively plants (see vegans and vegetarians), you’re getting the total calories from carbohydrates. This does not mean that you cannot lose weight or keep lean by eliminating sugar, flour, and starchy foods and consuming only leafy vegetables, cereals, and legumes. It probably won’t work for many of us.
Vegetables and legumes have the advantage of not containing carbohydrates that are digested quickly, what nutritionists call a “low glycemic index”. If we rely on these foods as the sole source of our diet, total carbohydrates we consume (glycemic load) will still be high. And this may be a sufficient reason for gaining weight. Particularly with regard to those who consume mainly vegetables, fruits, and cereals. In these people, it is not uncommon to find the physical type of “skinny-fat”, or a lean structure generally with a concentration of fat in the stomach.
Dr. Mercola on the glycemic index and fructose
The glycemic index, which measures how fast carbohydrates convert to sugar in the blood, has never been accepted by many dieticians. This premise, that certain foods can seriously raise the levels of sugar in the blood and as a result, cause damage to the body, is true. The problem is that the glycemic index is a valuable tool to determine which foods are the cause of this effect.
The glycemic index values have too many exceptions to be really useful. A classic example is fructose, which has a very low glycemic index, but was clearly identified as responsible for the increase of weight in many people. Many factors play a role in how a given food will affect blood sugar. The glycemic index, for example, takes no account of how a food ingredient or other specific impacts over time. Also, do not take into account the damage caused by chemicals such as sucralose, sorbitol or refined fructose (for those who do not follow the Paleo diet), supposedly “foods” low on the glycemic index.
Stephan Guyenet on the glycemic index and ‘fructose index’
In this study of Dr. Johnson, it is argued that the amount of fructose that is in a food, called “fructose index”, is more important to health than the glycemic index of a food. And since chronically elevated levels of sugar and insulin are part of the metabolic syndrome for a long time, it was thought that the glycemic index could be a good indicator of the metabolic effect of a particular food in the body.
My faith in this concept began to falter when I began to deepen my knowledge on diets taken from traditional cultures who enjoyed excellent health. For example, Kitava gets 69% of calories from foods with a high glycemic index (mostly tubers and vegetables) with little added fat. It is easily absorbed carbohydrate. Yet, overweight, elevated insulin levels, and other symptoms of metabolic syndrome are virtually non-existent.
Ultimately, the glycemic index can still be a useful tool for those who suffer from glucose control, such as those with type 2 diabetes, but I’m not sure whether the glycemic index is useful, in addition to the restriction of the consumption of simple carbohydrates. Reducing fructose can be a most effective way to fix insulin resistance instead of consuming a diet low on the glycemic index.