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Bugs in Our Guts—Not All Bacteria Are Bad
How Probiotics Keep Us Healthy

(Released September 2006)

  by Leila Kiani  


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What is Probiotics?

Let food be thy medicine and medicine be thy food.


At birth, the gastrointestinal tract is sterile and incapable of digesting food. Within hours, bacteria ingested during the birthing process rapidly colonize the gut. The gastrointestinal tract soon contains about ten times as many bacteria as there are cells in the body. Hundreds of species are present, many of which are uncultivable and remain unidentified. It is these bacteria that are responsible for priming the gastrointestinal immune system (1). This gut flora includes 100 trillion bacteria, some three pounds, which are intimately linked to the body's natural defense system (12).

distribution of nonpathogenic microorganisms in stomach and intestines

Probiotics are defined as live microbial food ingredients that benefit human health. Most probiotics fall into the group of organisms known as lactic acid-producing bacteria and are normally consumed in the form of yogurt, fermented milks or other fermented foods (2).

The concept of probiotics arose at the turn of the 20th century from a hypothesis first proposed by Noble Prize winning Russian scientist Elie Metchnikoff, who suggest that the long, healthy life of Bulgarian peasants resulted from their consumption of fermented milk products. He believed that when consumed, the fermenting Bacillus (Lactobacillus) positively influenced the microflora of the colon, decreasing toxic microbial activities (3, 4). The historical association of probiotics with fermented dairy products, still true today, stems from these early observations. Investigations in the probiotics field during the past several decades, however, have expanded beyond bacteria isolated from fermented dairy products to those of intestinal origin (3, 4).

There is some debate about whether or not yogurt starter bacteria should be considered probiotics. The yogurt starter cultures Lactobacillus bulgaricus and Streptotoccus thermophilus are used to ferment milk and turn it into yogurt. But these cultures are not very resistant to conditions in the stomach and small intestine and generally do not reach the gastrointestinal tract in very high numbers. Therefore, they cannot mediate some probiotic effects. But these starter bacteria have been shown to improve lactose digestion in people lacking lactase and have demonstrated some immunity enhancing effects. For these reasons, they are often considered 'probiotic' (6).

Most gastrointestinal organisms are relatively benign. Some are potentially more pathogenic; however, many are actually beneficial; it is these beneficial organisms that have attracted attention as possible probiotics (1). The table below lists some possible health benefits of consuming probiotics. Those that have significant research to back up the claims are discussed in more depth later in this article (15)

Possible health effects of probiotics

Intestinal effects

  • Relieve effects, promote recovery from diarrhea (rotavirus, travelers' and antibiotic-induced)
  • Produce lactase, alleviate symptoms of lactose intolerance and malabsorption
  • Relieve constipation
  • Treat colitis
Immune system effects
  • Enhance specific and nonspecific immune response
  • Inhibit pathogen growth and translocation
  • Stimulate gastrointestinal immunity
  • Reduce chance of infection from common pathogens (Salmonella, Shigella)
Other effects
  • Reduce risk of certain cancers (colon, bladder)
  • Detoxify carcinogens
  • Suppress tumors
  • Lower serum cholesterol concentrations
  • Reduce blood pressure in hypertensives
  • Treat food allergies
  • Synthesize nutrients (folic acid, niacin, riboflavin, vitamins B6 & B12)
  • Increase nutrient bioavailability
  • Improve urogenital health
  • Optimize effects of vaccines (e.g. rotavirus vaccine, typhoid fever vaccine)

Thanks to Deborah Whitman for all of her help, without which this Discovery Guide would never have been written

Go To Microflora in the Intestinal Tract

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