Examining the Glycemic Index
In part one of my Sweet Stuff series I addressed some basic sugar issues including what added sugars are, what natural sugars are, and how to recognize sugars on a food ingredient label. Here I explore the glycemic index, what it has to do with our food choices (including how various sugary foods rank on the index) and discuss its uses when planning one’s food intake. In my next Sweet Stuff blog post I’ll discuss how the Guiding Stars system takes sugars into account when rating foods.
What is the glycemic index?
If you follow nutrition news, you’ve no doubt heard of the glycemic index (GI), and maybe you’ve wondered if you should be taking the GI into consideration when choosing foods. Some folks think that the glycemic index is a way to tell how sugary a food is. In reality, it’s more complicated than that.
When carbohydrate foods are eaten and digested, they raise blood sugar levels in the body. The GI was developed as a means of ranking foods by comparing the degree to which they raise blood sugar, relative to a standard (glucose, with a GI of 100, is the standard). Foods receive a GI number between 9 and 100. Those with a high GI raise blood sugar higher and faster than foods with lower GI scores, and meats and fats are not ranked at all since they don’t contain carbohydrates. Foods that break down quickly in the body tend to have higher GI values than foods that break down more slowly.
Why should I care about my blood sugar levels?
Unless one has been diagnosed with diabetes or hypoglycemia, blood sugar is not usually given a second thought. We simply eat, digest and trust our bodies to keep humming along like always. Having an idea of what happens when we eat carbohydrates, however, can be useful for understanding things like appetite and weight gain, as well as more serious health issues.
So here we go: When we digest carbohydrate foods, they are eventually broken down into glucose. This glucose circulates around in our blood and triggers the release of insulin, a hormone that helps this glucose get into our body’s cells where it can be used for energy for things like moving our muscles and helping our brains work. This is all good, of course! And if we have excess glucose in our blood (more than is needed by the cells at that time) it is stored in the liver and in our muscles so it can be used later—also good in case we don’t have any food handy or are going to have a long, hard workout or something like that.
When our storage sites are full, any extra glucose is stored as fat. This is not necessarily a bad thing, since we all need some fat for a variety of reasons. This, however, is where the bad part can start….it’s easy to see how constantly having too much glucose circulating can lead to an excess accumulation of fat and therefore undesirable and unhealthy weight gain. Constant high levels of blood glucose can also lead to continually high levels of insulin secretion, which has been associated with increased appetite, high triglyceride levels, high “bad” cholesterol levels, insulin “resistance” and a host of disease-promoting conditions.
What is the glycemic index used for?
The GI is a way to predict the body’s blood sugar response to various foods, and therefore can be useful tool for people who have diabetes or for others who are concerned about maintaining even blood sugar levels throughout the day. However, the American Diabetes Association does not recommend solely relying on the GI to make food choices. Instead, people with diabetes should consider the GI as one of the tools available to help make appropriate food selections for their diets. Weight control is another area where adhering to a low-GI diet may be, though again, the glycemic index is not a stand-alone solution by any means. And, when it comes to weight loss, it’s important to realize that there isn’t one diet plan that works for everyone, and in the long run, it’s overall calories that really count.
What else should I know about the glycemic index?
The GI is not the be-all, end-all way to select carbohydrate-containing foods. Why? First, the GI reflects the quality or type of carbohydrate contained in a food, but does not take into account the quantity of carbohydrate the food provides. When trying to manage blood sugar, portion size also plays a role—and obviously, the same goes for weight loss. Just because a food has a low GI number doesn’t mean one can eat unlimited portions of it and still lose weight or maintain blood sugar control.
Also, there are a number of factors that influence the GI level of a food, including ripeness, how a food is processed or prepared and how long a food is cooked, for example. Many foods on the GI have only been tested once, in ten or fewer people, so the quality of the data needs to be viewed cautiously. When we eat, we typically do not eat foods all alone; we eat meals and snacks that usually contain multiple foods. Eating a high GI food combined with a low GI food tends to help balance their effects on blood glucose level.
Some high GI foods are highly nutritious. And some low GI foods are less nutritious choices. For example, many candies (such as chocolate) have a relatively low GI, but their saturated fat content and nutritional value make them poorer choices than some higher GI foods such as fruits and whole grains.
Where can I find information on the glycemic index?
An online appendix of GI tables is available via the American Diabetes Association.
International Table of Glycemic Index and Glycemic Load Values, 2008. (Atkinson, Foster-Powell & Brand-Miller)
The Glycemic Index: Physiological Significance. (Esfahani, et al.)