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How Do You Do Fiber?
April 7, 2009
An article in the March/April 2009 issue of Diabetes Self-Management, entitled “Counting Carbohydrates Like a Pro” and written by Gary Scheiner, MS, CDE, has provoked a lot of comments and questions from readers. Many of the questions concern how to deal with fiber when counting the carbohydrate in a meal or snack.
In the article, Scheiner recommends subtracting all the grams of fiber from the total carbohydrate before calculating the carbohydrate grams (or “choices,” if you prefer) in a meal. But many readers have heard different advice on this, and they want to know why.
One reader, for example, said she thought the correct thing to do was to subtract half the grams of fiber. Another reader said that a dietitian had instructed him to subtract only the amount of fiber over 5 grams.
I decided to investigate.
I found that the 2007 edition of Choose Your Foods: Exchange Lists for Diabetes, published by the American Diabetes Association (ADA), recommends subtracting half the grams of fiber from the total carbohydrate when eating foods with more than 5 grams of fiber per serving. So if a serving of food contained 8 grams of fiber, you would subtract 4 grams. If the food contained fewer than 5 grams of fiber per serving, you would subtract none of them before calculating the carbohydrate grams or choices in your meal.
Another consumer guide, the American Dietetic Association Guide to Eating Right When You Have Diabetes, published in 2003, says that you can subtract all the fiber from the total carbohydrate but that doing so may only be necessary if your meal contains 5 or more grams of fiber. It goes on to say, “And it may only be necessary for those who are being precise with their carbohydrate intake and adjusting a rapid- or short-acting insulin based on how much carbohydrate they are eating.”
Similarly, the Joslin Guide to Diabetes, published in 2005, says that “most people can also ignore the dietary fiber amount,” but that those who “are trying to be very precise with the carbohydrate amount” can subtract all of the fiber if there’s more than 5 grams of it in the meal. It concludes, “Dietary fiber is not absorbed, but it is unlikely that 5 to 10 grams will have much effect on your blood glucose level unless you eat more than one serving.”
I don’t know where the dietitian who advised subtracting the amount of fiber over 5 grams got that information.
According to an ADA representative, the advice in Choose Your Foods is based on nutrition guidelines published by the Institute of Medicine, the medical arm of the National Academy of Sciences. Those guidelines state that some of the soluble fiber in food can be broken down by bacteria in the large intestine hours after the meal, making calories available to the body.
However, soluble fiber usually represents a small proportion of the total fiber in food, and the portion that is broken down becomes fatty acids, not glucose. You wouldn’t think that fatty acids would raise blood glucose, but according to nutrition experts Madelyn L. Wheeler, MS, RD, and Xavier Pi-Sunyer, MD, MPH, writing in the April 2008 Supplement to the Journal of the American Dietetic Association, one of the three types of fatty acids produced, called propionate, is gluconeogenic in human beings, meaning that it can be turned into glucose in the body.
The author of our article Counting Carbohydrates Like a Pro says he recommends subtracting all of the fiber, regardless of the total amount present in the food eaten, because he has seen no noticeable blood glucose rise from fiber, whether soluble or insoluble.
Given the small amount of fiber most Americans eat, subtracting half versus all may not make much of a difference for most people most of the time. However, it could lead to hypoglycemia (low blood glucose) if a person who was highly sensitive to insulin ate a high-fiber meal and took insulin to cover carbohydrates that weren’t, in fact, going to raise his blood glucose.
What have you been told to do about fiber when counting carbohydrate? And what do you actually do?
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