In early May, Chelsea McPherson was ecstatic when she entered the Trader Joe’s in Orem, Utah, and spotted a display of sweet and sour gummy worms. She’d been looking for the new product for three days. She grabbed two packages.

“Immediately, the cashier’s eyes got really big,” said Ms. McPherson, 38.

Trader Joe’s lists resistant tapioca dextrin fiber as the candy’s first ingredient. An eight-piece serving contains only 35 calories but packs 14 grams of fiber. “If you didn’t know, and you ate a whole bag,” the cashier had warned her, “you’d probably be in trouble.’”

Rather than run screaming from the store, Ms. McPherson was thrilled. She immediately opened a package in her car but limited herself to just a couple of worms — to make sure they didn’t make her “regret her choices,” she said. But Ms. McPherson, a stay-at-home mother of five, loved them so much, she has since bought them dozens of times and keeps a package on her bedside table.

The gummies are just one example of candies marketed as “healthy” that are overwhelming shop aisles and social media feeds with promises of recognizable ingredients, less sugar or nutritional benefits. Diet candy, whether described as “better-for-you” or “functional,” has transcended the grocery and convenience store and found its way into gyms and supplement shops, blurring the line between protein bar and indulgence.

It was the cheerful red packaging of Tandy Chocolate’s Protein NomNoms that first caught the eye of Zack Baker, 33, as he shopped in a Harrisonburg, Va., Costco — that, and the word “protein” in uppercase letters.

Over the last few years, he has endeavored to rewire his candy habits. He’s tried Rotten “Gummy Cruncheez” — “healthier Nerds gummies,” as he described them — made from soluble vegetable fiber, allulose (a low-calorie sweetener) and a host of other ingredients that warrant an explanation from Bill Nye. He’s tried Better Sour gummy stars, which come in flavors like passion fruit, guava and calamansi lime. And he’s tried Hormbles Chormbles, a “protein candy” Willy Wonka might manufacture if he got really into creatine.

Mr. Baker’s bulk bag of Protein NomNoms, for its part, was gone within a week.

The trickle-down effects of the Make America Healthy Again doctrine and the ubiquity of GLP-1s have inspired many consumers’ shifting habits toward “functional” candy, sweets purporting to offer some added benefit. And given the online explosion of often-dubious nutrition advice, many Americans believe they’re not doing enough for their health, said Lisa Moskovitz, a dietitian and the owner of New York Nutrition Group. “People become more desperate for quick solutions to why they’re feeling the way they are,” she said.

Functional candy that offers a benefit like added protein, Ms. Moskovitz said, may be less easy to digest than, say, the naturally occurring protein in chicken. And, she added, one must consider what nutrients are being missed when consuming protein candy over a protein-packed whole food. “The concern I have comes from: Is this going to be looked at as a healthy snack?” she said. “The reality is, no. Whole foods have way more nutritional value.”

Pop Up Grocer, a shop in the West Village of Manhattan, specializes in consumer packaged goods aimed at health-conscious shoppers and carries a variety of diet candy. America’s pervasive obsession with diet and longevity has coincided with the “K-shaped” economy, a bifurcation of wealth and spending, to position these alternative sweets as “accessible luxury goods,” as Emily Schildt, the store’s founder, put it.

For some, that transforms candy from a mindless habit to a matter of identity. Pop Up Grocer’s candy is both “indulgent” and “little-treat priced,” she said, which encourages customers to be thoughtful in their selection. “If you’re going to buy something from my store at a premium price point, you’re probably going to want to share it and talk about it, so it’s like, ‘What is the product I want to buy that says something about me?’”

Before the onslaught of “functional candy,” there was “better-for-you” candy in spades.

Better-for-you brands like Unreal Snacks have appealed to the bulk bin set for at least a decade. The company’s most popular product, a dark chocolate coconut candy bar, has just three ingredients that even a Victorian boy might make sense of: organic coconut, organic cassava syrup and dark chocolate. SmartSweets, which advertises an absence of artificial sweeteners, soon followed with products on the gummy and sour sides of the confection spectrum.

“The American consumer has continued to demand more and better of their food and beverage purchases, especially over the last five years,” said Kevin McCarthy, the chief executive of Unreal Snacks.

Eventually, legacy candy caught up. In 2021, the Hershey Company acquired Lily’s, a low-sugar chocolate brand, and announced a relaunch of sugar-free Reese’s peanut butter cups, Twizzlers and other candies with the goal of meeting the needs of diabetic customers.

“The low-sugar approach felt like it was only half of the story,” said Jared Smith, a founder of Hormbles Chormbles. Mr. Smith, 40, was also a creator of the protein-bar company RXBar, which sold to Kellogg for $600 million in 2017. While hawking whole-food protein bars, he still found himself reaching for the nutritionally vacuous snacks of his youth. The Hormbles Chormbles customer base is skewed toward Gen-Z and millennial women, he said, as well as GLP-1 users and protein-maxxers who encounter the product at their gyms.

After seeing Hormbles Chormbles all over social media, Mary-Reagan Keeter, a Gen-Z woman, finally grabbed a bar at a Target in Mount Pleasant, S.C., despite a bit of sticker shock. A 1.05-ounce peanut butter crunch bar, which contains 10 grams of protein and zero grams of sugar, retails for $3.29 at Target.com. (A 1.55-ounce bar of Hershey’s milk chocolate is more than $1 less.)

Ms. Keeter, 24, works in social media advertising and credits much of this candy aisle renaissance to the proliferation of gym culture online. “Seeing all these influencers and famous people get onto the red carpet and look stick-thin,” she said, “will make you think a lot when you’re going into the grocery store to pick out a treat.”

Ms. McPherson, the mother in Utah, has amassed a trove of the Trader Joe’s fiber gummy worms to tide her over until the company restocks them later this summer. More than anything, she said, diet candy is simply fun. “If I find a joyful gummy or chocolate bar,” she said, “I’m like, ‘Absolutely.’ There should be moments of little joy every day.”

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