What is Glycaemic Index?

Glycaemic Index (GI) measures, on a scale of 0 to 100, how a carbohydrate-containing food increases blood glucose after digestion and absorption. Foods higher in GI would suggest a higher blood glucose-raising potential as compared to medium or low GI foods.

According to the American Diabetes Association (2014), carbohydrate-containing foods can be classified as high GI (≥70), medium GI (56-69) or low GI (≤55).

Table 1: Example of foods categorised based on their GI

Aside from considering the GI, it is important to note various other factors affecting blood glucose.

Factors Affecting Blood Glucose

• Portion Size
  

  The portion size of a carbohydrate-containing food would affect how quickly it raises the blood glucose level. This is attributable to the difference in glycaemic load (GL). Contrary to GI, GL is a measurement that considers the amount of carbohydrates consumed per serving and how rapidly it raises blood glucose levels. Hence, a food may have a high GI but low GL.
  GL is calculated by:
  GL = GI x carbohydrate of food (g) / 100

  Example:
  GI of 1 whole watermelon = 72
  GL of a wedge of watermelon (130g) = 6
  GL of 3 wedges of watermelon (130g x 3) = 17

  In general, eating bigger portions of carbohydrate-containing foods will cause your blood glucose to rise more than eating smaller portions. Though GI acts as a good reference to make food choices, GL provides a better reference for diabetic individuals to evaluate the portion size that is likely to be suitable for maintaining a good blood glucose level.

• Food Composition
  

  Blood glucose levels can also be affected differently – depending on whether you consume foods containing mainly carbohydrates or a mixture of carbohydrates, fats and protein. In general, meals with a mixture of carbohydrates, fats and protein (e.g. a serving of white rice, a serving of salmon and a serving of vegetables) would have a lower blood glucose-raising potential than consuming a serving of white rice. This is because fat, protein, and fibre help slow down the digestion rate, hence causing a more gradual and lower rise in blood sugar.

  GI: A reference for healthier food options?

  GI only suggests how rapid the carbohydrate-containing food would raise the blood glucose but does not necessarily suggest a healthier food option. For instance, many higher GI foods can have more nutritional value than lower GI food.

  Table 2: GI of some commonly consumed food

  Food	GI
  Short grain brown rice	76
  Nasi lemak (rice only)	69
  Long grain brown rice	65
  Chicken rice (rice only)	67
  Soda drink	63

  Example:
  Chicken rice (rice only), GI = 67
  Short grain brown rice, GI = 76

  Remarks: Though short grain brown rice has a higher GI, it contains fibre and phytochemicals that constitute a healthy diet. The lower GI of chicken rice (rice only) is attributable to its fat content, which delays digestion. Studies have suggested that excessive intake of saturated fats may increase the risk of cardiovascular disease.

  The use of GI should be balanced with variety and moderation. To combat chronic diseases, eat a balanced & healthy diet and lead an active lifestyle!

Article contributed by Mr Lim Kiat, Senior Nutritionist at SHF.