The Food and Drug Administration has approved the key ingredient in the vegetarian-friendly Impossible Burger. It's a big win for Silicon Valley-based Impossible Foods as it expands its distribution.

The ingredient, soy leghemoglobin, releases a protein called heme that gives the meat substitute its distinctive blood-like color and taste. Just as the Impossible Burger was gaining in popularity and reach, The New York Times published a report last year revealing that the FDA was concerned that the soy-based ingredient had never been consumed by humans.

In a letter to Impossible Foods released Monday, the FDA deemed soy leghemoglobin GRAS, or generally recognized as safe, in its most recent review.

“Getting a no-questions letter goes above and beyond our strict compliance to all federal food-safety regulations,” Impossible Foods founder and CEO Patrick O. Brown said in a statement. “We have prioritized safety and transparency from day one, and they will always be core elements of our company culture.”

Impossible Foods has been expanding despite last year's controversy. No longer only available at high-end restaurants, the meat substitute can be found at places like White Castle and the Oakland Alameda Coliseum. This spring, Impossible Foods made its first foray into the international market by expanding into Hong Kong.

The FDA's decision is also good news for Impossible Foods' big-name investors, including Microsoft founder Bill Gates, Google Ventures and UBS.

