*Geek Box: Glycaemic Index & Glycaemic Load

*Geek Box: Glycaemic Index & Glycaemic Load

Have you ever wondered, where does glucose go? Let’s use an example of glucose disposal after a hypothetical meal containing 100g of carbohydrate as glucose.

As the 100g enters circulation from the small intestine, the first port of call is the liver where around 30% of that glucose is taken up in liver cells. The remaining 70g goes on to enter general circulation, where around 25-30% is taken up next by skeletal muscle, 5-15% by adipose [fat] tissue, 8-10% by the kidneys, and 15-20% taken up directly by the brain. A further 7-15% continues in circulation and can be taken up again by the liver and other tissues, or stored in adipose tissue, as required.

Now, this is just an example of hypothetical disposal; what about the rate of that glucose uptake? And what about the dose of a given food, as it relates to rate of uptake? This is where the development of glycaemic index and glycaemic load come in. The glycaemic index [GI] of a food is based on a comparison of 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 that 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, wholegrains, and veg and fruit; there are multiple components to these foods that would contribute to long-term health benefits, independent of the mere quantification of impacts on blood sugar using GI/GL.