(CBSNews) Ramen noodles are familiar to most Americans for their low cost, long shelf-life and dose of salty calories.

Now the instant noodle dish has taken on another role: as the unofficial currency of choice inside the U.S. prison system. That’s according to research from Michael Gibson-Light, a doctoral candidate in the University of Arizona School of Sociology, who spent a year researching labor within a male state prison with more than 5,000 inmates. 

One surprising finding, he wrote, was “the role of ramen noodles” as money.

While tobacco products have long served as the de facto informal currency of the prison system, cigarettes are now relegated below the value of ramen noodles. The main reason appears to be cutbacks in meal spending as prisons seek to control costs by privatizing services such as food and health care. That has resulted in smaller rations and poorer food quality, which leads some prisoners to seek out ramen as a way to supplement their diets.

“Food service costs have been reduced by purchasing ever-cheaper provisions, shrinking serving sizes, and limiting the number of meals that inmates receive per week,” Gibson-Light wrote in the paper, which was presented on Monday at the American Sociological Association’s 111th Annual Meeting,

His research found that after the prison switched to a new private vendor more than a decade ago, prisoners were no longer served three hot meals a day. Under the new company, inmates had their second meal changed to a cold sandwich and a bag of chips, while lunch was eliminated from weekend menus. Portion sizes were also cut.

A worker at the food service company told Gibson-Light the changes meant the prison was spending $1.25 per tray for each inmate meal, compared with $2 per tray before that. 

The privatization of prison services is part of a growing trend that’s increasingly coming under scrutiny by prison-reform advocates and policymakers. Some businesses are making a bundle from the captive audience of 2.2 million people behind bars in America. Phone companies charge as much as $1 a minute for calls to people who are in prison, creating a $1 billion industry. 

That may bring a smile to some taxpayers and prison administrators, but inmates haven’t been happy about the food reductions, Gibson-Light found. The prisoners he interviewed or observed complained about portion sizes and food quality. He also said some correctional officers warned him not to eat the food “lest I get sick.”

Inmates told him the food wasn’t providing “enough calories for a grown man” and that “you’re gonna starve” if you can’t find other sources of nutrition.

Enter the ramen noodle economy.

Prisoners buy ramen noodles at the commissary, although Gibson-Light found that prices have increased while inmate work wages haven’t caught up. A pack of ramen noodles sells for 59 cents, or much higher than what consumers pay in stores. Walmart sells 12-packs of ramen for $2.39, or about 20 cents per pack.

“In many accounts across several months, all inmates reported that they use ramen packets to pay for goods or services from other inmates, with many stating that they acquire essential goods (e.g., denture cream or other food) primarily by paying others in ramen,” the paper said. “This change in prison monetary practices reflects the changing needs of inmates: nonessential luxury goods like tobacco (inmate wants) have been surpassed by essential forms of sustenance (inmate needs).”

Interestingly, the ramen economy has created a system not unlike the financial system outside prison. Inmates build up debts based on ramen, and some inmates provide credit to other prisoners who want to purchase ramen but at the moment lack the means.

“Inmates who repay their debts quickly were sometimes granted higher credit limits,” Gibson-Light wrote. “They could even refinance their debts by utilizing credit from different black market stores.”

This also creates a dark side to ramen: Inmates who don’t pay up. Some of them enter protective custody “to escape debt collectors,” he noted. “This is a strategy best saved for the desperate, however, since it left men permanently ‘marked’ among the inmate community.”