Slamming the glycemic index

Study casts doubt on ‘good carb’ diets
Following glycemic index not effective in controlling blood sugar

The Associated Press
Updated: 2:20 p.m. ET March 6, 2006

COLUMBIA, S.C. – Diets that distinguish between “good carbs” and “bad carbs,” are not an effective way of controlling blood sugar levels, a new study suggests.

But read a bit closer & there are plenty of problems with this study that even just an alert layperson like me can spot.

The new study, published in the February issue of the British Journal of Nutrition, relied on food questionnaires from more than 1,000 people over five years and assessed their consumption of high- and low-glycemic foods.

Food questionnaires are a notoriously unreliable way to get information about what people really eat. People forget. People lie. People eat craploads of refined foods which are almost by definition high-glycemic, It would be far more accurate to get them to keep actual day-by-day food diaries & to check their blood glucose frequently. But that would be too much work & cost too much.

Let’s not forget either that people are doing the assessment of the glycemic levels of the foods that these 1,000+ people wrote down in their food questionnaires: the foods they actually ate were not tested. This introduces at least two problems: (1) all kinds of biases can be introduced in the assessment process; and (2) it is extremely difficult to assess the glycemic index of an untested food.

Researchers tested their blood sugar levels twice during the study period and found no significant correlation between the glycemic index of foods and the blood-sugar levels of participants.

Twice?!!!! They checked them twice?!!!!!

What time of day: in the morning before eating? After a meal, & at what time? After how long a period of time? Geez — a well-controlled diabetic will test her or his blood glucose far more often than that over a five year period!

Let’s also not forget that there are all kinds of additional factors that can affect an individual’s blood glucose. How much stress in their lives, what time of day & how close to a meal their blood was tested, what other health concerns do they have, how much sleep do they get, to name just a few. Were any of these factors controlled for?

I’m not a scientist, but I am an intelligent person who has read quite a helluva lot about GI & blood glucose control since I started on this path in late December. From the details given in the article, I’d say this study’s methodology laughably poor, & its conclusions, at best, inconclusive.

Mayer-Davis said that researchers should develop a new measure of how different carbohydrates can affect health. She said a better index would be based on the physical characteristics of foods, such as fat content and calories, because numerous factors influence a food’s effect on blood-sugar levels.

Of course GI all by its lonesome is not the only factor that will affect blood glucose control. The GI people themselves say that, & say it often. But there is no doubt that paying attention to GI has significant benefits for the blood glucose control of people who are insulin resistant or fully diabetic — as has been demonstrated by numerous studies better-designed than this one appears to have been.

And on the purely anecdotal level, there’s what it’s doing for me.

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