Inulin: The 'In' Fiber
Fiber is the forgotten carbohydrate. Inulin, naturally derived food fiber, may just change all that.
By Mark Anthony, Ph.D., Contributing Editor | 04/04/2005
Mention the word carbohydrate at a party and you’ll likely get into a discussion about low-carb diets. Talk will rarely drift to fiber. We don’t think of dietary fiber as a carbohydrate. But for the most part dietary fibers are made of the very same building blocks as the sugars and starches currently in the health news limelight. They’re just put together differently. For example, cellulose, the most dominant carbohydrate on the planet, consists of chains of glucose molecules — as does the starch of rice or potatoes. The difference is the bonds linking the glucose molecules together in cellulose cannot be severed by our digestive enzymes. So while starch is systematically disassembled in the small intestines to provide energy, cellulose remains untouched and passes to the large intestines where it provides necessary bulk.
Most of us have heard of cellulose, even if under the epithet “fiber” instead of “carbohydrate.” However, there’s another ubiquitous carbohydrate fiber we rarely hear about — inulin — and it’s about to become more familiar. Inulin is the star in a class of compounds called fructans, plant storage carbohydrates made of chains of fructose rather than glucose units. Like cellulose, inulin resists digestion because of the bonds holding the sugar molecules together.
Its unique properties make inulin unlike cellulose. Consisting of relatively short chains of sugar molecules, inulin acts as a soluble fiber providing the type of bulk that aids the body’s absorption of calcium and magnesium in the small intestine. In the large intestine, inulin is broken down by beneficial bacterial through fermentation to yield short chain fatty acids. These beneficial products are believed to aid in the prevention of colorectal cancer.
Inulin has been a healthful part of our diet for thousands of years. It occurs naturally in over 36,000 plants, including many common foods such as bananas, wheat, asparagus, onions, garlic, leeks and Jerusalem artichokes. (One of the most abundant sources is chicory, the roots of which have been ground and used as coffee substitutes for decades.) As we process more foods, we lose the many beneficial properties inherent in this unique carbohydrate. To compensate for this loss, and with an eye toward adding greater health benefits to our modern cuisine, food manufactures embarked on a new food frontier: the creation of “functional” foods — food compounds added to the diet which provide two or more nutritional benefits.
Inulin leads a group of functional foods called fructooligosaccharides and characterized by their chains of two to 60 fructose units linked together like a string of pearls. Inulin is a mixture of these oligosaccharides. Recently food manufacturers learned to manipulate inulin to modify its properties. Inulin is first washed out of ground chicory roots by hot water, then treated with enzymes to break longer fructose chains into smaller pieces. The resultant product, oligofructose, is a mixture of fructose chains from two to seven units long. Chains of fructose can also be built by adding fructose molecules to a seed of sucrose using the process of fermentation. These products or fructooligosaccharides can be built to specified chain lengths.
Carbohydrates such as inulin are considered “prebiotics.” A prebiotic is a nondigestible carbohydrate that stimulates the growth of beneficial bacteria naturally residing in the colon. These helpful bacteria are referred to as probiotics. Probiotic bacteria, specifically bifidobacteria and lactobacilli, promote health by inhibiting the growth of harmful pathogens thus reducing the potential for infections. Other potential benefits of prebiotics may include the reduction of the risk of colorectal cancer.
The combined effect of prebiotics and probiotics is called the synbiotic effect. Many foods contain both prebiotics and probiotics. For example, yogurt and cheese contain live lactic acid bacteria plus various fructans—a potent symbiotic combination. Some natural cheeses supply both probiotic bacteria and inulin.
The secondary goal in adding inulin and other nondigestible carbohydrates as functional foods is to meet consumer demands of taste and texture in modern processed foods without adding calories. Shorter chain oligosaccharides can be used to provide sweetness, while longer chain products mimic the mouthfeel of fats. In a weight-conscious modern world, taste and texture of low-calorie foods often gains more followers than long-term health benefits. But if the immediately tangible effects of the addition of this class of functional foods is matched by long-term health gain, all the better for the consumer.
Fructan — naturally occurring carbohydrates containing linked fructose units
Inulin — a naturally occurring fructan
Oligosaccharide — short chains of sugars, usually less than 60 linked sugar molecules
Oligofructose — oligosaccharides consisting of fructose molecules
Prebiotic — a non-digestible food item that stimulates the growth of beneficial bacteria existing naturally in the colon
Probiotic — cultures of beneficial bacteria that reside in the healthy colon and tend to suppress inflammatory responses
Synbiotic — the combined beneficial effects of prebiotics and probiotics.