*Geek Box: Glycaemic Index & Glycaemic Load

The glycaemic index [GI] of a food is based on comparing how quickly a food makes blood glucose levels rise, compared to 100g of pure glucose. As a result, the scale is a numeric scale from 0 to 100. In general, foods <55 are considered low GI, 56-69 considered moderate GI, and >70 considered high GI.

However, this is quite artificial relative to how much of a given food people would actually consume. This is where glycaemic load [GL] comes in because the GL of a food considers how much glucose that food would contribute per serving. Watermelon is a commonly cited example of the difference; it has a GI of 80, but its GL is only 5 because the majority of the fruit would be water, fibre, and other factors which mean its net glucose value is low. Both the GI and GL have critics, particularly GI given it does not reflect actual food intake.

One thing to keep an eye out for is the fact that low GI/GL diets are often a proxy for diets containing minimally processed carbohydrates, fibre-rich foods, whole-grains, and veg and fruit; multiple components to these foods would contribute to long-term health benefits, independent of the mere quantification of impacts on blood sugar using GI/GL.