Restriction of dietary protein in rats increases progressive-ratio motivation for protein

Giulia Chiacchierini, Fabien Naneix, John Apergis-Schoute, James E. McCutcheon* (Corresponding Author)

*Corresponding author for this work

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2 Citations (Scopus)
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Low-protein diets can impact food intake and appetite, but it is not known if motivation for food is changed. In the present study, we used an operant behavioral task – the progressive ratio test – to assess whether motivation for different foods was affected when rats were maintained on a protein-restricted diet (REST, 5% protein diet) compared to non-restricted control rats (CON, 18% protein). Rats were tested either with nutritionally-balanced pellets (18.7% protein, Experiment 1) or protein-rich pellets (35% protein, Experiment 2) as reinforcers. Protein restriction increased breakpoint for protein-rich pellets, relative to CON rats, whereas no difference in breakpoint for nutritionally-balanced pellets was observed between groups. When given free access to either nutritionally-balanced pellets or protein-rich pellets, REST and CON rats did not differ in their intake. We also tested whether a previous history of protein restriction might affect present motivation for different types of food, by assessing breakpoint of previously REST animals that were subsequently put on standard maintenance chow (protein-repleted rats, REPL, Experiment 2). REPL rats did not show increased breakpoint, relative to their initial encounter with protein-rich pellets while they were protein-restricted. This study demonstrates that restriction of dietary protein induces a selective increased motivation for protein-rich food, a behavior that disappears once rats are not in need of protein.
Original languageEnglish
Article number113877
Number of pages9
JournalPhysiology and Behavior
Early online date29 Jun 2022
Publication statusPublished - 1 Oct 2022

Bibliographical note

Acknowledgements: The authors acknowledge the help and support from the staff of the Division of Biomedical Services, Preclinical Research Facility, University of Leicester, for technical support and the care of experimental animals as well as colleagues in the Department of Neuroscience, Psychology and Behaviour at the University of Leicester for their academic contribution. This work was funded by the Biotechnology and Biological Sciences Research Council [grant #BB/M007391/1 to J.E.M.], the European Commission [grant #GA 631404 to J.E.M.], The Leverhulme Trust [grant #RPG-2017-417 to J.E.M. and J.A- S.], and Tromsø Research Foundation [grant #19-SG-JMcC to J.E.M.).

Data Availability Statement

All data and custom analysis scripts are available: and


  • amino acids
  • protein
  • diet
  • motivation
  • progressive ratio
  • rat


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