Prebiotics: Oligosaccharides
Definition of a prebiotic
By definition, a prebiotic is a non-digestible food ingredient that beneficially affects the host (you and me) by selectively stimulating the growth and activity of specific “friendly” bacteria in the intestinal tract. In other words, prebiotics are foods not for us, but for our “good” bacteria because they stimulate their growth in our digestive tracts.
Benefits of prebiotics
By promoting the growth of one or more species of “healthy” bacteria, the environment of the gastrointestinal tract naturally benefits. Typically, bifidobacteria and lactobacilli are the organisms that grow best when prebiotic foods are ingested. The net advantage is that these “healthy” bacteria are deleterious to “harmful” bacteria such as bacteroides and clostridia.
At present, the two prebiotics for human use, that have been most widely studied, are inulin and oligosaccharides. Oligosaccharides are commonly produced by breaking down inulin. This process happens naturally in the body when inulin is ingested. The purpose for manufacturing the oligosaccharides, and not just using something like chicory root, is that the manufactured product is more “pure” and has stronger thickening abilities, as well as a “smoother” taste. Therefore, more “consumer appeal” is added to foods that it is used in.
Sources of oligosaccharides
Both human and cow’s milk does contain some naturally occurring oligosaccharides. Oligosaccharides are also found in small amounts in many foods. Inulin is naturally found in the following food:
chicory root
dandelion root
burdock root
Jerusalem artichoke
Artichokes
Onions
garlic and other roots
wheat
asparagus
raisins
prunes
Beneficial effect on sugars
It is now widely accepted that the sugars oligofructose and inulin selectively stimulate growth of bifidobacteria (Wang and Gibson 1993). In turn, bifidobacteria inhibit the growth of E. coli and Clostridium perfringes, two potentially disease-causing microorganisms (Gibson et al 1995; Wang and Gibson 1993). Additionally, we know that a naturally occurring sugar, called raffinose (which comes from inulin and is found in these same roots), stimulates the growth of lactobacilli (Tortuero et al., 1997). Lactobacilli suppress growth of numerous disease-causing micro-organisms by producing acids, peroxides and specific bacteriocins, just as bifidobacteria do.
The Lactobacillus and Bifidobacteria actually digest the inulin for us, and then increase as much as 5 to 10 times in volume. A synergistic relationship is developed, where the whole is greater than the sum of the parts. While inulin is not well known as a supplement or functional food (food that provides health benefits beyond basic nutrition), it is a natural substance that is found in more than 35,000 plants and vegetables throughout the world. Because it is a natural plant product to which humans have been widely exposed, the risk of allergic reaction or intolerance when it is added to foods is significantly minimized.
USDA allowed claims
The USDA allows for structure function claims, provided an efficacious dose of inulin is consumed based on clinical or literature references, and provided inulin is a part of the nutritional make up of the food.
Some of the structure function claims that could be made with inulin include:
“helps promote the growth of bifida bacteria”
“helps promote healthy digestion”
“helps maintain healthy cholesterol levels”
With the exception of structure-function claims regarding calcium, absorption for which higher inulin levels would be needed, most of the structure function claims about inulin fall into the 5g/day category.
Inulin
Natural inulin, or “native inulin,” is normally found in chicory root. It is a mixture of short, medium, and long-chain inulin. FOS, and oligosaccharides, when added to products as ingredients, are all manufactured products made by first extracting the inulin by the use of hot water extraction, and then using enzymes to break down the inulin. Usually inulin from chicory root is used.
Inulin is generally stable for baking, but it will break down some when heated. When inulin breaks down, the fructose chains break apart. This basically means you just added a little bit of fructose to the product and lose a bit of fiber. Inulin will break down very rapidly in very acidic solutions under pH 3.5 (the stomach usually contains a pH of around 2.0).
On average it is estimated that Americans eat less than 3 grams of inulin per day. Historically, humans have eaten significantly large amounts of inulin. The highest food concentrations occur in dahlia tubers, burdock roots, chicory roots and greens. Unfortunately these foods are not eaten in large amounts today. Sixteenth century Europeans consumed about 35 grams of inulin daily, while 19th century Central and South Americans consumed up to 100 grams daily!
Because inulin is a soluble fiber, it helps maintain normal bowel function, decreases constipation, lowers cholesterol and triglycerides, and helps normalize blood sugar levels. Everyone would benefit from more fiber in his or her diet. This is particularly true for people battling diabetes. Inulin doesn't raise blood sugar, or require insulin to metabolize it. Research is demonstrating that the nutritional value of inulin goes beyond what is typical of most classic fibers.
Calcium Absorption Booster
On average, we only absorb about 30% of our ingested calcium. Most people don't realize this. While our Recommended Daily Intake of calcium is 1000 mg, we need to ingest that amount just to provide ourselves with about 300 mg that we can actually absorb and use. During the human growth stage, there is a higher absorption rate.
The absorptive ability of the intestine decreases with age, however. There are other factors that also positively encourage the absorption of calcium: the presence of vitamin D, magnesium and phosphorus. The negative effects of phytate and oxalate found in plants bind with the calcium and make it unavailable. Too much protein and sodium in the diet cause increased excretion of calcium as well. Calcium is a nutrient that many people, particularly women, need to absorb more of.
A recent study on calcium absorption
A recent study compared the absorption of calcium of 29 teenage girls between the ages of 11 and 14, who normally consumed a calcium-rich diet. During the study, the girls drank calcium-fortified orange juice, containing either the inulin or a placebo, as part of a 1300 milligram calcium diet. The girls repeated the study. Those who had received the inulin during the first phase then got the placebo, and vice versa. None of the girls knew when the juice contained inulin or the placebo until the study was completed. Calcium absorption was monitored, using non-radioactive "tracers."
The results of the study
While on the placebo, the girls' 1300 milligram calcium diet yielded 416 milligrams of absorbed calcium, which was about what researchers expected. But while taking the supplemental inulin, absorption jumped 18 percent, to an average of 494 milligrams. This has implications for even greater results with those consuming a lower calcium diet. If the overall percent of absorption of calcium can be increased, this has broad appeal for helping those who are at risk for developing osteoporosis.1 Inulin has been shown to increase the absorption of other minerals as well, such as magnesium and iron.2,3
The effect of inulin on cancer
Inulin has potential to have a beneficial effect on cancer prevention as well. Bifidobacteria digest inulin to create short-chain fatty acids like propionic acid and butyric acid. Butyric acid has been shown to have cancer-preventing properties in the large intestine.4 There has also been animal research to suggest that inulin prevents pre-cancerous changes in the colon.5 More research needs to be done to be able to claim such positive effects, but the studies look promising.
All gastrointestinal-related disorders can be attributed, to some extent, to low-fermentable fiber diets. “If U.S. consumers actually knew that…most autoimmune diseases like Crohn’s disease, rheumatoid arthritis and diabetes have a link to diets low in fermentable fiber…they would be a little less concerned about their bowels and more concerned with the health-promoting properties of natural fibers like inulin,” presumes Tungland.
References:
1. Abrams, Steven, et al: Paper at World Congress of Pediatric Gastroenterology and Nutrition. August 2000.
2. Lopez, HW, et al: Fructooligosaccharides enhance mineral absorption and counteract the deleterious effects of phytic acid on mineral homeostasis in rats. J. Nutr. Biochem. 2000 Oct;11(10): 500-508.
3. van den Heuvel EG; et al.: Nondigestible oligosaccharides do not interfere with calcium and nonheme-iron absorption in young, healthy men. Am J Clin Nutr, 1998 Mar, 67:3, 445-51.
4. Spiller, GA: Dietary Fiber in Health and Nutrition. Boca Raton, FL: CRC Press, 1994.
5. Reddy, BS, et al: Effect of dietary oligofructose and inulin on colonic preneoplastic aberrant foci inhibition. Carcinogenesis. 1997 July;18(7):1371-1374.
Criteria for a prebiotic
Indigestible
In order for prebiotics to be effective, they must not be digested, nor be broken down in the harsh conditions of the digestive tract. This means prebiotics must reach the intestines (where the majority of bacteria reside) still intact. Therefore, prebiotics must be resistant to stomach acids, pancreatic enzymes, and digestive juices in the upper portions of the gastrointestinal tract.
Fermentation
Once prebiotics reach the large intestines, the sugars are fermented by bacteria (broken down by chemical reactions) into relatively simple substances that serve as energy sources for bacterial growth.
Interestingly, bacterial species differ in the types of sugars required for rapid growth. For example, early studies found that bifidobacteria grew well on fructose-type sugars, while lactobacilli, E. coli, and Clostridium perfringes grew poorly on these sugars (Cummings et al. 2001).
The effect of changing our diet
Since diet is the main factor that determines which bacteria live in our guts, it makes sense that the composition of gut normal flora can be modified through food; by changing our diet. Most intestinal bacteria get their energy from the “leftovers” that are passed on to them (the things we can not digest). They survive by metabolizing the carbohydrates in our gastrointestinal tracts that we haven’t used.
These sugars come from undigested food residues and our own mucus secretions. The quality and type of carbohydrates available for bacterial use depends mostly on the extent that these sugars do not get absorbed or used by the upper parts of the digestive tract. Any unabsorbed and undigested sugars that reach the bacteria living in the lower portions of our intestines are available to be metabolized and broken down by bacteria in a process called fermentation. Once these carbohydrates are broken down, the resulting products are primarily short-chain fatty acids and gases, namely hydrogen and carbon dioxide.
Protecting against colon cancer
When it comes to protecting against colon cancer, using a combination of prebiotics and probiotics seems to have greater protective effects than using either prebiotics or probiotics alone (Reddy et al. 1997; Rowland et al. 1998).
For example, in laboratory experiments, administration of Bifidobacterium longus (a probiotic organism) decreased the incidence of pre-cancerous changes in rats’ intestines by 26%, inulin (a prebiotic carbohydrate found in chicory root) reduced the incidence by 41%, but the combination of Bifidobacterium longus with inulin reduced the incidence of these changes by 80% (Rowland et al., 1998).
Also, for unknown reasons, inulin appears to have a greater protective affect against colon cancer than oligogructose (Reddy et al. 1997). Other studies also support anti-cancer effects of prebiotics. For example, the growth of experimental tumors was reduced in mice fed non-digestible carbohydrates (15% inulin, oligogructose or pectin) compared with mice receiving a placebo (starch) (Taper et al. 1997).
The theories
Although the reasons for protective effects of prebiotics are unknown, there are several theories. For example, inulin stimulates changes in gastrointestinal mucus that exert protective effects, and are associated with a reduced risk of colon cancer (Fontaine et al. 1996).
It is also possible that prebiotics stimulate protective enzymes in the gut (Treptow-van Lishaut et al. 1990). Additionally, it is clear that when wheat bran and other starches are fermented by probiotic bacteria, there is increased production of butyric acid in the gut.
Research has consistently shown butyrate directly stimulates cell growth in normal cells, while simultaneously inhibiting growth of cancerous cells. In fact, in cancerous cells, butyrate may even trigger a programmed cell death to prevent growth and spread of tumors (Hague et al., 1995; Marchetti et al., 1997).
Another way butyric acid protects against intestinal damage is by stimulating increased production of protective enzymes in the gastrointestinal tract (glutathione transferase) (Treptow-van Lishaut et al., 1990). Indeed, butyric acid is an important energy source for colon cells, and its presence also protects from damage caused by harmful cancer-causing chemicals (Abrahanse et al., 1999).
Summary
There is strong evidence for prebiotic effects in humans
There is strong evidence that prebiotics have beneficial effects on bowel habits in humans
There is promising evidence that inulin may increase calcium absorption in humans
There is preliminary evidence that inulin may have beneficial effects on lipid levels in the blood stream
There is preliminary evidence in experimental animals that probiotics have preventative effects on colon cancer (Van Loo et al. 1999)
Although the study of probiotics is a relatively new field, it is an area of research that is rapidly expanding. With all the positive health benefits that can be derived from prebiotics and probiotics, it is only a matter of time before both of these are commonplace in our diets.
In theory, it is possible to ingest sufficient amounts of prebiotics through dietary means alone. Numerous fruits and vegetables contain probiotic sugars. Examples that you may find in the produce department of your local store include onions, garlic, leeks, chicory, bananas, asparagus and Jerusalem artichokes.
You may also note Fructooligosaccharides (often referred to as FOS) on ingredient labels. Fructooligosaccharides are used for their thickening properties in items like bread and dairy products.
However, for most people that are eating a typical American diet, they probably only consume about 2 grams of oligosaccharides a day. This is considerably less than optimal. Research indicates that at least 4-8 grams of oligosaccharides are needed to significantly change gut flora for the good. Most clinical trials have used 10-15 grams. Because this is such a large amount, most people trying to re-establish good flora resort to taking FOS containing supplements.
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