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“Soda with benefits.” “Microbiome approved.” “A new kind of soda.” The latest crop of fizzy drinks like Olipop, Poppi, and SunSip are healthier than a sugary Pepsi or Coke. That much is clear. But do these pre- and probiotic sodas “support” your digestive health? Here’s a gut check.

What’s a gut-healthy soda?

How do you market a low-sugar soda for “gut health”? Toss in some prebiotics, probiotics, or both.

“Prebiotic” sodas like Poppi, Maya­well, and SunSip and Halfday iced teas add at least one kind of fiber that can feed your gut bacteria. “Probiotic” sodas like Culture Pop add a strain of microbes that can survive the stomach’s acidity (but they may not do much for the gut). Others mix it up. Wildwonder adds a probiotic plus a prebiotic. Olipop, a juggernaut of gut sodas, adds prebiotics plus botanicals (see “Olismart blend”).

One thing is certain: No soda offers the gut health benefits that you’d get from the array of intact fibers in a steady diet of fruits, vegetables, and whole grains. No matter how you spin it, bran flakes and beans beat root beer.

Pepsi vs. Poppi

Guts aside, there’s good reason to pick Soda 2.0 over the sugary stuff:

• Calories & sugar. A 12 oz. Coke or Pepsi has roughly 40 grams of added sugar (about 10 teaspoons). That’s as many calories (around 150) as 3 or 4 Olipops or 5 to 8 Poppis. Most gut sodas have no more than 2 tsp. of sugar.
• Low-calorie sweeteners. Poppi & Co. add stevia or monk fruit extracts. Both beat diet sodas’ aspartame and acesulfame potassium, which we rate as “avoid.”

Prefer your soda less sweet? Culture Pop adds no monk fruit or stevia extract to its diluted fizzy fruit juice.

On the downside, gut health sodas often sell for a pricey $2 to $3 a can. If you want a stevia-sweetened soda—and don’t want to pay for prebiotics or probiotics—try Zevia ($1 to $2 a can).

Inulin

Inulin is a naturally occurring prebiotic fiber found in onions, asparagus, wheat, leeks, and other foods. (Prebiotic fibers are poorly digested carbs that feed your gut bacteria.)

It’s hard to find a food or drink claiming to have pre­biotics that doesn’t use inulin. Most packaged foods that add inulin get it from chicory root, jerusalem artichoke, or agave.

Why is inulin so popular? It can be sweet, so companies may use it to curb the added sugar while upping the fiber. That’s a win-win for labels.

What about your gut? In studies where researchers gave people 5 to 20 grams of inulin a day for 2 weeks to 3 months, the volunteers had higher levels of Bifidobacteria in their stool (and therefore, in their gut) than the placebo takers. But it’s not clear that boosting Bifidobacteria  levels benefits your digestive tract...or any other aspect of your health.

And inulin has a downside. When the bacteria in your gut gobble it up, they release gas. In studies that tested 5 to 20 grams of inulin a day, inulin takers reported more flatulence than placebo takers. (Most “pre­biotic” sodas have 2 to 9 grams of fiber, largely from inulin.)

Do doses under 5 grams also cause gas? Few studies have looked. But people vary. If you tend to have a sensitive gut, odds are that you’ll feel inulin’s gaseous effects at low doses.

Olismart blend

“Olismart” is the proprietary blend of ingredients that Olipop adds to its soda. It includes three prebiotics (cassava root fiber, chicory root inulin, and Jerusalem artichoke inulin) and four botanical extracts (nopal cactus, marshmallow root, calendula flower, and kudzu root).

Cassava root contains resistant starch. Like inulin, resistant starch feeds gut bacteria.

Just don’t expect much from the botanicals. First, it’s not clear how much of each extract is in a can of Olipop. (The company didn’t respond when we asked.)

Second, the research on each of the four extracts is skimpy...or irrelevant.

Take calendula flower (aka marigold). Trials have tested its potential benefits in topical creams and ointments or mouth rinses, not what happens when people swallow it.

As for kudzu, “What we love most at Olipop is the fact that kudzu root contains prebiotic (indigestible) fiber,” says the website. What does kudzu fiber do for your gut? No trials have looked.

Only one decent trial has tested nopal cactus (prickly pear) on GI symptoms. Compared to taking a placebo, taking 20 or 30 grams of nopal fiber a day for one week relieved symptoms of irritable bowel syndrome. Ten grams a day didn’t. (A can of Olipop has 9 grams of fiber, but it’s unclear how much, if any, of that fiber comes from the drink’s nopal extract.)

Then there’s marshmallow root, which yields a gummy substance called mucilage. “Mucilage can also be soothing and protective for the mucous membranes lining your digestive tract,” says Olipop. “This may provide relief for conditions like heartburn, indigestion, and irritable bowel syndrome (IBS).” Interesting theory. Too bad no randomized trials have tested marshmallow root on people.

Bacillus subtilis

Both Wildwonder and Culture Pop add Bacillus subtilis, a shelf-stable probiotic bacteria. But a bacteria’s effects depend on the strain, and Wildwonder didn’t respond when we asked what strain of Bacillus subtilis it uses. Culture Pop’s strain (Bacillus subtilis DE111) “has been proven to support gastrointestinal health and to help reduce gas and bloating,” says the drink’s website.

Not exactly. In the only DE111 study to report on gas and bloating—a pilot study funded by DE111 makers—researchers randomly assigned 44 healthy adults to take either a placebo or 1 billion colony forming units of Bacillus subtilis DE111 every day.

After 4 weeks, the researchers reported, more DE111 takers had reported adverse events—like constipation, diarrhea, gas, and bloating—than placebo takers. Other symptoms (like “GI inflammation,” “gastric function,” and “colon pain”) didn’t vary between groups.

Bottom line: more—and better—studies are needed.