Costings released to the Scottish Conservatives show meals at HMP Kilmarnock cost £4.71 compared to £3.69 at NHS Ayrshire and Arran.
The figures also reveal prisoners at the Lilias Centre in Glasgow are served meals valued at £5.30 while those given to patients of NHS Greater Glasgow and Clyde are worth £4.32.
The party has also found prisoners held in England and Wales are fed for less than in Scotland, with the average cost per day for prisoners in Scotland put at £4.27 against an average of £2.70 south of the border.
Rachael Hamilton MSP, Scottish Conservative deputy leader, said: “It is completely outrageous that many prisoners in Scotland seem to be better fed than some hospital patients.
“Scots will be wondering why more money is being spent per prisoner here compared to what is being spent in England and Wales.
“Complaints about the food served up in Scotland’s hospitals is sadly all too common so it is appalling that prisoners seem to be getting better treatment.
“It is common sense that more should be spent serving up healthy and nutritional dishes to poorly patients.
“The public and victims of crime will rightly question why criminals behind bars receive better quality meals than patients stuck in Scotland’s hospitals.
“SNP ministers should urgently look into this spending disparity and ensure patients are prioritised over prisoners.”
A Scottish Government spokesperson said: “Prison food is the responsibility of the Scottish Prison Service, who have a responsibility to provide healthy and nutritious meals for everyone in their care, and health boards are responsible for patient food.”
A Scottish Prison Service spokesperson said: “Our staff work hard to serve a varied and nutritious diet to people in our care, while also ensuring value for money.”
Nicola Graham, director of infrastructure and support services at NHS Ayrshire and Arran, said: “NHS Ayrshire & Arran regularly receives positive feedback from patients on the quality of meals provided across our inpatient areas.
“At NHS Ayrshire & Arran, we develop menus for inpatients according to national guidance and standards. Available guidance provides information for NHS Scotland health boards on expected standards of nutritional care, nutrient and food provision for patients within hospitals.
“It also provides guidance on how the appropriate standards can be met, through assessment of the hospital population’s dietary needs, menu planning, and practical suggestions on food choices suitable for different dietary needs, including special and therapeutic diets.
“Through our in-house production, our aim is to meet the standards set out in the guidance in the most cost-effective way we can, providing meals for our patients that are nourishing, nutritious and appetising.”