Don’t get swept away by the marketing hype around probiotic products — those pills, powders and foods (mostly yoghurt) that are supposedly loaded with enough “good bacteria” to boost the health of your digestive and immune systems. 

For the science behind those claims is shaky, as science reporter Megan Scudellari explains in an article published last week on the Boston’s Globe’s health-and-science website, Stat.

“[Probiotic products are] touted as potential treatments for conditions ranging from inflammatory bowel disease to eczema to tooth decay,” she writes.  “Some marketing campaigns even hint that they can prevent the flu.”

“Scientific evidence, however, does not necessarily support those claims,” she adds.

As Scudellari points out, most of the studies to date have involved either animals or small groups of people. So although some of these studies’ results may be promising, they are not strong enough to support the long list of claims currently being made by the manufacturers of probiotic products.

Writes Scudellari:

Based on the smaller-scale studies done so far, there’s no indication that probiotics can treat obesity, autism, diabetes, or high cholesterol. Nor do they seem effective against the flu or common cold.

“The word ‘probiotic,’ meaning beneficial to health, is probably a term we use too liberally. The whole field is under a bit of a cloud,” said Stephen Allen, a professor of pediatrics at Liverpool School of Tropical Medicine in the United Kingdom.

Allen has conducted several clinical trials of probiotics, including studies that showed the bacteria had no effect on preventing eczema or diarrhea caused by antibiotics or infection.

“There’s no doubt that the gut interacting with bacteria has important effects,” Allen said. But, he said, we’re a long way from fully understanding that interaction, much less developing products to improve it. 

The uncertainty is so great that the European Union has banned the use of the word “probiotic” in marketing unless a product receives approval for a health claim. No such approvals have been granted.

Nor has the U.S. Food and Drug Administration (FDA) approved any health claims for probiotic products.

Unregulated supplements

In the U.S., probiotic products are considered dietary supplements. Manufacturers, therefore, can sell the products without proving either their effectiveness or their safety. The FDA can only take action on supplements — such as removing them from the shelves if they are found to harm people — after the products have been bought and used by consumers. (For background, I strongly recommend watching the Frontline documentary “Supplements and Safety,” which premiered last week on PBS.)

Research suggests that probiotics are safe for most people, with the exception, perhaps, of those with strong compromised immune systems or with multiple chronic diseases. But there has been growing evidence that many probiotic supplements (like many other dietary supplements) do not contain what’s on their label.

“At least seven studies have found discrepancies between what’s on the label and what’s in the product, especially in products containing multiple bacterial strains,” she says. “A 2015 analysis of 16 probiotic products, for example, found that only one of 16 exactly matched the bacterial species claims on the label in every sample tested.”

But these reports haven’t stopped the probiotic industry “from growing, growing, growing,” writes Scudellari.

“Shelves at Whole Foods and the Vitamin Shoppe are lined with bottles, powder packs, pills, capsules, even sour gummies packed with probiotics — up to 34 strains of bacteria for you, your kids, even your pet,” she reports. “The global market for probiotics, including both supplements and foods containing probiotics, hit an estimated $35 billion in 2014 and is projected to grow to $52 billion by 2020, according to consulting company Grand View Research.”

The most promising indications

The strongest evidence for probiotics being therapeutically beneficial has been found in the treatment of preterm infants with necrotizing entercolitis, a life-threatening condition in which intestinal tissue becomes injured and begins to die.

“Probiotic supplementation appears to prevent the severe form of the illness and save infant lives — but researchers still don’t know which types of bacteria, and in what combination, are best,” writes Scudellari. “Beyond that, there’s preliminary research showing probiotics could help treat inflammatory bowel diseases, such as Crohn’s disease. But scientists caution that they still have a lot to learn.”

So, asks Scudellari, “should a healthy person take a daily probiotic supplement to ‘maintain digestive balance’ or ‘support immune health,’ as the packaging claims?”

The half-dozen doctors and gastroenterologists she interviewed for her article said no — “some more vehemently than others,” she adds.

One expert who said “absolutely no” is Dr. Alessio Fasano, chief of pediatric gastroenterology and nutrition at Massachusetts General Hospital for Children in Boston.

His concern goes beyond the uncertainty of probiotics’ effectiveness in treating specific illnesses.

“He sees a parallel with penicillin, which was once believed to be a panacea for all infections, just as probiotics today are marketed as a cure-all,” writes Scudellari. “Overuse of penicillin led to the rise of “superbugs” resistant to antibiotics. Similarly, promiscuous use of probiotics could alter the human gut microbiome and limit the effectiveness of probiotics to treat health conditions in the future.”

FMI: You can read Scudellari’s article on the Stat website.