Mikalah Harp’s weekly Whole Foods run starts in the produce section, dutifully winds through the store and ends with the best part. On a shelf at the far end of the store is her favorite treat: Olipop’s grape-flavored “prebiotic” soda.

This category of beverage, which appeared seemingly everywhere almost overnight, is hard to miss thanks to its beckoning pastel packaging and brightly printed text. The flavors alone do not sound all that exciting: “Cherry Cola,” “Classic Grape,” “Crisp Apple,” but that’s part of their appeal. To shoppers like Ms. Harp, the simple names suggest the drinks are made with just a few clean ingredients that can help keep them healthy.

When Ms. Harp, 30, gets home, she patiently places her four-pack in the perfect spot in the fridge. By the time she reaches for a can at dinnertime, it’s perfectly chilled and fizzy. She does her best not to pop one open before dinner, she said, but after successfully drinking only water all day, every once in a while she just can’t resist.

“Sometimes, I get a little eager and I’ll open it up just before dinner’s ready and I tell myself I can go ahead and have a little sip now,” she said. “I use it as kind of a reward to myself.” As an added benefit, she says she does not feel guilty like she once did when she treated herself to traditional soda.

Ms. Harp, who loves this treat, is lucky. She’s living in the golden age — or fizzy bubble — of gut soda. From January 2024 to January 2025, Olipop and Poppi retail sales totaled more than $815 million in the United States. Coca-Cola, which recently introduced its own prebiotic soda, said it expected these products to generate more than $2 billion in sales by 2029. In announcing that it had purchased Poppi for nearly $2 billion this month, PepsiCo said it acquired the brand partly because it hoped to “offer more positive choices” to shoppers.

“People feel as though this is going to finally make them healthy,” said Gary Wenk, a psychology and neuroscience professor at Ohio State University. “It’s a fad, it’s a gimmick. But you know what? In this case, it’s kind of a good gimmick.”

Mr. Wenk, who has studied soda for decades, said the drinks were better alternatives to traditional soda because they had fewer sweeteners, which is a step in the right direction for people’s health. But more than anything else, he said, people are gravitating to them because they’re novel.

On the heels of Coca-Cola announcing its new prebiotic soda and PepsiCo entering the space, Atlanta — Coca-Cola’s hometown and the city with the third-highest soda consumption in the country — offers a window into the modern-day soda wars and the people who love the new drinks.

Fans, who in many cases were loyal traditional soda drinkers, said they noticed the arrival of the new-age sodas on shelves, at events and in restaurants, and they welcomed the change. After all, everyone needs a treat. And unlike traditional soda, which they’ve been told is unhealthy, they say popping a can of a prebiotic with lunch or at the end of a long shift comes with no guilt. Whether they’re watching their sugar consumption or trying to get through a sober spell, the new sodas are a way to balance decadence with abstinence.

In one Kroger in Atlanta, packs of Poppi sit in their own section at the very front of the store; at Publix, a mix of the most popular brands can be found in the “soft drink” aisle on a shelf above classic brands like Coke and Pepsi. A Walmart representative said that after seeing growth in the sparkling beverage market, especially among brands with purported added health benefits, the company created a special “modern soda” aisle to house the beverages around the country.

Kate Terentieva, an Atlanta-based creative director in the advertising industry, recalled spotting an enormous billboard for Olipop’s lemon-lime soda along the city’s constantly busy Piedmont Avenue last year. She said everything about the ad, from the flavor to the location, felt like an intentional play for Coke’s customers.

“Atlanta is home to Coca-Cola and that’s always getting shoved down our throat,” she said. “Brands like Olipop and Poppi may tap into people’s FOMO and deprivation of variety” in the city, she said.

Ms. Terentieva’s hunch about the flavor was not exactly wrong. Ben Goodwin, Olipop’s chief executive, mixes and tests Olipop’s flavors in a lab. Soda, in many ways, is an essential part of American life and culture, he said, and that’s why many of Olipop’s flavors are inspired by classic flavors that connect to deep memories for people.

“Ninety percent of the flavors have purposefully had some kind of nostalgia,” he said. The Crisp Apple flavor — the company’s “runaway hit” — is reminiscent of Martinelli’s, its Peaches and Cream shares the flavor profile of the peach gummy rings Mr. Goodwin grew up eating, and its Watermelon Lime flavor is like a watermelon jolly rancher.

Mr. Goodwin says he labors over the company’s flavors, trying to find the right balance of flavor-filled, but not too sweet because he does not want customers to feel guilty for enjoying their little treat. By all accounts, his plan is working.

In February, Olipop — whose investors include Gwyneth Paltrow, Mindy Kaling and the Jonas Brothers — reached a $1.85 billion valuation after raising $50 million in its latest round of funding. A week later, Coca-Cola released Simply Pop, its own prebiotic soda through its Simply brand. Simply’s senior director of brand marketing, Terika Fasakin, told Marketing Dive that “you would have to be under a rock” to miss the growth in the prebiotic soda market.

In Atlanta, people’s desire for nonalcoholic options is also most likely driving the turn to prebiotics. A 2024 study analyzing national search terms related to sobriety and nonalcoholic drinks concluded that Atlanta was the most sober-curious city in the country. The city’s first nonalcoholic bottle shop, the Zero Co, opened in December 2022; the next month, the Sober Social, an alcohol-free bar and coffee shop arrived; that summer, Soberish, a store selling nonalcoholic wines, beers and spirits along with CBD and THC adaptogenic drinks followed.

“There’s a really heavy presence of wellness offerings in Atlanta,” said Blair Crosby, a beverage recipe developer and drink content creator in the city. Prebiotics play into that.

A little peach purée, apple cider vinegar and honey mixed in with Olipop, Poppi or even a sparkling water and topped with basil leaves and peach slices can transform someone’s day, she said.

Ms. Crosby said the city’s “love of fizz” was most likely driven by people’s desire to bring an element of simple luxury into their homes while being mindful about their health, a trend she thinks began during another difficult time: the coronavirus pandemic.

“Things are expensive, life sometimes just overwhelmingly sucks and it’s great to be able to create a little moment of joy in your own place, whether that’s with a solo sleepy time mocktail or while hosting friends,” she said.

Doctors, dietitians and scientists agree that while prebiotic sodas are generally better than traditional sodas because of their lower sugar content (and better than the sugar replacements in most diet sodas), the jury’s still out on whether they contain enough fiber to have significant gut health benefits.

A can of Olipop has nine grams of fiber, almost a third of the recommended amount for adults, and a can of Poppi has about 2 to 3 grams of fiber, about 10 percent of the recommended amount. In June, Kristin Cobbs, a California resident, took Poppi to task, leading a class-action lawsuit against the company — whose cans used to say: “Be Gut Happy. Be Gut Healthy.” Poppi reached a settlement with the plaintiffs this month, agreeing to pay $8.9 million.

“Poppi acknowledges no fault, liability or wrongdoing, and instead, we are focused on bringing consumers the innovation they expect from the brand they love,” Farial Moss, Poppi’s communications director, said in an email.”

Keysha Milana, a wellness coach and Ph.D. student now living in Illinois, said she first tried a prebiotic soda after being flooded with Poppi ads while living in Atlanta. Though she’s a fan of both Poppi and Olipop, she now almost exclusively drinks Olipop.

“At first, it was an alternative to something bad, but now it’s just the norm,” Ms. Milana said, adding that when her 17-month-old son is older, she plans to keep traditional soda off-limits, but not prebiotic soda.

During the week, she takes Olipop’s tropical punch or strawberry vanilla to work and about 30 minutes before lunch, she sticks it in the freezer so it’s “ice, ice cold” when she drops a reusable straw in the can.

“That gives me an endorphin boost to signify that I’m getting something that I worked for,” she said. “I still feel good when I’m drinking that versus what I normally would have been drinking, so I feel proud of myself, too.”