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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 (JAMA 2008; 300(23):2742-2753). Their goal was to see if the Hemoglobin A1C (a measure of diabetic control) improved on either diet, and as a secondary goal, they also looked at whether that diet helped improve the participants' cholesterol scores as well.
Fiber for Breakfast!
Studies have shown that those who eat more fiber have a reduced risk of obesity and type 2 diabetes, but it's not clear whether this is an effect of the fiber itself, nor what type of fiber has this effect.
Being overweight decreases positive effects of high-fiber diet
Back in January I wrote about C-reactive protein (CRP), a blood marker of inflammation, which is related to chronic diseases like heart disease, diabetes, and cancer (Overweight? Here's another reason to lose the excess, 1/12/07). Several other studies have suggested that one way to control the levels of CRP in the bloodstream is diet, particularly a high-fiber diet. In a study published in the Archives of Internal Medicine this week (2007;167:502-506), researchers at the Medical University of South Carolina tested that theory by recruiting 35 men and women to participate in a dietary study.
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Fiber to Prevent Weight Gain
We know that a high fiber diet can help prevent cancers and reduces your risk of heart disease and diabetes. Those with high cholesterol levels can help improve their scores by getting more fiber in their diet, as well. All of these conditions are associated with being overweight; could getting more fiber in your diet actually help you avoid gaining weight? And if so, does it matter whether your fiber intake is from soluble fiber (from fruits, vegetables and oats) or insoluble fiber (whole grains like whole wheat grains and cereal grains such as rice or seeds)?
An international team of researchers utilized data gathered from a study performed in 5 European countries, including about 90,000 people and lasting almost fifteen years (Am J Clin Nutr 2010;91:329-36). At the beginning and end of the study, each participant was weighed, their height recorded and their waist measurements taken. In addition, at the start of the study the participants filled out a detailed food frequency questionnaire to assess their regular diet.
The researchers then totaled the amount of fiber each subject ate from fruits and vegetables or from whole grains. They then compared those totals to the changes in each person's weight and waist circumference from the beginning and the end of the study.
They found that those participants who ate more than 10 grams per day of fiber from all sources actually lost a small amount of weight, on average, over the course of the study. ("Small" meaning less than one-tenth of a pound per year.) Similarly, their waist measurements also decreased by a very small amount (about 1 millimeter per year).
But what's really interesting is that when the researchers further looked at what types of fiber people were eating, they saw that those who were getting their 10 grams of fiber from cereal grains (including foods such as rice, pasta, breads and breakfast cereals) were those least likely to gain weight or waist circumference. Those whose 10 grams of fiber per day was primarily from fruits and vegetables gained about the same amount of weight and waist circumference as those who actually ate the least fiber.
What this means for you
The results from this study suggest that eating more insoluble fiber (from cereals and whole grains) than soluble fiber (fruits and vegetables) may help you avoid weight gain over time. There have been other studies that suggest that if you're trying to lose weight, a higher fiber diet can help increase the amount of weight you lose over a diet with the same amount of calories but less fiber. What we do know is that higher fiber foods help you feel more satisfied and that most people don't get enough fiber from any source. Get more fiber - of any kind! - in your diet by choosing whole grains whenever you can and snacking on fruits and vegetables. Here's a guide to making better fiber choices.
First posted: April 14, 2010