“No matter how slowly a carbohydrate-rich food digests, eventually it does digest. And when that food digests, every single gram of carbohydrate it contains turns into one of two substances: glucose or fructose.”
–Jenny Ruhl, “The Glycemic Index Is a Scam”

Some carbs are processed very rapidly, and some carbs take much longer to process; that’s the whole rationale behind the glycemic index/glycemic load concept. To a non-diabetic, it’s important to have low glycemic foods to allow the body time to produce enough insulin to cover the carbs. For a diabetic, the glycemic index concept is virtually useless, because their insulin does not process the carbs properly, whether the carbs are slow or fast.

First, you should understand what the Glycemic Index is and what Glycemic Load means.

“The GI [glycemic index] value of a food is determined by giving people a serving of the food that contains 50 grams of carbohydrate minus the fiber, then measuring the effect on their blood glucose levels over the next two hours.”1 Note, however, they did this experiment on presumably non-diabetic persons, so it may not be meaningful for diabetics. It also does not state what the participants’ peak blood glucose would have been at one hour.

“Glycemic load [GL] estimates the impact of carbohydrate intake using the glycemic index while taking into account the amount of carbohydrates that are eaten in a serving…. Glycemic load is based on the glycemic index (GI), and is calculated by multiplying the grams of available carbohydrate in the food by the food’s glycemic index, and then dividing by 100.”2

I agree with the dietitians who “feel that focusing on the glycemic index and load adds an unneeded layer of complexity to choosing what to eat,”3 especially for diabetics, since our primary concern is how carbohydrates affect our bodies.

Dietitian Joy Kiddie asked an important question in her article, “How Reliable is Glycemic Index for Predicting Blood Sugar Response?” She answered, “A study published in the American Journal of Clinical Nutrition reported that individual response to individual carbohydrate-containing food varies so much that Glycemic Index values may not be useful in indicating blood sugar response in individuals.”4 She gives citation information at the end of her article5 which I have also placed in the Endnotes for this chapter.

A Diabetes Village writer says (about the same study) that “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.”6

Health writer and researcher Jenny Ruhl, in Blood Sugar 101, wrote the most comprehensive review of the studies on the glycemic index. She said:

“The Glycemic Index tells you only what these foods do to the blood sugar of a normal person two hours after they eat the food. It does not tell you what they do to that blood sugar one hour after eating them, or—and this can be very important for pasta—four hours after eating them.

“And even more importantly, the Glycemic Index does not tell you how much insulin the body had to secrete to process the glucose that resulted from the digestion of this food when it finally did digest.

“Because no matter how slowly a carbohydrate-rich food digests, eventually it does digest. And when that food digests, every single gram of carbohydrate it contains turns into one of two substances: glucose or fructose.

“If it turns into glucose—and most carbohydrate does—it goes into the bloodstream and raises the blood sugar until it encounters an insulin molecule. That insulin molecule can do one of two things. It can move that glucose into a hardworking muscle cell that burns it for energy, or it can move the glucose to a fat cell where it will be stored for later use, in the form of fat. Most of the time insulin does the latter.”7

Ms. Ruhl said it best with this section in her article: “When You Have Diabetes or Prediabetes Your Meter is the Final Authority.” In other words, “eat to your meter”!


1Ellis, Esther, MS, RDN, LDN. “What Is Glycemic Index?” Eat Right, November 19, 2019. https://www.eatright.org/food/nutrition/dietary-guidelines-and-myplate/what-is-glycemic-index (accessed 12/12/2020).

2“Glycemic load,” Wikipedia, n.d. https://en.wikipedia.org/wiki/Glycemic_load (accessed on 12/12/2020).

3“The lowdown on glycemic index and glycemic load,” Harvard Health Publishing, n.d. https://www.health.harvard.edu/diseases-and-conditions/the-lowdown-on-glycemic-index-and-glycemic-load (accessed on 12/12/2020).

4Kiddie, Joy, MSC, RD. “How Reliable is Glycemic Index for Predicting Blood Sugar Response?” The Low Carb Healthy Fat Dietitian, May 14, 2019. https://www.lchf-rd.com/2019/05/14/how-reliable-is-glycemic-index-for-predicting-blood-sugar-response/ (accessed on 12/12/2020).

5Matthan NR, Ausman LM, Meng H, Tighiouart H, Lichtenstein AH. “Estimating the reliability of glycemic index values and potential sources of methodological and biological variability,” Am J Clin Nutr. 2016;104(4):1004–1013. doi:10.3945/ajcn.116.137208

6“Diabetes and Glycemic Index: Research Round-Up,” Diabetes Village, n.d.
http://mydiabetesvillage.com/research-round-diabetes-glycemic-index/ (accessed on 12/12/2020).

7Ruhl, Jenny. “The Glycemic Index Is a Scam,” Blood Sugar 101, n.d. https://www.bloodsugar101.com/the-glycemic-index-is-a-scam (accessed on 12/12/2020)

Additional References

Diabetes and Glycemic Index: Research Round-Up

Glycemic index and glycemic load for 100+ foods
The glycemic index is a value assigned to foods based on how slowly or how quickly those foods cause increases in blood glucose levels.

‘Glycemic Index’ May Be Too Unreliable to Manage Diabetes: Study

Glycemic Values of Common American Foods

The Glycemic Index Still Matters for Diabetes