title: Food quality and motivation: a refined low-fat diet induces obesity and impairs performance on a progressive ratio schedule of instrumental lever pressing in rats.
abstract: BACKGROUND
  Purified high-fat diet (HFD) feeding causes deleterious metabolic and cognitive effects when compared with unrefined low-fat diets in rodent models. These effects are often attributed to the diet's high content of fat, while less attention has been paid to other mechanisms associated with the diet's highly refined state. Although the effects of HFD feeding on cognition have been explored, little is known about the impact of refined vs. unrefined food on cognition. We tested the hypothesis that a refined low-fat diet (LFD) increases body weight and adversely affects cognition relative to an unrefined diet.
  
  
  METHODS
  Rats were allowed ad libitum access to unrefined rodent chow (CON, Lab Diets 5001) or a purified low-fat diet (REF, Research Diets D12450B) for 6 months, and body weight and performance on an instrumental lever pressing task were recorded.
  
  
  RESULTS
  After six months on their respective diets, group REF gained significantly more weight than group CON. REF rats made significantly fewer lever presses and exhibited dramatically lower breaking points than CON rats for sucrose and water reinforcement, indicating a chronic reduction of motivation for instrumental performance. Switching the rats' diet for 9 days had no effect on these measures.
  
  
  CONCLUSIONS
  Diet-induced obesity produces a substantial deficit in motivated behavior in rats, independent of dietary fat content. This holds implications for an association between obesity and motivation. Specifically, behavioral traits comorbid with obesity, such as depression and fatigue, may be effects of obesity rather than contributing causes. To the degree that refined foods contribute to obesity, as demonstrated in our study, they may play a significant contributing role to other behavioral and cognitive disorders.
authors.affiliation: Department of Psychology, UCLA, United States. Electronic address: blaisdell@psych.ucla.edu.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Blaisdell
authors.affiliation: Department of Psychology, UCLA, United States.
authors.forename: Yan Lam Matthew
authors.initials: YL
authors.lastname: Lau
authors.affiliation: Department of Psychology, UCLA, United States.
authors.forename: Ekatherina
authors.initials: E
authors.lastname: Telminova
authors.affiliation: Department of Psychology, UCLA, United States.
authors.forename: Hwee Cheei
authors.initials: HC
authors.lastname: Lim
authors.affiliation: Department of Psychology, UCLA, United States.
authors.forename: Boyang
authors.initials: B
authors.lastname: Fan
authors.affiliation: Department of Psychology, UCLA, United States.
authors.forename: Cynthia D
authors.initials: CD
authors.lastname: Fast
authors.affiliation: Department of Psychology, UCLA, United States.
authors.forename: Dennis
authors.initials: D
authors.lastname: Garlick
authors.affiliation: Molecular Biosciences Degree Program, Kansas University, Edwards Campus, United States.
authors.forename: David C
authors.initials: DC
authors.lastname: Pendergrass
mesh_terms: D000818:Animals; D003071:Cognition / Q000187:drug effects / Q000502:physiology; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D004041:Dietary Fats / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D063427:Food Quality; D009042:Motivation / Q000187:drug effects* / Q000502:physiology; D009765:Obesity / Q000209:etiology* / Q000503:physiopathology; D011597:Psychomotor Performance / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D020318:Rats, Long-Evans
chemical_list: D004041:Dietary Fats
keywords: Junk food; Low fat diet; Motivation; Rat; Refined diet