http://www.med.nyu.edu/content?ChunkIID=38396 Quotes from the article: "The glycemic index measures blood sugar response per gram of carbohydrate contained in a food, not per gram of the food. This leads to some odd numbers. For example, a parsnip has a glycemic index of 98, almost as high as pure sugar. If taken at face value, this figure suggests that dieters should avoid parsnips like the plague; however, if you’ve ever eaten a parsnip, you know that it’s not exactly candy. In fact, parsnips are mostly indigestible fiber, and you would have to eat a few bushels to trigger a major glucose and insulin response. The reason for the high number is that the glycemic index rates the effects per gram of carbohydrate rather than per gram of total parsnip, and the sugar present in minute amounts in a parsnip itself is highly absorbable. The high glycemic index rating of parsnips is thus extremely misleading. Books such as The Glucose Revolution take care of issues like this on a case-by-case basis by saying, for example, that you can consider most vegetables “free foods” regardless of their glycemic index. But in fact the same considerations apply to all foods and distort the meaningfulness of the scale as a whole. A different measurement, the glycemic load (GL), takes this into account. The GL is derived by multiplying the glycemic index by the percent carbohydrate content of a food. In other words, it measures the glucose/insulin response per gram of food rather than per gram of carbohydrate in that food. Using this system, the GL of a parsnip is 10, while glucose has a relative load of 100. And remember the potato problem, that terrible bogey of GI diets? The GL of a typical serving of potato is only 27—not such a bogeyman at all. Such numbers make a lot more sense."
It's worthwhile to understand the difference between glycemic index and glycemic load. Various groups on the web (anti-carbers in particular) are using glycemic index as their yardstick and declaring numerous foods to be in the "danger zone" and to be avoided. It's a faulty way of assessing the blood glucose response of foods. The same groups are assuming that a high glycemic index will also cause insulin spikes, which isn't necessarily true either. Conversely, there are some foods with a relatively low glycemic index that cause a moderate to high response of insulin (yogurt and beef are examples, although this is often ignored by anti-carbers). Another issue with glycemic index is that the measurements are made on test subjects after they have fasted and have eaten only the test food by itself. This doesn't take into account eating the food while not fasted or when eating it with other foods (a mixed meal) which can result in a lower rise in blood glucose compared with what resulted for glycemic index test conditions. Still another issue is that the glycemic index does not consider satiety. Some foods are relatively high in glycemic index yet low in glycemic load and high in satiety. Such foods are usually desirable for health and weight management, as they don't spike blood glucose and they impart a feeling of fullness. Potatoes are an example.
I would pretty much agree with this. The glycemic index is very deceptive, and there are just too many variables that cause people's blood sugar to respond differently to certain foods. I mean, take fructose for instance. It is relatively low on the glycemic index, yet is still perhaps the biggest contributor to the obesity epidemic. So yeah, for the most part the glycemic index is completely bunk, yet there are some very popular diets, such as the South Beach Diet, which are based upon the glycemic index. Not surprisingly, these diets often fail to get people's blood sugar under control, unlike a truly low carbohydrate or ketogenic diet. A low-carbohydrate, high-fat ketogenic diet can not only get a person's blood sugar under control in a matter of days or weeks, but it can also reverse / cure Type II diabetes in people who have it almost just as quickly. To make it simple, the only carbohydrates people should really be eating (granted they're looking to improve their health) are those which come from green, fibrous vegetables and seeds such as chia and flax. Certain low-sugar fruits are fine when eaten in moderation, also. Things like dairy can have a pretty high glycemic, insulinogenic response in some individuals as well, though for me I tolerate full-fat dairy products extremely well, and things like heavy cream and cheese are staples in my diet.
