Dietary fiber is a term that is used for plant-based carbohydrates that, unlike other carbohydrates (such as sugars and starch), are not digested in the small intestine and so reaches the large intestine or colon.
Soluble and insoluble fiber:
You may have heard of the terms ‘soluble fiber’ or ‘insoluble fiber’– these are words that are sometimes used to describe the types of fiber in our diet. Although scientific organizations argue that these terms are no longer really appropriate, you may see these terms being used, with soluble fiber including pectin and beta glucans (found for example in foods like fruit and oats) and insoluble fiber including cellulose (found for example in whole grains and nuts). What is important to remember is that fiber-rich foods typically contain both types of fiber.
Current evidence from American Diabetes Association suggests that high-fiber diets, especially of the soluble variety, and soluble fiber supplements may offer some improvement in carbohydrate metabolism, lower total cholesterol and low-density lipoprotein (LDL) cholesterol, and have other beneficial effects in patients with non-insulin dependent diabetes mellitus (NIDDM).
Effects of High-Fiber Diets on Patients with Diabetes:
Two major approaches have been used to study the effects of fiber on carbohydrate metabolism in diabetes: the first uses purified fiber such as guar and pectin, and the second increases the fiber content of the diet with normally available fibers. There are different sources of fiber that may have very different effects, depending upon the dose of fiber taken. Soluble and insoluble fibers whose effects may counteract each other have been used in combination. The addition of the unabsorbable polysaccharides guar and pectin reduced postprandial glycemia in both normal and diabetic subjects, often with a reduced need for insulin secretion. The fibers that were most effective were those with the highest viscosity, which may be related to an effect on the slowing of gastric emptying, or limited diffusion of digestive products. To be effective, the fiber had to be incorporated into the food, because fiber that was given in capsule, sprinkled on food, or taken before a meal was found to be ineffective. The ingestion of fiber with one meal was found to retard the hyperglycemia with a second meal. Non viscous fibers such as those found in wheat bran had less marked effects than the viscous fibers that were reported to be successful. The acute effects of fiber may be dose dependent. Both glucose and insulin responses were lowered in diabetic subjects given test meals supplemented with a total of 26 g guar and pectin. Glucose response fell 30% in IDDM and from 30 to 60% in noninsulin- dependent diabetes mellitus (NIDDM) with a 42 to 60% decrease in the insulin response.
Study by Aaron and David published in Diabetes Care Journal reported that the reduction in the insulin response was not found with 9-18 g but did occur with 26 g, suggesting a dose-dependent effect.
Recommendations for the Use of Fiber:
Foods include legumes, roots, tubers, green leafy vegetables, all types of whole-grain cereals (including wheat, barley, oats, corn, and rye), and fruits. Fruit such as berries, pears, melon and oranges, Vegetables such as broccoli, carrots and sweetcorn, Peas, beans and pulses, Nuts and seeds, Potatoes with skin. Fruits and vegetables should be eaten raw and not pureed, which causes loss or reduction of the fiber effect. Abdominal cramping, discomfort, and flatulence can be minimized by starting with small servings and increasing gradually.
Fiber supplementation appears beneficial only if given with a diet comprising approximately half of the calories as carbohydrate. Foods should be selected with moderate to high amounts of dietary fiber from a wide variety of choices to include both soluble and insoluble types of fiber.