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

Physiol Behav. 2022 Oct 1;254:113877. doi: 10.1016/j.physbeh.2022.113877. Epub 2022 Jun 11.


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.

Keywords: Amino acids; Diet; Motivation; Progressive ratio; Protein; Rat.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Appetite
  • Conditioning, Operant
  • Diet, Protein-Restricted
  • Dietary Proteins* / pharmacology
  • Food Preferences
  • Motivation*
  • Rats


  • Dietary Proteins