Appetite (Encyclopedia of Food & Culture)
APPETITE. Appetite is a term implying a strong desire to acquire or participate in, exemplified by terms such as sexual appetite or appetite for life. In the context of food, appetite is used to describe a wanting or liking for particular foods, usually on the basis of their sensory properties (taste and texture) or a psychological attribute (perceived value or symbolic status). In this way appetite is usually distinguished from hunger, which implies a desire or seeking for food arising from a state of need or nutritional deficit. At the beginning of the twenty-first century the understanding of appetite achieves special importance because of its potential role in the worldwide epidemic of obesity, sometimes called a pandemic. Given that, in many parts of the world, people are surrounded by a plentiful supply of food that prevents chronic hunger (though permitting normal meal-to-meal hunger), the capacity to eat food in the absence of hunger or in a low state of hunger assumes special importance. Consequently, understanding appetite and how it can be controlled are urgent tasks in the fight against the obesity epidemic.
Appetite can therefore be defined as a liking for particular foods, or an attraction for foods based on their perceived pleasantness. This is normally referred to as the hedonic dimension of food selection. This characteristic can be described as the subjective pleasure that is derived from the consumption of food; in turn, this can be measured by asking people to rate the magnitude or intensity of pleasure associated with eating or tasting foods. This pleasure arises from the interaction between the person's perceptual capacity (acuity of taste, smell, and sensory feedback from the mouth) and the physical properties of foods. The intensity of the pleasure therefore depends in part on internal (personal) and external (food-related) factors. These food factors can be natural, such as the presence of sweet carbohydrates in fruits or, and much more common now, the deliberate construction of powerful properties in the manufacturing process. It can be hypothesized that the industrial production of foods (designed to possess a combination of properties, for example, sweetness, fattiness, flakiness) has saturated the food supply in many parts of the world with an abundance of appetite-stimulating products. These products include chocolates and desserts, cheese, meat, and pastry combinations, and many types of fried snacks. The inherent attractiveness of such products can stimulate eating in the absence of any obvious need for nutrients.
Biological Basis of Appetite
Is there a biological basis for appetite and for the degree of attractiveness of specific types of foods? It does seem that human beings derive pleasure from particular food propertieshe qualities of sweetness and fattiness are prominent. It is generally understood that, during the course of human evolution, a preference for foods with these properties would lead people to consume foods that possessed energyielding value, for example, the nutritional value of carbohydrates and the energy value of fats. Consequently the value of these traits for survival has almost certainly persisted until the present day, at which stage these genetic dispositions may be detrimental in the current "obesigenic" environment (but useful when foods with these properties were scarce). The word "obesigenic" was coined around the end of the twentieth century to suggest an environment that promoted weight gain through the abundance, attractiveness, and marketing of food consumption, together with reduced opportunities for physical activity. It is recognized that most cultures contain highly prized food habits based on foods that are either sweet or fatty, and sometimes a combination of bothhen the palatability can be intense.
Do these genetic traits based on the pleasurable qualities of food have a basis in brain processes? The intrinsic sensory attractiveness of food is mediated by "reward" pathways in the brain. These pathways promote various types of pleasure and can be artificially stimulated by drugs. By using drugs as tools it has been found that particular neurochemical transmitters are involved in the process of reward; these transmitters include dopamine, opioid, and cannabinoid molecules together with their specific receptors. It can also be demonstrated empirically that the areas of the brain that subserve the most intense pleasure can be stimulated both by food sensations (arising from sensory pathways), and modulated by signals of need (arising from the body's energy stores). This means that a nutritional deficit, indicated by a low body weight, for example, can sensitize the reward system so as to increase the measured pleasantness of foods. In practice this would mean that a person who had been coerced into losing substantial body weight would display an increased rating of pleasantness for certain foods. This can be seen as a useful biological mechanism and is given credibility via the long-known phenomenon called alliesthesia, which is perceiving an external stimulus as pleasant or not, depending on internal stimuli. This concept is based on the biological notion of pleasure being a useful trait.
However, it seems certain that another mechanism must also be at work. This mechanism is based on the recognition that some people who gain weight easily and become obese possess traits that lead them to derive a high degree of pleasure from food. Consequently, foods with potent sensory properties are attractive targets for such people and this increasing pleasantness can lead to overconsumption and weight gain. There is clear evidence that obese women rate sweet/fatty foods very highly and consume substantial quantities; other studies have shown that obese people show preferences for fatty foods and for the taste of fat. After eating, obese subjects frequently rate the same food as being more pleasant than do lean subjects. In this way the expression of appetite heightened pleasure of eatingan be seen to contribute to increasing body weight and obesity. This arises from endogenous traits to derive pleasure from food (sometimes specific foods) in conjunction with an abundance of foods possessing a profile of pleasure-stimulating properties.
Hedonics and Hunger
The identification of the pleasure response of appetite with a neurochemical substrate also helps to differentiate the hedonic dimension of food from the hunger dimension. The term "hedonic," derived from the Greek word hedone, refers to the seeking of pleasure. Experimental studies in human subjects have shown that a drug called naloxone that blocks opioid receptors can reduce the perceived pleasantness of food without diminishing hunger. In contrast a drug such as fenfluramine, that acts upon serotonin receptors, can substantially reduce hunger without changing the perceived pleasantness of food. This type of pharmacological dissection indicates that the overall control of food intake depends upon both appetite (signals of pleasure) and hunger (signals of absence of food). However, the separation of the systems is not complete since experimental investigations have shown that while people are eating very good-tasting food their hunger is elevated. This elevation serves to prolong the meal so that more food is consumed. The relationship is, however, asymmetrical: although pleasantness increases hunger, a state of satiety does not reduce the perception of pleasure. Indeed, even when people report feeling full, a very palatable food can often still be eaten. Surveys have shown that foods rated as most palatable (pleasant) are associated with the largest meal sizes and with the greatest amount of food consumed. The results of scientific observations are therefore consistent with the widespread belief that people eat more of good-tasting food. However, people do not always choose to eat the most delectable or most pleasure-giving food; eating also depends on the appropriateness of the food for the particular social context. This is a good example of a cultural rule overcoming a biological response. However, much overeating in certain cultures arises from the strength of the biological response or perceived intensity of pleasure overcoming the cultural convention.
The Palatability Dilemma
The potency of appetite in stimulating food consumption creates a problem in the present climate of escalating levels of obesity. There are now strong intentions in the nutraceutical sector of the food industry to encourage the production of functional foods for appetite control; that is, foods that possess satiety-inducing or hunger-suppressing properties. The word "nutraceutical" was coined to resemble the word "pharmaceutical" and refers to those foods that may have specific functional effects generated in a manner similar to the way in which drugs work. However, advances in food technology have, over the years, been able to bring about an increase in the overall pleasantness (palatability) of foods entering the market-place. Indeed, one of the legitimate goals of the food industry is to make eating a source of pleasure. It can be observed that for many people, eating is the cheapest form of pleasure available on a day-to-day basis. However, improving palatability means increasing the sensory attractiveness of foods and the willingness of people to consume such foods. Satiety implies reducing the willingness of people to consume. The question therefore arises whether it is possible for the food industry to increase the palatability of foods without weakening satietynd vice versa. The balance between palatability and satiety is the essence of the interaction between hunger and hedonics in the control of food intake. It remains to be determined how the interplay between these factors contributes to the current obesity epidemic.
See also Acceptance and Rejection; Anorexia, Bulimia; Eating: Anatomy and Physiology of Eating; Hunger, Physiology of; Obesity; Sensation and the Senses.
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de Castro, J. M., F. Bellisle, and A.-M. Dalix. "Palatability and Intake Relationships in Free-Living Humans: Measurement and Characterization in the French." Physiology and Behaviour 68 (2000): 271-277
Mela, D. J., and Peter J. Rogers. Food, Eating and Obesity: The PsychoBiological Basis of Appetite and Weight Control. London: Chapman and Hall, 1998.
Mela, D. J., and D. A. Sacchetti. "Sensory Preferences for Fats: Relationships with Diet and Body Composition." American Journal of Clinical Nutrition 53 (1991): 908-915.
Yeomans, M. R. "Taste, Palatability and the Control of Appetite." Proceedings of the Nutrition Society 57 (1998): 60915.
John E. Blundell Joanna Le Noury