Forget cigarettes, fish and postage stamps — the most popular currency in prison these days is ramen. In a study released Monday by the American Sociological Association, researchers found that hungry state inmates have been trading ramen noodles as a way to deal with declining prison funding.

"Prisoners are so unhappy with the quality and quantity of prison food that they receive that they have begun relying on ramen noodles — a cheap, durable food product — as a form of money in the underground economy," Michael Gibson-Light, the author of the study and a doctoral candidate at the University of Arizona, said in a news release. "Because it is cheap, tasty, and rich in calories, ramen has become so valuable that it is used to exchange for other goods."

State spending on corrections has been declining for a while. In 2001, state expenditures on corrections totaled $53.5 billion, according to a report from the Bureau of Justice Statistics cited in the study. By 2010, it was down to $48.5 billion.

Per capita expenditures also dropped, going from a mean of about $32,000 in 2001 to about $28,000 in 2010. 

In order to deal with this, some inmates have begun trading ramen noodles for snacks, services and clothing, according to Gibson-Light, who studied one male state prison for about a year. People gamble with them, as well.

"You can use it to barter — it's worth a dollar. You buy them at the commissary for a dollar apiece — I'm sure the prices have changed now," author Gustavo "Goose" Alvarez told NPR in 2015 while promoting his prison ramen-centered book. "Some people don't like them, some people will never eat them, but they use them — that's their funny money."

Ramen is easy to make and customize in prison. Even rappers Lil Wayne and Ja Rule, both of whom had to spend time in New York City prisons, have discussed how much they liked the dish. During a phone conversation with Ja Rule last year, Lil Wayne said crunching up Doritos and mixing the crumbs with ramen noodles made his favorite meal, MTV News reported.

However, the fact that prisoners have drastically switched up their unofficial currency system is worrisome, according to Gibson Light. It could point to real issues within American prisons' feeding schemes.

"The form of money is not something that changes often or easily, even in the prison underground economy," he said, adding that it could have "potentially serious implications" for institutions.