Prebiotics are carbohydrates that act as food for the beneficial bacteria that live inside the human digestive system.
Prebiotics are part of foods that cannot actually be digested by humans, but are instead broken down by intestinal flora.
They are often referred to as soluble fiber and include:
- inulin (also called chicory root fiber),
- fructooligosaccharides (FOS),
- galactooligosaccharides (GOS).
Because they are indigestible, prebiotics contain essentially no calories. They pass through the stomach and small intestine unaltered. When they enter the large intestine, however, these carbohydrates encounter bacteria that can break them down. Because they contain essentially no calories, they are attractive to food manufacturers that want to increase the fiber content or sweetness of foods.
Inulin is added to food because it adds fiber yet does not affect taste or texture. Although it is not a fat, it has a similar ‘‘mouth feel’’ and as a result food manufacturers use it in dressings, margarines, and ice creams as a fat replacement.
Oligofructose is used as a binder in granola bars, much like sugar but with fewer calories and more fiber. It also helps make low-fat cookies crisp and adds body to dairy products. Combined with other sweeteners, it is used to replace sugar and to mask the aftertaste of aspartame and acesulfame potassium, two artificial sweeteners.
Like inulin and oliogfructose, fructooligosaccharides are found in chicory, but they are also found in bananas, artichokes, asparagus, garlic, and onions. In foods, fructooligosaccharides are used as sweeteners.
Galactooligosaccharides are carbohydrates made up of of oligogalactose with some lactose and glucose. Like FOS, GOS are used as sweeteners.
The major benefit of prebiotics is that they nourish the beneficial bacteria that live symbiotically in the the large intestine, or colon, specifically bifidobacteria or bifidus. They may have additional benefits, including but not limited to preventing constipation, and lowering blood cholesterol.
Fructooligosaccharides may also help alleviate traveler’s diarrhea, as well as help increase mineral absorption and decrease cholesterol and triacylglycerol levels. However, more research with human subjects needs to be conducted.
GOS have been found to help alleviate constipation in elderly people, increasing the frequency and ease of bowel movements. In infants who received infant formula that included GOS, the consistency and frequency of bowel movements became comparable to those of breast-fed infants. However, studies on the effect of GOS on digestive difficulties in adults have been inconclusive.
Prebiotics may cause increased flatulence because of bacterial fermentation of undigested fiber, and excessive intake can lead to stomachache and diarrhea.
Inulin is extracted from chicory root through hotwater diffusion, and then is purified and dried. It naturally contains between 6 and 10% sugar (fructose, glucose, and sucrose).
Oligofructose is made in a similar manner, but after the extraction process it undergoes a process called hydrolysis, and the result is a carbohydrate that contains approximately 5% of the natural sugars mentioned. The molecules of oligofructose are shorter than those of inulin.
Fructooligosaccharides are made by further breaking down inulin, or by treating sucrose (a type of sugar) with Aspergillis niger, while GOS are formed by the action of enzymes on lactose, a milk sugar.