Glycaemic index values of the same foods can vary widely and may be an unreliable indicator of blood sugar response, according to a new study.
Variation in values
The glycaemic index was created to show how fast blood sugar rises after eating a specific type of food, the study authors said. It's considered a tool to help people with diabetes control their blood sugar levels.
Read: Great variations in people's blood sugar response
In the study, researchers checked blood sugar responses in 63 healthy adults after eating the same amount of white bread three different times over 12 weeks. The investigators found that glycaemic index values varied an average of 20 percent among individuals and 25 percent between different study participants.
"Glycaemic index values appear to be an unreliable indicator even under highly standardised conditions, and are unlikely to be useful in guiding food choices," said lead author Nirupa Matthan. She is a scientist at the US Department of Agriculture Human Nutrition Research Centre at Tufts University in Boston.
"If someone eats the same amount of the same food three times, their blood glucose response should be similar each time, but that was not observed in our study.
Read: 13 recommendations for healthy blood sugar levels
A food that is low glycaemic index for you one time you eat it could be high the next time, and it may have no impact on blood sugar for me," she explained in a university news release.
Unacceptable to many people
Based on these findings, Matthan said using the glycaemic index wasn't practical for food labelling or in dietary guidelines at the individual level.
"If your doctor told you your LDL ['bad'] cholesterol value could vary by 20 percent, it would be the difference between being normal or at high risk for heart disease. I don't think many people would find that acceptable," she concluded.
The study was published in the American Journal of Clinical Nutrition.
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