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August Newsletter

Soluble and Insoluble Fiber

By David Mendosa

Wouldn’t it be wonderful if the experts agreed that we should eat more carbohydrates, protein, or fat? But many authorities encourage us to eat less fat and others to eat less protein. Still others recommend a low-carbohydrate diet.

We get only 17 grams of fiber per day.

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Essentially all of them agree, however, that we should eat more fiber. While in the United States we count fiber among the carbohydrates, it’s different, because we don’t digest it and it provides no calories.

We get all our soluble and insoluble fiber from plants. There is no fiber in meat or seafood, dairy products, or eggs.

Soluble fiber dissolves in water and turns to gel during digestion. This helps control diabetes since it slows digestion and the rate of nutrient absorption from the stomach and intestine. It blunts the rapid rise of blood glucose after a meal.

In addition, soluble fiber also helps us to lower our cholesterol by increasing the passage of bile acids through the digestive tract. Then, our bodies remove some cholesterol from our blood to form more bile acids.

Insoluble fiber is chewy and doesn’t dissolve in water. It seems to speed the passage of foods through our stomachs and intestines and adds bulk to the stool.

Typically, we get only 17 grams of fiber per day, according to the government’s third National Health and Nutrition Examination Survey. People with diabetes average even less, 16 grams. In contrast, the American Dietetic Association and the American Diabetes Association say that adults should between 20 to 35 grams per day.

A recent study by scientists at the University of Texas Southwestern Medical Center that was reported in The New England Journal of Medicine compared an ADA-recommended diet of 24 grams of fiber (8 grams soluble, 16 grams insoluble) with a diet of 50 grams of fiber, equally composed of soluble and insoluble fiber. The study concluded that, “A high intake of dietary fiber, particularly of the soluble type, above the level recommended by the ADA, improves glycemic control, decreases hyperinsulinemia, and lowers plasma lipid concentrations in patients with type 2 diabetes.”

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What can we eat to get more fiber—particularly soluble fiber—in our diet? The problem is that most popular American foods are low in fiber. Servings of commonly consumed grains, fruits, and vegetables contain only 1 to 3 grams of fiber. Only okra, brussels sprouts, oat bran, and some beans provide 2 or more grams of soluble fiber per serving, according to James W. Anderson, M.D., Plant Fiber in Foods (HCF Nutrition Research Foundation, 1990).

Most people need to take concentrated fibers to even come close to the ADA’s recommended level. And fiber concentrates are frequently not all fiber, much less soluble fiber. But the main soluble fiber sources, gums—including guar gum, gum arabic, and carob bean gum—pectins and pectin-like fibers such as glucomannan, and psyllium seed husk are more than 90 percent fiber.

Certain fibers such as guar gum and glucomannan absorb lots of water in the stomach and form a gel, producing the sensation of fullness. The best results have been obtained with guar gum, which comes from the Indian cluster bean Cyamopsis tetragonoloba.

Guar gum is practically tasteless and inexpensive. One to three level teaspoons in 8 ounces of water can give you up to 30 more grams of soluble fiber in your diet than you would otherwise get. You must briskly stir it immediately or it will quickly turn to gel in the glass.

Adding a little Splenda makes the guar gum drink taste sweet. Pure vanilla extract made without sugar also improves the flavor.

It is critically important to take guar gum with lots of water. In the late 1980s several weight loss products promoted guar gum. But the Food and Drug Administration eventually recalled them due to reports of esophageal blockage from insufficient fluid intake. However, it remains approved for use as an emulsifier, thickener, and stabilizer as is generally recognized as safe (GRAS).

The other thing to watch for is that a fiber supplement can sometimes result in gas and abdominal discomfort. You can avoid that if you start with a low dose and gradually increase it.

Related Web Site Reviews
Manisha Chandalia et al. “Beneficial Effects of High Dietary Fiber Intake in Patients with Type 2 Diabetes Mellitus.” The New England Journal of Medicine, Vol. 342, No. 19, May 11, 2000, pages 1392-1398.

The full text of this article is free on-line (after registering) at

These researchers assigned 13 people with type 2 diabetes to diets each for six weeks in a randomized crossover study. A diet with a moderate amount of fiber—24 grams, of which 8 grams was soluble and 16 grams insoluble, as recommended by the American Diabetes Association was one diet. The other was high-fiber with 50 grams of fiber, of which 25 grams was soluble and 25 grams insoluble in unfortified foods. They compared glycemic control and plasma lipid (cholesterol) concentrations. Upon completion daily plasma glucose concentration was 10 percent lower with the high-fiber diet. Total cholesterol was 6.7 lower with the high-fiber diet.

M. Sierra et al. “Effects of ispaghula husk and guar gum on postprandial glucose and insulin concentrations in health subjects.” The European Journal of Clinical Nutrition, Vol. 55, No. 4, April 2001, pages 235-243.

The abstract of this article is free on-line on this page

These researchers from Spain’s University of Leon compared the effects of ispaghula husk (also known as psyllium husk) and guar gum on 10 healthy subjects in a randomized crossover study. Both fibers provided a significant decrease in mean serum insulin concentrations after 30 to 90 minutes. Guar gum reduced the area under the insulin curve 39.4 percent, while ispaghula husk brought it down 35.1 percent. Guar gum reduced the area under the glucose curve 2.6 percent, while ispaghula husk reduced it 11.1 percent.

S. Ou et al. “In vitro study of possible role of dietary fiber in lowering postprandial serum glucose.” Journal of Agricultural and Food Chemistry, Vol. 49, Number 2, February 2001, pages 1026-1029.

The abstract of this article is free on-line at

Researchers at China’s Jinan University used four soluble fibers including guar gum and two insoluble fibers to see how they reduced blood glucose levels after meals. They found three mechanisms: they increase the viscosity of the small intestine, which hinders the diffusion of glucose, they bind glucose, which decreases its concentration in the small intestine, and they capsulize starch, which retards alpha-amylase action. All three mechanisms decrease the rate of absorption and concentration of glucose in the bloodstream after meals. 

This article was originally written for the LXN Corp. Web site.

Last modified: October 22, 2012

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