Your blood glucose levels rise and fall when you eat a meal containing carbohydrates. How high it rises and how long it stays high depends on the quality of the carbohydrates (the GI) as well as the quantity. Glycemic Load (or GL) combines both the quantity and quality of carbohydrates. It is also the best way to compare blood glucose values of different types and amounts of foods. The formula for calculating the GL of a particular food or meal is:
Glycemic Load = GI x Carbohydrate (g) content per portion ÷ 100.
For example, a single apple has a GI of 38 and contains 13 grams of carbohydrates.
GL= 38 x 13/100 = 5
A potato has a GI of 85 and contains 14 grams of carbohydrate
GL=85 x14/100 = 12
We can therefore predict that the potato will have twice the glycemic effect of an apple.
Similar to the glycemic index, the glycemic load of a food can be classified as low, medium, or high:
Low: 10 or less
Medium: 11 – 19
High: 20 or more
The GL of a mixed meal or diet can simply be calculated by summing together the GL values for each ingredient or component. For example, if breakfast was composed of 2 wheat biscuits (GL = 15), ½ a cup of milk (GL = 4) and 2 teaspoons of sugar (GL = 6), its overall GL would be 25 (15 + 4 + 6).
For the whole day, a low GL diet has a GL less than 100 g/% for people consuming 8,700 kJ. Therefore, for people consuming 3 meals per day, a low GL meal would have a GL ≤ 33 g/%.
For optimal health, you should aim to keep your daily glycemic load under 100.
Should I use GI or GL?
Although the GL concept has been useful in scientific research, it’s the GI that’s proven most helpful to people with diabetes and those who are overweight. That’s because a diet with a low GL, unfortunately, can be a ‘mixed bag’ full of healthy low GI carbs in some cases, but too high in protein and low in carbs and full of the wrong sorts of fats (i.e., saturated) such as those found in some ‘discretionary foods’. If you use the GI as it was originally intended – to choose the lower GI option within a food group or category – you usually select the one with the lowest GL anyway because foods are grouped together for a reason because they contain similar nutrients, including amounts of carbohydrate. So, if you choose healthy low GI foods, at least one at each meal, chances are you’re eating a diet that not only keeps blood glucose ‘on an even keel’ but contains balanced amounts of carbohydrates, fats and proteins.
What is the Glycemic Response?
After eating a meal, the digestible or available carbohydrates are absorbed into the blood stream, producing an increase in blood glucose concentration. In time and in response to its tissue disposal, facilitated by the hormone insulin, the blood glucose concentration falls back to or below fasting levels. The magnitude of the rise and fall of blood glucose and the duration over which it occurs has been termed the glycemic response. More slowly digestible carbohydrates or minimally processed starchy foods produce a different response. Compared with rapidly digestible carbohydrates they show a slower and more prolonged increase in blood glucose, rising to a lower peak. Other factors include how much food you eat, how much the food is processed and even how the food is prepared For example, pasta that is cooked al dente has a slower glycemic response than pasta that is overcooked.