The Glycemic (GI) Index is the holy grail for many diabetics and dieters. Eat foods “low on the GI” people say, it’s easy, you just follow a chart. Food companies list GI on their products, giving a sense of security to those who purchase the packaged foods. As with all things simple, sometimes it’s not so simple.

The glycemic index essentially measures the rate at which different carbohydrates are digested and converted into glucose and transported to the blood. It has been around for many decades, and it was originally designed around a population of diabetics. Today, it is being applied to everyone – pre diabetic, metabolic syndrome, healthy, etc.

When researchers created the GI, they measured the rate of digestion of white bread, and assigned it the numerical value of 100.  They could have used any number, like 1 for example. This number is actually derived from an area under the curve. The area under the curve of is the glucose response that occurs after ingesting a load of white bread. So if you take the number of a glycemic index of 80, that means it is 80% of the response as compared to white bread (which is 100). A GI of 120 is 120% of white bread and so on.

Many dieticians and physicians use the GI to advise patients to eat below a certain GI. Granted it is a start for some people who are completely confused about dietary carbohydrates, but in the long run it doesn’t change much and just keeps people fat. The GI index probably has the most significant influence on diabetic management.  Patients are told to eat more foods with a low GI index (less than 55), eat a moderate amount of foods with a medium GI index (56-59) and eat less of foods with a high GI index (70+).


Mixing Foods Together Changes the GI

Adding fat and protein to food greatly affects the GI. Add a fat like olive oil, and it lowers the GI. Of course, people took this advice thinking its alright to add butter to sugar, thinking it would lower the GI. This did not work out so well and led only to more obesity.

A grain like quinoa can cause large spikes in blood sugar levels, but when consumed with vegetables like broccoli, carrots, cauliflower, the fiber in these vegetables slows down the digestion.  As a result, the carbohydrates from the quinoa will not cause as dramatic rises in blood sugar levels than it would if it was consumed on its own.

Fibre, which is an indigestible carbohydrate, can slow down the rate of digestion of the other foods you have consumed along with the fibre. Huge individual variance in GI – this study came out recently.

Real world – All of these tests are done under fasting laboratory conditions. No one is really asking how the GI is affected when you eat 3 meals a day, exercise, intermittent fast, etc. Exercise greatly affects the GI and lowers it because one is usually more insulin sensitive when they train consistently.

The GI Inaccurately Reflects the Insulin Response

Insulin response is the amount insulin goes up after consuming glucose or other foods. From the GI, everyone thought that blood glucose response would predict the blood insulin response. This turned out to be wrong as well. For example, adding protein or fat will increase the insulin response. One study even showed that lower GI foods, caused a larger spike in insulin than other higher GI foods. It is much more complicated than we thought.

IGNORES the Effect of Artificial Sweeteners like High Fructose Corn Syrup

The GI index completely ignores the effect of fructose and high fructose corn syrup (HFCS).  HFCS is composed of half fructose and half glucose molecules. Fructose can only be metabolized in the liver.  As a result, fructose is transported directly to the liver via the small intestine, and has a very little immediate effect on blood glucose levels, which is what the GI is supposed to be telling us!  Therefore, only the glucose portion of HFCS is reflected in the GI index.  This is why the glycemic index of watermelon is 71 and a Snickers bar is only 68.


The GI is Always Based on 50 g of a Particular Carbohydrate

Many people stat their morning eating 50 grams of carbohydrates by eating a couple slices of bread (GI of 70) or a bowl of cereal. That can be a high GI when talking about the consumption of certain carbohydrates. Carrots have a GI of 71, as much as a slice of bread. Who would of thunk it? But. if we multiply the 8 grams of carb in a half cup by .71, we get a GI value of roughly 6. Carrots are a low GI food. This means that, unless you truly are going to eat a pound and a half at a time, carrots don’t have a big impact on blood glucose levels. There is actually very little sugar in a single carrot, and even less of you cook it. Another unrealistic part about the GI is that it fails to consider the amount of fiber, water, vitamins and minerals in the carrot.

Of course, we could go on about the GI, but suffice it to say it is probably not going to help you much with your health goals. Learn to stick with whole unprocessed foods and it tends to solve many things.