Hedonic hunger: A new dimension of appetite?
Introduction
These aphorisms suggest that the attainment of pleasure is both desirable and dangerous. For the vast majority of human history and prehistory, the primary objective of seeking food was survival through the maintenance of energy homeostasis and the avoidance of starvation. In modern times, among well-nourished populations, most food consumption occurs for reasons other than acute energy deprivation [1]. As the growing prevalence of global obesity suggests, an increasing proportion of human food consumption appears to be driven by pleasure, not just by the need for calories.
The purpose of this paper is to propose and justify a distinction between homeostatic and hedonic eating and to discuss the potential consequences of what, from an historical perspective, represents an unprecedented societal phenomenon: the constant availability and frequent consumption of highly palatable foods. We agree with other observers [1] that this phenomenon is contributing to escalating obesity and its physical comorbidities (diabetes, heart disease, etc.). However, we also propose that the food environment may be creating an appetitive counterpart to the psychological effects of other hedonically-driven activities such as drug use and compulsive gambling. Just as compulsive gamblers or drug-dependent individuals are preoccupied with their habit even when they are not engaging in it, so may some individuals experience frequent thoughts, feelings and urges about food in the absence of any short- or long-term energy deficit. These experiences may or may not be prompted by exposure to food-related cues but by definition they do not occur in response to prolonged food deprivation (i.e., homeostatic hunger). We refer to this tendency here as “hedonic hunger”.
It is important to emphasize that the term hedonic hunger, like the traditional concept of hunger, is meant to refer to a subjective state (and to physiological mechanisms that may mediate it), not to actual food intake. Research suggests that traditional self-reports of hunger are only weakly related to the amount of food that is subsequently consumed [2], [3], and the same may be true for the concept of hedonic hunger. It also is possible that subjective hunger ratings are more reflective of a simple propensity towards eating, rather than serving as an index of how much food will be consumed. These observations do not mean that measures of hedonic hunger will not predict food intake, only that the term should be defined independently of actual food intake. In addition, the immediate food environment is presumed to play a much greater role in the generation of hedonic than of homeostatic hunger. The development of homeostatic hunger is based on the prolonged absence of energy intake. The palatability of the food that an individual is exposed to during and between eating bouts is assumed to be largely irrelevant to the generation of homeostatic hunger. The opposite appears to be true of hedonic hunger. That is, satiety has a relatively small effect on the pleasantness of foods (the pleasantness of a meal does not decline nearly as much as hunger as the meal is consumed). Rather, the availability and palatability of foods in the immediate environment has a major effect on whether they will be desired and consumed [4-6] and an individual's level of current caloric repletion is assumed to be relatively unimportant.
A further implication of these distinctions is a difference in the experimental methods one would use to study these two eating motives. Studies of homeostatic hunger would obviously involve the manipulation of hunger via differing lengths of food deprivation. Studying hedonic hunger appears to have two requirements. One is assuring that participants are in a state of short-term energy repletion — i.e., they are not in a state of impending or actual energy deficit (e.g., shortly before a meal). The other is that the experimental context examining hedonic hunger involves the introduction of some kind of highly palatable food stimulus. The reason for the second requirement is that the state of hedonic hunger is presumably a latent potentiality that can only be “called forth” by the introduction of highly-pleasurable food stimuli.
A final introductory comment is needed based on the distinction that Berridge and Robinson have made between “wanting” and “liking” a substance. Although these two motivational drives normally go hand-in-hand, these researchers have shown that they are subserved by neurophysiological mechanisms that can be experimentally differentiated. We previously addressed the relation of this distinction to the distinction we are drawing between homeostatic and hedonic eating motives (see reference [7], pp. 800–801). We simply point out here that when discussing hedonic eating motives, such motives could be driven by the incentive salience of food stimuli (i.e., “wanting”), by the taste of food (“liking”), or by both.
Section snippets
Differentiating between homeostatic and hedonic hunger
The term “hunger” has historically been used to describe a biological state of acute energy deprivation or the subjective state presumably reflecting an actual or impending state of energy deprivation. However, although the use of a period (e.g., at least 8 h) of food deprivation creates an unambiguous state of homeostatic hunger, it is much less clear what self-report measures of subjective hunger level used in hundreds of past studies are actually measuring. For instance commonly-asked
Animal research on hedonic eating motives
A large body of research indicates that there are neurophysiological substances (e.g., neurotransmitters, hormones) and pathways that operate within homeostatic and hedonic systems to help regulate eating behavior. Systems that control eating for energy homeostasis and for reward overlap but are also functionally dissociable [7]. Much of the research that supports the distinction between eating that is primarily motivated by energy deficits and by pleasure has been conducted with animal models.
Human research on hedonic eating motives
There is abundant evidence that BMI is related to preferences for and consumption of highly palatable (often, high-fat) foods [4], [7]. However, as noted by Blundell and Finlayson [4], this relationship may not be linear in nature. For instance, they review evidence that overweight individuals score higher on a measure of reward sensitivity than obese individuals [32] and that the availability of the dopamine D2 receptor (a possible mediator of the rewarding property of palatable foods) was
A new measure of appetitive responsiveness to the food environment
Despite living in an obesogenic environment, a substantial minority of individuals in the United States remain in the normal weight range their entire lives. Presumably, there is substantial variability in the extent to which individuals are affected by food or think about food even when eating is not imminent or underway. It is precisely during these time periods that hedonic hunger become potentially relevant. A measure that assessed individual differences in hedonic hunger could prove useful
What might be “new” about hedonic hunger?
We finally return to the title of this paper and specifically to the idea that there might be something “new” about the concept of hedonic hunger. We are of course referring not just to a new term but to the possibility that society-wide changes in both the physical and psychological availability of food has created a type of eating motive in whole populations that has never been seen before. By psychological availability we are referring to the types of norms and expectations governing eating
Acknowledgements
Some of the first author's research reported in this paper was supported by NIH grants HL073775 and DK057433.
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