This week, Subway found out customers don't like eating a chemical found in yoga mats, shoe rubber and synthetic leather.
After one blogger's petition against azodicarbonamide generated widespread uproar, the sandwich chain announced plans to remove the ingredient from its bread. Currently, its 9-grain wheat, Italian white and sourdough breads contain it.
"We are already in the process of removing azodicarbonamide as part of our bread improvement efforts despite the fact that it is a USDA and FDA approved ingredient. The complete conversion to have this product out of the bread will be done soon," Subway told CNBC in an email.
The move has at least one other major chain pondering its own products containing the chemical, but its use at other restaurant chains is fairly widespread.
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Although the product is approved for use in the U.S. as a dough conditioner and flour bleaching agent up to a certain limit, Europe and Australia have banned it as a food additive, writes Vani Hari, who drafted the petition and runs the site FoodBabe.com. Hari noted that her site's traffic has doubled since she began the petition. To date, it's drawn more than 75,000 signatures.
According to restaurant websites, here is a list of some products that contain it as an ingredient:
Burger King, Chick-fil-A, Wendy's, Arby's and Jack in the Box did not respond to multiple attempts for comment.
Following Subway's announcement, McDonald's spokeswoman Lisa McComb told CNBC: "Azodicarbonamide is commonly used throughout the baked goods industry, and this includes some of the bread goods on our menu. While this ingredient is recognized as safe and approved by the FDA, we listen to our customers and evolve to continue to serve the great tasting, quality food they expect from McDonald's. This ingredient, like all the ingredients we use, is available to consumers on our website."
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In an email to CNBC, Dunkin' Donuts said, "There are trace amounts of azodicarbonamide, a common ingredient approved as safe by the Food and Drug Administration, in three Dunkin' Donuts bakery items, including the Danish, Croissant and Texas Toast. All of our products comply with federal, state and local food safety standards and regulations. We are evaluating the use of the ingredient as a dough conditioner in our products and currently discussing the matter with our suppliers."
Following Hari's petition, the nonprofit Center for Science in the Public Interest lobbied for the USDA to consider barring it. It noted that when bread containing the chemical is baked, it produces the carcinogen urethane and "leads to slightly increased levels of urethane in bread that pose a small risk to humans" when azodicarbonamide is used at its maximum limit.
Evidence also suggests the product is harmful in its more industrial form. The United Kingdom's Health and Safety Executive lists it as a substance that can cause occupational asthma.
Meanwhile, a World Health Organization report states, "Case reports and epidemiological studies in humans have produced abundant evidence that azodicarbonamide can induce asthma, other respiratory symptoms, and skin sensitization in exposed workers. Adverse effects on other systems have not been studied."
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At Starbucks, a shift is already underway from the ingredient as part of its transition to La Boulange Bakery products. Currently, the company's butter croissants and chocolate croissants contain azodicarbonamide.
"Our new La Boulange Bakery goods do not contain the ingredients. Our goal is to transition all the stores to La Boulange. We're about halfway through that transition," Starbucks spokeswoman Linda Mills said in a phone interview.
Still, there are no plans to ax the ingredient from stores that have yet to switch.
"We're so close to the transition—so, no, we won't be changing the recipe for the current croissants," Mills said.
—By CNBC's Katie Little. Follow her on Twitter @KatieLittle.