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What is low GI? A simple explanation of low GI food for diabetics.

Low GI (Glycaemic Index) foods are those that release their carbohydrates very slowly. GI is a number that describes the rate at which sugar is released into the bloodstream after foods containing carbohydrates are eaten.  So, the GI of a food represents its ability to raise the sugar level in the blood.

low GI effect on blood sugar

Type 2 diabetes vs Type 1 diabetes

People living with Type 2 diabetes are encouraged to eat foods on the lower end of the GI spectrum because of the slower and more sustained release of sugar into the blood.  But there are different implications for people with Type 1 diabetes. Here, the goal is to try and align the GI with the insulin coverage of the carbs as closely as possible in order to achieve stable blood sugar.  Rapid acting insulin takes about 15 minutes to become active, reaches its peak after 1-2 hours and can stay active in the system for up to 4 hours. Let’s take a closer look at low, intermediate and high GI foods. Here’s a thorough list of all the foods that fit into a low GI diet, and a sample meal plan.

When to eat low GI foods (<55)

If you’re a Type 1 diabetic eating low GI foods in large amounts (rye or wholewheat bread, legumes and grains, for example), the release of the glucose into the bloodstream can last long after your rapid acting insulin has reached its peak. This can be problematic if very large amounts of said food are eaten: your insulin will ‘kick in’ before the glucose is fully released. Being on an insulin pump can solve this as the insulin bolus can be manipulated to mimic the slow release of sugar with an extended bolus setting.  You can also be careful with portion sizes to solve this issue – smaller portions will have less of an effect.

Very low GI foods are ideal for a meal before any long, slow forms of exercise like hiking as blood sugar will likely be better maintained.

When to eat medium GI foods (56-69)

In general, these foods are a good choice after low intensity exercise, directly after moderate activity, and the morning after intense evening exercise. These foods should be a relatively close match to insulin’s activity in the blood.

When to eat high GI foods (> 70)

High GI foods cause the blood sugar to rise rapidly and what usually happens after this is a rapid drop in blood glucose. It’s not a good idea to eat them by themselves, even if you’re covering the carbs with insulin.  High GI foods are, however, vital for times when you need to raise the blood sugar quickly and so are used in hypo management to correct low blood sugar. It’s important to remember that this level will probably drop again and that is why, if you are a Type 1 diabetic on injections, you need to have a small low GI snack after treating your hypo. This snack is not necessary for pump users.

What is glycaemic load? (GL)

‘Glycaemic load’ (GL) is a measure of the GI of a food combined with the amount of carbohydrate in a food. It will predict the level of impact that food will have on blood sugar.  Low GL foods simply contain very little carbohydrate and in the vocabulary of someone with diabetes, these would be called ‘carb-free’ foods: tomatoes, lettuce, cucumber etc.

low GI, medium GI from GI foundation of SA

Many thanks to Louise Ferreira, our expert dietician in East London, for these tips. For lists of the GI of different foods and recommended portion sizes, visit

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  1. Sally Faye Jallow Sally Faye Jallow

    Thanks Louise for sharing these useful tips. I have learn something about Low Gi.

  2. […] To balance your glucose levels, lower-GI carbs such as wholegrains, beans, sweet potatoes and some fruit (like plums and apricots) are great choices, as they are less likely to spike your blood glucose. Milk and yoghurt also have a low GI. Just remember that low GI food still has to be eaten in the right portion. Here’s a simple explanation of low GI. […]

  3. […] Of course! Things like lentils and beans and apples are not expensive and are great low GL foods. (Here’s a quick reminder of what low GI and low GL foods are.) […]

  4. […] are. (Check out our Healthy Food Guide for more information on portion control.) We speak about the low glycemic index (low GI) food guidelines. I explain the difference between simple and complex carbohydrates and highlight […]

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