A study by Michael Gibson-Light, a doctoral candidate in the University of Arizona School of Sociology, is pegging the shift on poor food quality and quantity.
"The chow is really bad. They give you little kid meals like that's enough calories for a grown man," one inmate lamented.
Gibson-Light spent 12 months researching at an unnamed state prison facility which housed more than 5,000 inmates. He spoke to 50 inmates and seven staff members.
In the early 2000s a major shift occurred as the prison switched to a different private firm to oversee the food service.
Inmates had been getting three hot meals a day "but, only a few years later, the second meal was reduced in size and changed to cold-cut sandwiches and a small bag of chips. Lunch was completely removed from weekend menus and portion sizes in every meal were reduced," his paper reads.
"One way or another, everything in prison is about money," another inmate said.
"A soup is everything ... many people will trade anything they own to get one," one of the inmates told Gibson-Light. "It's 'cause people are hungry. You can tell how good a man's doing by how many soups he's got in his locker. '20 soups? Oh, that guy's doing good!'"
A packet of ramen at this prison will set an inmate back $0.59 a pack. Down at your local grocery store you can often find them 10 for $10.00.
"Prison is like the streets -- you use currency for everything. In here, it's soups," one inmate said.
Gibson-Light said he was surprised to hear that soups (packs of ramen noodles) were being used as payment -- instead of tobacco products -- for services such as bunk cleaning and laundry, as well as for getting essential goods, like denture cream or other food.
He cited similar studies showing the same trend, where food products are replacing tobacco as informal money among inmates, and he called for a more extensive look at prison food services.
"The use of cigarettes as money in US prisons happened in American Civil War military prisons and likely far earlier. The fact that this practice has suddenly changed has potentially serious implications," Gibson-Light said.
He presented his research at the American Sociological Association's 111th Annual Meeting in Seattle.