T Nation

Glycemic Index Flaws


#1

Some interesting information I found.
It seems as if the Glycemic Index has some flaws.

Glycemic Index Deception Finally Understood

A new study shows that diets based on the glycemic index, like the South Beach Diet, do not effectively control blood sugar levels.

The glycemic index, which measures how quickly carbohydrates convert to sugar in your blood, has never been accepted by many dieticians.

This study, which examined food questionnaires from more than 1,000 people over the course of five years, did not find any link between the glycemic index of foods and the blood-sugar levels of participants.

Previous, smaller studies have had different results, including one that seemed to show that a low-glycemic diet lowered risk of heart disease. Supporters of the index claim that foods lower on the index make a person feel full longer and reduce cravings, helping with weight loss...

http://titania.ingentaconnect.com/vl=2930169/cl=13/nw=1/rpsv/cgi-bin/linker?ini=cabi&reqidx=/ij/cabi/00071145/v95n2/s25/p397


#2

Yeah, the Glycemic Index isn't all it's cracked up to be.

The problems with the Glycemic Index are:

-There are so many different charts that have varying values for the same foods. This may be a reflection of the control glucose source (If it was white bread, varying protein contents can affect the GI value), or test subjects.

-The response is different in different people.

-Most foods are eaten in combination with other foods, of which the fat, fiber, and protein content can make the values essentially meaningless.

-All values are based on 50g of carbohydrate. Not all typical servings include 50g, such as carrots, for instance Glycemic Load, which is the product of grams of CHO and GI/100, is thus a better indication.

The Glycemic Index is okay for getting a general idea of where carbohydrate sources rank, but as a tool that can be applied scientifically (i.e. with quantitative values predicting precise glycemic responses), it just doesn't work.

So when you see that Nutrisystem commercial claiming to use the "revolutionary science of the glycemic index," just laugh a little. It doesn't get much more scientific than ranking carbohydrates as "low," "medium," or "high."


#3

Something that might be of interest...

I just read in the March issue of the Journal of the American Dietetic Association that the National Cancer Institute may add Glycemic Load Values to their Diet History Questionnare to ascertain any connections between glycemic index/glycemic load and chronic diseases.


#4

Lol.
Yeah,I always laugh my ass off when I see the "Glycemic diet" on TV.
I just shake my head and wonder how and why on earth do people get pulled into these fad diets.I think the insulin index is much better for those who are watching what they eat.

         [quote]Angelbutt wrote:

Yeah, the Glycemic Index isn't all it's cracked up to be.

The problems with the Glycemic Index are:

-There are so many different charts that have varying values for the same foods. This may be a reflection of the control glucose source (If it was white bread, varying protein contents can affect the GI value), or test subjects.

-The response is different in different people.

-Most foods are eaten in combination with other foods, of which the fat, fiber, and protein content can make the values essentially meaningless.

-All values are based on 50g of carbohydrate. Not all typical servings include 50g, such as carrots, for instance Glycemic Load, which is the product of grams of CHO and GI/100, is thus a better indication.

The Glycemic Index is okay for getting a general idea of where carbohydrate sources rank, but as a tool that can be applied scientifically (i.e. with quantitative values predicting precise glycemic responses), it just doesn't work.

So when you see that Nutrisystem commercial claiming to use the "revolutionary science of the glycemic index," just laugh a little. It doesn't get much more scientific than ranking carbohydrates as "low," "medium," or "high."[/quote]


#5

Hmm,pretty interesting.
They they say what kind of diseases?


#6

Cthulhu-
Take note that the number of respondents actually taken into account in the study was 813, not over 1,000. Many failed to keep their appointment for the follow up exam and thus should have been excluded from the analysis (if they were not excluded or controlled for this would be quite a shortcomming in the methodology employed).

Unless I read the abstract wrong the study was based upon tests run on people and questionaires filled out by the same people with a five year period between the first examination/questionaire and the second examination/questionaire. I don't think that this is methodologically sound enough to warrant the claim that glycemic index is not linked to blood sugar levels. I am not as well acquainted with biological research as are others around here, but my knowledge of statistics and of social research methodology leads me to believe that this study is not as difinitive as proposed above.

All that said, I do not dispute that there are entirely too many glycemic indices out there to make sence of. Nor do I dispute that the concept of a "glycemic diet" is rather flawed.


#7

They weren't specific, but included diabetes, cancer, and heart disease--the biggies--as examples.

They also mentioned intermediate markers such as blood lipids, glycated hemoglobin, and C-reactive protein.


#8

as far as glycemic index diets go i think you guys are looking at it the wrong way..... The point is that when you eat carbs lower on the index they take longer to breakdown and digest so you have a better chance of burning the calories. That's why diets work that are based around the gylcemic index. If your meal should contain 30g of carbs and u are going to eat bread (for example) then the chance of your body burning the calories before they are broken down is greater with multi grain bread than flour based white bread


#9

I am not sure on this, but I think that one issue is that glycemic index has to do with the blood response to food, but not necessarily the absorption of the food in the gut. Also, the insulin response may be different as well. Fat, I believe has a very low GI because it is hard to turn to glucose, has a slow absorption rate, BUT stimulates a large insulin response.

Not sure. Anny clarifications?


#10

You're hitting on some important points.

It's a misconception that the GI is a reflection of the rate of glucose absorption. Regardless of the type of carbohydrate consumed, blood glucose levels peak at the same time. Rather, the GI reflects the level of glucose in the blood after eating a particular food.

This level does not always correspond with insulin levels. Insulin levels do not always correspond with total carbohydrate content, either.

For diabetics, who most would assume would benefit most from the GI, the GI is used second to counting carbohydrate grams, which is most important. The GI is basically a fine-tuning method for controlling blood sugar.