What is the Difference between Glycemic Index (GI) and the Glycemic Load (GL)?



 by Helen Papaconstantinos, CNP, ROHP, BA

 For many years, food scientists have advocated the use of the Glycemic Index as a useful tool in avoiding certain foods which might cause blood sugar to rise.  It is a ranking system that tells you how fast the sugar content of a food is released into your bloodstream.

The concept behind the GI was developed by Dr. David J. Jenkins and colleagues at the University of Toronto in 1980 while researching which foods were best for people with diabetes.[1] Jenkins began testing how quickly 50 grams of specific foods like beets and oatmeal convert to glucose (blood sugar), and compared them to either white table sugar or to white bread. His team set a standard measure. Today when you follow a GI diet, you use a chart that scores food on a range from 1-100. A high GI score indicates food to avoid; a low GI score, the ones to eat.

There have been some problems with the GI rankings.[2] If following the GI, you might be tempted to think that a cola, with a GI of 90 is better than cranberry juice, which carries a GI of 105. You might also think you should eliminate carrots from your diet due to their extremely high GI value. (A newly updated figure has Canadian carrots listed at 97 GI per serving).[3] Another problematic example is ‘fructose’, which has a very low glycemic index, and yet has been established as a major reason why so many people are overweight.[4]

Common sense, however, tells you that a cranberry juice should be better than a sugar-based soda, and that carrots are good for you.

GI and GL – Does it matter which one I use?

According to Patrick Holford, one of the world’s leading authorities on nutrition and health, Gylcemic Index food scores, while useful, only provide half the picture. While the GI value tells you how rapidly the carbohydrate in a food turns into sugar, it does not tell you the quantity of carbohydrates in a serving.[5]  You need to know both sets of data in order to understand how that food will impact your blood sugar.  The Glycemic Load measures both and combines this data into ‘one figure’.

Questions around juicing and blood glucose Levels

The newer Glycemic Load concept developed by Harvard School of Public Health Professor Walter Willet and his associates in 1997[6], sheds light on whether ‘juicing’ of fruits and vegetables, is really the high-sugar culprit it has long been made out to be. Yes, an 8-ounce serving of carrot juice contains approximately 11 grams/3 teaspoons of sugar – but you need to keep in mind that is about half the amount found in a large apple.[7] Carrots are an excellent food for your body’s cells. They are full of dietary fibre, and contain many important vitamins and minerals.[8] In short, you need to look at the whole picture. You never want to cut a natural form of beta-carotene from the diet, especially since you would be missing out its pro-vitamin A – important for immune system health, for skin repair, and for maintenance of the retinas of your eyes. For ideas on how to lower the glycemic load of any food, please see pages 3 and 4 of this article.

Calculating Glycemic Load easily:

An often-used example of watermelon is given here: Watermelon contains fast-releasing carbohydrate- for this reason it has a high GL score of 72. However, only 1/8 oz (6g) per 3 ½ oz (100g) of watermelon is carbohydrate. The rest of the fruit is mainly water. The impact of the fast-releasing sugar is very low, therefore, so ‘high glycemic index’ watermelon actually has a low GL score of only 4.

Here’s how to calculate the GL of any given food: take the GI value and multiply it by the actual number of carbohydrates in a serving. So…Quantity of Carbohydrate X Quality of Carbohydrate. Then simply divide by 100.

The GL score of watermelon is therefore calculated as:

72 X 6 = 4.32


(Rounded down you get = 4 GL)


GL food scores – What’s a safe range?

The glycemic load of a food varies according to portion size, and the range of measures runs from 0-35. Anything over 15 is to be avoided. Here is an easy guideline you can follow, sourced from Patrick Holford’s  ‘Holdford Low-GL Diet Made Easy’ book:

LOW GL – a score of 10 is good.

MEDIUM GL – 11-14 is OK in moderation

HIGH GL – 15 or more is ‘bad’ and to be avoided. (Contrast that with the GI, where a score of 55 is considered low).

If this sounds very complicated, do not worry. Many calculations have been done for you by trusted sources such as Harvard University, http://www.health.harvard.edu/newsweek/Glycemic_index_and_glycemic_load_for_100_foods.htm, and the University of Sydney http://www.glycemicindex.com. For a free, ‘2008 International Table of Glycemic Index and Glycemic Load Values’, see http://www.mendosa.com/GI_GL_Carb_data.xls and http://www.mendosa.com/gilists.htm. Mendosa.com is a well-respected resource for people living with diabetes. (Normally this information is available only via a subscription to the Journal of Diabetes Care, or to the American Journal of Clinical Nutrition).[9]

Examples of low GL foods include:

  • Oatcakes, wholemeal bread, baked beans, quinoa, all vegetables, (except for potatoes and parsnips), fish, white meat, eggs, fermented soy, dairy.

Medium GL foods are healthy in moderation:

They release glucose into the bloodstream at a slower rate than high GL foods, but still raise blood sugar to a level where it is likely to overproduce glucose, and some is turned into fat. If you want to lose weight, they should be limited and eaten alongside low GL foods. Examples include:

  • Rye crispbread, rice noodles, parsnips, boiled potatoes, rice milk.

High GL foods are to be avoided:

High GL foods release glucose into the bloodstream fast and raise sugar levels too quickly for the body to cope. The body cannot use all the glucose produced and deposits a large proportion of glucose for storage as fat. Your blood sugar level then crashes – leaving you hungry again (and so the cycle continues). Examples include:

  •  White baguette, muffins, cornflakes, all rice (except for brown basmati), couscous, puffed rice cakes, all potatoes (except boiled new and fingerling potatoes), honey.

Why we need to limit high GL foods:

Blood sugar levels are linked to hunger and the way you eat. High-glycemic-load foods cause a sharp, rapid rise in blood glucose, especially if you do not ‘space’ them over the day. Once in the cell, any glucose that is not used for energy is converted into fat. Insulin then blocks the enzyme that breaks fat into free fatty acids that are used up as an energy source.

Low GL foods are preferable because glucose is released into the bloodstream slowly, helping blood sugar to remain more stable. Maintaining blood sugar at a stable level is the key to steady long-term weight loss as well as preventing diseases such as diabetes[10], and heart disease.[11] Keeping blood sugar steady also prevents the energy slumps that trigger food cravings.

Several factors come into play when calculating the GL of a food:

  • Amount of cooking: Starches in food swell when cooked (whether it is boiled, broiled, baked or fried). The grains in a baked potato swell to the bursting point, whereas the starch grains in brown rice remain relatively unchanged.
  • Amount of processing: When grains are rolled, ground, or mashed, the protective (and harder to digest) outer coating is removed. Whole oats have a lower GI than oatmeal, which is made from steamed and rolled oat grains.
  • Amount of fibre: Some foods naturally have higher amounts of fibre than processed foods such as white rice.
  • Amount of fat: The higher the fat content in a food, the longer it takes to digest.

What you can do to stay healthy at home:

GL values are useful, however sometimes people make the mistake of avoiding high GL foods which contain valuable vitamins and minerals. To stay in optimal health:

Choose good carbs, not ‘zero carbs’.[12] Your brain’s primary fuel is glucose. Carbohydrates provide the body with the fuel it needs for proper organ function. Instead, choose from a wide variety of non-starchy vegetables (every colour in the rainbow).  Also:

  • Replace refined foods with whole-grain products.
  • Eat several small meals a day (to prevent glucose surges).
  • Eat fruits and starchy vegetables together with high-protein or high-fibre foods to slow their blood-spiking potential (this is a new, somewhat controversial method which goes against the principles of food-combining for optimal digestion).
  • Buy foods as fresh and unprocessed as possible and eat them soon afterwards.
  • Eat more raw food. Be adventurous. Try raw zucchini pasta, for example. Cook foods in their whole state, slicing or blending before serving, in order to preserve nutrients.
  • If juicing fruits and vegetables regularly, consider adding dark green leafy vegetables to lower the glycemic load, or add a teaspoon of flax, borage or olive oil. Adding 0.5-1.0 gram of a ‘good’ fat per gram of carbohydrate will likely slow gastric emptying, and the rate of blood glucose increase.[13]
  • Use as little water as possible, preferably steaming, poaching or steam-frying.
  • Avoid frying food. Use less heat, whenever possible. Avoid over-heating or burning food.
  • Use slow-cooking methods whenever possible (braising, stewing, slow-roasting, crock pot).
  • Lose weight if you are overweight.
  • Exercise regularly. The more conditioned you are, the less sensitive your body is to the effects of insulin, and the onset of Type II diabetes.


Instead of Have this
Boxed breakfast cereal Oatmeal or teff porridge
Fried egg and bacon Scrambled eggs on rye toast
Croissant and jam Egg pancake with chia seed fruit gel
Burger and French fries Turkey or chick pea burger and salad
Spaghetti carbonera Zucchini pasta with cauliflower or broccoli –parmesan sauce
Doner kebab Greek pita bread filled with aubergine
Chicken Biryani Brown rice pilaf with curried chicken
Smoked salmon and cream cheese sandwich Cottage cheese with smoked salmon and cucumber
Tea, coffee or cola Rooibos tea, herb teas, freshly made lemonade with stevia, fresh ginger tea

Source: Adapted from Patrick Holford’s, The Holford Low-GL Diet Made Easy, Piatkus Books, London, 2007 p. 74.

If you keep to the low GL guidelines:

  • You will stop producing more glucose than you can use
  • You won’t suffer from food cravings
  • Your body will be reprogrammed to burn fat rapidly.
  • You will also be able to sustain your weight loss over the long term.

[1] Jenkins, D.J., et al, (1981). “Glycemic index of foods: a physiological basis for carbohydrate exchange.” American Journal of Clinical Nutrition, 34; 362-366.

[2] Internationally, there have been inconsistencies between glycemic load and glycemic index ratings. Please see corrected, online reference, approved by the University of Sydney at http://www.mendosa.com/GI_GL_Carb_data.xls.

[3]A raw Canadian carrot, for example, has only 6 grams of carbohydrate per 80 gram/2.82 ounce serving. Its GI is 92, plus or minus 20 points according to the newly revised 2010 GL/GL figures. It carries a glycemic load of only 5.5 per ounce. Cooking method and country of origin will have an effect on the GL ratings. A Romanian carrot, for instance, has 8 grams carbohydrate per serving yet, rates only 1.3 on the Glycemic Load and 16 on the Glycemic Index scale. Comparing these figures to white bread – you would have to eat about a pound and a half of carrots to equal the glycemic index figure for a slice of white bread.

[4]According to Dr. Joseph Mercola, M.D., the glycemic index values contain too many exceptions to be consistently useful. For example, it does not measure how a specific ingredient affects you over time. It also fails to take into account the harm chemicals like sucralose, sorbitol and refined fructose contained in supposedly low-GI foods do to your body. (They convert directly into triglycerides and adipose tissue instead of blood glucose, accelerating obesity, diabetes, hypoglycemia and cardiovascular disease.

[5] Holford, Patrick: The Holford Low –GL Diet Made Easy. Piatkus Books, London, 2006.

[6] For a long time, Dr. Willet and his team did not publish many of the GL numbers. Professor Jennie Brand-Miller, and her associates from the University of Sydney, is credited with calculating the GL of approximately 750 foods. These were originally published in the July 2002 issue of the American Journal of Clinical Nutrition.

[7] According to the USDA foods data base, a 100-gram serving of raw carrots contains a total of 6.6 grams of sugar. Slightly less than a cup (230 mL) of carrot juice would contain 14 grams of sugar. See: USDA Agricultural Research Service. Nutrient Data Laboratory, http://www.nal.usda.gov/fnic/foodcomp/

[8] There are many benefits to juicing carrots. Carrots are high in vitamins B1, B2, B3 and B6, and contain vitamin C. They are also rich in magnesium, calcium and phosphorus. Best of all, carrots contain 77% betacarotene per 100 grams of carrot, which the body then converts to a safe form of vitamin A (hence its name – ‘provitamin A’). The retina of the eye requires vitamin A for optimal vision and to prevent night blindness. Vitamin A is also needed for the immune system.

[9] David Mendosa has been granted permission to reproduce this list from the author, Professor Jennie-Brand Miller of the University of Sydney. Also see: December 2008 journal publication of Diabetes Care, which incorporates data from the December 2002 publication of the American Journal of Clinical Nutrition.

[10] Harvard School of Public Health, ‘The Nutrition Source – Preventing Diabetes’, http://www.hsph.harvard.edu/nutritionsource/diabetes-prevention/.

[11] According to the April 12 2010 issue of Archives of Internal Medicine, high-carbohydrate diets increase levels of blood glucose and harmful fats known as triglycerides, while at the same time reducing ‘good’, protective HDL cholesterol levels. See Science Daily, “Women who eat foods with high glycemic index may be at greater risk for heart disease”,http://www.sciencedaily.com/releases/2010/04/100412161917.htm

[12]Harvard, Op. Cit., ‘The Nutrition Source – Carbohydrates: Choose good carbs, not no carbs’, http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/carbohydrates/

[13] Wolever TM, Bolognesisi C. Source and amount of carbohydrate affect postprandial glucose and insulin on normal subjects. Journal of Clinical Nutrition (1996); 126:2789-806.

Article originally appeared in September 2010 on the IHN website: http://www.instituteofholisticnutrition.com/ihn.asp?section=nutrition_research_glycemic