Western-style diet impairs stimulus control by food deprivation state cues: Implications for obesogenic environments

Abstract

In western and westernized societies, large portions of the population live in what are considered to be "obesogenic" environments. Among other things, obesogenic environments are characterized by a high prevalence of external cues that are associated with highly palatable, energy-dense foods. One prominent hypothesis suggests that these external cues become such powerful conditioned elicitors of appetitive and eating behavior that they overwhelm the internal, physiological mechanisms that serve to maintain energy balance. The present research investigated a learning mechanism that may underlie this loss of internal relative to external control. In Experiment 1, rats were provided with both auditory cues (external stimuli) and varying levels of food deprivation (internal stimuli) that they could use to solve a simple discrimination task. Despite having access to clearly discriminable external cues, we found that the deprivation cues gained substantial discriminative control over conditioned responding. Experiment 2 found that, compared to standard chow, maintenance on a "western-style" diet high in saturated fat and sugar weakened discriminative control by food deprivation cues, but did not impair learning when external cues were also trained as relevant discriminative signals for sucrose. Thus, eating a western-style diet contributed to a loss of internal control over appetitive behavior relative to external cues. We discuss how this relative loss of control by food deprivation signals may result from interference with hippocampal-dependent learning and memory processes, forming the basis of a vicious-cycle of excessive intake, body weight gain, and progressive cognitive decline that may begin very early in life.

Keywords: Cognition; Hippocampus; Memory; Obesity; Saturated fat; Vicious cycle.

Fig. 1

Mean ± S.E.M. percent magazine entries during 4-minute period preceding sucrose delivery on reinforced (+) and nonreinforced (−) deprivation sessions for Group 0+ (left panel) and Group 24+ (right panel) during Experiment 1 acquisition.

Fig. 2

Mean ± S.E.M. percent magazine entries during the last two rewarded (+) and nonrewarded (−) sessions of Compound Training (i.e., food deprivation cues and auditory cues presented as compound discriminative stimuli), the Deprivation Cue Test (i.e., deprivation cues only), Compound Retraining with the deprivation/auditory cue compound, and the Cue Competition Test (external cue contingencies reversed while deprivation contingencies remained the same).

Fig. 3

Mean ± S.E.M. percent magazine entries during the 4-minute period preceding sucrose delivery for rewarded (+) and nonrewarded (−) sessions during Experiment 2 acquisition. The left panel shows data for Group 0+, while the right panel shows data for Group 24+.

Fig. 4

Mean ± S.E.M. difference scores (i.e., nonreinforced subtracted from reinforced responding) of percent magazine entries during the 4-minute period preceding sucrose delivery for WD-fed and chow-fed rats during first and last rewarded and nonrewarded sessions (i.e., +/− session) of each phase including: the last block of training prior to the introduction of the WD (Last Block of Training), the first +/− session following six weeks on the diets (Dep. Cue Test 1), the seventh +/− session with the deprivation cues only (Dep. Cue Test 7), the first +/− session in which the external light and tone cues were introduced (Ext. Cue Test 1), the tenth and last session with the external light and tone cues in combination with the deprivation cues (Ext. Cue Test 10), and the last +/− session in which external light and tone cues were removed for the Final Deprivation Cue Test.