Probiotic supplements and foods containing "friendly" bacteria or yeast have become popular among people hoping to improve bowel function, immunity, and even mood. But consumers might be surprised to know that many products contain only a fraction of the probiotic organisms they claim. New tests by ConsumerLab.com found that out of 19 probiotics for people, five contained only 16 percent to 56 percent of the listed amounts of organisms. Levels of organisms in probiotics for pets were so low as to question their usefulness - including one product apparently reformulated to provide less than 2 percent of the organisms it had in the past.

"Consumers who don't do their homework with probiotics might not get what they want or think they're paying for," says Tod Cooperman, M.D., president of ConsumerLab.com. "Not every product has what it claims and even those that do may not have the right type and amount of organisms for a specific condition."

Probiotics represent one of the largest and fastest-growing segments of the dietary supplement market, with 2012 sales up 24.5 percent to $947 million in the U.S., according to Nutrition Business Journal. A survey of over 10,000 supplement users by ConsumerLab.com in November 2012 found probiotics were used by 37.4 percent of women and 30.5 percent of men. Probiotics are also one of the most expensive dietary supplements, with a daily dose often costing more than one dollar.

In its new test report , ConsumerLab.com discusses the specific species of bacteria and yeasts used for the treatment of diarrhea, bowel pain, vaginal infection, cold and flu, and even anxiety. ConsumerLab.com found products listing anywhere from one to over 30 different strains of Lactobacillus, Bifidobacterium, Streptococcus or Saccharomyces (a yeast). The quantity of organisms in products for people ranged from one hundred million to more than 900 billion in a daily dose, a difference of nearly 900,000 percent. Much lower amounts of organisms were found in pet probiotics—amounts so small that the cost to obtain 1 billion cells (which was as little as just 1 cent for some products for people) was $120 for one pet product.

A disturbing trend identified by ConsumerLab.com among probiotic supplements is the inclusion of footnotes on labels qualifying the listed amounts of organisms to be "At time of manufacture." This disclaimer holds no value with the FDA, which expects products to contain 100 percent of what they list. Dr. Cooperman suggests that "Supplement companies must not only be accountable for what they claim on their labels but need to make sure their products are properly transported and stored all the way to the consumer." Probiotics are particularly sensitive to their environment. Once purchased, consumers should store probiotics in sealed containers, away from heat, light, and humidity. Some probiotics require constant refrigeration, even if the bottle hasn't been opened.

The complete Probiotic Supplements Review is available at consumerlab.com/reviews/Probiotic_Supplements_Lactobacillus_acidophilus_Bifidobacterium/probiotics/. The report includes results for 41 products. ConsumerLab.com selected 22 of these, and 19 were tested at the request of their manufacturer or distributor through CL's Quality Certification Program and are included for having passed the same testing. Two products similar to one that passed testing are also listed. Products included in the report are 21st Century High Potency Acidophilus Probiotic Blend, Accuflora Advanced CD Probiotic Acidophilus, Align Probiotic, Best Pet Health Probiotics with Wild Alaskan Salmon Oil for Dogs and Cats, Culturelle, CVS/pharmacy Probiotic Acidophilus, Dr. David Williams Probiotic Advantage, Dr. Mercola Complete Probiotics, Enzymatic Therapy Acidophilus Pearls, FloraStor Kids, Garden of Life Raw Probiotics Ultimate Care, Jarrow Formulas Jarro-Dophilus EPS, Jarrow Formulas Senior Jarro-Dophilus, Kyo-Dophilus, Lee Swanson Genetic Designed Nutrition Ultimate Probiotic Formula, Metagenics UltraFlora Advanced, Nature Made Digestive Health Probiotic, Nature's Answer For Kids Probiotics, Nature's Bounty Advanced Probiotic 10, Nature's Plus Animal Parade AcidophiKidz, NOW Gr8-Dophilus, Nutri-Health Flora Source Multi Probiotic, Nutrition Now PB 8, Only Natural Pet Probiotic Blend, Petco Digestive Enzymes & Probiotics For Dogs, Phillips Colon Health, Puritan's Pride Probiotic 10, Renew Life Ultimate Flora, Renew Life Ultimate Flora Adult Formula, Renew Life Ultimate Flora Critical Care, RepHresh Pro-B, Rexall Probiotic Acidophilus, Schiff Digestive Advantage Daily Probiotic, Sedona Labs iFlora Multi-Probiotics, Solgar Advanced Multi-Billion Dophilus, Spring Valley Probiotic Acidophilus, TruBiotics, Trunature (Costco) Chewable Probiotic, UAS Laboratories DDS, USANA Probiotic, Vitacost Probiotic, Vitamin World Probiotic 10, and VSL#3. The report identifies which products contained what they claimed, provides product comparisons on types and amounts of probiotic organisms, and price, and includes information about the usage, dosage, and potential side-effects of probiotics.