Glycemic Index

What is the glycemic index?

The glycemic index (GI) is a scale used to rank the effect a foods carbohydrates has on raising blood glucose levels after eating.

Blood glucose levels are sometimes referred to as blood sugar levels.

In most cases the glycemic index scale is from 0-100.

Glucose is normally chosen as the reference food (see GI measurement) as it has the fastest effect of raising blood glucose levels when consumed.

Low GI foods rank between 0-55, moderate GI foods between 56-69 and high GI foods are over 70.

A Foods GI Category & GI Rating
CategoryGI Rating
Low GI Food 0 - 55
Moderate GI Food 56 - 69
High GI Food 70 or more

Low GI Foods

Foods positioned low down on the scale are those which are slowly digested and absorbed by the body.

Referred to as low GI foods, they produce gradual rises in insulin and blood glucose levels after eating. Low GI foods release glucose slowly and gradually.

High GI Foods

By contrast, high GI foods have a more pronounced effect on blood glucose levels.

High GI foods are quickly digested and absorbed by the body and cause marked fluctuations in blood sugar and insulin levels. High GI foods are further up the GI scale.

Graph showing blood glucose levels of high and low GI foods over time

The graph shows the typical effect of low GI and high GI food on blood glucose levels over a 2 hour period.

In both foods peak blood glucose level is after 30 minutes.

However the high GI food gives rise to a much higher level of blood glucose compared to a low GI food.

After 2 hours blood glucose levels are significantly reduced being much closer to baseline before the food was consumed.

After 2 hours the blood glucose levels from high GI food is still elevated more than the blood glucose level from the low GI food.