We present a theory of normal eating, based on three fundamental elements: hunger, palatability, and norms of appropriateness. These three elements can account for food intake and choice, although not all three elements are equally important and they vary in terms of their importance in different situations. We suggest that various factors that are regarded as influential in food intake and choice (e.g., dieting, emotional arousal) may be understood in terms of our three basic elements.
In this chapter, we present a theory of normal eating. There has been surprisingly little formal or theoretical attention paid to normal eating, perhaps because researchers (and people in general) assume that everyone already knows what normal eating is and how it works. A “negative” approach to the understanding of normal eating is evident in discussions of eating disorders, which are often seen as pathologies of normal eating but without specifying what normal eating is other than the default condition from which the pathologies deviate (Herman and Polivy 1996). Researchers and people in general – when asked to explain why people (and they themselves) eat the way they do, why they choose (or reject) particular foods to eat, and why they eat as much (or as little) as they do on a given occasion – tend to fall back on two explanations, hunger and palatability (Vartanian et al. 2008). These explanations are taken for granted and rarely explored, because they are assumed to be self-evident. When given a choice of foods to eat, people (believe that they) choose the foods that they find most palatable. If given a choice among equally palatable foods, people may explain their choice in terms of hunger: a hungry person will often select the food that is higher in calories or at least perceived to be more satiating. In the absence of choice of food, people will typically explain why they ate a lot of the available food by claiming that they were particularly hungry or that the food was particularly palatable. Reduced intake is conversely attributed to low palatability or an absence of hunger (Vartanian et al. 2017).
We have recently outlined a theory of normal eating (Herman 2013; Herman et al. in press) in an attempt to provide a positive and comprehensive analysis of why people eat the way they do. This theory is not derived from the absence of disordered eating. It likewise does not assume that “everyone” already knows what normal eating is. Rather, it starts with the basic elements of normal eating and describes how they are related to each other and how they operate in particular eating situations. This theory is not self-evident. We hope to draw attention to aspects of eating that are generally taken for granted or overlooked altogether.
We propose that there are three principal factors that govern normal eating: hunger, palatability, and norms of appropriateness. These three factors all have an impact on normal eating, but they are not equally powerful. Once we have described these three factors, we shall elaborate on them by postulating how they operate conjointly. For the record, we define normal eating as how people in modern societies eat when there is sufficient, culturally acceptable, and at least minimally palatable food. We acknowledge that many people in the world do not have the luxury of engaging in normal eating.
Hunger is experienced subjectively as a desire to eat, sometimes with accompanying symptoms such as stomach pangs or light-headedness. This desire presumably reflects an underlying biological need for food. The intimate connection between the need for food and the desire, pursuit, and consumption of food is thought to reflect the “wisdom of the body,” (Cannon 1932) which has evolved to detect an energy deficit and to remedy that deficit. Historically, most research on hunger and eating has been conducted on animals who cannot report on their internal states – not that humans are particularly adept at reporting on their internal states. In the case of rats, for instance, researchers have tended to beg the question of the connection between hunger and eating: if the rat eats, it is assumed to be hungry. Correspondingly, if it doesn’t eat, or stops eating, the rat is assumed to be not hungry, or sated. This tautological connection between hunger and eating quickly falls apart upon inspection. First, we can all think of times when we were hungry and nevertheless did not eat. This disconnect between hunger and eating may arise because, even though the individual feels hungry, the available food is unpalatable or perhaps the individual is on a diet or perhaps no one else in the group is eating and so the individual feels awkward giving in to her hunger or perhaps the individual is so focused on some event or activity that she doesn’t attend to her hunger sensations. By the same token, there are situations in which people continue to eat despite feeling sated – perhaps because the food is simply irresistible or because of social pressure to eat.
Hunger as perceived or reported at the beginning of an eating episode is often not a good predictor of how much food will be consumed (see Bellisle chapter in this volume). If hunger or food deprivation is the only variable involved, then there is a reasonable correspondence between hunger/deprivation and intake (Kissileff and Thornton 1982), although Le Magnen (1971) suggests that hunger may be more evident in terms of latency to eat than in terms of amount eaten. Moreover, hunger/deprivation is rarely the only factor involved, and the effect of hunger on food intake is often overridden by other factors (in particular, palatability and norms of appropriateness), with the result that more often than not hunger/deprivation is ultimately only weakly reflected in the actual amount of food consumed.
Weingarten (1985) distinguishes between depletion-based hunger, which is how we normally think about hunger, and externally controlled hunger. He has demonstrated that rats will act as if they are hungry, eating additional food, if they encounter a stimulus (e.g., a visual or auditory cue) that has previously been paired with eating. Thus, you can make a sated rat start to eat even more if you provide an “eating cue.” This situation certainly forces us to reconsider whether hunger as traditionally understood – arising from a true nutritional deficit – is always present when people (or rats) eat. Another example of eating that does not reflect hunger as we traditionally understand it is temporally conditioned hunger. We tend to become hungry as mealtime approaches. Of course, this could simply be equivalent to saying that we tend to become hungry as more time goes by since we last ate; in that case, the traditional depletion/repletion view of hunger would apply. But if for some reason – something comes up – you fail to eat at your normal mealtime, you may well find that your hunger, instead of continuing to grow, abates. Note also that “hunger is not at its daily peak upon awakening” (Mattes 2010, p. 24), even though the interval since the last meal is generally longer than just before lunch or dinner. And despite the lengthy interval since the last meal, breakfast is typically not the largest meal of the day. This phenomenon certainly defies the depletion view of hunger; it suggests instead that mealtime itself acts as an “eating cue,” much like Weingarten’s visual or auditory stimuli, and that once the cue is no longer there, cue-based hunger subsides.
There is some debate about whether most of us ever experience “true” hunger. Rogers and Brunstrom (2016) argue that whatever caloric deficits we experience over the course of hours or even days are insignificant compared to our basic energy stores. “Energy requirements meal-to-meal are trivial compared with total body energy stores, and energy supply to the body’s tissues is maintained if a meal or even several meals are missed” (p. 465). It may be that only when we are truly deprived of food for days on end will we experience genuine hunger of the sort that drives the frantic food intake of starving people, food intake that proceeds irrespective of the palatability of the food and the behavior of other people. (Needless to say, it is virtually impossible to study such extreme food deprivation in the laboratory.) In any case, it is evident that hunger is not a simple matter and that we may need to develop a vocabulary that distinguishes between “true” hunger and the sort of everyday hunger that we experience most of the time. How everyday hunger drives eating remains a matter of debate. For now, suffice it to say that it may not be as unambiguously important a driver of eating as is usually assumed.
Like hunger, palatability is generally acknowledged as a principal factor governing eating. Palatability refers to the extent to which the eater enjoys the sensory properties of the food. Palatability is often considered to be equivalent to taste, but it is a broader construct and also includes aspects of food enjoyment such as texture, temperature, and appearance. As with hunger, researchers often beg the question of how palatability affects food intake, especially when studying animals who cannot provide us with independent measures of those two constructs. If a rat eats a lot of a particular food, it is assumed that the rat finds it palatable. If it rejects the food, we may be tempted to infer that the food is unpalatable. Of course, in making these inferences, we often forget that we are prepared to make parallel inferences about hunger; so if a rat rejects a particular food, is it because the food is unpalatable or because the rat simply isn’t hungry? It is possible to devise studies that separate these two influences on eating, but we are often careless about distinguishing them in real life. Thus, when we ask people why they ate so much, they are likely to cite hunger and/or palatability, more or less indiscriminately.
Palatability is more obviously in play when we present a rat or a human with two different foods and assess which one is chosen. In such a study, hunger (or at least food deprivation) can be held constant, allowing us to ascribe higher palatability to the more frequently chosen food. There are two qualifications here, however. First, we all acknowledge that one man’s meat is another man’s poison, so judgments of palatability are to a large extent idiosyncratic. Even though we can combine judgments over several raters to document that chocolate is generally more palatable than is broccoli, their relative palatability may be reversed for a handful of individuals, particularly if we are talking about humans. Also, we must acknowledge that the choice of chocolate versus broccoli may be driven by considerations other than palatability. Some people will select the broccoli, even though they prefer the taste and other properties of the chocolate; considerations of health or social appropriateness will sometimes lead people to select the less palatable option. For example, Sullivan et al. (2019) found that when presented with a choice between a food item that was tasty but not healthful versus an item that was healthful but not tasty, 78% of their sample chose the tasty-but-not-healthful item, but 22% chose the healthful-but-not-tasty item. The same considerations may lead people to behave “perversely” in terms of amount eaten, with health or appropriateness considerations leading them to eat less of their preferred food and more of their non-preferred food.
Just as hunger declines over the course of a meal, so does palatability. Rolls (2000) has studied “sensory-specific satiety,” the phenomenon whereby an initially palatable food becomes less palatable over the course of the meal. This decline in palatability arises from repeated exposure to the same taste (and to some extent other sensory properties such as texture). This reduction in palatability acts as a brake on eating, whence it is referred to as “satiety,” although it is acknowledged that the satiety here is largely metaphorical. The fact that true satiety has not developed is evident when the individual is offered food that differs dramatically in its sensory properties from the original food (Pliner et al. 1980). This “variety” induces a resumption of eating, which presumably would not occur if true satiety had been achieved.
We refer to the decline in the palatability of a particular food over the course of a meal as sensory-specific satiety. There is a similar decline in palatability when the same food is served repeatedly, meal after meal. This effect is referred to as monotony and can be reversed by providing distinctly different foods (see Remick et al. 2009 for a review).
People often cite palatability when explaining why they ate as much or as little as they did (Vartanian et al. 2017). We concur that palatability is an important driver of food intake and food choice. In the research literature, however, palatability is often neglected as a principal factor governing food intake for the simple reason that research participants are usually offered palatable food to eat. The role of palatability in food intake becomes evident only when it is manipulated over a large range of values; we can then observe that people eat more palatable food than unpalatable food. If palatability is held constant at a high level, as it often is in research studies, its importance in controlling eating will be masked (Pliner et al. 1990).
Norms of Appropriateness
The last – but by no means the least – driver of food intake and choice is norms of appropriateness. Norms of appropriateness are rarely cited by researchers or eaters themselves as important in the regulation of eating, but we maintain that they are very important, at least in humans. “Norms of appropriateness” refer to people’s concerns about eating in a manner that is socially approved. People are social creatures, and they are sensitive to the judgments of others. They want to be seen as – and see themselves as – eating appropriately. When it comes to food choice, there are widely shared cultural norms about which foods are suitable for consumption, and people tend to feel some pressure to eat suitable foods. This pressure is strongest when the individual is eating in a group and everyone else has chosen to eat the “appropriate” food and to reject the “inappropriate” food. It takes a strong individual – someone who doesn’t care what others think – to order a rich dessert for himself when everyone else at the table is ordering something “healthy” or not ordering dessert at all.
Insofar as culture affects eating, then, we suggest that it does so through the inculcation of norms of appropriateness. Cultural variations in eating – the particular foods that are eaten, how food is eaten, how much is eaten, and so on – are evident in the variations in norms of appropriateness from one culture (or subculture) to another.
Norms of appropriateness apply to food intake as well as to food choice. For instance, one powerful norm in our culture involves people’s fear of being seen as having eaten excessively. People who eat excessively are judged negatively; they are viewed as less attractive, less intelligent, less moral, and generally less worthy as individuals (see Vartanian et al. 2007, for a review). Women who eat excessively are seen as less feminine (Chaiken and Pliner 1987). The only positive trait associated with excessive eating is “fun-loving.”
Avoiding the imputation of eating excessively is thus an important consideration affecting how much people eat. The problem for the eater, however, is to figure out how much she can eat without eating excessively. Unless she is on a diet that specifies food intake for each eating occasion – and most people aren’t on such a diet – it’s not intuitively obvious how much one can “safely” eat. What happens is that people eating with co-eaters learn to observe the co-eaters’ intake; and they use that intake as a measure of what is “allowed.” If you eat no more than your co-eaters do, then you may avoid the imputation of eating excessively (Herman and Polivy 2008). Note the opportunity here for collusion by the group eaters, who may explicitly or tacitly agree to eat more food than they would normally eat. If they all go along, “permissible” food intake increases, with everyone enjoying the splurge. There are some complications in the group scenario, as when your co-eaters eat varying amounts, muddying the line beyond which eating becomes excessive; but these complications can generally be handled by our theory of normal eating – or at least studied.
It is worth noting that social norms are typically internalized, which means that the individual may be governed by these norms even when eating alone (Feeney et al. 2017). Thus, people judge themselves and are concerned to avoid eating excessively even when they are eating alone. In one research paradigm – what we call the “remote confederate” paradigm – the research participant eats alone but is provided with information about how much others have previously eaten in the same situation. This information is concocted by the researcher; there are no other “prior participants.” Participants are powerfully affected by this information (e.g., Feeney et al. 2011; Roth et al. 2001), even though there is no chance that these other people will be judging them. Of course, in this situation, as in most studies of food intake, research participants are led to believe that the researchers are not judging – or even measuring – their food intake.
Politeness/consideration, as when we feel compelled to eat more than we might otherwise be inclined to and to eat foods that we might otherwise avoid, when we find ourselves in a situation in which our host enjoins us to “have another helping” or serves us something that we do not like. A variation on this normative pressure was documented by Exline et al. (2012), who found that at least some people eat more than they otherwise would simply in order to make their large-intake eating companions feel more comfortable.
Regulatory balance, as when we believe that we ought to eat less if we have recently eaten a lot. Thus, if we mislead research participants into believing that what they recently ate was highly caloric, they will eat less in a subsequent eating situation (Wooley 1972). A variation on this theme is provided by Higgs (2008), who has demonstrated that if people are asked to recall their lunch today, they will eat less in a mid-afternoon snack than if they are not asked to recall their lunch today or are asked to recall their lunch yesterday.
Portion size (see Rolls chapter in the present volume). People eat more when served larger portions, and there is accumulating evidence that this effect is driven by the fact that people who are served larger portions consider larger portions to be “appropriate” (Herman et al. 2015; Robinson and Kersbergen 2018). This conclusion is reinforced by recent evidence that rats do not eat more when portion size is increased, suggesting that the effect in humans is mediated by higher cognitive processes (Naneix et al. 2019).
Segmentation effects. People eat more when presented with one large item of food than when the same item is subdivided into segments. Kerameas et al. (2015) demonstrated that this effect is mediated by changes in the perceived appropriateness of eating a single larger (unsegmented) item versus several small (segmented) items.
Drivers and Inhibitors
We have identified hunger, palatability, and norms of appropriateness as elements governing food intake and choice. It should go without saying that these factors do not operate unopposed. Indeed, our description of norms of appropriateness has already included several examples of norms that inhibit eating: concern about eating excessively is basically an inhibitory factor, setting an upper limit on how much one may eat without making a negative impression on observers and even on oneself. Some norms of appropriateness may increase the likelihood of selecting a particular food (see Higgs and Ruddock’s chapter in this volume) or the likelihood of eating more than one normally would (e.g., the politeness norm mentioned above), but norms of appropriateness more often act as inhibitors of eating; they allow a certain intake but no more. Hunger, of course, normally drives eating and has an “opposite,” satiety, which terminates eating. Technically, satiety is not quite the opposite of hunger, either in terms of its basic nature or its parameters. For instance, hunger arises much more slowly as a function of time spent continuously not eating than satiety does as a function of time spent continuously eating. Still, for our purposes, we may say that whereas hunger promotes eating, satiety inhibits eating. Palatability, likewise, has its opposite. Unpalatable food suppresses eating. In research studies, the food is typically palatable, but occasionally researchers will explore the effects of unpalatable food (see Pliner et al. 1990, for a review). Of course, there is a continuum of palatability, ranging from highly palatable to highly unpalatable, and we all acknowledge that the palatability of a particular food may vary from individual to individual.
Relative Weight of the Three Factors
Of the three main drivers of eating, hunger is the weakest. This assertion is based not on people’s reports – recall that people tend to identify hunger and palatability as the principal reasons for eating as much as they do – but on a more careful examination of the research literature. We ourselves, making the same assumptions that most people (and researchers) do, were relatively slow in coming to the realization that hunger is a weak influence. Several years ago, for instance, we outlined a “boundary model for the regulation of eating” (Herman and Polivy 1984). This model proposed that eaters, at any given moment, were either hungry, sated, or in a “zone of biological indifference,” neither hungry nor sated. When in this zone of indifference, we argued, people’s food intake is affected by all sorts of factors, including palatability and what we would now call norms of appropriateness. Moreover, we argued that most of us spend most of our time within that zone of indifference, so that our eating is affected by factors other than hunger/satiety. If, however, we allow ourselves to drift into a state of hunger (by eating too little or too late) or satiety (by eating too much or too soon), then these powerful biological conditions would take over and either (in the case of hunger) drive eating regardless of palatability or norms of appropriateness or (in the case of satiety) suppress further eating regardless of palatability or norms of appropriateness.
We conducted (and replicated) a study designed to demonstrate that sufficiently hungry people would eat even if the food is unpalatable (Kauffman et al. 1995). That prediction followed from our commonsense boundary model and had been articulated earlier by Jacobs and Sharma (1969). In the Kauffman et al. study, participants were deprived of food for up to 24 h and then given access to either a good-tasting milkshake or to a bad-tasting milkshake (the same milkshake but adulterated with bitter quinine). Across two versions of the study, hungry participants ate more of the good-tasting milkshake than did non-hungry participants, as expected; but contrary to common sense and contrary to our boundary model, hungry participants ate less of the bad-tasting milkshakes than did non-hungry participants. Jacobs and Sharma, who found the same thing in dogs, suggested that this “paradoxical” effect of hunger on intake of bad-tasting food may stem from bad-tasting food being potentially toxic and thus being particularly dangerous to those eating on an empty stomach. (Note that this effect does not require conscious awareness; people and dogs have evolved to reject bad-tasting food when they are hungry.) In any case, it is evident that when we examine the effect of hunger conjointly with the effect of palatability, the effect of palatability on intake dramatically overrides the effect of hunger. It is worth noting that in our study, people were food-deprived for 24 h, which is considerable but by no means comparable to what some people have endured under conditions of extreme starvation. We concede that truly starving people might be more enthusiastic about eating bad-tasting food, but 24 h worth of hunger is apparently not enough to increase intake of bad-tasting food in people who are otherwise not undernourished. In other words, hunger is not as powerful as is palatability in normal people.
Another set of two studies (Goldman et al. 1991) examined food intake in hungry and non-hungry people. In these studies, we did not manipulate the taste of the food; rather, we manipulated the food intake of an experimental confederate who ate alongside the naïve participant. The boundary model and common sense both predicted that the (large versus small) intake of the confederate would have an effect on the intake of the naïve participant, but if the naïve participant was hungry – again, up to 24 h without eating – then she ought to eat enthusiastically even if the confederate ate sparingly. What we found, however, was that the confederate’s intake strongly influenced the naïve participant’s intake, irrespective of the naïve participant’s hunger level. A very hungry person eating with someone who eats sparingly will herself eat sparingly. Indeed, the impact of the confederate’s intake was so strong that hunger/deprivation had virtually no impact whatsoever on intake. These studies demonstrate that norms of appropriateness – in this case, the example set by a confederate eating a lot or a little – powerfully influenced food intake, whereas up to 24 h of food deprivation had virtually no impact on eating. Again, hunger is not as powerful as are norms appropriateness in normal people.
These studies provide convincing evidence that hunger is not a powerful driver of normal eating, certainly not when compared directly to the influence of palatability or norms of appropriateness. We concur with Mattes (2010, p. 30), who concludes that “hunger and thirst are only weak predictors of energy and fluid intake, respectively.” (See also Mattes 1990, who found at best very weak associations between hunger reports and intake occurrences and amounts in free-living humans.)
If palatability and norms of appropriateness are both more powerful than is hunger in the acute control of eating, we might now ask which of these two powerful factors is more powerful. At this point, we are reluctant to pursue this question, because it is probably unanswerable. Palatability drives eating in a direct fashion – the more palatable food, the greater the intake – but norms of appropriateness do not drive eating in the same way. Occasionally a norm of appropriateness requires that we eat more than we otherwise might; the politeness/consideration norm cited above would be an example. Most of the time, however, norms of appropriateness do not drive intake so much as permit it. An experimental confederate’s intake indicates an upper limit of intake beyond which one may not proceed; but there is no requirement that the limit be reached. Indeed, in most experiments involving large-eating confederates, the intake of the naïve participants increases above control levels but does not come close to matching the inflated intake of the confederates. In other words, whereas highly palatable food directly promotes increased intake, high-intake norms only allow increased intake; they do not drive it in the same way. Thus, palatability and norms of appropriateness are incommensurate. They both override hunger, but we cannot regard one as more powerful than the other. Highly unpalatable food will suppress eating even if confederates eat a lot of it (Pliner and Mann 2004), and confederates who eat minimally will suppress intake even if the food is highly palatable, as we saw in the Goldman et al. (1991) study.
A Dynamic Theory of Normal Eating
Having provided a rough weighting of the three factors driving eating (with hunger relatively weak compared to palatability and norms of appropriateness), we may now turn our attention to how these factors combine dynamically to control eating. In our review of the effects of social factors on eating (Herman et al. 2003), we postulated that “in the presence of palatable food, and in the absence of inhibitory forces…, people continue to eat indefinitely.” This deceptively simple formulation includes just about everything required to account for food choice and food intake.
Food choice is the simpler case, with palatability accounting for most decisions. Some inhibitory factors – say, a concern about how observers (or you yourself) might judge your choice of a highly palatable but unhealthy food – may interfere with food choices based entirely on palatability; but by and large, people tend to select the food that has sensory appeal for them. (Of course, in the real world, factors such as cost and convenience may affect food choice, but these factors are rarely studied in the lab.) Pliner and Mann (2004) found that people tend to disregard the example of others when those others select a disliked food. We may imagine an obverse case, in which the individual is confronted with a relatively unpalatable food (which she normally would not be eager to eat) but experiences pressures to eat it nevertheless. Considerations of politeness or health may drive food selection. For example, Girz et al. (2012) found that in the absence of caloric information about menu items, people concerned about their weight chose the “healthy” salad option rather than the (more palatable) pasta option. When they were told – correctly, as it happens – that the salad and the pasta were equally caloric, however, people shifted their choice to the pasta. So here we have an instance of “the presence of norms of appropriateness that promote the choice of an unpalatable food,” which may then be overcome by information suggesting that the less palatable food is not actually more calorically appropriate.
When it comes to food intake, palatability is again crucial, in the sense that it is a precondition for further eating. If the food tastes bad, people won’t eat (much of) it. Most of the time, however, both in the lab and in the real world, people have at least reasonably palatable food available to them. What is crucial to note here is that our formulation requires the presence of (reasonably) palatable food, but it does not require the presence of hunger. We thus acknowledge what has become increasingly evident recently – namely, that many of us eat in the absence of hunger. The mere presence of attractive food appears to be enough to drive eating. As Fay et al. (2015, p. 156) put it, “increased frequency of eating in the absence of homeostatic need, notably through snacking, is an important contributor to overconsumption and may be facilitated by increased availability of palatable food in the obesogenic environment.”
Our dynamic theory suggests that palatability alone will drive intake and drive it indefinitely. People do not eat indefinitely, though, so we must now turn our attention to the “inhibitory factors” that terminate eating, sooner or later. The most obvious terminator of eating is satiety. Even though satiety often lags intake – it can take 20 min or more for inhibitory feedback from ingestion to trigger feelings of satiety (Booth et al. 1970), and so people often eat more than they wish they had – eventually satiety registers, and the eater will stop. (Our theory, then, weighs satiety as a “stop” signal more heavily than hunger as a “start” signal.)
Although satiety is the ultimate backstop, intake often ceases well before satiety occurs. Other inhibitory forces often come into play earlier. We have already discussed sensory-specific satiety, the metaphorical satiety that we experience when our meal is dominated by a single food or flavor. We may think of sensory-specific satiety as a preemptive form of satiety or, alternatively, as a decline in palatability; in either case, it stops food intake before true satiety occurs. This is one instance of an inhibitory force.
One prevalent reason for stopping eating is when we run out of food, as happens, for instance, when we have cleaned our plate. In the lab, researchers usually try to ensure that there is more food available that can be eaten. In any case, if all the food is gone, then the eater is no longer “in the presence of palatable food,” and so the basic precondition for eating is no longer satisfied.
Other forces that inhibit eating may be found among the many norms of appropriateness that govern eating, many of which reflect the appropriateness of eating moderately or even sparingly, usually with the goal of making a positive impression on our co-eaters, on observers who are not eating alongside us, or even just on ourselves.
Elements of the situation that convey norms of appropriateness almost always establish an upper limit of food intake beyond which we dare not go. Even when the situation appears at first glance to encourage eating, it nevertheless entails a maximum permissible amount. Thus, large portions encourage more eating than do small portions, but even the large portion must not be exceeded. Research participants eat more when they eat with experimental confederates who eat a lot than when they eat with confederates who eat only a little; but even when the research participants eat a lot, they do not eat more than the large-eating confederates (Vartanian et al. 2015). We are aware of only one study in which the amount eaten by large-eating confederates did not establish an upper limit for naïve research participants (Leone et al. 2007); and in that case, we argued, the ambiguity in the conflicting amounts eaten by the various confederates prevented the naïve eaters from perceiving a clear upper limit on intake. In our previous list of norms of appropriateness, we included politeness/consideration as a norm that could lead people to eat more than they might otherwise be inclined to. Obviously, we cannot argue that eating more as a way of complimenting the host or making a large-eating companion feel better is an inhibitory factor, but we do suggest that these examples of eating more than one really wants to are exceptional. Moreover, concern-about-excessive-eating norms of appropriateness ensure that our politeness and consideration for others do not lead to any more eating than is absolutely necessary to discharge these social obligations and may even dictate eating less than we would prefer, so as to leave enough for others to eat.
Extensions and Distortions of Normal Eating
Now that we have established the basic drivers (and inhibitors) of eating, we are in a position to enquire about problematic eating.
Obesity: Normal eating is not necessarily optimal eating. Consider the obesity epidemic. While we cannot say with certainty what is responsible for the epidemic (see Herman 2018; Keith et al. 2006; and McAllister et al. 2009), it is easy to see how normal eating processes might lead to overeating.
Consider palatability. Nisbett (1968) served ice cream varying in palatability – using the same quinine adulteration that Kauffman et al. (1995) later employed – to normal-weight, overweight, and underweight people. As palatability increased, people ate more of the ice cream, but the precise pattern for the different groups showed an interesting anomaly. Whereas normal-weight and underweight people ate more ice cream as a continuous function of increasing palatability, the overweight people showed what Nisbett called a “step function”: once the palatability level rose above neutral, the overweight people ate a lot of it; and further increases in palatability made no difference. This finding suggests that obese people do not discriminate between decent-tasting food and highly palatable food; alternatively, it suggests that people who do not discriminate between decent-tasting food and highly palatable food are prone to becoming obese. This is a simple example of how an anomaly in the domain of palatability might produce overeating and weight gain.
Overeating may arise from “inappropriate settings” in norms of appropriateness. We have already discussed how the intake of your eating companions can influence your own eating; so if you regularly eat with people who eat a lot, odds are that you will end up eating a lot as well. In fact, simply eating with other people seems to lead to greater eating. There is a sizable literature documenting the social facilitation of eating (Herman 2015): people eat more when they eat with others than when they eat alone. One interesting explanation for this effect is that, when people eat in groups, they arrange for more food (per capita) to be available; in effect, groups arrange for larger portions. More generally, if we are constantly served (or serve ourselves) large portions, it stands to reason that we will end up overeating. These examples of “inappropriate norms of appropriateness” have not yet been shown conclusively to lead to overeating (Herman 2018; Herman et al. 2016), but the notion is tantalizing.
Dieting or restrained eating: Restrained eaters (dieters; see van Strien chapter in this volume) are committed to suppressing their food intake, owing to their conviction that it is desirable and appropriate to eat less than hunger and palatability considerations would otherwise demand. Indeed, restrained eaters struggle to overcome the hunger produced by whatever success they have in suppressing their intake; and they struggle to overcome the pervasive lure of palatable food, which is often high in calories and which may become even more alluring as one’s weight decreases and/or as one expends more energy avoiding such desirable foods (i.e., psychological deprivation).
Polivy and Herman (1987) note that restrained eaters comprise a large proportion of some populations, including females in Western societies. Indeed, one could argue that in many subpopulations, restrained eaters are in the majority, and so we might consider dieters to be normal eaters, at least statistically. Polivy and Herman invoke our boundary model (Herman and Polivy 1984) to explain how dieters differ from nondieters. Specifically, dieters have a “diet boundary” that sets an upper limit on their permissible intake and that is reached well before satiety. Thus, dieters will often eat less than will nondieters; and yet, they often eat more. This breakdown of dietary restraint may be explained in terms of the elimination of the diet boundary. This may happen in situations in which the dieter breaks her diet by eating more than the diet allows; once the diet boundary has been breached, there is nothing to stop additional eating until the satiety boundary is reached. (Herman and Polivy argue that the satiety boundary is displaced for dieters, so that dieters experience satiety later – after more food is consumed – than do nondieters.) Another scenario in which the diet boundary becomes inoperative is when it is temporarily abandoned altogether in favor of more urgent priorities; for instance, when the dieter becomes emotionally agitated, she may abandon her diet, at least temporarily. This analysis allows us to interpret the behavior of dieters as “normal,” both in the sense that it is statistically prevalent and also in the sense that it is responsive to the sort of controls or boundary pressures that regulate eating in (almost) everyone, the only difference being the presence of a “diet boundary” that reflects the dieter’s commitment to eating less, a commitment that is vulnerable to being overridden.
Thus, problematic eating may arise both when the normal controls on eating are “broken” and when the normal controls are intact but set at levels that conduce to overeating and/or choosing unhealthy foods. Normal controls may also be set at levels that conduce to undereating. Most analyses of the classic eating disorders (i.e., anorexia nervosa, bulimia nervosa, binge eating disorder) depict these disorders as stemming from true pathologies of hunger, satiety, emotion, and body image. Our theory of normal eating does not specifically pertain to these eating disorders, but it is interesting to speculate as to how these recognized eating disorders might arise not because of pathology but through extensions of normal eating mechanisms. Crandall (1988), for instance, discusses how binge eating can spread through a sorority through the enforcement of social norms. Websites promoting certain eating disorders may serve to normalize these pathologies (Norris et al. 2006). In short, certain forms of abnormal eating may just be extensions of normal eating, making it all the more important for us to understand normal eating and how it operates.
Emotional eating: It is a common belief that eating is driven by emotions; and indeed, emotional arousal can both promote and suppress food intake and certain food choices (e.g., Macht 2008). Bruch (1973) speculated about the possibility that some people confuse other internal or emotional states with hunger, with resultant overeating. At the same time, clinical depression has been associated with both weight loss and weight gain (Polivy and Herman 1976). We concur that emotional arousal affects food intake and choice. We propose, however, that the effect of emotional states on eating is not direct but rather is mediated by the effects of emotional states on the basic factors that control eating. Thus, insofar as emotional arousal suppresses food intake, it may do so by inducing satiety, as Schachter et al. (1968) argued, citing Cannon (1915). Insofar as emotional arousal increases food intake, it may do so by altering (or removing) inhibitory norms that typically keep food intake in check (Polivy and Herman 1999). In short, we do not deny that emotional eating can have a strong effect, but we suggest that this effect is best understood in terms of our basic theory of normal eating. Indeed, we suggest that virtually every aspect of eating can be best understood in terms of our theory of normal eating, whose relative simplicity offers a concise approach to what has heretofore been an unduly complicated analytic enterprise.
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