Prebiotics, probiotics, and synbiotics (Sponsored by Iams)


Prebiotics and probiotics promote beneficial intestinal bacteria numbers and improve gastrointestinal and overall health.

It is widely accepted that the intestinal bacterial ecosystem plays a crucial role in gastrointestinal (GI) health and is considered by some to represent an organ.1 The metabolic processes of the various bacteria and the interactions with dietary inputs impact GI tract health and have systemic influences. The natural bacterial population found in the canine and feline gut can be categorized into beneficial and potentially pathogenic groups. Beneficial bacteria can

1. Inhibit the presence of harmful bacteria

2. Stimulate immune function

3. Aid in food digestion and absorption

4. Synthesize vitamins.

The lactate-producing genera, such as Lactobacillus and Bifidobacterium, are commonly recognized for their health-promoting properties.

There is growing interest in manipulating the intestinal flora to increase the relative numbers of beneficial bacteria. Until recently, this enhancement was typically accomplished by providing supplements consisting of a strain or strains of live beneficial bacteria, referred to as probiotics. Presently, nutritional modulation of the intestinal microbiota has expanded into the use of prebiotics, which are nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of beneficial bacteria in the gut and, thus, improve host health. Prebiotics are nondigestible carbohydrates or fibers that resist enzymatic digestion in the upper digestive tract. When the prebiotics reach the colon, they serve as a substrate for the resident bacteria and are digested through fermentation. Unlike other fibers, prebiotics selectively feed the beneficial bacteria.

Client education: Prebiotics in a nutshell

The benefits of prebiotics

Fructooligosaccharides (FOS) have been the most studied prebiotics. FOS occur naturally in several plants (e.g. wheat, bananas, barley, garlic) and are synthesized commercially. Dietary supplementation with FOS positively influences gut health by increasing the concentration of beneficial bacterial populations (bifidobacteria, lactobacilli) and decreasing concentrations of potential pathogens (Clostridium perfringens).2 Increases in the beneficial lactate-producing populations of bifidobacteria and lactobacilli are associated with these health benefits3 :

  • Enhancement of intestinal structure and functions

  • Inhibition of pathogen growth

  • Stimulation of enteric and systemic immune systems

  • Enhanced utilization of indigestible dietary components

  • Treatment of GI disorders

  • Increased mineral absorption

  • Improved stool characteristics

Investigating the synergistic relationship of prebiotics and probiotics

The concept of nutritionally using a prebiotic and probiotic in a synbiotic relationship to increase the relative number of beneficial bacteria in the gut is a new and promising area of investigation. Synbiotics is the combination of a prebiotic and a probiotic in which the prebiotic is used to increase the intestinal survival of the probiotic.

Results of a recent in vitro study demonstrated a synbiotic relationship between the prebiotic FOS and the canine-derived probiotic Bifidobacterium animalis AHC7 (Iams Prostora, P&G Pet Care).4 Previous clinical studies in dogs have demonstrated that this probiotic promotes a desirable microflora balance, moderates stress responses, and speeds resolution of diarrhea. The in vitro study evaluated fermentation of seven dietary fibers by the probiotic B. animalis AHC7.4 The fibers included FOS, mannanoligosaccharides (MOS), gum arabic, beta-glucan, cellulose, beet pulp, and psyllium husk. Increasing colony-forming units (CFU) of B. animalis AHC7 indicated effective utilization of the fiber substrate. A previous study has shown that in vitro fermentation correlates well with in vivo fiber digestion by dogs and cats.5

After 24 hours of single fiber substrate fermentation with B.animalis AHC7, the prebiotic FOS significantly increased (P < 0.05) the CFU of the probiotic bacteria compared with the other fibers.4 The fibers ranked in order of effectiveness as follows: FOS, beet pulp, MOS, psyllium husk, gum arabic, cellulose, and beta-glucan (see Figure 1). This study demonstrates the synbiotic relationship between FOS and B. animalis AHC7.

Figure 1. Bifidobacterium animalis AHC7 colonization growth when combined with different fibers. After 24 hours, FOS significantly increased the CFU of the probiotic B. animalis AHC7 compared with other fibers.

Striking the right balance of fermentable fibers

As demonstrated in this study, the population of beneficial bacteria was enhanced, by varying degrees, through fiber fermentation. The magnitude of bacterial digestion depends on factors such as the type of fiber in the diet, the GI transit time, and the intake of other dietary constituents.6 For example, in dogs and cats, pectin is highly fermentable, beet pulp is moderately fermentable, and cellulose has lowfermentability. Bacterial fermentation or digestion produces short-chain fatty acids and other end products. The short-chain fatty acids produced in greatest abundance are acetate, propionate, butyrate, and lactate.

Short-chain fatty acids provide a number of benefits for dogs and cats. They act as a primary energy source for the intestinal cells, contributing up to 70% of their required needs. Short-chain fatty acids are important for cell renewal, especially since the epithelial cells of the gut have a rapid turnover. Dogs fed a moderately fermentable source of fiber (beet pulp) had increased colon weights, increased mucosal surface areas, and mucosal hypertrophy when compared with dogs fed a low-fermentable fiber source (cellulose).7 Short-chain fatty acids also enhance sodium and water absorption as well as colonic blood flow.

As the fermentation rate of fiber increases, GI transit time decreases and fecal bulk decreases. Fibers with lowfermentability (e.g. cellulose, peanut hulls, oat fiber) are poorly metabolized by intestinal bacteria and produce limited amounts of short-chain fatty acids. They retain their structure and act as bulking agents. Highly fermentable fibers (e.g. pectin, guar gum) are rapidly metabolized and produce an abundance of short-chain fatty acids, which can lead to gas and poor stool quality. Moderately fermentable fibers (e.g. beet pulp, rice bran) produce a balanced level of short-chain fatty acids and bulking properties. Dogs and cats can benefit from a moderately fermentable fiber source that generates sufficient short-chain fatty acids as fuel for stimulating intestinal cell proliferation and that provides bulk for enhanced peristalsis.


1. O'Hara AM, Shanahan F. The gut flora as a forgotten organ. EMBO Rep 2006;7(7):688-693.

2. Swanson KS, Grieshop CM, Flickinger EA, et al. Fructooligosaccharides and Lactobacillus acidophilus modify gut microbial populations, total tract nutrient digestibilities and fecal protein catabolite concentrations in healthy adult dogs. JNutr2002;132(12):3721-3731.

3. Buddington RK, Buddington KK, Sunvold, GD. The use of fermentable fibers to manage the gastrointestinal tract. In: Recent advances in canine and feline nutrition. Vol. III. Iams Nutritional Symposium, 2000;169-179.

4. Data on file, P&G Pet Care, 2009.

5. Vickers RJ, Sunvold GD, Kelley RL, et al. Comparison of fermentation of selected fructooligosaccharides and other fiber substrates by canine colonic microflora. Am J Vet Res 2001;62(4):609-615.

6. Watson TDG, Mackenzie JA, Stewart JP, et al. Use of oral and intravenous fat tolerance tests to assess plasma chylomicron clearance in dogs. Res VetSci 1995;58(3):256-262.

7. Hallman JE, Moxley RA, Reinhart GA, et al. Cellulose, beet pulp and pectin/gum arabic effects on canine colonic microstructure and histopathology. Vet ClinNutr 1995;2(4):137.

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