After a number of failed marketing and rebranding efforts, McDonald’s––one of the biggest purchasers of chicken in the U.S.––has announced that they will begin phasing out the use of antibiotics in their chicken sold at 14,000 U.S. locations. This change applies to their McNuggets and other chicken products.

The phasing out of antibiotics in chicken will take place over the next two years. However, McDonald’s says they will allow suppliers to continue the use of antibiotics that are not important for human medicine.

There are a few theories circulating as to why McDonald’s has decided to go through with such a bold move. First, nontraditional fast food chains such as Chik-fil-A, Chipotle and Panera Bread––who appear to be gaining market share as healthier on-the-go food options––have earned massive success with their sustainable, antibiotic-free meat. Out of the three, Chipotle has been the clear leader in educating consumers about the effects of antibiotics in meat. Also, major retailers such as Walmart and BJ’s have begun selling antibiotic-free chicken, gradually making it the new normal for consumer cooking at home.

In an email to franchisees earlier this week, McDonald’s U.S. president Mike Andres says, “People want to know what’s in their food. Some people say we’re too big and too stuck in the past to make big moves, but I can tell you that we can and we will.”

Andres has only been at the helm of the world’s largest fast food chain for less than a week. His predecessor, Don Thompson, just exited after two years of unsuccessful attempts to improve the chain’s worsening sales record.