The shift was a response to a decline in the quantity and quality of food on offer, the study says.
Study author Michael Gibson-Light said: “Because it is cheap, tasty, and rich in calories, ramen has become so valuable that it is used to exchange for other goods.”
According to US prison data, spending has not kept pace with the number of inmates.
Michael Gibson-Light said staff and inmates at the prison he visited said the amount of food being provided had decreased steadily over decades and warned the shift could have serious implications.
“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,” he said.
“The form of money is not something that changes often or easily, even in the prison underground economy; it takes a major issue or shock to initiate such a change,” Michael Gibson-Light added.
The noodles are exchanged for goods including other food items, clothing, hygiene products and even services such as laundry and bunk cleaning, he said.
Other inmates use them as bargaining chips in gambling when playing card games or participating in football pools.
Ramen noodles are also replacing other traditional forms of prison currency, such as stamps and envelopes, the study found.
The shift was taking place across different groups within prisons and was not a response to bans on tobacco products within the prison system, Michael Gibson-Light said.
The researcher called for more research into what the reduction in food could mean for the care of prisoners.
All states spent about $48.5 billion on prisoners in 2010, 5.6% less than in 2009, according to the US Bureau of Prisons.
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