Glycemic Index and Glycemic Load

The main point:

When considering how a food will affect your blood sugar and thereby insulin levels, you need to consider, not only the quality of the carbohydrate (unprocessed, whole food) but the amount eaten at one time.

By now, most of you know that I believe that considering the affect that the foods you eat have on your blood sugar is important for health. Avoiding foods with added sugars and processed carbohydrate is a good place to start, but like most things when it comes to health, there is more to the story. In short, both the quality and quantity of carbohydrate determines an individual’s glycemic response to a food or meal. What I mean is that while quality is important, the amount we eat also matters when it comes to controlling blood sugar. To better understand this, let’s look at a couple of terms that describe this. These terms are glycemic index (GI) and glycemic load (GL). Classically these concepts are used for those with diabetes, but understanding these terms can help all of us, diabetic or not, decide whether or not to include certain foods in our diets.

The GI is a rating system that goes from 1 to 100, with 50 grams of pure glucose (sugar) being scored at 100. Foods are categorized as low (55 or under), medium (under 70), or high (70 or over) based on how they are expected to make someone’s blood sugar levels respond after consumption. The lower a food's glycemic index, the slower blood sugar rises after eating that food. In general, the more processed a food is, the higher its GI, while whole or high-fiber foods will rank lower on the index. This is great but it doesn’t tell you the whole picture of how a given food will actually affect your blood sugar. While GI tells me how fast my BG will go up, it’s not considering the portion that I am eating. An extra-large portion of a low-GI food would still produce a considerable blood sugar spike, while one bite of a high-GI food probably wouldn’t do very much. To understand a food's complete effect on blood sugar, you need to know both how quickly it makes blood sugar rise and how much carbohydrate/sugar per serving it can deliver. This is where the glycemic load (GL) comes into play. GL tells you a more complete picture of what the actual impact a given food will have on your blood sugar.

The GL is another rating system that uses the GI of a food as well as the total carbohydrate in the serving. It is calculated by taking the product of a food’s GI and its total available carbohydrate content: glycemic load = [GI × carbohydrate (g)]/100. Foods under 10 are low, under 20 are medium, and 20 or greater are high on the GL scale. In healthy individuals, increases in GL have been shown to predict increased elevations in postprandial (post meal) blood glucose and/or insulin levels.

So, what is the takeaway? Referring back to our main point, quality AND quantity matter. I often see people frustrated that they are not losing weight, or their blood sugar is not improving as much as they would like to see when they make healthy changes to their diet. They might start eating whole grains rather than refined grains and whole fruits instead of fruit juices, and while these are commendable changes, unfortunately the amount they consume still matters. This is one of the reasons a low carbohydrate diet is so effective for controlling blood sugar. It essentially does the work of reducing GI and GL for you in that it restricts not only high glycemic carbohydrates, but the total amount of carbohydrate as well.


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