Fasting for 24 hours heightens reward from food and food-related cues.
BACKGROUND
We examined the impact of a 24 hour complete fast (vs. fed state) on two measures of food reward: 1) 'wanting', as measured by response to food images and by the relative-reinforcing value of food (RRV), and 2) 'liking', as measured by response to food images and the hedonic evaluation of foods consumed.


METHODS
Utilizing a randomized crossover design, 15 subjects (9 male; 6 female) aged 28.6±4.5 yrs with body mass index 25.3±1.4 kg/m(2) were randomized and counterbalanced to normal feeding (FED) and 24-hour fast (FASTED) conditions. Trait characteristics were measured with the Three Factor Eating Questionnaire. Two computer tasks measured food reward: 1) RRV progressive ratio task, 2) explicit 'liking' and 'wanting' (Leeds Food Preference Questionnaire, LFPQ). Also measured were ad libitum energy intake (EI; buffet) and food 'liking' (visual analogue scale) of personalized stimuli.


RESULTS
There were no significant anthropometric changes between conditions. Appetite scores, hedonic ratings of 'liking', and ad libitum EI all significantly increased under the FASTED condition (p<0.05). Under the FASTED condition there were significant increases in the RRV of snack foods; similarly, explicit 'wanting' and 'liking' significantly increased for all food categories. 'Liking' of sweet foods remained high across-meals under FASTED, but savory foods decreased in hedonic saliency.


CONCLUSIONS
Relative to a fed state, we observed an increase in hedonic ratings of food, the rewarding value of food, and food intake after a 24 hr fast. Alliesthesia to food and food cues is suggested by heightened hedonic ratings under the FASTED condition relative to FED.
Children's Hospital of Eastern Research Institute Ottawa, Ottawa, Ontario, Canada.
Jameason D
JD
Cameron
School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada ; Children's Hospital of Eastern Research Institute Ottawa, Ottawa, Ontario, Canada.
Gary S
GS
Goldfield
University of Leeds, Leeds, United Kingdom.
Graham
G
Finlayson
University of Leeds, Leeds, United Kingdom.
John E
JE
Blundell
School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada.
Eric
E
Doucet
D000328:Adult; D001066:Appetite; D018592:Cross-Over Studies; D005215:Fasting / Q000523:psychology*; D005247:Feeding Behavior / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D012201:Reward; D064232:Visual Analog Scale; D055815:Young Adult