SAO PAULO (AP) — Prosecutors in Brazil's largest city opened an inquiry Thursday into the mayor's plan to offer school meals with pellets made of reprocessed food.

The investigation comes amid a growing outcry over the pellets, which Sao Paulo Mayor Joao Doria says will help improve nutrition for poor children.

The pellets are made of dehydrated leftovers and resemble popcorn. Some are mixed into other foods, like cakes, while others can be eaten directly. Doria did not specify which kind would go to schools.

Prosecutor Jose Carlos Bonilha told The Associated Press that officials had requested data and tests on the pellets to determine their nutritional value.

"It is not an accusation, but it is a procedure we need to do so we can understand what these pellets are," Bonilha said. "We need forensics to tell us whether this actually has nutritious value or not. If we see that is not the case, we will open a suit."

The company that makes the pellets, Plataforma Sinergia, says they are as nutritious as food in nature.

Brazil made great strides at reducing extreme poverty this century, but it is in a severe economic slump that is affecting millions of families.

Sao Paulo officials do not have data on people living in extreme poverty, so it's unclear how many children Brazil's richest city expects to benefit from the pellets. The U.N.'s Food and Agriculture Organization says in a report based on data from 2015 that less than 5 percent of Brazil's population was undernourished.

Human rights groups have criticized the pellets, calling them degrading. Sao Paulo's nutrition council also has criticized the plan.

On Wednesday, Sao Paulo's city council also requested information on the pellets.