Use of the glycemic index is an excellent way to choose healthier food however it doesn’t give the complete picture. If you are serious about using this powerful and effective tool for health and weight loss you also need to know about the glycemic load.
The way GI (glycemic index) was determined is that took an amount that had 50g of carbohydrates and then determined how rapidly it raised the blood sugar. But the problem with this is every food has a different percentage of carbohydrate content. For example a corn tortilla is about half carbohydrate, 48% to be precise. So it would take about a hundred grams (very slightly higher) to get the 50g of carbohydrate out of corn tortillas.
On the other hand watermelon being very high water content only has 5% carbohydrate. So now you are going to need a whopping 1000grams of watermelon just to get the same 50grams of carbohydrate.
In other words you need almost 10 times as much watermelon as you do corn tortillas to get the same 50g of carbos. So choosing foods by glycemic index alone is a little misleading which is why they came up with the glycemic LOAD.
The glycemic load is more realistic because it counts the carbs in a usual and customary portion size (rather then how rapidly 50g will raise blood sugar). So to figure out the glycemic load of a serving of food you divide the glycemic index of that food by 100 and then multiply by the grams of carbos in that serving.
To demonstrate let’s go back to our watermelon example. You take the glycemic index of the food, with watermelon it’s 72 and you divide by 100. That gives you .72. Now let’s say you have a 100g slice of watermelon that would mean there is only 5g of carbohydrate (remember watermelon is 5% carbohydrates). So you multiply the .72 by the 5g (of actual carbos) and you get a glycemic load of only 3.6.
If you run the same calculation on corn tortillas you would get a whopping glycemic load of 25 which is vastly greater then the measly 3.6 of watermelon.
And yet watermelon has a higher glycemic index (GI of 72) then corn tortillas at 52. Corn tortillas are considered to have a LOW glycemic index (anything 55 or less is low) and watermelon is considered to have a HIGH glycemic index (anything 70 or above is high). Yet it’s just the opposite when you look at the glycemic load.
Just like there is a scale for the glycemic index so there is a scale for the glycemic load which is as follows: 10 or less is low. Medium is 11 – 19 and 20 or more is high.