Other Factors Affecting the Glycemic Index

Your individual glycemic response to a particular food is affected by many factors, such as its fat and protein content, the type and amount of carbohydrate it contains, the amount of fiber and the nature of any starches in it, its preparation (raw or cooked), its ripeness, and even its acidity. In addition, the exact response to a particular food can vary considerably between individuals, just as metabolism does.

While you may be able to easily understand why the higher fiber content of whole-grain bread makes it more slowly digested than a French baguette made of white flour, not all GI differences may be quite as obvious. For example, the glycemic response to diced potatoes is somewhat lower than to mashed potatoes, and thick linguine has a lower GI value than thinner spaghetti. Moreover, cooking in general–and particularly overcooking of foods–can raise their GI value, so al dente pasta is always better (although your pasta intake should always be limited due to its large amount of carbs). Values for many ripe fruits (such as bananas), though, are actually lower than their greener, unripe precursors. Highly acidic foods, such as vinegar, can lower the GI value of another food when they are eaten in combination.

Critics of the GI concept like to point out that GI rankings reflect glycemic responses only over a two-hour time span after a particular food is eaten and that individual responses to any given food may vary widely. Such debates over the GI have led some to conclude that low-GI diets are not necessarily effective for blood glucose control or diabetes prevention because the GI value of a particular food may or may not reflect its entire glycemic effect. However, what’s important to remember is that GI testing of foods is performed on people who are diabetes-free. Moreover, an excessive intake of high-GI carbohydrate foods has been shown to increase insulin resistance even in people without diabetes. Since people with diabetes generally lack the ability to immediately release enough insulin in response to food intake (their “first phase” secretion), GI tables more than likely underestimate, rather than overestimate, the glycemic spikes caused by most carbohydrate-rich foods if you have diabetes.

More on the GI next week.


6 thoughts on “Other Factors Affecting the Glycemic Index

  1. Florian

    I have been using the Glycemic Index in my meal plan and it seems to work for me with some foods. I use pumpernickel bread for sandwiches in place of white bread and for the most part the 2 hr post prandial glycemic spike is lower. Of course what is on the sandwich is important also. So many variables ! ! !

    I think the timing of my meal bolus is something I need to work on. Sometimes giving the insulin a head start by taking my bolus 15 to 20 minutes or more before I start eating seems to have an effect on post prandial glycemic spikes.

    I would appreciate your comments on insulin bolus timing. Thanks.

  2. Sheri Colberg, PhD

    Actually, giving the insulin bolus a head start is an excellent idea, particularly if your blood sugars are elevated at all at the start of your meal. The only danger is if you’re eating really low GI foods and the insulin hits your system before the food does. It just takes a little practice to time it out right for different meals. Another option is to give part of your normal dose 15-20 minutes before and the rest afterwards when you have a better idea of exactly how many carbs you ate.

  3. Greg

    I have a question for you that may or may not be related to this topic, but I’m going to ask anyway. 🙂 Following long (2-3 hours) or intense aerobic (running or cycling) workouts, I’ve been experiencing blurry vision. This blurry vision is the same symptom/feeling when my blood sugar gets extremely low (below 30). However, when I test, it’s usually in the 130-160 range. So I’m confused.

    I think this might be glucuse related because the blurry vision is exactly the same feeling/symptom as when my bg gets really low. It’s not life threatening by any means, but it would be nice if it didn’t happen. Do you have any ideas on what might be causing this? Or more importantly, how do I make it go away? Thanks in advance!


  4. Sheri Colberg, PhD

    I really don’t know what is causing your post-exercise blurry vision. Continue monitoring your blood sugars like you have been doing. If it persists, you may want to check with your ophthalmologist to see if he/she has any ideas. Sheri


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