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What is the Glycemic Index

Q & A

How important is glycemic index?

You might have noticed a number of snack bars, granola, and breakfast cereals have been proudly displaying the “Low GI” label on its packaging. But unlike ‘low sugar’, ‘low fat’, or ‘low sodium’ labels, the concept of GI can be a little trickier to understand. What exactly are low GI foods, and why are food companies persuading us to buy more of them?

What is GI?

As you probably remember from high school biology, our bodies digest carbohydrates from our foods by breaking it down into simple units of sugar, which can then be transported by our blood to different parts of the body. Simply put, the glycemic index is a way for us to measure how quickly your blood sugar levels would rise after eating a particular type food, on a scale of 1-100.

The smaller and simpler the carbohydrate, the easier it is to digest. This translates into sugars being released rapidly into our blood, and the food is described as having a high glycemic index. We generally categorize foods with a GI of 70 or above, such as sweets, polished white rice, white bread, and sugary cereals, as high GI foods.

On the other hand, high fibre carbohydrates, as well as foods that are relatively rich in protein and fats, release sugars into our blood more gradually, and so are considered low GI foods. We usually interpret this as foods with a GI of 55 or lower, which includes whole oats, brown rice, nuts, beans, lentils and most vegetables.

Should I eat more low GI foods? 

Generally speaking, a low GI diet could be healthier for you because it encourages you to eat more fresh fruits and vegetables, whole grains, and legumes. As tempting as it may look, that bowl of coco pops probably won’t be able to keep you full until lunchtime because of how quickly its sugars will be released and absorbed. A smarter breakfast option could be a bowl of whole oats cooked in milk, with some berries added in for sweetness. The oats and berries provide fiber, while the milk provides protein and fats, which all helps to release sugars more slowly to keep you fuller for longer. On top of this, eating a balanced diet with enough fiber also helps to reduce risks of cardiovascular disease, diabetes, and high cholesterol in the long run. 

Avoiding high GI foods could be especially important for people who have diabetes, since they aren’t able to use insulin to process sugars in the same way the healthy people can also risk of cardiovascular disease, diabetes, and high cholesterol in the long run. 

Avoiding high GI food may be especially important for people who have diabetes, since they can’t use the insulin hormone to process sugars normally. Following a low GI diet could be very helpful for keeping their blood sugar levels stable and prevent any spikes.

Are low GI foods the be-all and end-all? 

As useful as GI can be, it doesn’t provide a very well-rounded picture of a food’s healthiness. In fact, it can actually be misleading at times. For example, both watermelon and pumpkin have high GI values around 75 – 85, while potato chips and snickers bars have moderate GIs around 55 – 65. I’m sure we can all agree that a few slices of watermelon is far healthier than a bag of chips!

These misleading values are due to the fact that GI is measured using 50g of carbohydrates (without fibre) from a particular food, while being eaten on an empty stomach. For foods like watermelon, it doesn’t take into account the fact that its 70% water, and you’d have to eat 2 small watermelons to reach 50g of carbs! Your blood sugar levels would also rise much slower if the food isn’t eaten on an empty stomach, or is eaten as part of a mixed meal. Because we rarely ever eat meals or snacks like that, GI values can be pretty misleading about the effects of a food on our bodies. 

Whether to follow a low GI diet also depends a lot on the type of lifestyle you have. If you exercise and train regularly, you might find it useful to eat a carb heavy, high GI snack (like some dried fruit, a ripe banana, or an date energy ball) just beforehand for an energy boost. But if you mostly alternate between sitting at your desk at work and in front of your TV at home, a low GI diet might be worth a try.


Dietitians Association of Australia. (n.d.). Making sense of the glycaemic index. Retrieved June 26, 2017, from

Goff, L., Cowland, D., Hooper, L., & Frost, G. (2013). Low glycaemic index diets and blood lipids: A systematic review and meta-analysis of randomised controlled trials. Nutrition, Metabolism and Cardiovascular Diseases,23(1), 1-10. doi:10.1016/j.numecd.2012.06.002

Larsen, T. M., Dalskov, S., Baak, M. V., Jebb, S. A., Papadaki, A., Pfeiffer, A. F., . . . Astrup, A. (2010). Diets with High or Low Protein Content and Glycemic Index for Weight-Loss Maintenance. New England Journal of Medicine,363(22), 2102-2113. doi:10.1056/nejmoa1007137