Stacked, smothered, loaded: Why fast food's stayed extreme

Michael Abt knows what his customer likes.

That's why the Huddle House CEO is bucking the health-conscious trend with his new hash-brown stuffed and cheese-smothered omelet line, available in bacon, chicken tender and three-cheese varieties.

"We know what our customers are telling us they want. A very small percent of our customers say they want a wider selection of healthier items," Abt said, adding what they do want are rich, flavorful and somewhat indulgent foods.

Source: Car's Jr. and Huddle House

Huddle House is far from alone in offering this craveable food, even as about 64 percent of consumers say it's important to pay attention to nutrition and eat healthily, according to market research firm Technomic.

Recently, Yum Brands-owned Taco Bell launched the quesarito—a burrito wrapped up in a quesadilla—while KFC brought back the Double Down, a dish of bacon, cheese and sauce sandwiched between two fried chicken filets. On its late-night menu, Jack in the Box is advertising a hella-peno burger, which comes with both stuffed and sliced jalapeños, cheese and taco sauce.

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Burger chains Carl's Jr. and Hardee's, which are both owned by CKE Restaurants, have also added to their over-the-top food offerings, items aimed at their demo of "young hungry guys."

"We test all kinds of things … from the very low-calorie items to the very indulgent offerings. Typically the very indulgent ones tend to sell better so more of those survive our testing process and end up being products that we introduce because they're really popular," said Bruce Frazer, CKE's SVP of product marketing and research and development.

Two recent introductions include a fry side item topped with buttermilk ranch dressing and crispy bacon crumbles available at Carl's Jr. Another, the Western X-Tra Bacon Cheeseburger, comes stacked with four strips of bacon and onion rings and sells at both chains.

Both Huddle House and CKE stress they do have some healthier fare. So far, though, customers haven't flocked to it.

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Abt says "there's not a high velocity" of dishes purchased featuring oatmeal, egg whites, multigrain bread and low-fat cheese, though Huddle House does sell them. Meanwhile, salad sales are low while turkey burgers "sell fairly well," CKE's Frazer said.

As far as consumers' desire to eat better, Darren Tristano, executive vice president of Technomic, said "what consumers are saying and what they're doing are a little bit out of sync." Even as many customers pick restaurants based on the availability of more wholesome foods, research shows they typically only order the healthy items about half the time, he added.

Tristano said fast-food restaurants frequently offer items that are noteworthy for their quantity, flavor combinations and spice level to draw attention—especially among millennial and Gen Z customers.

"What we're seeing today is a number of brands that are focusing their promotions on items that are so over-the-top indulgent that it's creating buzz across social media, younger generations and creating kind of a reason for people to not only try it, but to see it," Tristano added.

In the first quarter, 14,801 items on menus nationwide mentioned the words "loaded," "stacked," "smothered" or "stuffed," a slight drop from the year-ago period, Technomic said.

Moving forward, Tristano forecasts the practice will maintain its popularity.

"Healthy food continues to rise in terms of popularity, but indulgency is by no means going away," he said.

—By CNBC's Katie Little.