A study on the value of the Glycemic Index of food, released in February 2006, claims that there is no correlation between the glycemic index and blood sugar levels. Let's evaluate this study.
First, of course, it's important to understand what the glycemic index is. I have a Full Definition of Glycemic Index, but in short, glycemic index is how quickly a given food kicks up your blood sugar levels. If you eat white rice, it makes your blood sugar levels spike high - then plummet again when the sugar is absorbed. This roller coaster effect is of course not great for you. If you eat brown rice instead, it is absorbed slowly by your body - so you get a nice, smooth influx of sugar. This is easier for your body to handle. Even if both had the "same carbs", the brown rice would be better for you.
Now, on to the study, discussed in the British Journal of Nutrition. They asked 1,000 people about their eating habits - high glycemic or low glycemic - over 5 years. So far, so good. However, apparently they only tested the blood sugar levels of the people TWICE! TWO TIMES! Doesn't this seem a little odd to you? Note that it seems so odd to me that I'm personally writing the study lead, to get exact clarification on this.
The whole point of glycemic index is that when you eat a food, you have something happen shortly after you eat it. But say you ate a plate-load of Ring Dings at noon. Say your sister ate a plate-load of broccoli at noon. If you tested both of your blood sugar levels the next day, they'd probably be the same! Nobody was ever saying that eating Ring Dings would *permanently* affect your blood sugar levels for the rest of your entire lifetime. If it did, then you wouldn't have the roller-coaster effect, where your blood sugar levels spike high, then trough down low, enticing you to eat more sugary food. We wouldn't have the "Chinese Food Effect" where you eat a lot of starchy Chinese food, get a high from it, then feel really hungry again when you come down from that high.
In a press release, the study lead explained that part of her issue with glycemic index numbers is that they were determined in a lab and are always estimates, subject to situational adjustments. That is, if you ate a carrot on an empty stomach, it might be absorbed differently than if you ate it after eating 2 tons of whole wheat bread.
Sure, that's true! That's true with anything. That's true with alcohol. If you drink alcohol on an empty stomach, it reacts differently than alcohol with a meal. If you eat an orange, it is absorbed differently than if you drink orange juice. Heck, if you eat a super sweet variety of apple, you get more calories/carbs/etc. than if you eat a really non-sweet variety of apple, but all of the charts only have one "apple" value.
Life is like that. No number is absolute. All numbers are guidelines. Still, if you know the *range* of a celery stick is really low, and that the *range* for a piece of pineapple is really high, it gives you relative weights to start working with.
There have been other studies that have shown that low glycemic foods do help maintain an even keel and therefore control hunger. For example, a study done at the Boston's Children's Hospital had a group of people eat low glycemic food and another eat high glycemic food. Later THAT SAME DAY, the people who ate the high glycemic food were hungry again, quickly. It's the Chinese Food effect. This is the way you test the impact of glycemic index issues - not over five years.
Read the study details for yourself, to see how glycemic index should actually be tested.
High Glycemic Study Details
Similar High Glycemic Study at Oxford