Randy Kidd, DVM, PhD
In recent years we've become more and more aware of the important relationship between diet and health for both ourselves and our pets. Recent pet food scares have made this relationship even more evident for pet caretakers. As a result, consumers are now looking for food sources for their pets that support health above and beyond providing basic nutrition. In this article, we'll take a look past basic nutrition at beneficial food ingredients called prebiotics and probiotics that are present in natural foods or can be added to prepared foods.
In both natural and prepared foods, prebiotics and probiotics create health benefits related to their interactions with the microflora (tiny organisms) in the animal's digestive tract. In addition, both prebiotics and probiotics apparently have health-providing activities of their own, independent of interaction with the digestive tract.
The health benefits of prebiotics have only come to light in recent years, but recognition of the beneficial effects of probiotics actually dates back to the 19th century when the French scientist, Louis Pasteur, postulated the importance of microorganisms to human life. These ideas were further reinforced by the work of 1908 Nobel Prize-winner Elie Metchnikoff.
So, what exactly are prebiotics? They are, by definition, non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth of one of a limited number of beneficial bacterial species in the colon. Beneficial bacteria include Bifidobacteria and Lactobacilli, which have the potential to improve host health, while at the same time working to inhibit the growth of pathogenic, "bad-guy" microorganisms. In other words, prebiotics are "health food" for beneficial bacteria.
For a food ingredient to be classified as a prebiotic, it has to be demonstrated that it is:
Not broken down in the stomach or absorbed in the GI tract.
Fermented by the gastrointestinal microflora.
Selectively stimulates the growth and/or activity of intestinal bacteria associated with health and well-being.
Probiotic bacteria, when taken together with prebiotics that support their growth, are called "synbiotics" that promote the probiotics' benefits. Several commercial products available for both humans and pets now contain prebiotics, and other products contain both prebiotics and probiotics.
Commonly available prebiotic oligosaccharides (oligosaccharides are carbohydrates composed of varying numbers of sugar molecules) include the following:
Fructo-oligosaccharides - Also referred to as "FOS" or "neosugars", they are composed of units of fructose (the sugar commonly found in many fruits and honey) that are resistant to digestion in the upper digestive tract. FOS act by stimulating the growth of Bifidobacterium species in the large intestine. FOS food components are found in a number of common foods, including garlic, onions, leeks, wheat, bananas, asparagus, and artichokes.
Fructo-oligosaccharides are classified as prebiotics because they have the ability to selectively promote the growth of healthy intestinal bacteria (such as bifidobacteria and lactobacilli) at the expense of the less friendly putrefactive (capable of producing foul-smelling by-products) bacteria such as bacteroides, clostridia, and other coliforms. Bifidobacteria produce acetic and lactic acids, which inhibit the growth of pathogenic bacteria and stimulate intestinal peristalsis.
Inulins - Thse are a group of naturally occurring fructose-containing oligosaccharides. In commercially available products, the inulins are usually derived from the roots of chicory (Cichorium intybus) and Jerusalem artichokes, (Helianthus tuberosus); other plant sources include dandelion, burdock, wild yam, jicama, agave, onion, and garlic. Inulins stimulate the growth of Bifidobacterium species in the large intestine.
Most commercially available products that contain prebiotics for pets use the roots of chicory as their source. Chicory, also known as "Blue Sailor" grows wild along the highways throughout the Midwest United States. Roasted chicory roots are often used as a coffee substitute, and chicory coffee is considered a treat in some parts of the country. Dogs seem to like the bitter taste of chicory, and chicory root is also used to improve the texture of some human foods, which may add to its appeal for dogs.
There are several other classifications of prebiotics, including: soy oligosaccharides, lactilol, lactosucrose, pyrodextrins, and isomalto- and xylo-oligosaccharides. Many of these are being used, in Japan and other countries as either food supplements or for treating specific diseases. Some are still considered experimental and can only be used by prescription in the U.S., though many are now being commercially developed here.
Interestingly, it has been found that human milk also contains a significant level of unique oligosaccharides, which are similar to the fructo-oligosaccharides. These prebiotics are known to provide various health-promoting properties for the infant, including: protecting the baby's intestinal tract from unwanted pathogenic bacteria, lowering the risk of diarrhea, modulating important immune responses in the baby, and, according to recent evidence, helping prevent skin allergies.
Here is how prebiotics work: Prebiotics are essentially health food for probiotics, meaning that they act to enhance the growth and colonization of the good-guy micro-organisms of the intestinal tract, including species of the Bifidobacteria and Lactobacilli bacteria. In addition, prebiotics may have a number of other beneficial actions, including:
antimicrobial, hypolipidemic (decreasing circulating fats in the bloodstream)
glucose-modulatory (the ability to help maintain normal blood glucose levels) activities
Prebiotics may also play a role in improving mineral absorption and thus decrease bone thinning in older (human) patients. And, as mentioned, they may also play a role in the health of the young, especially as related to skin allergies.
Most of the actions of the prebiotics are currently under study, so specific actions are not always known. However, the following is a brief rundown of some possible ways the prebiotics work to enhance health:
Anticarcinogenic (anti-tumor) activity of prebiotics is not well understood, but it may be related to the beneficial bacteria's ability to produce substances that arrest the growth of cancer cells. Prebiotic oligosaccharides may also aid in increasing the concentrations of calcium and magnesium in the colon, which helps control the rate of cell growth.
Finally, vitro and animal data suggests that the bifidobacteria and lactobacilli bacteria can bind to and inactivate some carcinogens, directly inhibit the growth of some tumors, and inhibit bacteria that may convert precarcinogens into carcinogens.
Antibiotic activity of the prebiotics may be accounted for by their growth-promoting effects on bifidobacteria and lactobacilli. These bacteria can reinforce the barrier function of the intestinal mucosa, helping in the prevention of the attachment of pathogenic bacteria, essentially by crowding them out. These bacteria may also produce antimicrobial substances and stimulate antigen specific and nonspecific immune responses.
Prebiotic activity to lower triglyceride and blood glucose levels are less understood, but the effects have been noted in many users, especially in humans. In addition, human osteoporosis may respond to prebiotics, possibly because the bacterial fermentation of the oligosaccharides facilitates the colonic absorption of calcium and possibly magnesium.
A recent trial compared human breast-fed babies with bottle fed babies, with some of the formula-fed infants receiving prebiotics. The results strongly suggest that formula supplemented with prebiotics can modify the bowel bacteria and so reduce the chance of children developing atopic dermatitis. The results of this trial might indicate that prebiotics could have a role in helping to prevent allergic dermatitis in our pets. Stay tuned for more information.
In addition to providing intestinal and general, overall health, some prebiotics have been used pharmaceutically for the treatment of a variety of diseases, including the following:
Inflammatory bowel disease
A variety of tumors
Protect against osteoporosis
Help correct problems of fat or glucose metabolism
Prebiotics are not recommended for those who are hypersensitive to any component of a prebiotic-containing supplement. That is, anything added to the prebiotics to make it more marketable may be a problem. There are also some prebiotics that are prescription only. Use of these needs to be monitored by your veterinarian, but even high doses of prebiotics are tolerated by most. Some users may experience transitory gastrointestinal symptoms such as flatulence, bloating, or diarrhea.
Not much is known about the correct and effective dosage levels of prebiotics for dogs or cats, but preliminary evidence seems to indicate that very low levels (0.3% of a dog's diet) are most effective and produce the least number of side effects (bloating, gas, etc.) I feel that the best way to supplement any nutrient is to go to the source. In this case, herbs such as dandelion root, burdock root, and chicory are easy to find, organically grown in your own backyard or found at your local health food store. Simply sprinkle a pinch or two of the herb ground up, fresh or dried herb, atop the pet's food every day or so and your pet will not only receive a healthy dose of prebiotics, he'll get the added benefits of the whole herb. Note that when wild-harvesting plants, be cautious of plants that could have picked up toxins, especially the lead from the exhaust of passing cars. You should also check with your holistic vet for recommended doses and methods of adding the prebiotics and probiotics to your pet's food.