Fiber is a vital part of a healthy diet, aiding in digestion and normalizing transit time, or the passage of food through the digestive system. It sounds contradictory, but adequate fiber relieves both constipation and diarrhea. Fiber provides indigestible bulk and soaks up liquid to promote healthy bowels. It is very important to eat fermentable fiber foods.
Fiber plays another important part in the digestive process. Fiber contains simple sugars known as oligosaccharides. Oligosaccharides encourage fermentation throughout the intestinal tract, providing nutrients to beneficial intestinal microbes, or probiotics. Increasing the health and population of intestinal bacteria improve nutrient absorption, reduces symptoms of irritable bowel syndrome and protects against Clostridium difficile, a strain of potentially-deadly bacteria capable of causing life-threatening diarrhea and colon inflammation.
Soluble and Insoluble Fiber
Fiber may be soluble or insoluble. Soluble fiber partially dissolves in water, forming a gel-like substance which slows digestion, producing feelings of fullness. Because soluble fiber slows stomach emptying, it affects blood sugar levels and may help prevent insulin sensitivity or diabetes. Soluble fiber also reduces the absorption rate of LDL cholesterol (often referred to as Bad cholesterol).
Insoluble fiber doesn’t dissolve. Instead, insoluble fiber adds bulk to diets, while acting as a laxative. While most dietary soluble fiber comes from fruits, vegetables, and nuts, the bulk of insoluble fiber comes from whole grains and vegetables.
Sources of Oligosaccharides
Three types of oligosaccharides are known for their ability to increase probiotics and improve digestion: inulin, fructooligosaccharide and galactooligosaccharide. All three prebiotics (nutrient sources for microflora) can be found in fiber supplements, fruit, and vegetables.
Inulin is naturally present in asparagus, bananas, garlic, leeks, onions, and wheat. Fructo-oligosaccharides are present, to some extent, in most fruits and vegetables, including asparagus, garlic, and onions. Barley is also a good source of fructooligosaccharides. Galacto-oligosaccharides are found in most legumes.
Like most digestive aids, fiber is best consumed in moderation: too much can cause intestinal cramping and flatulence. However, most of us don’t get sufficient fiber in our diets. The average American only consumes 15 grams of fiber a day.
The exact amount of fiber we need depends on our body weight, metabolism, and microflora, but according to 2005 Dietary Guidelines for Americans, most men should aim for 30 to 38 grams of dietary fiber, while women should ingest approximately 25 grams.
If you have difficulty meeting your daily fiber requirements, supplements can provide much-needed prebiotics. Prebiotin, for instance, contains high concentrations of inulin and other oligosaccharides to provide a daily dose of prebiotics.