Glycemic Index and Glycemic Load.  What are they ?

This page about the Glycemic Index and Glycemic Load was last reviewed or updated on 30 May 2016


So what is the Glycemic Index and Glycemic Load ? The Glycemic Load is the GI’s more important and useful sibling

The Glycemic Index measures how quickly a food you have eaten raises your blood sugar (blood glucose). The Glycemic Load indicates how much blood sugar is produced by a food portion.

The GI is calculated in this way. Following a 12 hour fast, the GI score of a food measures the amount of blood glucose, two hours after eating an amount of food that contains 50 grams of net carbohydrates (net carbs in grams minus fibre/fiber also in grams = net carbs). Net carbs are the effective carbs.

All GI measured foods (many have been not been done because calculating it is expensive and takes time), are scored between 0 and 100, based on 50 grams of net carbohydrate eaten. One hundred is the standard, of pure glucose, (a carbohydrate) to which all foods are compared. Sometimes the GI score for white bread is used as the standard which gives an alternative set of GI values for foods. It was once called the bread index.

The GI scores GI numbers of a food/drink between 70 – 100 mean fast (high) blood glucose (blood sugar) conversion; GI numbers between 56 – 69 mean medium glucose conversion; GI numbers between 0 – 55 mean slow (low) glucose conversion.

The fast raising of blood glucose (blood sugar) levels means insulin is called forth quickly out of the pancreas to transport that glucose into cells to be turned into energy.

Insulin and resistance and gout Speedy conversion is more likely, over time, to cause insulin resistance. Insulin resistance in many studies has been shown to raise uric acid blood levels and may be to-day’s  leading cause of gout world wide.

But low or medium GI foods produce glucose more slowly, and thus call forth insulin from the pancreas, more evenly and slowly, and that is better.

Because Glycemic numbers vary, one food may increase blood glucose more, and more quickly, than another despite both containing an equal, or more or less equal, amount of net carbohydrate. And therefore they also produce  different amounts of blood sugar and therefore insulin at different speeds.


Now, why is there a Glycemic Index and Glycemic Load ? The Glycemic Index is useful but it does not explain how much blood sugar is produced by a typical food portion. So the Glycemic Load (GL) concept was developed. The key point here - it indicates how much a serving of food is likely to increase your blood sugar, which makes it more relevant than the GI.

The GL scores  The Glycemic Load of foods is scored in this way. For one serving a GL of 20 + is high blood sugar/glucose; 11-19 is medium (better); 10 and under is low (best). It is calculated by multiplying the grams of net (i.e. effective) carbs in a food  portion x  that food’s Glycemic Index number, divided by 100.

The GL can mean less glucose is produced  The Glycemic Load can make quite a difference to how you perceive the net carbs in a food. Here are some examples and a story. The good news is the Glycemic Load can allow you to eat more of something you like if it is low.

Here’s a story which demonstrates the effect of the GI and GL on blood glucose production. I remain on a low carb diet, but am now losing weight at a slower level, quite deliberately. I thought  I had remembered the net carbs in bananas correctly but it turned out I was wrong – by about 100%. I began eating a pudding (dessert) of mashed bananas – about 100 grams of cream (which is  low carb) and some artificial sweetener.

I was eating a bit too many carbs at least in the bananas’ dish.The carbs in that pudding are around 22 grams. It turned out that the Glycemic Load of bananas is borderline low/medium, which meant  bananas’ carbs  did not  have too much effect on my blood sugar. I did not stop losing weight. In other words, the carbs may be above my daily allowance, which would normally lead to higher blood sugar and more insulin called for, but if the GL is low or lowish, the carbs won’t have such an effect.

The Glycemic Index and Load can mean less disappointment When you judge a food by its net carbs it might be a disappointment because the carbs can mean (in restricted  carb dieting), you must be very cautious about how much of that food you eat. But check the GI and GL and you may get a pleasant surprise. Precisely how much you can eat is not now determined only by its net carbs.

If you are on the Atkins diet, by doing this you have shifted slightly away from it. How much more to eat, when the GL is low,  is some guesswork, so be careful and monitor for any negative effect on your weight loss.

Here’s an example of being able to eat more. Parsnips can be  a fairly costly vegetable in carbs terms at 13.1 net carbs grams per 100 grams of parsnip.  This might be easy to fit into a daily allowance of 60 carbs a day, even 40, but it might not. Especially if you want to eat other favourites which are high carb too. However, the real number for its effect on your blood sugar is less. How much less than 13.1 is a bit of guesswork but it will be less because the GL of parsnips is only about 5, which puts it into the low category.

HIgh GI and high GL  What about potatoes ? Just about evertyone loves potatoes but these vegetables are foods you have to be very careful about on a low or restricted carb diet, because they are high in carbs. There are many numbers for potatoes but I'll take just one type of potato to illustrate the point. 

The GI of a small boiled white potato weighing 150 grams is 82 which is a high number. When 82 is multiplied by the number of carbs in 150 grams and divided by 100, the GL is 21 (1), which is high

.Or how about a high GI but low GL? Watermelon is a good example of this. It has a very high GI of 76, but a low GL for the amount usually eaten because it has only a small number of effective (net) carbs. Carbs per 100 g 7.55 minus 0.4 fibre (fiber) = 7.51 The GL is 7.51 x 76/100 = 5.7 which is low (10 and under).

GI and GL can be used as an extra tool in restricted carbohydrate dieting, or as a diet in themselves. You can find books about the GL/GL in online bookshops.

You can look up Glycemic Index and Glycemic Load numbers here. If not there try Google searches elsewhere.

(1) Harvard Health - Glycemic Index and Glycemic Load for 100 foods 


Visit our first page about a new development in gout treatment, using the Glycemic Index

The Atkins diet is not the only low/restricted carbohydrate diet, but it's the most famous. Go to our first page about gout and the Atkins diet.

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