Glycaemic Index and Glycaemic Load

Glycaemic Index

The glycaemic index is essentially a numeric value assigned to a wide range of carbohydrate sources to indicate their ability to influence blood glucose level after being ingested. Carbohydrates are scored on a scale of 0-100 with 100 causing the greatest spike in blood glucose level in the shortest amount of time (7.8mmol/L under 15-30 minutes post-prandial) after a meal.

Spikes in blood glucose concentrations after a meal are normally mitigated by insulin which is secreted by the pancreas. In normal individuals, the pancreas secretes adequate insulin to remove the excess blood glucose from the blood stream, returning to normal levels. In diabetics however, they either have insufficient insulin (type 1 diabetes) or their insulin receptors are not responsive (insulin resistance). In their case, constant levels of raised blood glucose which goes uncorrected is the cause of many complications such as neuropathy, retinopathy and cataracts as well as heart diseases. Therefore the GI comes in handy to keep them informed about the various types of carbohydrates they should stick to and avoid.

In normal individuals, the sudden spike and dip in blood glucose after eating refined carbohydrates can result in a ‘food coma’ as the carbohydrate transits the gut relatively quickly. This could also lead to a feeling of hunger shortly after consuming our food, potentially making you eat more than you have to, leading to weight gain in the long run.

Table 1 gives an example of foods and their associated GI ranges.

Table 1. Foods and their associated GIs (Diabetic Society of Singapore, 2011)

Typically, we would want to choose carbohydrate sources low in GI because these foods usually come with the vitamins, minerals and fibre which we require for general health and weight management.

Factors affecting GI

Unknown to many, the GI of a carbohydrate can be influenced by a multitude of factors such as: 

1. Increasing the amount of  fibre present by adding green, leafy vegetables to our meals can decrease GI
2. Increasing the amount of protein or fat present in our foods by choosing dishes with lean meat or adding legumes can decrease GI 
3. The amount of amylose present in the starch - a lower amylose content typically results in a lower GI (potatoes & corn starch) 
4. Acidity of food - the addition of an acid such as balsamic vinegar to your carbohydrate source may lower its GI 
5. Degree of cooking - undercooked pasta/rice tends to have a lower GI as compared to those cooked to a greater degree

With these in mind, you now have a good idea what to do when eating out and faced with endless healthy carbohydrate options!

Glycaemic load

Another measure to take into consideration when choosing your food carbohydrate source is glycaemic load (GL),which is derived by the equation below:

GI tells us how quick the particular carbohydrate raises our blood glucose whereas GL indicates how elevated your blood glucose will be after food consumption, which is primarily determined by the amount of carbohydrate ingested. For example, a serving of Gatorade (250mL when diluted)that contains 14g of carbohydrates has a GI of 89 (very high) but has a GL of only 13 (medium) (Refer to table 2).

Table 2. Glycaemic load tiers and corresponding values