Glycemic load

Glycemic load estimates the impact of carbohydrate intake using the glycemic index while taking into account the amount of carbohydrates that are eaten in a serving. GL is a GI-weighted measure of carbohydrate content. For instance, watermelon has a high GI, but a typical serving of watermelon does not contain many carbohydrates, so the glycemic load of eating it is low. Whereas glycemic index is defined for each type of food, glycemic load can be calculated for any size serving of a food, an entire meal, or an entire day's meals.

Glycemic load of a 100g serving of food can be calculated as its carbohydrate content measured in grams (g), multiplied by the food's GI, and divided by 100. For example, watermelon has a GI of 72. A 100 g serving of watermelon has 5 g of available carbohydrates (it contains a lot of water), making the calculation (5 × 72)/100=3.6, so the GL is 4. A food with a GI of 90 and 8 g of available carbohydrates has a GL of 7.2 (8 × 90/100=7.2), while a food with a GI of just 6 and with 120 g of carbohydrate also has a GL of 7.2 (120 × 6/100=7.2).

For one serving of a food, a GL greater than 20 is considered high, a GL of 11–19 is considered medium, and a GL of 10 or less is considered low. Foods that have a low GL in a typical serving size almost always have a low GI. Foods with an intermediate or high GL in a typical serving size range from a very low to very high GI.

One 2007 study has questioned the value of using glycemic load as a basis for weight-loss programmes. Das et al. conducted a study on 36 healthy, overweight adults, using a randomised test to measure the efficacy of two diets, one with a high glycemic load and one with a low GL. The study concluded that there is no statistically significant difference between the outcome of the two diets.[2]

Glycemic load appears to be a significant factor in dietary programs targeting metabolic syndrome, insulin resistance, and weight loss; studies have shown that sustained spikes in blood sugar and insulin levels may lead to increased diabetes risk.[3] The Shanghai Women's Health Study concluded that women whose diets had the highest glycemic index were 21 percent more likely to develop type 2 diabetes than women whose diets had the lowest glycemic index.[4] Similar findings were reported in the Black Women's Health Study.[5] A diet program that manages the glycemic load aims to avoid sustained blood-sugar spikes and can help avoid onset of type 2 diabetes.[6] For diabetics, glycemic load is a highly recommended tool for managing blood sugar.

The data on GI and GL listed in this article is from the University of Sydney (Human Nutrition Unit) GI database.[7]

The GI was invented in 1981 by Dr Thomas Wolever and Dr David Jenkins at the University of Toronto and is a measure of how quickly a food containing 25 or 50 grams of carbohydrate raises blood-glucose levels. Because some foods typically have a low carbohydrate content, Harvard researchers created the GL, which takes into account the amount of carbohydrates in a given serving of a food and so provides a more useful measure. Liu et al. were the first to show that based on their calculation, the glycemic load of a specific food—calculated as the product of that food's carbohydrate content and its glycemic index value—has direct physiologic meaning in that each unit can be interpreted as the equivalent of 1 g carbohydrate from white bread (or glucose depending on the reference used in determining the glycemic index).[8][9][10][11] It became immediately apparent that such direct physiological quantification of glycemic load would allow patients with diabetes to do “glycemic load” counting as opposed to the conventional “carbohydrate counting” for monitoring the glycemic effect of foods.[12][13][10][11] The concept of glycemic load addresses the concern about rating foods as good or bad solely on the basis of their glycemic index. For example, although the glycemic index for carrots is reported to be as high as 1.31 times that of white bread, the glycemic load for one serving of carrots is small because the amount of carbohydrate in one serving of carrots is minimal (≈7 g carbohydrate). Indeed, ≈700 g carrots (which provides 50 g carbohydrate) must be eaten to produce an incremental glucose response 1.31 times that of 100 g white bread (which also contains 50 g carbohydrate) Special notes : it's a received idea due to a mistake in 1980, carrots do not have a GI (glucidic index) similar to white bread. They have 19 when they are raw and 47 (moderate) when they are boiled. Source : [14] [15][16][10]

All numeric values provided in the table are approximate. Note that 100g may not represent a typical serving size. For example, a typical rice serving would be 150-200g with a corresponding increase in GL, whilst a banana may weigh more than 100g. Reference tables which give GL by typical serving size will show different values.