First off, I hope everyone had a great Christmas. Hope Mr. Claus treated you well this year and I hope you had a good sleep after your turkey hangover. I want to talk about the Glycemic Index (GI), Glycemic Load (GL), and Insulin Index (II). These three indices are used to calculate the rise in blood sugar or rise in insulin after eating different kinds of food.
The GI compares the blood sugar spike in a food compared to the spike in blood sugar of 50 grams of glucose. Since glucose is the form of sugar our body uses after carbohydrates are broken down, it digests incredibly fast. The GI of, say, dried oats is 103. Meaning it digests slightly quicker than glucose and causes a rapid rise in blood glucose. The GI of apples is 30, meaning it will digest slower and cause a more gradual spike in blood glucose.
There are many issues with the GI. First, if you take the GI of carrots it comes out to 47 (according to the site given). Now, remember that we must compare the amount of carbohydrates of carrots compared to 50 grams of glucose. In order to eat 50 grams of carbohydrates contained in carrots you would need to eat about 5 servings or 5 cups of carrots! That’s a completely bogus amount of carrots for anyone to eat in one sitting. So there is one downfall of GI.
Second, according to this link the GI of carrot juice is 90! How can the GI of a food have a differential of 43? This number was apparently found in one study and was never replicated again. Pretty accurate eh?
Third, the GI of food is measured when ONLY that food ALONE is consumed. For instance, you don’t sit down to eat a meal and only eat a potato with nothing else. You probably have some meat, maybe some butter on there, sour cream, chives and bacon bits. I’ll stop myself there because I’m getting hungry just thinking about that. When you mix the potato with foods with lower GI’s, the GI of that food will also change. In the case above, the GI of the potatoes will decrease. The new GI is unknown though, and even if it were found, would most likely have a high variance.
According to Berardi (2010) the GI of a food has a few influences, such as: food preparation; the age of the food, the meals fat, protein, and/or other fiber content; the time of the day the meal is s consumed; and the time of the last exercise session. So as you can see the GI has a few big flaws.
Next up is the GL. Since the GI index is measured in 50 gram of carbohydrate increments, it isn’t very real world applicable. Most people don’t eat exactly 50 grams of carbs from their meals. So the GL was invented. The glycemic load equals the GI of a food multiplied by the serving size of a food, divided by 100. Or:
GL = (GI X Mass of food in grams)/100. The GL not only accounts for the type of carbohydrate but also the amount. So if you used the GI of carrots (47) then multiplied it by it’s standard serving size, (120 g of carrots is ~12 g of carrots) then divide that by 100, you get a GL of 9.6.
The GL has another issue. It does a good job of showing the rises in blood glucose levels. It does not predict increases of blood insulin levels though.
Thus the Insulin Index (II) was invented. The II measures the amount of insulin the body produces in response to set amount of carbohydrate load for a particular food.
The II has some interesting relationships with GI. There are some foods that have a high GI and low II and vice versa. There are also high-protein and high-fat foods that can produce large insulin responses. For instance Milk causes large insulin spikes. Interestingly, whey protein causes large insulin spikes. The amino acid Leucine especially causes large spikes in insulin. This is one of the properties of Leucine that has the supplement industry pushing it. It is one of the few supplements that I endorse. Increases in blood insulin, can increase protein synthesis, if the proper amounts of protein are available for use.
The main problem with the II is that testing for a food will produce different numbers in different individuals. A perfectly healthy person will produce a lower insulin response compared to an individual who is insulin resistant. Many diabetics and pre-diabetics are insulin resistant so they will have inflated responses.
Then there is the whole debate about having high levels of insulin. As well as how it can be unhealthy. However, most people agree that a high protein diet is healthy, yet protein causes insulin spikes. So if we wanted to constantly have low levels of insulin we would have to eat low-carbs, low-protein and high-fat. You would starve on a diet such as this. Another little known fact about insulin is that is actually decreases appetite, so having chronically low levels of insulin would not be very comfortable. This is part of the reason that protein is so satiating.
I hope this gives you a decent understanding of the GI, GL and II. I’m not trying to trash any of these indices, I’m just giving the pros and cons. You really can’t go wrong with eating the typical healthy foods: fruits, veggies, lean meats, eggs, whole-wheat, oatmeal. All these foods will have a low GI, they are all-high in nutrient density and reasonably low in calorie density. The indices above are used to further refine our understanding of food.
The Essentials of Sport and Exercise Nutrition. Berardi J., Andrews R. Precision Nutrition, Inc. 2010
Insulin… An Undeserved Bad Reputation. Krieger, J. Weightology Weekly (Retrieved December 2010)