Understanding synbiotics (Sponsored by Iams)


Sherry Sanderson, DVM, DACVIM, DACVN, answers questions about the advantages of feeding a prebiotic and probiotic in a synbiotic relationship.

1. What are the advantages of feeding a prebiotic and probiotic in a synbiotic relationship?

The gastrointestinal (GI) tract is populated with as many as 1,000 different types of bacteria. Some of these bacteria are beneficial, while others are pathogenic. The balance between these two types of bacteria helps the overall health of the animal. All bacteria require a source of nutrition for survival, and beneficial bacteria and pathogenic bacteria compete for nutrients and attachment sites on the gastrointestinal mucosa. However, some of the beneficial bacteria in the GI tract, such as bifidobacteria, use specific substrates for nourishment that pathogenic bacteria cannot. Feeding a prebiotic that serves as a source of nutrition for the probiotic organism—but not for the pathogenic bacteria—gives beneficial bacteria a competitive advantage over pathogenic bacteria. For example, simultaneously feeding the probiotic Bifidobacterium animalis ACH7 with the prebiotic fructooligosaccharide (FOS) encourages the growth and survival of the Bifidobacterium animalis ACH7. Feeding the prebiotic also results in increased persistence of the probiotic in the GI tract.

Sherry Sanderson

2. Are there other benefits?

When probiotic bacteria ferment prebiotic fiber, such as FOS, they produce the short-chain fatty acids butyrate, lactate, acetate, and propionate. Short-chain fatty acids enhance the solubility and absorption of minerals, such as sodium and potassium, in the large intestine. Short-chain fatty acids are also the preferred energy source for the enterocytes lining the large intestine and provide as much as 70 percent of their energy needs. Increasing the supply of prebiotic substrate for probiotic bacteria in the large intestine increases bacterial fermentation products, including short-chain fatty acids. Short-chain fatty acids improve mucosal blood flow and mucosal cell proliferation in the gut, and this increases the surface area over which minerals and other nutrients can be absorbed.

3. Can any type of fiber be added to a probiotic product to produce an effective synbiotic?

In order for a synbiotic to be effective, it is important that there is a synergistic relationship between prebiotic and probiotic. Probiotic bacteria preferentially metabolize certain fiber sources; therefore, it is essential that any synbiotic product demonstrate that the probiotic organism is able to adequately ferment the prebiotic fiber. Not all types of fiber are effective substrates for bacterial fermentation. Some fibers, such as cellulose, are poorly fermentable and do not function as prebiotics in food. In addition, the rate of fermentation of fiber depends, in part, on the chain length of the fiber. For example, the prebiotic FOS is a fermentable fiber that is preferentially utilized by many probiotic bacteria.

However, the chain length of FOS impacts its rate of fermentation and varies depending on the source of FOS. Short-chain FOS, such as that commercially produced by fungal enzyme action on sucrose, has a chain length of three to five carbons. Probiotic bacteria, such as Lactobacillus species and Bifidobacterium species, readily metabolize short-chain FOS. Inulin is a naturally occurring prebiotic found in chicory; however, the chain length for this source of FOS can be up to 60 carbons. Long-chain prebiotics are fermented slower than short-chain prebiotics are, and this can limit its prebiotic function in a synbiotic.

4. Are there advantages to feeding dogs a wellness diet supplemented with prebiotics?

Consumers are becoming more interested in foods with health benefits beyond basic nutrition, not only for themselves but also for their pets. Feeding dogs a diet on a daily basis that already contains a prebiotic is a proactive approach to maintaining health. A balanced intestinal microflora is important to the animal's overall health, and prebiotics can impact the bacterial balance in dogs. For example, the intestinal bacterial population was evaluated in 47 healthy adult dogs fed a diet not supplemented with FOS and compared to the intestinal bacterial population when the dogs consumed the same diet supplemented with FOS. (Data on file, P&G Pet Care, 2009.) The diet with FOS not only increased beneficial bacteria (Lactobacillus species) in the GI tract, but it also reduced possible pathogenic bacteria (Esherichia coli, Bacteriodes and Eubacteria species). Both of these results were statistically significant when compared to results from these same dogs when they consumed the diet without FOS.

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