The Glycemic Index Explained

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Read more :

• What is the glycemic index?
• What is the glycemic load?
• Does a low GI/GL diet help you to lose weight?
• Can the GI and the GL be used to manage or prevent diabetes?
• What are you eating? Glycemic ratings of common foods
• Putting the glycemic index into practice

What is the glycemic index?

Counting carbs is not just a matter of adding two and two together. Other factors also 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 glycemic index (GI) takes these factors into account when rating a carbohydrate food. A food with a low-GI rating will cause a small, slow rise in blood sugar levels, while a high GI food will cause a fast and dramatic spike. The GI rating of a food is based on glucose – the fastest releasing carbohydrate – having a rating of 100 . A food that releases glucose at half the rate of pure glucose has a GI of 50; a food with a quarter the rate of glucose release 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 or more. 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.

What is the glycemic load?

The glycemic load (GL) goes a step further than the GI by taking into account the amount of carbohydrate in a food. A weak point of the GI is that it fails to do this.

For example, pumpkin has a high GI of 75, but you would have to eat a lot of pumpkin for there to be a steep rise in blood sugar. Because pumpkin has a high GI number, it seems like it is a food to avoid, whereas in fact it is full of excellent nutrients and, when eaten in normal proportions, is unlikely to cause a dramatic influx of blood sugar levels. The GL provides a more practical way of evaluating the effect of carbohydrates on blood sugar by combining both quantity and quality of carbohydrate into one number. Foods low in carbohydrates, such as pumpkin which has only 8g carbs per 100g, do not have much 'power' to raise your blood sugar levels. According to the GL system, therefore, pumpkin is given a relatively low rating of 4.

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.

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) in grams. For example, the GI of an apple is 38 and its carbohydrate content is 16. Therefore: 0.38 X 16 = 6.08. So an apple has a GL of around 6.

Food	GI Rating	GL Rating
Watermelon	72	4
Coca Cola	53	14
Corn on the cob	48	5

Does a low GI/GL diet help you to lose weight?

There are some reasons why a low GI diet can contribute to weight loss. For example, 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, e.g. legumes take longer to process than bread. Consuming these foods therefore helps people to feel fuller for longer and means they are less likely to overindulge. Low GI foods also produce less insulin, and low insulin levels help people to burn fat instead of carbohydrate.

However, following a low GI or GL diet does not automatically mean that you will lose weight. These indexes only measure the carbohydrate content of foods and do not account for calories, fat, and other nutrients. It is vital to consider overall calorie and fat intake, as well as carbohydrate intake, for effective weight management. It is 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, but bread has more nutrients and less calories and fat than chocolate, and is therefore a much better option.

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 about 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 should never suggest free reign on portion sizes. This is as important to those who are controlling their blood sugar levels as it is to those who are controlling their weight.

It is good to keep in mind that GI and GL are really research tools for analysing carbohydrates in 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 do not produce enough insulin in their bodies to effectively manage glucose and maintain their blood sugar levels. Consequently, it is very important for people with diabetes to manage their glucose intake carefully. Low GI and GL diets are believed to be helpful to people with diabetes because low GI and GL foods release glucose into the bloodstream slowly and more evenly than high GI and GL foods, making glucose levels easier to regulate.

Brand-Miller says that "choosing low GI sources of carbohydrate is a natural way of keeping blood glucose levels on an even keel, which helps people avoid marked fluctuations." However, the GI or GL should clearly not be the only point of reference in managing carbohydrate intake; instead they should be used as tools.

A low GI diet may also help to 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 that diets high in both high glycemic index and high glycemic load foods have been 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 answer the question of whether there is a link between a diet of high GI foods and the development of diabetes. But as it stands, the current research gives a fairly strong indication that 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	Glycemic Load Per serving	Serving Size (g)
Fruit and Fruit Products:	Apples	32	5	120g
	Grapefruit	25	2	120g
	Oranges	40	4	120g
	Peaches	28	2	120g
	Pears	34	4	120g
	Plums	24	2	120g
	Mangos	51	8	120g
	Apricots, dried	30	8	60g
Vegetables:	Carrots, boiled	41	2	80g
	Corn on cob, boiled	48	5	50g
Legumes and Nuts:	Butter beans, canned	36	4	75g
	Chickpeas, canned	38	4	70g
	Hummus	6	1	30g
	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
	Peanuts	13	1	50g
Grains and Breads:	Tortilla, wheat	30	6	50g
	All-bran, Kellogg's	30	6	30g
	Toasted Muesli	43	7	30g
	Popcorn, plain, microwave	55	4	20g
	Mixed-Grain Bread	34	4	30g
	Wheat crispbread	55	9	25g
Miscellaneous:	Honey, Yellow box	35	7	25g
	Honey, Iron Bark	48	10	25g
	Nutella	33	4	20g
	Fruche	34	7	150g
	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	Glycemic Load Per serving	Serving Size (g)
Fruit and Fruit Products:	Banana	58	14	120g
	Grapes, black	59	11	120g
	Apple juice	44	12	262g
Vegetables:	Potato, boiled	56	11	150g
	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	Glycemic Load Per serving	Serving Size (g)
Fruit and Fruit Products:	Dates, dried	103	42	60g
	Sultanas	56	25	60g
Vegetable Products:	French Fries, frozen, reheated	75	50	150g
Grains and Breads:	Basmati rice	58	24	150g
	Jasmine rice	109	46	150g
	Gluten-free Rice & Corn Pasta	76	34	180g
	Corn Thins	87	17	25g
	White Bread	70	9	30g
Cereals:	Corn Flakes	77	19	30g
	Coco Pops, Kellogg's	77	20	30g
	Weet-Bix, Sanitarium	69	13	30g
	Instant Oats, Uncle Toby's, cooked with water	82	28	60g (dry)
Miscellaneous:	Jelly Beans	80	20	30g
	Skittles lollies	70	21	30g

Putting the glycemic index into practice

Low GI, high GL, swapping rice for sweet potato... All of these figures and rankings can seem a little confusing at first. It's important to remember that GI and GL are simply tools to use for controlling your blood sugar levels and carbohydrate intake.

Try our tips for some 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
• Consider which food will give you the most nutritional value, as well as the GI rating
• Remember portion size - low GI foods can still be high in fat
• 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 potatoes instead of potato, basmati rice instead of white rice, and so on

Related articles :

• Carbohydrates and Diabetes: Breaking it down

Related links :

• The Glycemic Index
• Low GI Recipe: Birchjalna Muesli
• Low GI Recipe: Hearty Apple & Cinnamon Porridge
• Low GI Recipe: Tangy Chickpea Dip
• Low GI Recipe: Cracked Wheat and Vegetable Pilaf
• Low GI Recipe: Orecchiette with Minted Lentils and Feta
• Low GI Recipe: Bean Moussaka
• Low GI Recipe: Mushroom and Tomatoes with Steak
• Low GI Recipe: Mushrooms, Beef & Bok Choy Stir-Fry

References :

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

Last updated: November 3rd, 2005