A breakdown of the glycemic index

You may have heard that some foods are higher on the glycemic index than others. Or maybe you’ve heard of “slow” carbs vs “fast” carbs. The glycemic index is a way of rating carbohydrate-containing foods based on how quickly they are digested and absorbed in the body. But what exactly does this mean?

Low glycemic index, low-GI foods (like non-starchy vegetables, and nuts) are digested slowly, causing less of a spike in blood sugar levels. A low-GI diet has been shown to improve glucose tolerance and menstrual cycle regularity.

What does the ranking mean?

The glycemic index is a comparative ranking of the effect that 50 grams of carbohydrate from a given food has on blood sugar. Foods with a score of 1-55 are considered low-glycemic, 56-69 are considered medium, and 70 or more are high-glycemic. Pure glucose, a simple sugar, has a GI of 100. For the most part, less-processed, fiber-rich foods such as non-starchy vegetables, nuts and seeds have a lower GI than highly processed, sugar-laden foods such as sodas and white bread.

So why does this matter? Well, our blood sugar levels are incredibly important. When we eat a meal that rapidly raises our blood sugar, the release of insulin is triggered, which then causes our blood sugar to crash, leaving us brain-foggy, irritable, and hungry soon after eating. But these are only the short term negative effects. A chronic blood sugar issue, something that happens over and over again, will put us at risk for diabetes and heart disease and is linked to both obesity and cancer. Not so good.

The Flaws of the Glycemic Index

The glycemic index has been proposed as a solution to this problem. However, it has its flaws. One issue with the glycemic index is that it doesn’t take portion size into account, so the blood sugar impacts of different foods are inflated compared with a typically consumed portion.

Another tool, the glycemic load (GL), helps to correct this issue by taking portion size into account. On the GL scale, 1 to 10 is considered low-glycemic, 11 to 19 moderate, and 20 and above high-glycemic.

Many variables affect a food’s GI/GL, including how it is processed, its ripeness and how it is cooked. The more finely a grain is milled, the higher its GI/GL, so unprocessed whole wheat has a lower GI/GL than white flour. Well-ripened fruit has a higher GI/GL than less-ripe fruit, as do grains that are cooked longer.

The GI of a food doesn’t measure how the food affects blood sugar when eaten in combination with other foods. It purely measures one singular food. However, typically we eat foods in combination, like brown rice pasta with olive oil, lemon, and zucchini, as opposed to just brown rice pasta with nothing else. These food combinations change the glycemic index of the meal as a whole.

What does that mean for you?

Just because a food has a low GI/GL doesn’t mean it is healthy. In general, fructose has a lower GI than glucose, because fructose is metabolized in the liver before it gets into our blood, so it doesn’t raise blood sugar as quickly. Contrary to what we might think, this isn’t necessarily a good thing. For example, agave nectar has a low GI and is often labeled a healthy replacement for sugar. Although this sweetener raises blood sugar slower than white cane sugar, our blood sugar could go just as high, and stay there longer. It will just take longer to get up there due to agave’s fructose content. On top of that, fructose can be harder on our livers than sucrose.

Perhaps the biggest variable in determining someone’s glycemic response to a food is that person’s unique body. Ah, isn’t this always what it comes down to? According to a study in Cell, each person has a unique blood sugar response that differs from what the GI/GL would predict. Lead researchers found that a set of personal factors, including sleep, activity and overall dietary habits, but most importantly, an individual’s gut microbiome, had a huge influence on one’s blood sugar response.

This proves that any general dietary guidelines, like the glycemic load of food, will have limited utility. For example, it’s like saying that a banana contains 100 calories. While that may be true in a general sense, bananas come in different sizes, at different times of the year, from different places. They are then processed by our unique bodies a little differently. They can’t all possibly be equivalent to 100 calories. So, glycemic index and glycemic load can be important tools to utilize for our health, however, they are only part of the story.

Written by Hannah Aylward

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