Probiotics: The Bugs in Our Bodies

The path that food takes through the body is known as the alimentary canal or gastointestinal (GI) tract. Food’s trip through the GI tract begins in the mouth, continues down through the esophagus, where it passes through a muscular opening (sphincter) into the stomach. From the stomach, the food, which is now a mushy clump of mechanically broken-down mass called “chyme” passes into the small intestine. In the small intestine, nutrients are absorbed and passed into the liver via the bloodstream, where they are processed as needed, and then re-released accordingly to the bloodstream where they can be delivered to cells throughout the body. Food particles and nutrients that are not absorbed in the small intestine continue traveling down the GI tract to the colon (large intestine), and are eliminated as waste via the rectum and anus.

The digestive system has approximately 100 trillion bacteria, and the vast majority of them live in the colon. Most of these bacteria aid in digestion, and are necessary for proper digestive functioning. 80% of the dry weight of our stool is made up of bacteria from our digestive system, and ½ of that is still alive!  There are between 400 to 500 different types, and 20 compose about 75% of the total. The most common are anaerobic, meaning they do not require oxygen, while a few do require oxygen (aerobic).

Bacteria have both protective and nutritive functions in the gut during food digestion. Some bacteria help break down food we can’t digest and in so doing, help release usable energy and minerals.  Other bacteria product beneficial compounds like Vitamin K and short chain fatty acids (SFCAs), the latter of which appear to have a role in colon cancer prevention.  These bacteria also aid our ability to fight infection by stimulating antibody secretion in the gut and tightening the barrier between cells of the intestine to prevent foreign substances from slipping through.  They can also increase our resistance to food poisoning by crowding out harmful bacteria that try to attach to the lining of our gut.

Probiotics are dietary supplements that contain certain species of these helpful bacteria for the purpose of aiding digestion, preventing diarrhea or enhancing immune functioning.  Depending on the strain used and the potency of the strain, they may decrease the frequency and severity of conditions such as vaginal yeast infections, diarrhea, lactose intolerance, or inflammatory bowel disease.

Prebiotics are foods that humans cannot digest but that out good gut bacteria can.  In this way, prebiotics are like food for probiotics, and can help maintain a healthy population of gut bacteria.


Bacteroides assist in breaking down food products and supply some vitamins and other nutrients that we cannot make ourselves.

Lactobacillus produces vitamin K, lactase (for lactose digestion), and anti-microbial substances.

Bifidobacteria alleviates the symptoms of inflammatory bowel disease.

Streptococcus thermophilus and lactobacillus can mitigate lactose intolerance.

Lactobacillus bulgaricus stimulate disease-fighting cells. The bacteria also appear to reduce the amount of nitrite (cancer causing chemical) in the body.

Peptococcaceae support immune function and nutrient production.


Fermented and cultured foods naturally contain various strains of probiotic bacteria, though if you’re looking for a specific benefit, you’ll need to find a food (or supplement) that contains a specific strain of probiotic demonstrated to have that benefit.  If you’re looking for general wellness benefits like maintaining a healthy gut bacteria population, you can incorporate foods such as:

  • any yogurt that contains live, active bacteria (special, expensive “probiotic” yogurts are just marketing hype; any yogurt with live, active bacteria should offer benefits.)
  • cultured beverages such as kefir, buttermilk, probiotic soy or fruit drinks or fermented beverages such as kombucha
  • fermented foods such as miso (soybean paste), natto (fermented soybean food), sauerkraut or kimchi

There are also reputable probiotic supplements sold in pharmacies and health food stores such as VSL#3 or Culturelle that have been shown to offer specific benefits; talk to your doctor if you’re interested in trying them out.

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