Probiotics — the missing nutrients

A balanced intestinal microbiome is crucial to good health in dogs and cats, as well as in humans. Probiotics can play an important role in maintaining this balance.

Maintaining a healthy and balanced intestinal microbiome in our patients (and in ourselves) is becoming increasingly difficult. This can lead to a multitude of health issues, in which probiotics can be of significant assistance. In the first of this two-part article, we’ll look at the discovery of probiotics (see sidebar on page xx) and how they can alleviate microbial imbalance in the gut and support the integrity of the intestinal lining.

The microbiome

“The intestinal microbiota is the collection of the living microorganisms (bacteria, fungi, protozoa, and viruses) inhabiting the gastrointestinal tract.”1 The term “microbiome” includes the organisms, their interactions and their environment.

Microbiomes are extremely unique between even closely-related individuals. Each gut hosts thousands of bacterial species and strains. There are between 100 and 150 times more bacterial genes than human genes in our bodies. And there is an intricate interaction between the host and both the intestinal bacteria and their genes.

About 500 cultivable species of bacteria exist in the gut. An additional 1,000 species have been identified by modern molecular techniques (specifically ribosomal RNA sequencing, known as metagenomics). “This microbial community…varies quantitatively and qualitatively along with the different environments from the stomach, small and large intestines…. This complex community is metabolically active and contributes to homeostasis.”2

A functional microbiome breaks down foods to liberate more nutrients, manufactures several vitamins, inhibits disease-causing bacteria, and nourishes the enterocytes by producing the short-chain fatty acids used for fuel. Thus, the intestinal microflora maintains the integrity of the intestinal lining that protects the entire body from the inflammation associated with leaky gut syndrome.3 Furthermore, the microbiome acts as a detoxification organ; an imbalance in the bacteria can stress the liver. Gut bacteria influence the systemic immune system. They also affect brain chemistry and structure.

Animals have co-evolved with their microbiomes, and so they have developed a symbiotic relationship with them.4 In fact, some researchers assert that the microbiome should be considered an organ of the body5 – an organ as vital as the kidneys or liver.

At a phylogenetic level, the gastrointestinal microbiomes of humans, dogs and mice are similar.6 This indicates that microbiome research from one of these species applies to the others. In dogs and cats, more than ten bacterial phyla have been identified, with Firmicutes, Bacteroidetes, Proteobacteria, Fusobacteria and Actinobacteria constituting more than 99% of all gut microbiota.7

Some of the gut bacteria that are beneficial for people are also helpful for dogs. In one study, Lactobacilli were isolated from the jejunal chyme of five fistulated beagles. They found that Lactobacillus acidophilus was dominant.8

According to recent research, “The symbiotic relationship that exists between GI microbes and the host is critical for proper function of nutritional, developmental, immunological, and physiologic processes in animals, and thus contributes to host health… Decreased GI pH also results in decreased solubility of bile acids, thus decreased reabsorption and enterohepatic circulation of bile acids, increased absorption of minerals, and reduced absorption of ammonia.”9

The discovery of probiotics

The story of probiotics begins with Elie Metchnikoff (1845-1916). This Russian-born biologist was the first to understand the importance of white blood cells for immunity, which earned him the Nobel Prize in medicine in 1908. In fact, Metchnikoff is considered the “Father of Natural Immunity”. He noticed that Bulgarian peasant farmers were healthier, more robust, and lived longer than their city-dwelling countrymen. He insightfully realized their consumption of fermented foods, more specifically the bacteria those foods contained, was responsible for the farmers’ good health.

Metchnikoff coined the word “probiotics” (literally “for life”) for the beneficial bacteria in fermented foods. He reasoned that for health, the intestines must harbor more “good” than “bad” bacteria. He said that “Death begins in the colon.” This statement echoes that of Hippocrates who said: “All disease begins in the gut.”

The fermentation of food dates back 6,000 years when the Chinese began fermenting cabbage. A critical component of food safety, fermentation has been embraced by almost every culture around the globe. From Korean kimchi and Indian chutney to African garri and European pickled vegetables, to Hawaiian poi and the ubiquitous yogurt and sauerkraut, fermented foods are utilized worldwide.

In some countries, the fermentation process involves burying the food, reminiscent of carnivores that bury their uneaten prey. When you think about it, it seems obvious that any other carnivore that wandered past a shallow grave would smell, exhume and consume its contents. So if predators don’t bury their leftovers to hide them, then why do they do it? Perhaps it’s to support fermentation, so the carnivores can benefit from probiotic bacteria. At the very least, it must be acknowledged that our pets’ ancestors of did not eat sterile food.

Fermenting food involves creating an environment that promotes the growth of acid-forming bacteria. These microbes convert sugars into organic acids. The low pH that is created inhibits the growth of pathogenic bacteria, and thus keeps the food from spoiling. The formation of acid is also responsible for the ability of probiotics to kill off pathogenic bacteria in the gut.

The balance of intestinal microflora has broad effects on an animal’s health, and on ours. There are 100 trillion microbial cells in our bodies. In fact, we consist of ten times more bacterial cells than human cells. So, at the cellular level, we are more bacterial than we are human! The same is no doubt true for pets.

Dysbiosis and leaky gut

The term “dysbiosis” is used to indicate a state of gastrointestinal microbial imbalance or maladaptation. Another common factor of dysbiosis is a serious decrease in microbiota diversity. According to recent research, molecular interactions link the gut microbiota with host energy metabolism, lipid accumulation and immunity. These researchers go on to state: “Altered gut microbial ecosystems have been associated with increased metabolic and immune disorders in animals and humans.”10 Unbalanced gut microbiota is associated with disorders such as obesity, diabetes mellitus, schizophrenia, autistic disorders, anxiety disorders, and major depressive disorders.11

Many GI diseases linked to dysbiosis lead to an increase in intestinal permeability, a condition commonly known as “leaky gut syndrome”. Certain pathogenic bacteria damage tight junctions and produce toxins that then pass into the systemic circulation. According to research, leaky gut may allow the passage of toxins, antigens or bacteria into the portal circulation and may play a pathogenic role in advanced liver cirrhosis and its complications.

Furthermore, translocated bacterial antigens can result in a cross-reaction with the self-antigens and the induction of autoimmunity. A growing number of diseases have been shown to involve an increase in intestinal permeability related to changes in tight junction competency.12 In fact, when translocated bacterial antigens affect metabolically-active tissues, it may result in a chronic inflammatory state and impaired metabolic function.13

The solution to this problem is probiotics. Multiple studies show that probiotics decrease intestinal permeability.14,15

Messing with the microbiome

Modern medicine has found many ways to disturb the delicate balance of the microbiome. Obviously, antibiotic therapy of any kind indiscriminately kills the “good” bacteria along with the “bad”.   Other drugs also cause a deleterious change in the gut bacteria – these include NSAIDs, proton-pump inhibitors, antidepressants and laxatives. Researchers have concluded that, “Bacteria in the gastrointestinal tract reflect the combinations of medications that people ingest.”  Just about any pharmaceutical can lead to a state of intestinal dysbiosis.

Health benefits of probiotics

Probiotics are defined as “live microorganisms, which when administered in adequate amounts confer a health benefit on the host.”16 The most commonly-used probiotic bacteria are species belonging to the genera Lactobacillus and Bifidobacterium for humans and Aspergillus, Bacillus, Enterococcus, Lactobacillus and Saccharomyces for animals.17

One key to the efficacy of a probiotic supplement is that it must provide an adequate number of bacteria. For people, the agreed upon range is 5-10 X 109 Colony Forming Units (CFUs), while pets need at least 1 X 108 CFUs. An ideal probiotic should have microbes that originate in the species being treated, and should also be nonpathogenic, resistant to digestion by gastric acid and intestinal enzymes, able to adhere to the intestinal epithelium, and capable of influencing host immune responses.18


In this article, we have reviewed the discovery of probiotics, as well as research documenting the importance to health of a balanced intestinal microbiome. We have seen how modern medical practices can disturb the microbiome, and looked at the role that probiotics play in mitigating dysbiosis and maintaining the integrity of the intestinal lining.

In Part 2 of this series (IVC Journal, Summer 2018), we will delve more deeply into the research on probiotics and how they affect the immune system, microbiota-gut-brain axis, and systemic detoxification. We will further explore the influence of probiotics on such diverse conditions as chronic gastrointestinal disease, mood disorders/behavior, obesity, pancreatitis, diabetes mellitus and cancer. The sum of this research will allow the conclusion that probiotics are essential nutrients that are missing from modern conventional diets in both humans and pets.

1Honneffer JB, Minamoto Y, Suchodolski JS. “Microbiota alterations in acute and chronic gastrointestinal inflammation of cats and dogs”. World J Gastroenterol. 2014;20(44):16489-97.

2Ferreira CL, et al. “Terminology concepts of probiotic and prebiotic and their role in human and animal health.” Rev Salud Anim. 2011;33(3):137-139.

3Suchodolski JS. “Companion animals symposium: microbes and gastrointestinal health of dogs and cats”. J Anim Sci. 2011;89(5):1520-30.

4Hooda S, Minamoto Y, Suchodolski JS. “Current state of knowledge: the canine gastrointestinal microbiome”. Anim Health Res Rev. 2012:13(1);78–88.

5O’Hara AM, Fergus S. “The gut flora as a forgotten organ”. EMBO reports. 2006;7(7):688-693.

6Swanson KS, et al. “Phylogenetic and gene-centric metagenomics of the canine intestinal microbiome reveals similarities with humans and mice”. ISME J. 2011;5(4):639-649.

7Suchodolski JS. “Companion animals symposium: microbes and gastrointestinal health of dogs and cats”. J Anim Sci. 2011;89(5):1520-30.

8Tang Y, Manninen TJ, Saris PE. “Dominance of Lactobacillus acidophilus in the Facultative Jejunal Lactobacillus Microbiota of Fistulated Beagles”. Appl Environ Microbiol. 2012;78(19):7156–7159.

9Hooda S, Minamoto Y, Suchodolski JS. “Current state of knowledge: the canine gastrointestinal microbiome”. Anim Health Res Rev. 2012:13(1);78–88.

10Boulangé CL, Neves AL, Chilloux J, Nicholson JK, Dumas ME. “Impact of the gut microbiota on inflammation, obesity, and metabolic disease”. Genome Med. 2016 Apr 20;8(1):42.

11Evrensel A, Ceylan ME. “The Gut-Brain Axis: The Missing Link in Depression”. Clin Psychopharmacol Neurosci. 2015;13(3): 239–244.

12Fasano, Alessio. “Leaky gut and autoimmune diseases.” Clin Rev Allergy Immunol. 2012;42(1):71-78.

13Brown K, et al. “Diet-induced dysbiosis of the intestinal microbiota and the effects on immunity and disease”. Nutrients. 2012;4(8):1095-1119.

14Rosenfeldt V, et al. “Effect of probiotics on gastrointestinal symptoms and small intestinal permeability in children with atopic dermatitis”. J Pediatr. 2004;145(5):612-616.

15Madsen K, et al. “Probiotic bacteria enhance murine and human intestinal epithelial barrier function”. Gastroenterology. 2001;121(3):580-91.

16Nomoto K. “Prevention of infections by probiotics”. J Biosci Bioeng. 2005;100:583–592.

17Ferreira CL, et al. “Terminology concepts of probiotic and prebiotic and their role in human and animal health”. Rev Salud Anim. 2011;33(3):137-139.

18Dotan I, Rachmilewitz D. “Probiotics in inflammatory bowel disease: possible mechanisms of action”. Curr Opin Gastroenterol. 2005;21:426–430.

*This article has been peer reviewed.