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, according to new tests from ConsumerLab.com, White Plains, NY. A recent review found that out of 19 probiotics for people, five contained only 16-56% 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% 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,” said Tod Cooperman, MD, 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% to $947 million in the U.S., according to Nutrition Business Journal. A survey of more than 10,000 supplement users by ConsumerLab.com in November 2012 found probiotics were used by 37.4% of women and 30.5% 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 discussed 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 more than 30 different strains of Lactobacillus, Bifidobacterium, Streptococcus or Saccharomyces (a yeast). The quantity of organisms in products for people ranged from 100 million to more than 900 billion in a daily dose, a difference of nearly 900,000%. 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% of what they list. Dr. Cooperman suggested 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 here. 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.