At the end of the first 12 weeks, the women taking the probiotics lost an average of 9.7 pounds, versus the 5.7-pound average weight loss for women taking the placebo.
But here's the kicker: During the second 12 weeks, the placebo group of women maintained their weight loss, but the women who were taking probiotics kept right on losing weight, for a total average weight loss of 11.5 pounds.
In other words, the women in the probiotics group lost nearly twice as much weight overall on average. They also lost more fat mass. What's more, women in the probiotic group also saw a 25 percent drop in their blood levels of leptin, a hormone that seems to be a key player in regulating appetite and metabolism.
While the researchers only looked at one type of probiotics, they say other probiotics found in dairy products may well have a similar effect.
So what about the fellows, you ask? The menfolk who took the probiotics didn't seem to lose any more weight than those who took the placebo.
"We don't know why the probiotics didn't have any effect on men. It may be a question of dosage, or the study period may have been too short," Angelo Tremblay, an obesity researcher at Laval who led the research, said in a statement.
One interesting difference among the genders occurred in the gut. The men taking probiotics didn't experience any significant changes in the makeup of the microbes living in their stomachs.
But it was a different story altogether in women: The probiotic treatment, the researchers note, appeared to "substantially and significantly" reduce the amount of bacteria in the Lachnospiraceae family in the ladies' bellies. Those beasties belong to a group of bacteria that have previously been linked with obesity — although, as the researchers note, scientists are still trying to pin down exactly what role they may play.
That hint that the probiotics might somehow be affecting the women's gut microbiome is intriguing. That's because in recent years, studies have shown that lean people have more species and more numbers of critters living in their gut than obese people do. And in one highly publicized study from last year, researchers were able to make mice lean or obese by altering their gut bacteria.
"The link between the gut microbiota ... and weight maintenance is very compelling," Colin Hill, a microbiologist at University College Cork in Ireland, tells The Salt in an email.
But here's the thing: The bacteria that live in our gut are completely different from the ones we consume in yogurt or probiotic supplements. In fact, Lactobacillus and other bacteria in yogurt don't even stick around for long in our bodies after we eat them. And while evidence is growing that eating probiotics may have an overall good effect on health, researchers are still trying to puzzle out which strains might be helpful, why and how.
So what everybody in the probiotics world wants to know is: Can the party-hopping bugs in your Yoplait really influence the long-term inhabitants in your belly?
The new study has "thrown up several interesting leads," says Hill, but it really doesn't answer those big questions.
One thing that's clear, though: No matter how those friendly bugs in our food may be working, you still have to eat the right stuff to get the weight loss effect. In other words: Keep the kale salads coming; hold the burger and fries.
Copyright 2014 NPR.