Once ubiquitous in products ranging from soda to ketchup, high-fructose corn syrup has fallen out of favor since scientists and consumer advocates identified a possible link between consumption of the compound and obesity and diabetes. Many food and beverage companies, including PepsiCo Inc. and ketchup maker Kraft Heinz Co. , already have removed the sweetener from products or introduced separate lines without it.

At a press event on Monday, McDonald’s supply chain chief, Marion Gross, said it takes time to make changes at a company with 14,000 U.S. restaurants. “It’s been a journey,” she said.

The chemical composition of high-fructose corn syrup, derived from corn, is nearly identical to that of sugar, and it is unclear whether natural sugar is indeed healthier. Medical research has reached conflicting conclusions on whether corn syrup causes weight gain and other health problems.

 The American Journal of Clinical Nutrition in 2008 published a paper concluding that there is no such link. But a 2010 Princeton University study found that rats that consumed high-fructose corn syrup gained significantly more weight than rats that consumed table sugar, even when their overall caloric intake was the same.