The number of investigations on the glycemic index and glycemic load is constantly increasing. It should not surprise us, therefore, that in the field of human nutrition there is more and more talk of these two concepts. But it is not always spoken properly: on many occasions, scientific reality is distorted to unsuspected limits and even “miraculous” diets are created based on these concepts to which portentous health benefits are attributed. That is why today I dedicate a few lines to this issue.
The concept “Glycemic Index” was first coined by Professor Walter Willett and his colleagues in 1997 (Diabetes Care. 1997 Apr; 20(4): 545-50). From then until today hundreds of investigations have been published based on this index, as is the case of a recently published study (October 2015) in the Journal of the American Geriatrics Society, and coordinated by Dr. Mónica Bulló. Unfortunately, it is not always spoken as well as Dr. Bulló and her team have done: false and exaggerated promises of improving health related to the glycemic index or glycemic load periodically appear, so I think that today it is very necessary to look these “constructs” closely.
What do we mean by glycemic index or glycemic load?
Before talking about something, it is necessary to describe that “something”, so I am going to try it. The Glycemic Index (GI) is a value that theoretically allows us to quantify how our blood glucose levels respond after eating a food with 50 grams of carbohydrates (although sometimes it is valued with half, 25 grams), compared to how they do after consuming the same amount of carbohydrates from a glucose solution or, sometimes, bread.
Glucose (or bread) is given a GI value of 100, and all other foods are ranked based on that pattern. We will say that a food has a high GI if it ranges between 70 and 100. If the values are between 40 and 70, we will consider that we are facing a medium GI, and it would be low if it has less than 40 (or, according to other documents, 55).
In most cases, the closer the GI of a food is to the GI of glucose, that is, the closer it is to 100, the worse its nutritional profile and the greater the risk that we are dealing with a product that increases the risk of suffering from chronic diseases related to nutrition, such as diabetes or obesity.
What do we mean by “glycemic load”?
The concept of “glycemic load” (GL), on the other hand, is somewhat more complicated, since it arises as a product of the Glycemic Index (GI) and the amount of carbohydrates ingested (GL=GI x carbohydrates in a specific amount of food) . In other words, it allows us to differentiate what happens when we eat, for example, a carrot (which, although it has carbohydrates, its proportion is very low), from what happens when we eat a food rich in carbohydrates, such as rice. Indicates the amount of glucose available to metabolize or store after the ingestion of a food that contains carbohydrates.
Doubts
Both concepts have been proposed on several occasions (in many cases forming part of “miracle diets” such as the zone diet) so that we make food selections that improve the nutritional profile of our diet.
However, the latest update of the FAO-WHO on the role of carbohydrates in human nutrition, advised “to maintain a cautious attitude when choosing foods based only on the glycemic index or on the glycemic load”.
Shortly after, the European Food Safety Authority (EFSA) concluded that the evidence linking GI and GL with weight maintenance or the prevention of diet-related diseases is inconclusive. The EFSA, which is the highest European authority on food, addressed this issue in its document “Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fiber”, published in 2010.
In the obesity consensus of the Spanish Federation of Societies of Nutrition, Food and Dietetics, published two years later, it was concluded that “There is not enough evidence to affirm that the GI and GL of the diet are associated with an increase in body weight in disease-free adults.
And in people with diabetes?
As for people with diabetes, although both the glycemic index and the glycemic load can be of some use, it should be noted that the American Diabetes Association indicates that its use to manage this pathology can have “modest” benefits in relation to other less complicated dietary approaches.
More restrictive is the American Dietetic Association, who indicated to dietitians-nutritionists who use the GI in patients with diabetes that the scientific evidence on this strategy is “conflicting”.
Dietary fiber
We know that dietary fiber is most likely a “confounder” involved in observations related to glycemic index or glycemic load. Where do we find dietary fiber? In “little processed” plant-based foods. I put “little processed” in quotation marks because both an alcoholic beverage and white sugar are foods of plant origin, but since they are not “little processed”, their dietary fiber content will be null or negligible.
