McDonald's USA on Wednesday announced that its iconic burgers, including the Big Mac and the Quarter Pounder with Cheese, no longer have artificial preservatives, artificial flavours or added colours from artificial sources.

Only the pickle slices still contain an artificial preservative, the American fast-food giant said, noting that "customers are able to skip it if they prefer." The changes are going into effect in all 14,000 US restaurants, the company's statement said.

It's a big attempt for McDonald's -- often vilified as a champion of junk food -- to attract or retain customers concerned about their diets.

"From switching to 100% fresh beef in our quarter-pound burgers, cooked right when ordered, to removing artificial preservatives in our Chicken McNuggets, and committing to cage-free eggs by 2025, we have made significant strides in evolving the quality of our food," said Chris Kempczinski, the company's USA president.

As of now, almost two-thirds of the company's burgers and sandwiches are free of artificial products, which were removed from the company's cheese slices, Big Mac special sauce and several types of buns.

The move is a response to a growing trend of health-consciousness in the United States, particularly attuned to organic products as well as increased concern for product origin and quality.

It's also a way to meet competition from trendy burgers like Five Guys, which emphasises freshness, or more traditional beef patties like Wendy's, which boasts the slogan "always fresh, never frozen." Such moves are not easy to implement in the United States, where McDonald's is generally one of few restaurants accessible to lower-class populations, with price factor often taking precedence over quality.