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Could Probiotics Help With Weight Loss?

Researchers are learning more about the link between weight and gut bacteria

Probiotics in digestive track of woman

In the quest for a weight loss magic bullet, some Americans have turned their attention to probiotics. Some believe that probiotic supplements — which support the friendly bacteria that naturally live in the gut — can help them shed extra pounds.


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Are probiotics the weight loss tool we’ve been waiting for? Gail Cresci, PhD, RD, a researcher and expert on the gut microbiome, explains.

How it all started

Years ago, scientists discovered that the makeup of friendly gut bacteria (known as the gut microbiota) was different in people who have obesity than in people with an average weight.

To learn more, researchers implanted friendly gut bacteria from the different types of people into special mice without gut bacteria and found:

  • No weight change when the mice received gut bacteria from people of average weight.
  • Weight gain when the gut bacteria was from a person with obesity.

Given these findings, it seemed possible that gut bacteria play a role in regulating weight.

In humans, the only comparison researchers have to the mice study is with gut microbiota transplants (known as fecal transplants), Dr. Cresci says. Doctors perform fecal transplants for people who have an overgrowth of bad pathogenic gut bacteria called Clostridioides difficile. They place stool from a healthy person into the colon of the person with C. diff.

“Researchers are finding that many naturally thin patients who receive a fecal transplant become overweight over time,” Dr. Cresci says. “Since 40% of Americans have obesity, it’s likely that 40% of the gut microbiota transplants came from a person with obesity, possibly causing this unexpected weight gain.”

Is probiotic-induced weight loss a myth?

These findings created hope and hype that simply popping a pill with the right gut microbiota could be the key to weight loss.

“The problem with this logic is that fecal transfers include trillions of diverse microbes that include bacteria, viruses, fungi and yeasts,” Dr. Cresci says. “With a probiotic, it’s likely a person could only receive a fraction of that, with one to just a few beneficial microbes so there’s no guarantee it will affect weight loss.”

And even newer research looking at synbiotics (the combination of a probiotic and prebiotic) found they didn’t affect weight loss or body composition. It wasn’t a total buzzkill, though: Synbiotics did positively impact the composition of friendly gut bacteria.

“I think it’s safe to say that the available probiotics probably won’t help people lose much, if any, weight,” says Dr. Cresci. “But researchers continue to explore the link between weight and gut bacteria — there’s still potential.”

The right diet may improve your gut microbiota … and your health

Probiotics’ main claim to fame is enhancing your good bacteria and keeping you in tip-top health. Even if a supplement won’t cause the weight to fall off, should you take one anyway for your gut health?


What researchers do know is this: Healthy diet first, supplement second. A balance of healthy sources of proteins, fats and carbohydrates is the most important factor in maintaining good gut bacteria. The friendly bacteria survive and thrive when fed high-fiber foods.

A low-fiber diet (low-carb and high-protein and/or high-fat), though, reduces the number of good bacteria.

“Since a low-carb diet doesn’t offer enough nutrition for the good bacteria, the gut microbiota blend shifts, and the beneficial ones get depleted. The bad bacteria then begin to take over,” says Dr. Cresci.

In one study, researchers found that the bad bacteria consumed the protein and produced byproducts linked to higher rates of colon cancer.

So while the jury is still out on whether probiotics can lead to weight loss, it’s clear, once again, that a healthy diet is key. A high-fiber diet can help you maintain gut — and overall — health. For some people, a probiotic could work alongside a nutritious diet to shore up gut health. Talk to your doctor to see if it’s right for you.


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