For optimal blood glucose levels (BGLs), we know it is important to choose the appropriate amounts and types of carbohydrate-rich foods. Did you know there are two useful tools to help us navigate this? Introducing glycaemic index (GI) and glycaemic load (GL).
In brief, GI assists us with understanding how quickly carbohydrate-rich foods raise BGLs. GL demonstrates how portions of different carbohydrate-rich foods compare with regards to raising BGLs. Essentially, high GI foods result in a faster and higher rise in BGL, whereas low GI foods result in the opposite. However, large portions of low GI foods can result in a high GL, so portions are also important to consider
What is Glycaemic Index?
Just like a car needs fuel, we need energy from foods containing protein, carbohydrates and fats for optimal function. Read more here about carbohydrate digestion
Glycaemic index (GI) was established to rank carbohydrate-rich foods and drinks based on the time is takes for digestion to occur and blood glucose levels to increase within 2 hours.
Carbohydrate rich foods that digest into glucose quickly and released into the bloodstream rapidly are classified as high GI (>70). On the other hand, foods containing carbohydrates that digest into glucose slowly and released into the bloodstream gradually are classified as low GI (<55). Foods containing carbohydrates that digest into glucose at a moderate rate and released into the bloodstream steadily are classified as medium GI (55-70).
High GI foods: watermelon, brown rice, potato, jelly beans, rice crackers and white bread
Medium GI foods: sweetcorn, honey, basmati rice, Weet-bix, orange juice and wholemeal bread
Low GI foods: milk, legumes, beans, lentils, apples, dark chocolate, soy foods (e.g. tofu), grains, raisin toast, oats and wholemeal pasta
Factors that increase GI
Ripen fruits and vegetables are easier for the body to digest.
A yellow (ripe) banana has a higher GI than a green (unripe) banana.
Processed foods are more easily absorbed.
Fruit juice has a higher GI than a fresh piece of fruit and quick oats have a higher GI than traditional rolled oats.
Cooking breaks down the structure of carbohydrates which is easier for the body to digest.
Soft boiled pasta has a higher GI than al dente (cooked but firm) pasta.
Factors that decrease GI
Cooking and cooling carbohydrates
When foods are cooked and cooled in the fridge, the structure of the carbohydrates change and becomes harder for the body to digest.
Cold potato salad has a lower GI than a hot baked potato.
Fibre delays digestion.
Oats and legumes have a low GI because of their soluble fibre content.
Protein and fat
Protein and fat content within foods slows digestion
Full fat Greek yoghurt has a low GI because of the protein and fat content.
Phytates store phosphorus in plant based foods and slow the rate of absorption
The phytates in wholegrain breads and cereals (e.g. oats) lower their GI.
Fructose and lactose
These types of sugars are more complex than glucose and take longer to digest.
Fruit contains fructose and milk and cheese contain lactose so no need to cut fruit and dairy from your diet.
Slows stomach emptying and digestion.
Pouring vinegar, lemon juice or acidic fruit to carbohydrate-rich foods lowers the overall GI.
How can I use GI?
GI can come in really handy for diabetes management and weight management.
Diabetes management: Low GI foods are ideal for people living with insulin resistance as the body has more time to produce enough insulin to match the release of glucose into the blood. This helps with maintaining BGLs within an optimal range. Recent research has highlighted that lower GI diets can reduce average BGLs which significantly decreases the risk of diabetes progression (Diabetes Australia, 2020).
Weight management: As lower GI foods take longer to digest than higher GI foods, these foods improve satiation and satiety (feelings of fullness) resulting in eating less food.
GI is helpful for selecting the appropriate types of carbohydrates to eat for good diabetes management, but GI is not the only tool to determine the healthfulness of a food. The total carbohydrate amount, and energy (kJ/calorie) content is also important to consider. Research has shown that the total amount of carbohydrates has a bigger influence on BGLs than the GI rating (NHS, 2018).
A number of low GI foods are excellent nutrient-dense everyday foods. However, not all low GI foods are every day foods and not all high GI foods are discretionary (sometimes foods). For example, nutrient-dense foods like watermelon, brown rice and parsnips have a higher GI than nutrient poor foods like chocolate, potato crisps and ice cream. This does not mean we should replace watermelon with chocolate. Remember to also consider the nutrients foods contain.
What is Glycaemic load?
Glycaemic load (GL) considers carbohydrate-rich foods based on their GI and the total amount of carbohydrates in the portion of food. For example, even though oats have a low GI, a large portion of oats results in a quicker rise in BGLs compared with a smaller portion. Let’s look at an example comparing 100g of watermelon (a high GI food) with 250ml of milk (a low GI food).
The equation for calculation GL is
(GI x the amount of carbohydrates (g) in a serving of food) ¸ 100
72 x 6g / 100 = 4.3
2 x 15g / 100 = 4.1
100g of watermelon and 250ml of milk have a similar GL, despite different GIs, hence watermelon and milk have a similar effect on BGLs.
How can I use GL?
GL can be used to compare similar foods and portions and their effects on BGLs. For example, you are deciding whether to have 150g of cooked white rice or 150g of cooked quinoa with beef stir fry for your evening meal.
150g white rice:
75 x 39g / 100 = 29.3
53 x 25g / 100= 13.3
Because rice has a higher GI and contains more total carbohydrate, the GL of rice is more than double the quinoa despite the same portions. As a result, rice increases BGLs quicker than the quinoa. In this case, quinoa is a better choice for people with diabetes.
Tips for using GI and GL to support diabetes
Try to include at least one low GI food at each meal and snack throughout the day. This will help you to keep your BGLs stable and feel fuller for longer.
Pair your higher GI foods with a lower GI food. This will decrease the overall GI of the meal. For example, cooking potato (high GI) into mashed potato and pouring in milk (low GI) will decrease the GI of the mashed potato.
Replace cornflakes with rolled oats and white bread with wholemeal and wholegrain bread. These foods have a lower GI, helping you to feel fuller for longer and stabilise your BGLs.
Use the University of Sydney’s ‘Search for the Glycaemic Index’ database. It is an excellent tool providing the GI, serve size, total carbohydrates per serve and GL of thousands of foods https://www.glycemicindex.com/
Remember, when constructing a healthy eating plan, GI is one of many aspects to consider. For personalised advice about how the GI and GL of foods can support you to eat well and manage your BGLs, book an appointment at www.nourishadl.com/dietitian
Co-authored by student dietitian, Charlotte Manning
Reviewed by dietitian, Rebecca Greco
Better Health Channel. (2020). Carbohydrates and the Glycaemic Index. Retrieved from https://www.betterhealth.vic.gov.au/health/healthyliving/carbohydrates-and-the-glycaemic-index#:~:text=fruit%20and%20vegetables).-,Glycaemic%20Load%20(GL),the%20glycaemic%20load%20(GL).
Diabetes Australia. (2020). Glycaemic Index. Retrieved from https://www.diabetesaustralia.com.au/food-activity/eating-well/glycemic-index/
Diabetes.co.uk (2019). Glycaemic Load. Retrieved from https://www.diabetes.co.uk/diet/glycemic-load.html
National Diabetes Services Scheme. (2016). The Glycaemic Index Fact Sheet. Retrieved from https://www.ndss.com.au/about-diabetes/resources/find-a-resource/glycemic-index-fact-sheet/
NHS. (2018). What is the Glycaemic Index (GI)?. Retrieved from https://www.nhs.uk/common-health-questions/food-and-diet/what-is-the-glycaemic-index-gi/
Nutrition Education Material Online. (2014). Glycaemic Index of Foods. Brisbane: Queensland Government.
Steenkamp, G. (2014). Factors affecting the Glycemic Index of foods. Retrieved from https://gabisteenkamp.co.za/factors-affecting-the-glycemic-index-of-foods/