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Which is more important: a food's glycemic index or its fiber?
There has been a lot of good research about the impact of a higher fiber diet on helping control blood sugars. We have less information about the impact of glycemic index (GI) on diet and diabetics but what we have is getting better. One study in 2008 compared a low glycemic index diet with a high cereal fiber diet and the diabetics on the low GI diet did slightly better.
Low Glycemic Index vs. High Fiber Diet: Which is Better for Diabetics?
There's been a lot of talk about low-glycemic-index diets being better for helping diabetics control their blood sugars, but the studies that have been done tend to be small and of short duration. Back in 2008 researchers in Canada decided to improve on past studies by designing a larger, more long term study to compare the effects of a low glycemic index diet with a high cereal fiber diet.
Hunger, Blood Glucose, and the Glycemic Index
We don't exactly know how the feeling of hunger is caused in the body. One theory, first formulated in the 1950's, is that low levels of glucose in the brain are a cause of the feeling of hunger and the increase in appetite that goes along with it. More recent theories expand on that theory by speculating that it's the changes in blood glucose levels that lead to the feeling of hunger.
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Glycemic Index (GI) is a concept that has been around for decades and has moved in and out of favor for use with weight loss and for diabetics. It's a great tool in many ways, but it does add another number to learn and there has long been debate as to whether diets that specifically use foods with a low GI are effective.
GI is based on the speed with which sugars in foods will reach your system. The value is measured as a percentage of glucose, since it is a sugar that reaches the blood stream very quickly. Pure glucose is given the value of 100, while a banana has a value of 56 and the GI of lentils is 30. This is significant because of important research showing that how high our blood sugars peak after meals appears to be important in the development of illness such as diabetes and heart disease.
A study published in this week's Archives of Internal Medicine (2006:166(14);1466-1475) compares four different diets. Two of the diets are higher in total carbohydrate and two higher in total protein. Each of these were further divided into two plans that contained a greater amount of either low or high GI foods.
The most important finding was that all four diets resulted in weight loss. I want to say that again -- eating fewer of any calories results in weight control. All the groups lost about the same percentage of pounds: right around 5% of total body weight.
Those eating the different GI diets had surprising effects with respect to weight loss. 56% of those eating a high carbohydrate / low-GI diet lost more than 5% of their body weight. Interestingly, 66% of the high protein / high-GI dieters also lost more than 5% of weight. Even though high protein / high-GI group lost weight at a higher rate, the high carb / low-GI group had a better outcome with respect to their risk factors for heart disease. They had a greater loss of fat mass and reduction of their LDL (bad) cholesterol in spite of lower weight loss than any of the other diets (although this was not statistically significant).
The other diets (high carb / high-GI and high protein / low-GI) had similar numbers of participants losing weight.
There are a few factors in the results that might have an impact on the validity of the research. The group of high carbohydrate / low-GI dieters may have had better reduction in their cardiac risk factors but they also ate a lot more fiber. Those dieters also ate less fat than prescribed. Another drawback is that this is a small study lasting only 12 weeks. Dietary studies such as this are very difficult to do and the researchers and participants are to be commended. Unfortunately, the results often end up needing more questions to be answered.
Eating fewer calories is better for you. Eating a diet that is higher in more complex carbohydrates is good for you. While there may be finer points to a low-GI diet that prove to be of benefit, this study does not prove that simply eating a diet with more low-GI foods is the best choice. Stick to what we know for sure: a higher carbohydrate (with emphasis on complex carbs), moderate protein, low-fat diet is good for you.
First posted: July 26, 2006