Glycemic index

Some interesting research was recently published regarding the accuracy of selecting foods according to their glycemic index (GI) number. It turns out that this system may not be as reliable as we once thought.  Let’s break it down to see what it all means and how it might affect a person with diabetes (PWD).


The glycemic index is a value assigned to foods based on a scale of 1-100.  The number tells you how slowly or how quickly those foods cause increases in blood sugar levels. Carbohydrates with a low GI value (55 or less) are more slowly digested and cause a lower and slower rise in blood glucose and insulin levels.

Some examples of low GI foods are strawberries, raspberries, black beans and apples.  High GI foods include potatoes, white bread, pasta and watermelon…and most of the foods that come to mind when you think of big glucose spikes.  Popular glycemic index based diets have been promoted to guide a PWD in separating out the “good carbs” from “bad carbs.”

Study details:

A study published recently in the American Journal of Clinical Nutrition calls into question the reliability of choosing foods based on the GI system.

Healthy adults were given white bread or a glucose drink (50 g glucose load).  Then their blood sugar was measured several times over the next 5 hours. They completed 3 of the same food testing challenges over 6 weeks.  According to the study, though they were eating the same amount of the same food each time, each subject’s blood sugar levels varied by 20 percent. There was even greater variation between different people eating the same foods.

Key Points:

The study proved that GI varies quite a bit and shouldn’t be counted on as a reliable guide for choosing foods to control our blood sugar.  We already knew that whether a food is eaten raw or cooked, cooking method used and level of ripeness could all influence the GI. What was surprising was that the SAME food had a variable effect in the SAME person on different days.  Meaning, there’s not even reliability of the number within ourselves!  Along the same line, the level of blood sugar rise in one person after eating the white bread was NOT the SAME as the next person. There was up to 25% variation.  That can make quite a difference between glucose levels being consistently in the target range or not.

It’s important to note that only people without chronic diseases were used in this research.  We don’t know for sure how the results might be different in a diabetic population, but one can speculate that not much would change. If anything, there might even be more variation!

What does this mean for PWD?

PWD are frequently given recommendations from dietitians, doctors, educators, friends with diabetes and family members on how and what they should eat.  Rarely do the recommendations all agree with each other.  Many PWD follow the low-carb-high-fat (LCHF) lifestyle.  For those in this camp, nothing here will be surprising. They haven’t used GI to select a food in years!  They would even say they’ve known it to be faulty all along, so this research doesn’t affect them one bit.  They are nodding and saying, “I told you so,” with a little smile.  I fully support an individual’s decision to manage their diet in a way that works for them. Following the latest nationally-sponsored nutrition guidelines is not the only way to attain success in managing diabetes. LCHF achieves stable blood sugar results and leads to weight loss in plenty of cases.

But there are many PWD who do not want to exclude all carbohydrates from their diet. Some become experts at carb-counting, while others struggle to even get close to accurate.  A person who is careful about self-experimentation and frequently checking blood glucose can learn over time how certain foods affect them.  By pairing protein and fats with carbs, the blood sugar spike can be lessened.  However, if you’ve been trying to control your blood sugar by using GI lists alone, it’s time to reconsider.  The current study proves that it’s not reliable, and strictly using the GI number likely won’t help you consistently achieve your target blood sugar goals.  While there is clear value in knowing how much a specific food will raise glucose, the glycemic index isn’t the best way to make this determination.

Join the conversation!

Have you been successful using glycemic index lists?  Does the latest study influence your opinion on using GI to control your blood sugar?

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