Oh come on, I think we all know that results in science are driven by the needs of those paying the bills. This is just simple interpretation of the reality of our world. Big drug companies have been fined billions of dollars for falsifying data, the US FDA approves chemicals to be added to foods that the US EPA has declared too toxic to be ingested by humans in any amount, and of course Genetically Modified foods are approved with short term feeding studies that legitimate scientists aren't allowed access to for review. It happens, it's part of our existence. And the glycemic thing is helpful, we just have to take the interpretations of those trying to sell you something for what they are.
Anyway, what is the Glycemic Index? This is a very interesting concept and the reality is that although it gives us a measure of how specific food items are digested and broken down within the human digestive system; it is an imperfect and subjective measurement at best, and at worst, it gives pseudo-scientific credence to internet gurus as well as those selling books, supplements and the ideal way of life to unsuspecting people. It isn't the panacea for those that want you to drink the Kool-Aid, even though they want you to believe that it. It isn't snake oil, but it is helpful. Back in 1980 this guy, Dr. David Jenkins working at the University of Toronto developed the concept. Since then, there have been a bunch of other researchers doing the testing to produce their very own GI charts. Probably the one most often cited as gospel on the internet is the one done by Harvard University. The way that the GI is measured is a group of test subjects, usually students needing extra money, are first given control foods to eat. Normal controls are table sugar and then on a separate day, white bread. The blood glucose is then tested over several hours and the changes are plotted as a curve comparing time and rise in blood glucose levels. These are the BASE LINE results and then differing foods are then fed to the test subjects to get similar graphs for each food item and this is then compared to the base line graphs for white bread and sugar. From that comparison we derive the Glycemic Index rating for that particular food. For a very simple explanation of how it is calculated, the Linus Pauling Institute has a great one that's easy to understand. (Linus Pauling)
Now comes the bad part that I have to explain. The whole thing is subjective, and interpretation of the data is not in anyway conclusive proof of any specific individual food item when consumed by any specific individual. The GI charts are drawn up giving a MEDIAN average of individuals with those individuals being young students in much better health and vitality than the people reading about it all. And of course the big one, the chart gives the GI for the food items that the researchers chose to test. It may have very little to do with the diet that you or anyone else might be consuming. It has little to do with the food I eat. And in fact a huge portion of it just doesn't make any sense at all. Although the Harvard chart states that 30 grams of a baguette has a glycemic index of 95, a 30 gram portion of a hamburger bun has a GI of 61. That part is hard to understand, a baguette by definition is nothing but flour water salt and yeast whereas most hamburger buns contain High Fructose Corn Syrup. So how does that work out? The chart also tests commercial baked breads that aren't common in the Western US with most of those that have high percentages of cracked or unprocessed whole wheat to have much lower GI numbers than plain processed whole wheat flour breads. This makes sense as plain wheat kernels have a GI of 30. I can't examine those breads to determine how they were made but since they are commercial brands I can only assume they are made as cheaply and quickly as all the commercial brands made around here. Now comes the part where we can't really use the GI charts to determine what's good for us or not. When the Harvard, and well all the others doing this testing, did their research, they don't tell us how the foods they test were prepared. We do know that the big ways to make whole natural foods healthier for us are soaking, sprouting, fermenting and steaming. All of these preparation techniques make food better for us by breaking down the lectins and phytic acids and they also breakdown the cellular structure to make them more digestible. However, we have no idea if that in anyway alters the GI ratings of any of the foods.
Also one big thing that I do is use a wheat grinder to make my fermented breads. A wheat grinder for home use is a lot different from the high speed roller mills used by commercial flour mills and commercial bakers. We have no idea if that alters the GI rating of the breads that I and a million other home bakers produce. The thing to remember about all of this is that the science behind it all is all subjective and open to interpretation and that even though certain websites out there make big claims (all the Paleo diet gurus wanting you to buy their crap) that it isn't true that a slice of bread has a greater Glycemic Index than table sugar. The truth is that GI charts are just one minor tool that can be used to help you determine what sort of diet you as an individual needs to consume. I think that most reputable doctors and scientists will tell you that your life will be better if you stick to less meat, more unprocessed foods and never ever eat at McDonalds