In his article “Carbs: Are they Good or Bad for You?”, Andrew writes about carbohydrates and touches on the glycemic index (“GI”) which is the rate at which different foods raise your blood sugar levels. Furthermore, in his article: “How Do We Get Fat?”, he explains how high blood sugar levels lead to fat storage and increase. Today we will delve further into this crucial topic in nutrition and briefly distinguish glycemic index vs glycemic load.
The GI level is measured by feeding 10 individuals a particular food containing 50g of carbohydrates and then taking blood samples every 15 minutes to measure their blood sugar levels. Then the same 10 people are given 50g of glucose and blood samples are once again taken. Their blood sugar response to the test food is compared to their response to the test glucose which has a GI of 100. The GI of the test food is then calculated by taking the average GI value for the 10 people expressed as a percentage. So if the GI of the test food was given a value of 75, then it means that eating this food produces a rise in blood sugar which is 75% as great as a rise in blood sugar after eating an equivalent amount of glucose.
The GI is a useful tool/measure to help understand which foods have a higher impact on blood sugar levels, however when considered on its own it can be a bit misleading because it is actually the combined effect of the amount of carbohydrate ingested as well as a food’s GI level that counts. What I mean is the GI does not take into account the portion size you are eating.
To explain this concept further let us take a high GI food like watermelon. You may shy away from eating watermelon because it has a high GI of 72 (except immediately after a workout when it is ideal to take high GI foods), however the average slice of watermelon weighs only about 120g which equates to about 6g of carbohydrates which is not enough to raise your blood sugar level significantly (source: The Complete Guide to Sports Nutrition). You would need to eat quite a bigger serving of watermelon in order to consume 50g of carbohydrates (the amount of carbohydrate used in the GI test to develop the GI of the food). This concept is known as the Glycemic Load (“GL”). So in the case of watermelon, although the GI is high, its GL is low.
The GL gives you a more accurate measure of the rise in your blood sugar and insulin levels and can be calculated using the following formula:
Using the watermelon example the GL for the watermelon is (72 x 6g)/100 = 4.3. Even though a food may have a high GI, depending on the amount of carbohydrate per serving, the GL may be low. The table below summarizes the values for Low, Medium, and High Glycemic Load:
The following shows a graphical representation of the effect on blood sugar for high GL vs low GL foods:
If you want to optimise glycogen (energy) storage and minimise fat storage then aim to eat foods that will provide a low to medium glycemic load and stick to a balanced combination of protein, carbohydrates and fat. So fear not, there is no need to cut out high glycemic foods so long as you eat them immediately after a workout, in smaller proportions, or combined with protein and/or a little healthy fat to slow down the rise in blood sugar. Managing the speed at which your blood sugar rises will create a lower insulin response and as a result less of a chance for fat storage.
To fitness with love,