We are not alone. The average human body contains approximately 30-40 trillion cells, but also about 40 trillion microorganisms including bacteria, fungi and viruses. In fact, there are so many microorganisms in our bodies that they actually make up between one to three percent of our weight—if you weigh 150 pounds, roughly two or three pounds of that is made up of bacteria and other tiny living organisms.
For decades, it was impossible to accurately estimate just how many different strains of microorganisms we play host to. A few hundred had been isolated at most. But recently developed genome sequencing methods have enabled the Human Microbiome Project (HMP), in partnership with the National Institutes of Health, to differentiate human and microbial DNA. The facts are now in: more than 10,000 microbial species occupy the human ecosystem.
HMP researchers report that this astonishing variety of microbes contributes more genes to aid human survival than the human body itself. Genes carried by bacteria in the gastrointestinal tract, for example, allow humans to digest foods and absorb nutrients that otherwise would be unavailable for absorption.
"Humans don't have all the enzymes we need to digest our own diet," says Lita Proctor, PhD, HMP program manager. "Microbes in the gut break down many of the proteins, lipids and carbohydrates in our diet into nutrients that we can then absorb. Moreover, the microbes produce beneficial compounds like vitamins and anti-inflammatories that our genome cannot produce."
The microbial landscape also
varies enormously across the human body. The mouth, nose, skin, lower intestine, and vagina have wildly diverse 'microbial ecosystems'—as different as the Amazon rainforest and Sahara Desert.
In the early 20th century, French pediatrician Henri Tissier noticed that babies fed formula were more prone to diarrhea than breastfed babies, and observed that the formula-fed children also had a lower number of Y-shaped bacteria ("bifid" bacteria) in their stools compared to healthy breastfed babies.
Way back in 1906, he suggested that giving bifid bacteria to the babies with diarrhea could restore their health. Today this approach is commonplace, and the added microorganisms used to boost the properties of the indigenous flora in the body are called probiotics.
'Probiotic' is derived from Greek, meaning 'for biological life.' Lactobacillus and Bifidobacterium microorganisms are the most commonly used probiotics, but with over 10,000 different strains in the human body, sorting out the beneficial from the not-so-helpful is a mind-boggling task.
With the increasing popularity of probiotics and prebiotics (the non-digestible fiber compounds that feed probiotics) in everything from yogurt to fermented foods, experts like Mary Ellen Sanders, PhD, executive science officer at the International Scientific Association for Probiotics and Prebiotics, advises that people become more educated about what does and doesn't constitute a viable commercial probiotic.
Says Sanders: "Most probiotics don't have to be linked to a prebiotic in order to function. And fermented foods are not probiotics per se. In order to call something probiotic, it has to be isolated and studied in a human trial and shown to have a health benefit. Probiotics are definitely a higher bar than your off-the-shelf fermented food."
It doesn't help that the exact mechanisms involved in probiotic function aren't clearly understood. So far, probiotics are known to assist in the production of short-chain fatty acids, lower gut pH, reduce competition for nutrients, stimulate and strengthen the mucosal barrier of the gut, and modulate the immune system. Notably, they induce the secretion of immunoglobulin A, an antibody necessary for the normal immune function of mucous membranes, and enhance the ability of T cells to fight infections.1
For a potential probiotic strain to be considered viable as a health product, it must be able to survive stomach acid and bile, adhere to the cells lining the gut surface, and provide antimicrobial action against disease-causing bacteria. Their ability to break down bile salts (a process called hydrolysis), which is necessary for their own survival, is also critical for fat metabolism.2
Effects on health
Health benefits of probiotics include aiding in digestion, reducing inflammation and increasing nutrient absorption. They've been shown to help numerous conditions including allergic reactions, Crohn's disease, constipation, candidiasis, urinary tract infections and lactose intolerance,3 and they induce the remission of ulcerative colitis symptoms.4 Certain probiotics including Lactobacillus rhamnosus GG and Saccharomyces boulardii are effective for acute gastroenteritis in children and infants.5
Probiotics have shown an effect on lowering blood cholesterol levels and are believed to lower the risks of cardiovascular and coronary heart diseases.6 They can also help people suffering from psychological problems such as depression, anxiety and cognitive symptoms.7
"Certain probiotics actually help you absorb calcium and other minerals in your gut," says Kristin McGary, LAc, MAc, CFMP, a holistic health practitioner in Boulder, Colorado. "Others make B vitamins for us. They provide protection from infection. They positively impact our metabolism. I see huge changes when I've done testing on people before and after extensive probiotic use. I see a greater diversity in their microbiome and a marked decrease in autoimmune issues."
There is also clinical evidence that probiotics and prebiotics may aid in the prevention and treatment of certain cancers, including colon cancer, the second leading cause of cancer death in the United States. In addition to decreasing intestinal inflammation and boosting the immune system, probiotics also bind to possible toxins and food-based carcinogens and reduce bacterial enzymes in the colon that promote cancer.8
Evidence suggests that an imbalance in the gut microbiome triggers inflammation in the lining of the esophagus (the mucosa) and eventually the formation of tumors there.9 Laboratory studies have also suggested that probiotics might be useful for preventing esophageal adenocarcinoma,10 and they've additionally uncovered promising evidence that probiotics can dramatically slow the growth of liver cancer by impeding the creation of new blood vessels to feed the tumor.11 While these results may not apply to humans, there is also data showing that the microbiome on the tongue of patients with liver carcinoma differs from that of healthy people, giving even more credence to the idea that probiotics might benefit such patients.12
For probiotics to have a health benefit, they must be ingested in sufficient amounts. In most countries, including the US, regulations do not yet require manufacturers to include the amounts of probiotics on the label. In Canada and Italy, however, foods labeled as 'probiotic' must contain at least 1 billion colony-forming units (CFUs) of probiotics per serving—that's the number of living bacteria in the product.
According to McGary, "I like adults to use products that are rated to contain around 100 billion CFUs. I'll start them with 25 billion per dose and slowly build them up."
Sources and side-effects
There are few side-effects to using probiotics. McGary says those mainly occur when the newly introduced good bacteria kill off the bad guys and 'die-off' occurs, creating a short-term toxic effect as the dead bacteria are flushed out of
Some patients become constipated, she says. Others get loose stools and can feel really uncomfortable—which is why it's a good idea for people to work with a healthcare provider when they're dealing with their immune system and gut issues. "It can take from two to four weeks for the gut to balance with the introduction of new flora," McGary says.
Another confusing aspect of probiotics is what form to take them in. "What we lack in the literature base are studies that compare a probiotic as a dried supplement to a probiotic in yogurt," says Sanders. "We have no head-to-head comparisons where you can say one works better than the other or that both of them are equivalent."
Overall, Sanders says she sees benefit from taking probiotics in a food source like yogurt or kefir for the added nutrition the food provides. McGary, on the other hand, disagrees.
"The Lactobacillus, Acidophilus, Bifidophilus and all of those different strains in yogurt that help the fermentation process are not resistant to stomach acid," she says. This is why so many yogurt brands include statements like "contains Lactobacilli and Bifidobacteria in addition to the yogurt cultures" on the label. Adding these strains to the yogurt ensures that some probiotics will survive intestinal transit and reach your colon. But even with the added strains, McGary says, you're not getting a high enough dosage to be effective.
Another big concern is freeze-dried probiotics in stores or online. Tests done on probiotics show they are often only 30 to 50 percent viable right off the shelves because of poor handling, high heat conditions during shipping, lack of refrigeration or the simple fact that they've been stored in the warehouse too long before being sold.
WHEN TO TAKE PROBIOTICS
When you're taking antibiotics
Antibiotics are well known to wreak havoc on the gut flora, killing off good bacteria as well as bad. In the past, people were advised not to take probiotics while on antibiotics—to wait until afterward because it was believed the antibiotics would kill ingested probiotics. The trouble with this approach is that it allows pathogenic microorganisms to proliferate unopposed by beneficial bacteria, often resulting in antibiotic-associated diarrhea and other problems. Probiotics should be taken at least one hour before or two hours after ingestion of antibiotics.
When you're under stress
Stress threatens homeostasis in the body and has both short- and long-term effects on the gastrointestinal tract. Stress can lead to inflammatory bowel disease, irritable bowel syndrome, ulcers and gastroesophageal reflux disease, food allergies, depression and various cognitive symptoms. Probiotics can help.1
When you're traveling
Changing geographic locations means both stress and a change in food and water that potentially play host to new and unfriendly bacteria and virus strains. Bolstering gastrointestinal strength by taking viable probiotics is just common sense.
Probiotics are not a 'cure all' and it is not necessary to take them to be healthy. But according to Mary Ellen Sanders, PhD, executive science officer of the International Scientific Association for Probiotics and Prebiotics, probiotics support the immune system; decrease respiratory, gut, vaginal and urinary tract infections; relieve diarrhea, constipation and bloating; help support an effective gut barrier and manage symptoms of irritable bowel syndrome—even help manage cholesterol levels. What's not to love about that?
Food sources of probiotics
Yogurt and kefir. As with raw cheese (below), these are not advised if you're lactose intolerant. If so, investigate sources from goat's or sheep's milk and make sure the product comes from grass-fed, organic animals. Strains of healthy bacteria added to yogurt and kefir include L. bulgaricus, S. thermophilus, L. acidophilus, L. casei and B. bifidus.
Raw cheese. Raw and unpasteurized cheeses contain probiotics including: S. thermophilus, B. bifudus, L. bulgaricus and L. acidophilus.
Kombucha. Black tea fermented with a 'starter' colony of bacteria and yeast called a 'SCOBY,' kombucha is loaded with good bacteria.
Tempeh/natto. Fermented soybeans can be found in Japanese food stores. They contain the probiotic B. subtilis, which favorably stimulates the immune system.
Fermented vegetables. Sauerkraut and kimchi are both made from fermented cabbage and other vegetables. While not high in probiotics, these prebiotics are high in organic acids that support the growth of good
One of the biggest gaps in our understanding of probiotics is knowing exactly what each strain is good for and what kind of probiotic to take for what situation. However, there are a few well-studied species with consistent results in the following areas.