By Justin Worland, TIME

For years, Jamba Juice has marketed healthy and nutritious smoothies blended with 100% fruit juice. But the website Hack the Menu points out a “secret menu” with items like “Red Gummy Bear” and “Pink Starburst“—both allegedly blended to taste like their candy namesakes. The rumored off-menu offerings sound a little sweeter, but potentially less healthy.

Jamba Juice (JMBA) is not alone in its reputation for having a secret menu: according to Hack the Menu, restaurant chains like Starbucks(SBUX), In-N-Out Burger and Chipotle (CMG) also oblige off-menu requests for those in the know. TIME looked into why restaurants might bother with a whole other menu, and whether secret menu options are always less healthy than their advertised counterparts. The answer is more complicated than we expected.

Surprisingly, most nutritionists we spoke to had never heard of the concept of secret menus. Their feelings were mixed, but most said they were concerned about the lack of readily accessible nutritional information for off-menu items.

“So many consumers are looking for transparency,” said Keri Gans, a registered dietitian and author of The Small Change Diet. “If you want a secret menu, at least make it obvious what the calories are and [put] the nutrition analysis where it’s available for people to see.”

Excluding unhealthy items from a menu helps avoid having to disclose their lack of nutritional value. This is especially true in places like New York, where the law requires restaurant chains to display certain nutritional information in menus. That regulation doesn’t apply to items that aren’t on the menu, or those listed on a menu for less than 30 days, the New York City Department of Health and Mental Hygiene wrote in an e-mail to TIME. Secret menu items “undermine the intention of the rule,” though they’re technically legal, it said.

A lack of transparency becomes a potential problem for people with allergies, who may not be aware of what ingredients are included in the item they’re ordering, nutritionists said.

“To me, the most important thing is that the staff would be educated on what the ingredients are,” said Gans.

Spokespeople for most of the chains contacted by TIME denied the existence of a “secret menu,” but acknowledged that customers can customize their orders.

“Our people are trained to make what customers want with the ingredients we have,” said Chipotle communications director and spokesperson Chris Arnold in a statement. Nachos and a quesarito, a mammoth burrito inside a quesadilla, are among the items that customers order off-menu at Chipotle, according to Hack the Menu.

But despite their shroud of secrecy, secret menus don’t appear to be all bad news, nutritionists said. Some have options that appear healthy, while others allow customers to modify a menu offering in a way that makes it healthier, said Jessica Levinson, founder of nutrition consulting business Nutritioulicious. She cited an option to swap out mayo for mustard at Burger King (BKW) as one such option.

Registered dietitian Judy Caplan praised efforts to offer healthy options, but said she wasn’t surprised that some fast food restaurants would offer less healthy options off the menu. While fast food has become more nutritious in recent years, and chains have recently cut calories in new menu items by 12%, there are still many customers who want unhealthy food, she argued.

“When you’re in business,” she said, “the customer is always right.”