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Why Diabetics Should Beware of the Glycemic Index

glycemic index

If you have diabetes, the glycemic index (GI) may not be as helpful as you think it is. That was the consensus of researchers at the Jean Mayer United States Department of Agriculture (USDA) Human Nutrition Research Center on Aging at Tufts University.


Use of the glycemic index, which indicates how quickly blood sugar will likely rise after someone consumes specific foods, is widespread. In addition to its personal use by diabetics, there are various diets that are based on the index, many food items that provide consumers with GI values on the label, and apps people can use to track the GI of various foods.

The glycemic index ranks foods from 0 to 100 and is divided into three categories: low (0-55), medium (56-69), and high (70+). The lower a food’s glycemic index, the slower your blood sugar levels will rise. Generally, the more processed or cooked a food is, the higher its GI value, while foods with more fat or fiber tend to have a lower GI.

Why the glycemic index may be unreliable

Basically, the researchers found that how an individual responds to a specific food can vary greatly. For example, consider the findings based on the 63 healthy adults who participated in six food testing sessions over three months.

Before each session, the individuals fasted and did not exercise or consume any alcohol. They then ate either white bread (GI of 62) or a glucose beverage (control), in random order.

All of the participants had their blood glucose levels measured several times over a five-hour period following each session. Here’s what the investigators learned:

  • Blood sugar response was low in 22 participants
  • Response was medium in 23
  • Response was high in 18
  • Overall, the scores varied as much as 15 points either up or down, which essentially placed the white bread in all three GI categories.
  • Individual responses to the challenge varied by as much as 60 points between tests

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These findings are food for thought: How do you know the response your body has to individual foods? How do you think you would do if you took this challenge?

What do the study results mean for diabetics?

According to the study’s lead author, Nirupa Matthan, individuals who consume the same amount of the same food three different times should demonstrate a similar blood sugar response each time. However, that’s not what she and her colleagues witnessed in this study.

Based on their findings, Matthan suggested that glycemic index values are “unlikely to be useful in guiding food choices,” and that the “glycemic index is impractical for use in food labeling or in dietary guidelines at the individual level.”

Instead, the study’s senior author, Alice H. Lichtenstein, suggested that people with diabetes focus on eating lots of fruits and vegetables along with whole grains, fish, legumes, lean meats, and nonfat or low-fat dairy foods. When applicable, foods should be prepared with liquid vegetable oils.

Also Read about 10 bad foods for diabetes and some good alternatives

Matthan NR et al. The reliability of glycemic index values and potential sources of methodological and biological variability. American Journal of Clinical Nutrition 2016 Sep 7

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