Counting carbs is out; the glycaemic index is in. But is the glycaemic index just another dose of diet hype, or can it really help support your health goals?
If used properly, the glycaemic index (and even better, glycaemic load) may actually help you improve your diet and make better food choices. It can also be a great tool for people with diabetes.
Let’s get into how to use the glycaemic index and the glycaemic load, and check out how your favourite foods perform in our glycaemic ratings table.
What is the glycaemic index?
Carbs have been given a bad reputation in recent years, however they’re not all bad… In fact, carbs are your brain’s preferred source of energy, and are essential to include as part of a healthy diet. However, all carbs aren’t equal, and this is where the glycaemic index comes in…
To determine the nutritional quality of carbohydrates, various factors have to be taken into consideration, such as how fast the carbohydrate is digested, and how much it causes your blood sugar levels to rise.
The glycaemic index (GI) takes these factors into account when rating carbohydrate foods. A food with a low GI rating will cause only a small, slow rise in your blood sugar levels, while a high GI food will cause a fast, dramatic spike.
The GI rating of a food is based on glucose – the fastest releasing carbohydrate – which has a rating of 100 . A food that releases glucose at half the rate of pure glucose has a GI of 50; a food releasing glucose at a quarter of the rate of pure glucose has a GI of 25, and so on.
High GI foods, such as white bread, white rice, and jelly beans, have a GI of 70 and above. Medium GI foods, such as bananas, cherries and ice cream have a GI between 56 and 69. Low GI foods, including mixed-grain breads, legumes, milk and yoghurt, and most fruits, have a GI of 55 or less. These low GI foods are the ones you want to prioritise, as they’ll provide you with longer-lasting energy, without the dreaded blood sugar crashes associated with sugary, processed or refined carbs.
What is glycaemic load?
The glycaemic load (GL) goes a step further than the GI by taking into account the amount of carbohydrate in a food. GI fails to do this.
For example, pumpkin has a high GI of 75, but you’d have to eat a lot of pumpkin to experience a steep rise in blood sugar. Because pumpkin has a high GI, on first glance it seems like a food you should avoid, whereas it’s actually full of excellent nutrients and, when eaten in normal proportions, is unlikely to cause a dramatic rise in blood sugar levels.
A GL of 20 or more is high, a GL of 11-19 is medium, and a GL of 10 or less is low. Almost all foods with a low GI will also have a low GL, but foods with an intermediate or high GI often have a low GL.
The GL provides a more practical way of evaluating the effect of carbohydrates on your blood sugar by combining both quantity and quality of carbohydrates. Foods low in carbohydrates, such as pumpkin which has only 8g carbs per 100g, don’t have much ‘power’ to raise your blood sugar levels. According to the GL system, therefore, pumpkin is given a relatively low rating of 4.
GL is calculated by dividing the GI of a food by 100 and then multiplying by the food’s available carbohydrate (i.e. not including fibre content) in grams. For example, the GI of an apple is 38 and its carbohydrate content is 16g. Therefore: 0.38 X 16 = 6.08. So an apple has a GL of around 6.
|Food||GI Rating||GL Rating|
|Corn on the cob||48||5|
Does a low GI/GL diet help you lose weight?
A low GI diet can contribute to weight loss. Many low GI foods are bulky, high in fibre, and more satiating than high GI foods because they take longer for the body to process, for example legumes take longer to process than bread. Consuming these foods therefore helps you feel fuller for longer and means you’re less likely to overeat. Low GI foods also produce less insulin, and given low insulin levels help you to burn fat instead of carbohydrates, this can assist in your fat loss efforts.
However, following a low GI or GL diet doesn’t automatically mean you’ll lose weight. These indexes only measure the carbohydrate content of foods and don’t account for calories, fat or other nutrients. It’s important to consider your overall calorie and fat intake, as well as carbohydrate intake, for effective weight management.
It’s also easy to make unhealthy choices based on GI or GL rating alone. For example, chocolate has a low GI compared to a slice of white bread, yet bread contains more nutrients and fewer calories and fat than chocolate, making it a much healthier food choice.
According to Jennie Brand-Miller, Professor of Human Nutrition at the University of Sydney and a leading researcher in the development of the GI, the GI/GL is essentially about making smart carbohydrate choices and should be thought of in terms of swaps. “People should not think that chocolate is a good swap for watermelon!” she warns.
Portion control also remains vital for weight loss when using the GI or GL. A low GI or GL rating doesn’t mean you can go ham on your portion sizes. This is important for controlling your blood sugar levels and your weight.
Keep in mind that GI and GL are primarily tools for analysing the carbohydrate content of foods. Calculating the GI or GL of every carbohydrate food before you eat it is neither practical nor sensible. However, being familiar with the GI/GL rating of foods can help you improve the quality of your carbohydrate choices, whether for insulin moderation or weight loss purposes.
Can the GI and the GL be used to manage or prevent diabetes?
People who have diabetes don’t produce enough insulin to effectively manage glucose and maintain blood sugar levels. Consequently, if you have diabetes, it’s important you manage your glucose intake carefully. Low GI and GL diets can be helpful for people with diabetes as low GI and GL foods release glucose into your bloodstream slowly and more evenly than high GI and GL foods, making glucose levels easier to regulate.
Brand-Miller says, “Choosing low GI sources of carbohydrates is a natural way of keeping blood glucose levels even, which helps avoid fluctuations.”
However, the GI or GL should clearly not be your only point of reference in managing carbohydrate intake; instead they should be used as tools.
A low GI diet may also help prevent Type 2 diabetes. A report on GI, GL, and the risk of Type 2 diabetes in the American Journal of Clinical Nutrition (July, 2002) found diets high in both high glycaemic index and glycaemic load foods were associated with a greater risk of type 2 diabetes in both men and women.
Researchers agree that larger studies and clinical trials are needed to definitively determine whether there is a link between a diet including high GI foods and the risk of developing diabetes. However, current research indicates a low GI/GL diet is a wise choice for both managing and preventing diabetes.
What are you eating? Glycemic ratings of common foods
|SLOWER ACTING CARBOHYDRATE
Low GI (55 or less)
Low GL (10 or less)
|Food Item||Glycemic Index
Glucose = 100
|Fruit and Fruit Products:||Apples||32||5||120g|
|Corn on cob, boiled||48||5||50g|
|Legumes and Nuts:||Butter beans, canned||36||4||75g|
|Red Kidney Beans, canned||36||5||75g|
|Soya Beans, boiled||20||1||150g|
|Split Peas, boiled||32||4||150g|
|Cashew nuts, salted||22||3||50g|
|Grains and Breads:||Tortilla, wheat||30||6||50g|
|Popcorn, plain, microwave||55||4||20g|
|Miscellaneous:||Honey, Yellow box||35||7||25g|
|Honey, Iron Bark||48||10||25g|
|Milo, made with full-cream milk||35||8||258g|
|Pizza Hut, Super Supreme, pan pizza||36||8||100g|
|MEDIUM ACTING CARBOHYDRATE
Medium GI (56 to 69)
Medium GL (11 to 19)
|Food Item||Glycemic Index
Glucose = 100
|Fruit and Fruit Products:||Banana||58||14||120g|
|Sweet potato, boiled||44||11||150g|
|Grains and Breads:||Corn chips||42||11||50g|
|Cereals:||Froot Loops, Kellogg’s||69||18||30g|
|Just Right, Kellogg’s||60||12||30g|
|Special K, Kellogg’s||54||11||30g|
|Miscellaneous:||Milk Chocolate, Dove||45||14||50g|
|FAST ACTING CARBOHYDRATES
High GI (70 or more)
High GL (20 or more)
|Food Item||Glycemic Index
Glucose = 100
|Fruit and Fruit Products:||Dates, dried||103||42||60g|
|Vegetable Products:||French Fries, frozen, reheated||75||50||150g|
|Grains and Breads:||Basmati rice||58||24||150g|
|Gluten-free Rice & Corn Pasta||76||34||180g|
|Coco Pops, Kellogg’s||77||20||30g|
|Instant Oats, Uncle Toby’s, cooked with water||82||28||60g (dry)|
Putting the glycaemic index into practice
All of these figures and rankings can seem a little confusing at first. It’s important to remember GI and GL are simply tools to help you control your blood sugar levels and carbohydrate intake.
Try these tips for simple ways to make the switch to low GI foods:
- Don’t worry about exact GI values. Instead consider whether the food falls into the low, medium or high GI category. For example, a food with a GI of 40 is as suitable a choice as a food with a GI of 30 – they’re both low GI foods.
- Consider which food will provide the most nutritional value, as well as looking at the GI rating
- Remember portion size – low GI foods can still be high in fat and calories.
- It’s okay to eat some moderate and high GI foods. Try to combine them with low GI foods to reduce the overall GI rating of the meal.
- Use the GI ratings to make food swaps. Swap a high GI food for a low GI food – such as sweet potato instead of white potato, basmati rice instead of white rice, and so on.
This article was compiled in consultation with CalorieKing.com.au experts and in reference to the following sources:
‘Carbohydrates and Sugars,’ American Heart Association , American Heart Organization
‘Diet, Glycemic Index, and Health,’ Harvard Women’s Health Watch, Feb. 2002
Brand-Miller, Foster, Powell, ‘International Table of Glycemic Index and Glycemic Load Values:2002,’ American Journal of Clinical Nutrition , July 2002: pp 5-56
Brand-Miller, Hayne, Petocz, Colagiuri, ‘Low-Glycemic Index Diets in the Management of Diabetes: A meta-analysis of randomized controlled trials,’ Diabetes Care: 26:2261-2267, 2003
The Glycemic Index, http://www.glycemicindex.com/
‘The Glycemic Load Concept’, The Glycemic Index Foundation of South Africa
Willet, Manson and Liu, ‘Glycemic Index, Glycemic Load, and Risk of Type 2 Diabetes,’ American Journal of Clinical Nutrition:76 (1) 274s-80s, July 2002