As discussed last time, the GI is an index that measures the rate at which blood glucose levels rise in response to a 200 calorie portion of a particular food relative to the rate at which the same amount of either raw glucose or plain white bread will raise blood glucose levels. Glucose and white bread, the basis foods (either one or the other is used), are assigned values of 100, and all other foods are assigned values to indicate how they compare to this standard.
A food that scores 55 or lower is generally considered to be a low-glycemic food; a food that scores above 70 is considered to be a high-glycemic food. Those that score between 55 and 70 are considered to be of middle glycemic values.
One major problem with this methodology, however, is that the CALORIC DENSITY of foods varies tremendously. This is a practical issue that greatly sabotages the utility of the GI. Consider, for example, that a person can more often than not readily consume 200 calories of chocolate because it is a very calorie dense food item.
On the other hand, it is definitely not so easy for one to consume 200 calories of carrots or celery in a single sitting because most of the volume of these food items is accounted for by water and fiberâ€"neither of which contributes significantly to the total caloric content. So, what we have here is a case of comparing apples to oranges... or so to speak! So, is there a viable solution to this quandary?
Well, what if one were to compare the glucose response of certain foods while defining the absolute VOLUME of the foods ingested and taking into account only the usable energy within that prescribed volume (ie the serving size)? Now we can make a direct comparison between the effects of chocolate and the effects of carrots on blood glucose levels based upon BOTH the GI AND the amount of food ingested. A brilliant solution to the aforementioned practicality problem, is it not? This method of gauging glucose levels is known as the Glycemic Load (GL).
The Glycemic Load
The Glycemic Load is an index, devised by Jennie Brand Miller, a researcher in Sydney Australia, that takes into account both the Glycemic Index of the food in question and the amount of energy-providing carbohydrate that is available per serving. Because it takes into account the practical information concerning an edible serving size, the GL is a much more functional tool than the GI alone. A GL value of ten or less is considered low, and thus indicates that a serving of a particular food with this value will likely result in a slow and gradual increase in blood glucose levels. On the other hand, a serving of a food with a GL of 20 or greater will likely result in rapid blood glucose spikes.
Foods that possess GL values between 10 and 20 inclusively typically stimulate moderate responses in glucose levels. As previously noted, in order to calculate the GL of a given substance, one must know both the GI value of the food and the number of caloric carbohydrates per given serving (fiber provides no substantial calories, so it is not considered in the caloric carbohydrate count). The two numbers are simply multiplied together and subsequently divided by 100. So let us look at a carrot as an example of how this works. A carrot has a very high GI value of 131. However, there are only four grams of carbohydrates total (16 calories) within this single carrot.
Hence, to obtain the GL of this carrot, which represents a single serving, we calculate (131 x 4)/100 = 5.24. We see from this example that a serving of carrots, although having a very high GI value, in fact possesses a very low GL value. This is accounted for by the fact that most of the volume of the carrot is fiber and waterâ€"substances that contribute no calories. With this information, we can safely predict that a carrot will provide a person with substantial amounts of nutrients and appetite-suppressing bulk, while simultaneously deterring rapid and unwanted glucose spikes.
Knowing ONLY the GI value of the carrot would NOT have indicated such results! So fellow warriors and seekers, it appears as though the GI has indeed been challenged by a rather formidable opponent! However, we would be rash to throw in the towel at this time; for the GI has a thick beard and can take a very heavy punch! Moreover, it is crucial to recall that the very strength of the GL directly depends upon the tested merit of the GI!
No, GI fans, it is not necessary to call the fight just yet. The cagey veteran may have given up a couple of rounds, and he may at this time have his back against the ropes... but hands are high as he continues to bear the brunt of the load! Yes, he staggers and stumbles back to the neutral corner. But for NOW at least, the GI has been saved by the bell! To be continued...