The sodas come in fun flavors like Cherry Vanilla and Orange Cream, and carry an alluring claim: They’re good for your gut. That pitch has helped prebiotic soft drink brands like Poppi and Olipop stand out in the soda aisle.

The drinks contain prebiotics, or dietary fibers that can’t be digested by humans, but can feed the beneficial microbes that live in our guts, said Hannah Holscher, an associate professor of nutrition at the University of Illinois Urbana-Champaign. (Probiotic products, by comparison, contain live microbes themselves.)

But nutrition experts say you don’t need a special soda to reap those benefits: Many foods, like garlic, onions, peas, beans, lentils, grains and some fruits, are naturally rich in prebiotic fibers.

“If you eat a high fiber diet, you’re taking care of your prebiotics pretty well,” said Marion Nestle, an emeritus professor of nutrition, food studies and public health at New York University.

Inulin, the main prebiotic fiber used in these sodas, can be isolated from plants, such as agave or chicory root, said Dr. Holscher, who has accepted travel and speaking fees from Beneo, a company that manufactures ingredients, including prebiotic fibers.

The amount of fiber in prebiotic beverages varies. A can of Orange Cream Poppi has two grams of dietary fiber; a Strawberry Vanilla Olipop has nine grams. U.S. dietary guidelines recommend 28 grams of fiber for a 2,000 calorie per day diet, but most Americans fall far short of this goal.

It’s best to get your fiber from a variety of foods like fruits, vegetables, whole grains, nuts and legumes, because they’re also rich in vitamins, minerals and beneficial compounds called phytochemicals that can only be found in plants, Dr. Holscher said. A medium apple, a cup of cooked broccoli, and a cup of cooked steel cut oatmeal each contain five grams of fiber; a half cup of lentils and a cup of raspberries each contain eight grams.

These foods also provide multiple types of fibers — not just one or two, as you might find in sodas or other products with supplemental fiber. “It’s these complex mixtures of different fibers that support lots of different microbes” and general gut health, Dr. Holscher said.

But, Dr. Holscher added, foods or beverages with added fibers can help you meet your fiber goals. And some small studies have linked prebiotics, in both supplements and added to foods, with a healthier gut lining, improved insulin sensitivity and increased feelings of fullness. They also suggest that prebiotics may be able to provide some relief from constipation. That said, this evidence is mixed; other studies have not found benefits of prebiotics.

You typically need at least three grams of prebiotic fibers to begin to see any benefits, and at least 12 grams of inulin are generally needed to relieve constipation, Dr. Holscher said.

But there can be downsides to fiber, too, especially if you increase your consumption too suddenly. Inulin fiber, which is used in prebiotic sodas, can cause digestive discomfort, Dr. Holscher said. As little as one to five grams can cause mild flatulence, for instance, and larger doses may lead to bloating. Some people “can’t even look at a food product that contains inulin without getting gas and bloating,” Dr. Holscher said, while others may experience no symptoms.

People with irritable bowel syndrome can be particularly sensitive to these effects; inulin and other prebiotic fibers are considered FODMAPs, types of carbohydrates that can worsen I.B.S. symptoms in some people. While these drinks typically have significantly less added sugar than a traditional soda, they still contain sugar — which might also exacerbate I.B.S. symptoms, said Dr. Sean Paul Spencer, a gastroenterologist and researcher at Stanford University.

The best way to nourish the microbiome, he said, is to eat whole foods and limit sugar, processed foods and emulsifiers, which may negatively affect it.

Poppi soda also contains apple cider vinegar, which some small studies suggest can help lower blood sugars when consumed before a meal. But whether there is enough vinegar in a can of Poppi to have that effect isn’t clear, said Carol Johnston, a professor of nutrition at Arizona State University. The company did not respond to a question about the amount of apple cider vinegar in its beverages.

Olipop is marketed as containing “botanicals,” with several plant extracts like calendula and nopal cactus listed among its ingredients. As to whether there are any benefits of these substances, Dr. Johnston said: “Who knows?” These ingredients haven’t been well studied.

Prebiotic sodas aren’t likely to harm your health, Dr. Nestle said, but it’s also not likely that they’ll be beneficial.

“Really, if people are concerned about their microbiome, they need to eat vegetables,” Dr. Nestle said. “Vegetables would do wonders.”