Probiotics have become trendy in food labeling and increasingly popular among doctors, but they don’t appear to make any difference in the treatment of stomach bugs in children.

A national research network, including a Minneapolis pediatrician, tested probiotics on 482 preschool children with stomach illnesses and found they suffered just as much vomiting, diarrhea and down time as a comparison group of children who didn’t receive the supplements.

The outcome disappointed doctors, who say they can do little else but manage symptoms and prevent dehydration when children are sickened by noroviruses or rotaviruses, but the study at least resolved a lingering question in pediatric care.

“It would have been nice to say, ‘Hey, there is something we can offer that might make you better, faster,’ ” said Dr. Marc Gorelick, chief executive of Children’s Hospitals and Clinics of Minnesota and a co-author of the study. “But it is gratifying to at least have a definitive answer … so people don’t waste their time, attention and resources.”

Stomach bugs cause 1.7 million ER visits and 70,000 ­hospitalizations each year in the United States. While some are linked to bacterial infections, especially foodborne contaminants such as salmonella, most are believed to be caused by viruses, which can’t be treated with antibiotics.

Probiotics contain so-called good bacteria for the body, and range from over-the-counter dietary supplements to foods such as yogurt. They have emerged as a treatment option over the past decade, based on the theories that they boost the immune system and restore healthy bacterial balances in the stomach that are disrupted by viral illnesses. A handful of small studies even supported their use against gastrointestinal illnesses.

“It’s an intuitive argument,” said Dr. Robert Sicoli, an ER doctor at Children’s Minnesota in St. Paul, who has recommended probiotics for many cases of stomach flu. “It seems like they should [work]. That’s where this study is a little bit surprising.”

The size of the latest study makes its findings persuasive, said Gorelick, who participated through his prior executive role with a Milwaukee hospital, which is one of 18 in a coalition known as the Pediatric Emergency Care Applied Research Network.

Children in the study received probiotic supplement powder that was mixed with beverages while they were in ER care for stomach illnesses. They continued to take the supplements over five days.

Children’s hospitals in the Twin Cities were not involved and are not part of the national network, which among other things has been credited with research that reined in the use of imaging scans for pediatric head injuries and appendicitis.

Results of the study were published Wednesday, in tandem with a similar Canadian study, by the New England Journal of Medicine. The U.S. study used a probiotic supplement marketed as Culturelle, while the Canadian study used two other common probiotics. None worked. Results also didn’t vary by the types of viruses causing illnesses.

“It was pretty definitive across the board,” Gorelick said. “It didn’t work for anybody, for anything.”

The studies found that probiotics didn’t trigger allergies or cause harm. So doctors said they suspect that parents might try them anyway if they don’t have anything else to do for their distraught and vomiting children.

A $20 to $30 can of probiotic powder might even seem worth the risk to parents, Gorelick said, but if that is extrapolated over the entire country, it means millions of wasted health care dollars each year.

The studies took no stance on probiotics in general, or their uses to prevent illness, support immune system health, or treat bacterial stomach illnesses. And probiotics are still recommended for other conditions, such as colic in infants.

Analysts have predicted billion-dollar growth for the probiotic industry through the inclusion of its products in yogurt and dietary supplements.

Sicoli said his “reflex” will no longer be to offer probiotics for stomach flu cases that he thinks are caused by viruses. However, for now, he said he won’t quarrel with parents who want to try them anyway.

“If I’m in the exam room, and someone says, ‘Hey, I really believe in probiotics. It works for my kids,’ I’m not going to argue with them,” he said, “because the risk is low.”