New Study Casts Doubt on Reliability of Glycemic Index Values

The findings challenge the notion that specific foods have set glycemic values.

Tufts University researchers say those relying on the glycemic index of foods may be misled because the numerical values assigned to different foods may have limited usefulness in food labeling and in predicting how food affects someone’s blood sugar.

The glycemic index is used to measure how quickly someone’s blood sugar rises after eating.

In the study published Wednesday in The American Journal of Clinical Nutrition, researchers tested how quickly blood sugar rose in 63 healthy adults after they ate a particular food.

The adults were given white bread or a glucose drink in testing sessions over six weeks, and their blood sugar was measured afterward. 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.

The results challenge the notion that specific foods have consistent glycemic indexes. The findings could mean that the glycemic index – which millions of people, including diabetics, use to monitor what foods they should eat – may not be as useful, or as reliable, as previously thought.

Given these issues, the study’s authors believe that assigning a glycemic index value to foods isn't helpful.