By Amy Fitzpatrick
Humans have consumed a variety of bacteria through foods for millennia, but it wasn’t until the turn of the 21st century that anyone suggested that ingested bacteria could have a positive influence on the microbial flora of the intestinal tract, which, in turn, could benefit human health. Fast forward to today: Researchers now estimate that the adult human body contains more than 100,000 billion bacteria from more than 400 different species that play an important health role. When probiotics latch on to and temporarily colonize the intestinal mucosa, they help prevent attachment of pathogenic bacteria. From improved immunity to better digestion, the multiple benefits of probiotic intake are confirmed by numerous studies.
Some researchers suggest that multiple probiotics may have a greater effect on the intestine than individual strains. Jacques Goulet, PhD, scientific director of the Institut Rosell in Montreal, which supplies Lacidophilus Rosell-52 and L. rhamnosus Rosell-11 probiotics, says, “From a scientific point of view we are noticing that a single strain won’t do the best job in improving health. Scientists are suggesting that probiotic supplements be a mixture of four, five and even eight strains to get the most benefit.” Here, we review the evidence and reveal the strain combinations that are proving effective for preventing or treating health conditions.
Diarrhea. Research consistently supports probiotic use for antibiotic-associated diarrhea and acute infectious diarrhea such as traveler’s diarrhea or viral-related diarrhea. A 2006 meta-analysis of 34 studies published in The Lancet Infectious Diseases found that probiotics reduce the risk of antibiotic-associated diarrhea by 52 percent, and acute diarrhea by 57 percent in children and 26 percent in adults. Effective probiotic species include L. acidophilus, L. rhamnosus GG, L. bulgaricus, Saccharomyces boularrdii, L. reuteri and B. lactis. In addition, a 2007 study published in the Canadian Journal of Gastroenterology looked at hospital patients and showed that a combination of L. acidophilus and L. casei reduced the occurrence of antibiotic-associated diarrhea and length of hospital stays, compared to placebo.
Constipation. Experimental studies indicate that intestinal transit time—the time it takes for fecal matter to move through the intestines—is prolonged in animals that don’t have established microflora. The benefit of healthy gut microflora on regularity is proven in humans that take L. acidophilus and B. lactis. In addition, at least two trials have found that two different strains of L. casei can help relieve constipation. One 2007 Pediatrics International study involved children given L. casei rhamnosus and the other 2003 Canadian Journal of Gastroenterology study used L. casei Shirota in adults. Both studies showed improvements in stool frequency and consistency.
Inflammatory bowel. Characterized by recurrent intestinal inflammation, bowel disorders include ulcerative colitis, irritable bowel syndrome, Crohn’s disease and pouchitis. To date, the strongest findings are in favor of probiotic use in UC and IBS. In addition, a specific probiotic blend (VSL#3) has been shown to improve remission in patients with pouchitis, an inflammatory condition of the small intestine that can occur after gastrointestinal surgery due to various intestinal problems.
At least nine randomized, controlled studies have reported higher remission in UC patients taking probiotics compared with controls. Two studies showed increased efficacy, and five trials did not show any significant difference between probiotic and control groups.
Currently, trials evaluating the effect of probiotics on IBS are limited; but overall, researchers report a beneficial effect over placebo in the relief of some IBS symptoms. One large controlled trial published in a 2006 edition of the American Journal of Gastroenterology found that B. infantis was significantly more effective at reducing abdominal pain and discomfort in women with IBS compared to those taking placebo. Another controlled trial published in the European Journal of Gastroenterology & Hepatology found that L. plantarum given to women with IBS for four weeks significantly reduced abdominal pain and improved overall IBS symptoms compared to placebo. However, one controlled study evaluating the use of L. casei GG did not find any significant improvement in pain, urgency or bloating in women with IBS, but did note a reduction in diarrhea frequency.
Not all probiotics are created equal
Probiotic products contain different genera (e.g., Lactobacillus), species (e.g., rhamnosus) and strains (e.g., GG or GR-1), and not all microbes sold as probiotics have been tested for health effects, nor should all products be expected to work the same. In general, studies have consistently shown that various strains of L. acidophilus, L. rhamnosus, L. casei, B. bifidum, B. longum, B. lactis, L. paracasei and others can survive stomach acid and have beneficial effects on gastrointestinal or immune health.
Required doses vary for different strains and the specific health effect under investigation. The most common dosage used in clinical trials for antibiotic-associated diarrhea was 3 billion CFUs daily of L. acidophilus or L. rhamnosus, but studies using 10 billion CFUs or more daily showed greater effectiveness. Clinicals showing a benefit for constipation used at least 1 billion CFUs daily of B. lactis or a combination of L. acidophilus and B. lactis in doses ranging from 1 billion to 200 billion CFUs daily. Other strains shown to improve constipation were L. casei rhamnosus (2 billion CFUs a day) or L. casei Shirota (6.5 billion CFUs a day).
While research has reported some improvement in IBS with doses of 100 million to 20 billion CFUs a day of B. infantis and L. plantarum, respectively, much higher doses (e.g., 900 billion CFUs a day) may be required in individuals who are critically ill or have more serious conditions such as pouchitis or UC (1,800 to 3,600 billion CFUs a day).
Most importantly, probiotics need to be consumed at least a few times a week, preferably daily, on a regular basis to maintain their effect on intestinal microecology. For instance, levels of bifidobacteria in the colon have been reported to decline after age 55, and lactobacilli concentrations may be negatively influenced by stress. Preliminary research has found that supplementing the diet with several probiotic species can restore levels of important immune-system markers found in younger people, and that probiotics may counteract stress-induced changes in intestinal barrier function.
Amy Fitzpatrick, RD, is a nutritionist and research consultant for Natural Health Solutions.