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Intestinal Flora


Intestinal flora are harmless microorganisms such as bacteria, yeasts, and fungi that inhabit and grow in the intestines. These microorganisms are essential to the normal functioning of the digestive tract, and certain species of intestinal flora are beneficial to the human body. These "good" bacteria often have a symbiotic relationship with the human body as both derive benefit from one another. For example, "The normal [intestinal] flora derive from their host a steady supply of nutrients, a stable environment, and protection and transport. The host obtains from the normal [intestinal] flora certain nutritional and digestive benefits, stimulation of the development and activity of immune system, and protection against colonization and infection by pathogenic microbes."(1) Beneficial bacteria such as intestinal flora are often referred to a probiotics. " an umbrella term given to any live microorganism that is beneficial to its host."(2)

Small Intestine

The intestinal flora of the small intestine is comprised mainly of microorganisms known as lactobacilli, which are a type of bacteria found in the digestive tract that produce lactic acid. "Lactobacilli are one of the most important types of friendly bacteria found in the digestive tract. They play a key role in producing fermented foods, fermented milk, yogurt, and cheeses [and] are often referred to as "probiotic" since they are positive or supportive microorganisms."(3) Lactobacilli include bacteria such as Lactobacillus caseii, Lactobacillus bulgaricus, Lactobacillus acidophilus, and Lactobacillus helveticus just to name a few. Each of these types of bacteria provide various benefits to the human body. For example, Lactobacillus caseii (L. casei) "exhibit[s] immune-enhancing effects by producing "bacteriocins", [which are] compounds that restrict [the]growth of pathogens in the small intestine."(3) Lactobacillus bulgaricus (L. bulgaricus) "aids [in the] digestion of dairy products, helps reduce cholesterol levels, breaks down complex proteins for easy assimilation, and alleviates acid reflux."(3)

Large Intestine (Colon)

While lactobacilli can be found in the large intestine as well, one of the most "predominant species [that inhabit the large intestine is]...anaerobic lactic acid bacteria in the genus Bifidobacterium (Bifidobacterium bifidum)"(1)

Lactobacilli and Bifidobacteria maintain a healthy balance of intestinal flora by producing organic compounds. These organic compounds include lactic acid, hydrogen peroxide, and acetic acid that increase the acidity of the intestine and curb the reproduction of many harmful bacteria.(4)

Furthermore, "Bifidobacterium bifidum has been used to maintain or restore a normal, healthy condition in the intestines."(5) The various types of Bifidobacterium include but are not limited to: Bifidobacterium adolescentis, Bifidobacterium breve, Bifidobacterium infantis, and Bifidobacterium longum. Each of these bacteria are beneficial to the human body as "bacteria in the human GI tract have been shown to produce vitamins and may otherwise contribute to nutrition and digestion. But their most important effects are in their ability to protect their host from establishment and infection by alien microbes and their ability to stimulate the development and the activity of the immunological tissues."(1)

Intestinal Flora Studies

Probiotics were first discovered sometime during the 19th century, and since that time many studies have been conducted to determine the benefits of probiotics. In the last couple of decades researchers have been able to gain a better understanding of the many benefits of probiotics thanks to various scientific and technological advances. Today researchers understand that "certain bacterial strains, especially the Lactobacillus and Bifidobacterium genus have high mucus membrane chemical affinity and play important roles in human health."(7)

Essentially, probiotics such as Bifidobacterium and Lactobacillus help enhance the growth of beneficial bacteria or intestinal flora thereby furthering the health and well-being of the individual. The following studies show the various types of probiotics studied and the effects they have on the human body in relation to various diseases. By promoting the growth of intestinal flora these probiotics assist in disease reduction and prevention.


A study conducted in 2009 hoped to provide evidence of the ability of the probiotic Bifidobacterium breve (B. breve) strain Yakulton to prevent infection, fecal micro flora, and intestinal environments in cancer patients on chemotherapy.(8) Results of the test showed that "the frequency of fever and the use of intravenous antibiotics were lower in the probiotic group than the placebo group."(8) The study concluded that "administration of B. breve strain Yakult could be an effective approach for achieving clinical benefits in immunocompromised hosts by improving their intestinal environments."(8)

A new study published in the July issue of the American Journal of Gastroenterology found that Bifantis (Bifidobacterium infantis 35624) may help relieve many of the symptoms associated with irritable bowel syndrome (IBS) in women, including diarrhea and constipation.(9)

This randomized study was conducted with a group of women suffering from irritable bowel syndrome (IBS). These women reported experiencing symptoms such as abdominal pain and discomfort, bloating and distension, sense of incomplete evacuation, straining at stool, urgency of bowel movement, and passage of gas.(9) The results of the study indicated that at the end of the 4-week period these women experienced an overall improvement in symptoms after taking Bifantis. As a conclusion to this research, it would be fair to say that "Bifantis may be especially helpful for people who experience one or more of the symptoms commonly associated with IBS, including diarrhea, constipation, bloating, gas, urgency and abdominal discomfort."(9)

Lactic acid producing bacteria, such as Bifidobacterium longum (B. longum), help support immune system functions. Bacterial supplements such as B. longum have been administered to patients who take antibiotics, suffer from bacterial, viral or fungal infections or have various digestive problems.(10) B. longum has been described as "one of the most important residents in the human gastrointestinal tract [because it] keeps the digestive system running smoothly, blocks the growth of harmful bacteria, and boosts the immune system."(10)


Lactobacillus acidophilus is generally considered to be beneficial because it produces vitamin K, lactase, and anti-microbial substances such as acidolin, acidolphilin, lactocidin, and bacteriocin. Multiple human trials report benefits of L. acidophilus for bacterial vaginosis.(11)

A study conducted in 2007 using milk fermented with Lactobacillus helveticus (L. helveticus) provided evidence that milk fermented with this probiotic significantly improved the arterial stiffness of those involved in the study. Other studies conducted using milk fermented with L. helveticus indicates that this probiotic not only helps with arterial stiffness but also supports bone mineral density and increases calcium absorption in postmenopausal women.(12)


"A stable, healthy intestinal microflora is thought to contribute to overall health by excluding foreign, potentially harmful bacteria."(6) Scientific studies indicate the multiple benefits that various types of intestinal flora offer the human body. Whether ingested through foods containing these bacteria or taken in supplement form, these probiotics aid in the proliferation of "good" bacteria in the body and help reduce and/or prevent infection and disease.


(1) Todar, K. (2008). The Normal Bacterial Flora of Humans. Todar's Online Textbook of Bacteriology.
(2) Welter, S. (2007). Probiotcs: Friendly Bacteria, Keeping Your Intestinal Flora Healthy and Happy.
(3) Lactobacilli List, A List of the Key Lactobacilli (Friendly Bacteria) and Their Role in the Health of Your Digestive System. Published by NuFerm, Nutrition from Nature. 2006.
(4) Learn the Benefits of Bifidobacterium. Published by VAXA International. Unknown.
(5) Generic Name: Bifidobacterium Bifidum Oral. Published by 2005.
(6) Partial Characterization of Bifidobacterium Breve C50 Cell-Free Whey Compounds Inducing Modifications to the Intestinal Microflora. Journal of Dairy Science, American Dairy Science Association. 2002.
(7) Probiotics. Published by Unknown.
(8) Effects of the Enteral Administration of Bifidobacterium Breve on Patients Undergoing Chemotherapy for Pediatric Malignancies. Published in Supportive Care in Cancer. 2009.
(9) New Study Demonstrates That Bifantis (Bifidobacterium infantis 35624) Offers Relief for Women With Irritable Bowel Syndrome. Published in American Journal of Gastroenetrology, Medical News Today. 2006.
(10) Bacteria Genomes Bifidobacterium Longum, Bifidobacterium Longum Keeps the Human Digestive System Running Smoothly. European Bioinformatics Institute, European Molecular Biology Laboratory. 2009.
(11) Lactobacillus Acidophilus. Published by Natural Standard Patient Monograph, 2009.
(12) Narva, M. (2004). Effects of Lactobacillus Helveticus Fermented Milk and Milk-Derived Bioactive Peptides (CPP, IPP, and VPP) on Calcuim and Bone Metabolism. Institute of Biomedicine, Pharmacology. University of Helsinki.

For more information:

A complete description of probiotics, along with groundbreaking recent clinical research illustrating the many ways probiotics can prevent disease, can be found in Probiotics - Protection Against Infection: Using Nature's Tiny Warriors To Stem Infection. This new compendium from one of contributing authors of the content on this page, Dr. Casey Adams, PhD., takes the confusion out of selecting and supplementing with probiotics. Referencing over 500 scientific studies and reports, and with detailed instructions on how to make your own probiotic foods, this book is a must for anyone seeking to understand the power of probiotics, and improve their immunity and vitality. Click here for ordering information.

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categories : Probiotics

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