For Chipotle, tortillas stand between the Mexican chain and eliminating preservatives.
"Only the tortillas have preservatives. Right now, our focus there is eliminating GMO ingredients, which we hope to finish by the end of this year," said Chris Arnold, Chipotle's communications director.
On its nutrition page, Chipotle said it is working with its suppliers to eventually eliminate artificial preservatives from its tortillas.
McDonald's spokeswoman Lisa McComb said the fast food giant's chefs work closely with suppliers to continue to evolve its menu and serve customers quality, safe good.
"All of our ingredients are commonly used by the food industry and meet recognized food quality and safety standards in the U.S." she said. "We will continue to listen to our customers and evolve our menu to meet their changing needs."
Read MoreFast food CEO: Minimum wage hikes closing locations
In a nod to menu transparency, McDonald's also recently revamped its website to address common questions about its food and stress that its ingredients meet "recognized food quality and safety standards."
Burger King said it did not have any news to share regarding its ingredients.
In an email, Michelle King, Dunkin' Brands' senior director of global public relations, said Dunkin' Donuts and Baskin-Robbins use high-quality ingredients that have been FDA approved and comply with the company's "stringent" quality and food safety standards.
"We review our ingredients on an ongoing basis and optimize our formulas based on current market trends and regulatory activity," she added.
During the last few years, Taco Bell has been in talks with its suppliers about clean label ingredients. The company has already made headway into removing transfat.
"Our food innovation teams have worked quietly behind the scenes to make important ingredient changes over the years. For example, we've reduced sodium in menu items by 20 percent, switched to a zero-grams transfat oil and are committed to removing all artificial transfats and palm oil from our menu," said Rob Poetsch, Taco Bell's director of public affairs and engagement.
Wendy's did not respond to CNBC's emails for comment.
CORRECTION: A previous version had an incorrect spelling of the first name of Vani Hari.