Glycaemic index is a poor predictor of how foods raise blood sugar

A study of people with prediabetes shows that the same foods affect blood sugar levels very differently. The findings add to a growing body of evidence undermining the idea of a standard glycaemic index

By Grace Wade

People with prediabetes who eat the exact same foods can have very different blood sugar levels.

These findings, which were presented at the American Society of Nutrition conference last week, are the latest to suggest that glycaemic index (GI) is an unreliable predictor of how foods affect blood sugar levels.

The idea behind GI is simple: foods are scored based on how quickly they increase glucose levels in the blood. Those above 70 are high GI foods, meaning they rapidly raise …