A yogurt aimed at easing digestion with the help of "good" bacteria may not be much help for children's chronic constipation, a new study suggests.

The study, of 159 children with persistent constipation, looked at whether an Activia-brand yogurt could help make the kids more "regular."

Activia yogurts and other cultured dairy products contain a strain of friendly bacteria, or probiotic, called Bifidobacterium lactis, which is thought to help regulate the digestive system.

Some studies of adults have found the products to help ease chronic constipation.

But in the new study, researchers found that the probiotic yogurt was no better than a non-cultured dairy product without probiotics in easing kids' constipation.

Over three weeks, children who were randomly assigned to eat the probiotic yogurt each day did start to have more bowel movements, on average. But so did children in the comparison group.

In both groups, children went from having fewer than two bowel movements per week, on average, to about four per week.

It's not clear why both groups improved to a similar degree, according to the researchers.

But based on the findings, the probiotic cannot be recommended for children's constipation, lead researcher Dr. Merit M. Tabbers told Reuters Health in an email.

Some parents may still want to try it or other probiotic products, noted Tabbers, a pediatric gastroenterologist at Emma Children's Hospital in Amsterdam. And it's possible, the researcher said, that for certain kids, probiotics will help.

But for now, Tabbers said, "there is not sufficient evidence to support a general recommendation about the use of probiotics in the treatment of childhood constipation."

The study, which appears in the journal Pediatrics, was funded by Paris-based Danone (Dannon in the U.S.), which makes Activia. Two co-researchers on the study work for the company.

The findings are based on 159 children who were 7 years old, on average, and had been suffering from constipation for at least two months.

They were randomly assigned to have two servings of either the probiotic yogurt or the non-probiotic every day for three weeks. In the end, both groups showed similar improvements.

Tabbers said that children in the comparison group did better than expected. One reason might be the general attention that kids in both study groups received, the researcher explained.

All of the children were told, for example, they should try to go to the bathroom after each meal.

In general, less-than-ideal bathroom habits -- like trying to "hold" it in -- are thought to underlie many cases of constipation in children.

That and other differences between children's constipation and adults' might help explain why the probiotic appears to have different effects in kids and adults, according to Tabbers.

Typically, Tabbers said, the first step in easing children's constipation includes teaching them better bathroom habits and making diet changes, like adding more fiber-rich foods such as fruits and vegetables.

If that fails, a doctor might prescribe laxatives.

If parents want to try a probiotic, Tabbers said, they still can. But if there's no improvement within a few weeks, they should move on, according to the researcher.

One theory on why probiotics might help with constipation is that the products help restore any imbalances in the natural, friendly bacteria dwelling in the gut. However, Tabbers said, researchers don't know whether the gut bacteria in healthy children differ from those of children with constipation.

"Further research should therefore also focus on the composition of the microbiota in healthy and constipated children," Tabbers said.