Hunger, Eating, and Health Why Do Many People Eat Too Much? 12. 1 12. 2 12. 3 12. 4 Digestion, Energy Storage, and Energy Utilization Theories of Hunger and Eating: Set Points versus Positive Incentives Factors That Determine What, When, and How Much We Eat Physiological Research on Hunger and Satiety 12. 5 12. 6 12. 7 Body Weight Regulation: Set Points versus Settling Points Human Obesity: Causes, Mechanisms, and Treatments Anorexia and Bulimia Nervosa ISBN 0-558-78571-9 Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon. Copyright © 2011 by Pearson Education, Inc. 12. ¦ Digestion, Energy Storage, and Energy Utilization 299 ISBN 0-558-78571-9 ating is a behavior that is of interest to virtually everyone. We all do it, and most of us derive great pleasure from it. But for many of us, it becomes a source of serious personal and health problems. Most eating-related health problems in industrialized nations are associated with eating too much—the average American consumes 3,800 calories per day, about twice the average daily requirement (see Kopelman, 2000). For example, it is estimated that Watch 65% of the adult U. S. popuYou Are What You Eat lation is either overweight or www. mypsychlab. om clinically obese, qualifying this problem for epidemic status (see Abelson & Kennedy, 2004; Arnold, 2009). The resulting financial and personal costs are huge. Each year in the United States, about $100 billion is spent treating obesity-related disorders (see Olshansky et al. , 2005). Moreover, each year, an estimated 300,000 U. S. citizens die from disorders caused by their excessive eating (e. g. , diabetes, hypertension, cardiovascular diseases, and some cancers). Although the United States is the trend-setter when it comes to overeating and obesity, many other countries are not far behind (Sofsian, 2007).
Ironically, as overeating and obesity have reached epidemic proportions, there has been a related increase in disorders associated with eating too little (see Polivy & Herman, 2002). For example, almost 3% of American adolescents currently suffer from anorexia or bulimia, which can be life-threatening in extreme cases. The massive increases in obesity and other eatingrelated disorders that have occurred over the last few decades in many countries stand in direct opposition to most people’s thinking about hunger and eating.
Many people—and I assume that this includes you—believe that hunger and eating are normally triggered when the body’s energy resources fall Watch below a prescribed optimal Thinking about Hunger level, or set point. They apwww. mypsychlab. com preciate that many factors influence hunger and eating, but they assume that the hunger and eating system has evolved to supply the body with just the right amount of energy. This chapter explores the incompatibility of the setpoint assumption with the current Thinking Creatively epidemic of eating disorders.
If we all have hunger and eating systems whose primary function is to maintain energy resources at optimal levels, then eating disorders should be rare. The fact that they are so prevalent suggests that hunger and eating are regulated in some other way. This chapter will repeatedly challenge you to think in new ways about issues that impact your health and longevity and will provide new insights of great personal relevance—I guarantee it. Before you move on to the body of the chapter, I would like you to pause to consider a case study. What would a severely amnesic patient do if offered a meal
E shortly after finishing one? If his hunger and eating were controlled by energy set points, he would refuse the second meal. Did he? The Case of the Man Who Forgot Not to Eat R. H. was a 48-year-old male whose progress in graduate school was interrupted by the development of severe amnesia for long-term explicit memory. His Clinical amnesia was similar in pattern and Implications severity to that of H. M. , whom you met in Chapter 11, and an MRI examination revealed bilateral damage to the medial temporal lobes. The meals offered to R. H. ere selected on the basis of interviews with him about the foods he liked: veal parmigiana (about 750 calories) plus all the apple juice he wanted. On one occasion, he was offered a second meal about 15 minutes after he had eaten the first, and he ate it. When offered a third meal 15 minutes later, he ate that, too. When offered a fourth meal he rejected it, claiming that his “stomach was a little tight. ” Then, a few minutes later, R. H. announced that he was going out for a good walk and a meal. When asked what he was going to eat, his answer was “veal parmigiana. ” Clearly, R. H. ’s hunger (i. e. motivation to eat) did not result from an energy deficit (Rozin et al. , 1998). Other cases like that of R. H. have been reported by Higgs and colleagues (2008). 12. 1 Digestion, Energy Storage, and Energy Utilization The primary purpose of hunger is to increase the probability of eating, and the primary purpose of eating is to supply the body with the molecular building blocks and energy it needs to survive and function (see Blackburn, 2001). This section provides the foundation for our consideration of hunger and eating by providing a brief overview of the processes by which food is digested, stored, and converted to energy.
Digestion The gastrointestinal tract and the process of digestion are illustrated in Figure 12. 1 on page 300. Digestion is the gastrointestinal process of breaking down food and absorbing its constituents into the body. In order to appreciate the basics of digestion, it is useful to consider the body without its protuberances, as a simple living tube Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon. Copyright © 2011 by Pearson Education, Inc. 300 Chapter 12 ¦ Hunger, Eating, and Health Steps in Digestion Parotid gland Salivary glands Esophagus Stomach 1 2 3 4 5 6 7 8
Chewing breaks up food and mixes it with saliva. Saliva lubricates food and begins its digestion. Swallowing moves food and drink down the esophagus to the stomach. Liver The primary function of the stomach is to serve as a storage reservoir. The hydrochloric acid in the stomach breaks food down into small particles, and pepsin begins the process of breaking down protein molecules to amino acids. The stomach gradually empties its contents through the pyloric sphincter into the duodenum, the upper portion of the intestine, where most of the absorption takes place. Pyloric sphincter Gall bladder
Pancreas Digestive enzymes in the duodenum, many of them from the gall bladder and pancreas, break down protein molecules to amino acids, and starch and complex sugar molecules to simple sugars. Simple sugars and amino acids readily pass through the duodenum wall into the bloodstream and are carried to the liver. Fats are emulsified (broken into droplets) by bile, which is manufactured in the liver and stored in the gall bladder until it is released into the duodenum. Emulsified fat cannot pass through the duodenum wall and is carried by small ducts in the duodenum wall into the lymphatic system.
Most of the remaining water and electrolytes are absorbed from the waste in the large intestine, and the remainder is ejected from the anus. Duodenum Large intestine or colon Small intestine Anus FIGURE 12. 1 The gastrointestinal tract and the process of digestion. with a hole at each end. To supply itself with energy and other nutrients, the tube puts food into one of its two holes—the one with teeth—and passes the food along its internal canal so that the food can be broken down and partially absorbed from the canal into the body. The leftovers are jettisoned from the other end.
Although this is not a particularly appetizing description of eating, it does serve to illustrate that, strictly speaking, food has not been consumed until it has been digested. Energy Storage in the Body As a consequence of digestion, energy is delivered to the body in three forms: (1) lipids (fats), (2) amino acids (the breakdown products of proteins), and (3) glucose (a simple sugar that is the breakdown product of complex carbohydrates, that is, starches and sugars). The body uses energy continuously, but its consumption is intermittent; therefore, it must store energy for use in the intervals between meals.
Energy is stored in three forms: fats, glycogen, and proteins. Most of the body’s energy reserves are stored as fats, relatively little as glycogen and proteins (see Figure 12. 2). Thus, changes in the body weights of adult humans are largely a consequence of changes in the amount of their stored body fat. Why is fat the body’s preferred way of storing energy? Glycogen, which is largely stored in the liver and muscles, might be expected to be the body’s preferred mode of energy storage because it is so readily converted to glucose—the body’s main directly utilizable source of energy. But there ISBN 0-558-78571-9
Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon. Copyright © 2011 by Pearson Education, Inc. 12. 1 ¦ Digestion, Energy Storage, and Energy Utilization 301 Fat in adipose tissue (85%) Protein in muscle (14. 5%) Glycogen in muscle and liver (0. 5%) FIGURE 12. 2 person. Distribution of stored energy in an average are two reasons why fat, rather than glycogen, is the primary mode of energy storage: One is that a gram of fat can store almost twice as much energy as a gram of glycogen; the other is that glycogen, unlike fat, attracts and holds substantial quantities of water.
Consequently, if all your fat calories were stored as glycogen, you would likely weigh well over 275 kilograms (600 pounds). ISBN 0-558-78571-9 Three Phases of Energy Metabolism There are three phases of energy metabolism (the chemical changes by which energy is made available for an organism’s use): the cephalic phase, the absorptive phase, and the fasting phase. The cephalic phase is the preparatory phase; it often begins with the sight, smell, or even just the thought of food, and it ends when the food starts to be absorbed into the bloodstream.
The absorptive phase is the period during which the energy absorbed into the bloodstream from the meal is meeting the body’s immediate energy needs. The fasting phase is the period during which all of the unstored energy from the previous meal has been used and the body is withdrawing energy from its reserves to meet its immediate energy requirements; it ends with the beginning of the next cephalic phase. During periods of rapid weight gain, people often go directly from one absorptive phase into the next cephalic phase, without experiencing an intervening fasting phase.
The flow of energy during the three phases of energy metabolism is controlled by two pancreatic hormones: insulin and glucagon. During the cephalic and absorptive phases, the pancreas releases a great deal of insulin into the bloodstream and very little glucagon. Insulin does three things: (1) It promotes the use of glucose as the primary source of energy by the body. (2) It promotes the conversion of bloodborne fuels to forms that can be stored: glucose to glycogen and fat, and amino acids to proteins. 3) It promotes the storage of glycogen in liver and muscle, fat in adipose tissue, and proteins in muscle. In short, the function of insulin during the cephalic phase is to lower the levels of bloodborne fuels, primarily glucose, in anticipation of the impending influx; and its function during the absorptive phase is to minimize the increasing levels of bloodborne fuels by utilizing and storing them. In contrast to the cephalic and absorptive phases, the fasting phase is characterized by high blood levels of glucagon and low levels of insulin.
Without high levels of insulin, glucose has difficulty entering most body cells; thus, glucose stops being the body’s primary fuel. In effect, this saves the body’s glucose for the brain, because insulin is not required for glucose to enter most brain cells. The low levels of insulin also promote the conversion of glycogen and protein to glucose. (The conversion of protein to glucose is called gluconeogenesis. ) On the other hand, the high levels of fasting-phase glucagon promote the release of free fatty acids from adipose tissue and their use as the body’s primary fuel.
The high glucagon levels also stimulate the conversion of free fatty acids to ketones, which are used by muscles as a source of energy during the fasting phase. After a prolonged period without food, however, the brain also starts to use ketones, thus further conserving the body’s resources of glucose. Figure 12. 3 summarizes the major metabolic events associated with the three phases of energy metabolism. Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon. Copyright © 2011 by Pearson Education, Inc. 302
Chapter 12 ¦ Hunger, Eating, and Health Cephalic Phase Preparatory phase, which is initiated by the sight, smell, or expectation of food Insulin levels high Glucagon levels low Promotes
• Utilization of blood glucose as a source of energy
• Conversion of excess glucose to glycogen and fat
• Conversion of amino acids to proteins
• Storage of glycogen in liver and muscle, fat in adipose tissue, and protein in muscle Inhibits
• Conversion of glycogen, fat, and protein into directly utilizable fuels (glucose, free fatty acids, and ketones)
Absorptive Phase Nutrients from a meal meeting the body’s immediate energy requirements, with the excess being stored Fasting Phase Energy being withdrawn from stores to meet the body’s immediate needs Glucagon levels high Insulin levels low Promotes
• Conversion of fats to free fatty acids and the utilization of free fatty acids as a source of energy
• Conversion of glycogen to glucose, free fatty acids to ketones, and protein to glucose Inhibits
• Utilization of glucose by the body but not by the brain
• Conversion of glucose to glycogen and fat, and amino acids to protein
• Storage of fat in adipose tissue
FIGURE 12. 3 The major events associated with the three phases of energy metabolism: the cephalic, absorptive, and fasting phases. 12. 2 Theories of Hunger and Eating: Set Points versus Positive Incentives One of the main difficulties I have in teaching the fundamentals of hunger, eating, and body weight regulation is the set-point assumption. Although it dominates most people’s thinking about hunger and eating (Assanand, Pinel, & Lehman, 1998a, 1998b), whether they realize it or not, it is inconsistent with the bulk of the evidence.
What exactly is the set-point assumption? Set-Point Assumption Most people attribute hunger (the motivation to eat) to the presence of an energy deficit, and they view eating as the means by which the energy resources of the body are returned to their optimal level—that is, to the energy set point. Figure 12. 4 summarizes this set-point assumption. After a meal (a bout of eating), a person’s energy resources are assumed to be near their set point and to decline thereafter as the body uses energy to fuel its physiological processes.
When the level of the body’s energy resources falls far enough below the set point, a person becomes motivated by hunger to initiate another meal. The meal continues, according to the set-point assumption, until the energy level ISBN 0-558-78571-9 Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon. Copyright © 2011 by Pearson Education, Inc. 12. 2 ¦ Theories of Hunger and Eating: Set Points versus Positive Incentives 303 Hypothetical Energy Reserves FIGURE 12. The energy set-point view that is the basis of many people’s thinking about hunger and eating. Hunger Meal returns to its set point and the person feels satiated (no longer hungry). Set-point models assume that hunger and eating work in much the same way as a thermostat1 2 regulated heating system in a cool climate. The heater increases the house temperature until it reaches its set point (the thermostat setting). The heater then shuts off, and the temperature of the house gradually declines until it becomes low enough to turn the heater back on.
All set-point systems have three components: a setpoint mechanism, a detector mechanism, and an effector mechanism. The set-point mechanism defines the set point, the detector mechanism detects deviations from the set point, and the effector mechanism acts to eliminate the deviations. For example, the set-point, detector, and effector mechanisms of a heating system are the thermostat, the thermometer, and the heater, respectively. All set-point systems are negative feedback systems— systems in which feedback from changes in one direction elicit compensatory effects in the opposite direction.
Negative feedback systems are common in mammals because they act to maintain homeostasis—a stable internal environment—which is critical for mammals’ survival (see Wenning, 1999). Set-point systems combine negative feedback with a set point to keep an internal environment fixed at the prescribed point. Set-point systems seemed necessary when the adult human brain was assumed to be immutable: Because the brain couldn’t change, energy resources had to be highly regulated. However, we now know that the adult human brain is plastic and capable of considerable adaptation.
Thus, there is no longer a logical imperative for the set-point regulation of eating. Throughout this chapter, you will need to put aside your preconceptions and base your thinking about hunger and eating entirely on the empirical evidence. 3 4 5 6 7 8 9 10 11 Hours regulated by a system that is designed to maintain a blood glucose set point—the idea being that we become hungry when our blood glucose levels drop significantly below their set point and that we become satiated when eating returns our blood glucose levels to their set point. The various versions of this theory are collectively referred to as the glucostatic theory.
It seemed to make good sense that the main purpose of eating is to defend a blood glucose set point, because glucose is the brain’s primary fuel. The lipostatic theory is another set-point theory that was proposed in various forms in the 1940s and 1950s. According to this theory, every person has a set point for body fat, and deviations from this set point produce compensatory adjustments in the level of eating that return levels of body fat to their set point. The most frequently cited support for the theory is the fact that the body weights of adults stay relatively constant.
The glucostatic and lipostatic theories were viewed as complementary, not mutually exclusive. The glucostatic theory was thought to account for meal initiation and termination, whereas the lipostatic theory was thought to account for long-term regulation. Thus, the dominant view in the 1950s was that eating is regulated by the interaction between two set-point systems: a short-term glucostatic system and a long-term lipostatic system. The simplicity of these 1950s theories is appealing. Remarkably, they are still being presented as the latest word in some textbooks; perhaps you have encountered them.
ISBN 0-558-78571-9 Glucostatic and Lipostatic Set-Point Theories of Hunger and Eating In the 1940s and 1950s, researchers working under the assumption that eating is regulated by some type of setpoint system speculated about the nature of the regulation. Several researchers suggested that eating is Problems with Set-Point Theories of Hunger and Eating Set-point theories of hunger and eating have several serious weaknesses (see de Castro & Plunkett, 2002). You have already learned one fact that undermines these theories: There is an epidemic of obesity and overweight,
Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon. Copyright © 2011 by Pearson Education, Inc. 304 Chapter 12 ¦ Hunger, Eating, and Health not occur if eating is Thinking Creatively which should set point. Let’s look at regulated by a three more major weaknesses of setpoint theories of hunger and eating. First, set-point theories of hunger and eating are inconsistent with basic eating-related evolutionary pressures as we understand them. The major eatingrelated problem faced by our ancestors was the inconEvolutionary istency and unpredictability of the food Evolutiona Perspective supply. Thus, in order to survive, it was important for them to eat large quantities of good food when it was available so that calories could be banked in the form of body fat. Any ancestor— human or otherwise—that stopped feeling hungry as soon as immediate energy needs were met would not have survived the first hard winter or prolonged drought. For any warm-blooded species to survive under natural conditions, it needs a hunger and eating system that prevents energy deficits, rather than one that merely responds to them once they have developed.
From this perspective, it is difficult to imagine how a set-point hunger and feeding system could have evolved in mammals (see Pinel, Assanand, & Lehman, 2000). ? Second, major predictions of the set-point theories of hunger and eating have not been confirmed. Early studies seemed to support the set-point theories by showing that large reductions in body fat, produced by starvation, or large reductions in blood glucose, produced by insulin injections, induce increases in eating in laboratory animals.
The problem is that reductions in blood glucose of the magnitude needed to reliably induce eating rarely occur naturally. Indeed, as you have already learned in this chapter, about 65% of U. S. adults have a significant excess of fat deposits when they begin a meal. Conversely, efforts to reduce meal size by having subjects consume a high-calorie drink before eating have been largely unsuccessful; indeed, beliefs about the caloric content of a premeal drink often influence the size of a subsequent meal more than does its actual caloric content (see Lowe, 1993). Third, set-point theories of hunger and eating are deficient because they fail to recognize the major influences on hunger and eating of such important factors as taste, learning, and social influences. To convince yourself of the importance of these factors, pause for a minute and imagine the sight, smell, and taste of your favorite food. Perhaps it is a succulent morsel of lobster meat covered with melted garlic butter, a piece of chocolate cheesecake, or a plate of sizzling homemade french fries.
Are you starting to feel a bit hungry? If the homemade french fries—my personal weakness—were sitting in front of you right now, wouldn’t you reach out and have one, or maybe the whole plateful? Have you not on occasion felt discomfort ? after a large main course, only to polish off a substantial dessert? The usual positive answers to these questions lead unavoidably to the conclusion that hunger and eating are not rigidly controlled by deviations from energy set points. Positive-Incentive Perspective
The inability of set-point theories to account for the basic phenomena of eating and hunger led to the development of an alternative theoretical perspective (see Berridge, 2004). The central assertion of this perspective, commonly referred to as positive-incentive theory, is that humans and other animals are not normally driven to eat by internal energy deficits but are drawn to eat by the anticipated pleasure of eating—the anticipated pleasure of a behavior is called its positive-incentive value (see Bolles, 1980; Booth, 1981; Collier, 1980; Rolls, 1981; Toates, 1981).
There are several different positive-incentive theories, and I refer generally to all of them as the positiveincentive perspective. The major tenet of the positive-incentive perspective on eating is that eating is controlled in much the same way as sexual behavior: We engage in sexual Evolutiona Evolutionary behavior not because we have an internal Perspective deficit, but because we have evolved to crave it.
The evolutionary pressures of unexpected food shortages have shaped us and all other warm-blooded animals, who need a continuous supply of energy to maintain their body temperatures, to take advantage of good food when it is present and eat it. According to the positiveincentive perspective, it is the presence of good food, or the anticipation of it, that normally makes us hungry, not an energy deficit. According to the positive-incentive perspective, the degree of hunger you feel at any particular time depends on the interaction of all the factors that influence the positiveincentive value of eating (see Palmiter, 2007).
These include the following: the flavor of the food you are likely to consume, what you have learned about the effects of this food either from eating it previously or from other people, the amount of time since you last ate, the type and quantity of food in your gut, whether or not other people are present and eating, whether or not your blood glucose levels are within the normal range. This partial list illustrates one strength of the positive-incentive perspective. Unlike set-point theories, positive-incentive theories do not single out one factor as the major eterminant of hunger and ignore the others. Instead, they acknowledge that many factors interact to determine a person’s hunger at any time, and they suggest that this interaction occurs through the influence of these various factors on the positive-incentive value of eating (see Cabanac, 1971). In this section, you learned that most people think about hunger and eating in terms of energy set points and ISBN 0-558-78571-9 Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon.
Copyright © 2011 by Pearson Education, Inc. 12. 3 ¦ Factors That Determine What, When, and How Much We Eat 305 were introduced to an alternative way of thinking—the positive-incentive perspective. Which way is correct? If you are like most people, you have an attachment to familiar ways of thinking and a resistance to new ones. Try to put this tendency aside and base your views about this important issue entirely on the evidence. You have already learned about some of the major weaknesses of strict set-point theories of hunger and eating.
The next section describes some of the things that biopsychological research has taught us about hunger and eating. As you progress through the section, notice the superiority of the positive-incentive theories over set-point theories in accounting for the basic facts. rats learn to prefer flavors that they experience in mother’s milk and those that they smell on the breath of other rats (see Galef, 1995, 1996; Galef, Whishkin, & Bielavska, 1997). Similarly, in humans, many food preferences are culturally specific—for example, in some cultures, various nontoxic insects are considered to be a delicacy.
Galef and Wright (1995) have shown that rats reared in groups, rather than in isolation, are more likely to learn to eat a healthy diet. Learning to Eat Vitamins and Minerals How do animals select a diet that provides all of the vitamins and minerals they need? To answer this question, researchers have studied how dietary deficiencies influence diet selection. Two patterns of results have emerged: one for sodium and one for the other essential vitamins and minerals. When an animal is deficient in sodium, it develops an immediate and compelling preference for the taste of sodium salt (see Rowland, 1990).
In contrast, an animal that is deficient in some vitamin or mineral other than sodium must learn to consume foods that are rich in the missing nutrient by experiencing their positive effects; this is because vitamins and minerals other than sodium normally have no detectable taste in food. For example, rats maintained on a diet deficient in thiamine (vitamin B1) develop an aversion to the taste of that diet; and if they are offered two new diets, one deficient in thiamine and one rich in thiamine, they often develop a preference for the taste of the thiamine-rich diet over the ensuing days, as it becomes associated with improved health.
If we, like rats, are capable of learning to select diets that are rich in the vitamins and minerals we need, why are dietary deficiencies so prevalent in our society? One reason is that, in order to maximize profits, manufacturers produce foods that have the tastes we prefer but lack many of the nutrients we need to maintain our health. (Even rats prefer chocolate chip cookies to nutritionally complete rat chow. ) The second reason is illustrated by the classic study of Harris and associates (1933).
When thiamine-deficient rats were offered two new diets, one with thiamine and one without, almost all of them learned to eat the complete diet and avoid the deficient one. However, when they were offered ten new diets, only one of which contained the badly needed thiamine, few developed a preference for the complete diet. The number of different substances, both nutritious and not, consumed each day by most people in industrialized societies is immense, and this makes it difficult, if not impossible, for their bodies to learn which foods are beneficial and which are not.
There is not much about nutrition in this chapter: Although it is critically important to eat a nutritious diet, nutrition seems to have little direct effect on our feelings of hunger. However, while I am on the topic, I would like to direct you to a good source of information 12. 3 Factors That Determine What, When, and How Much We Eat This section describes major factors that commonly determine what we eat, when we eat, and how much we eat. Notice that energy deficits are not included among these factors.
Although major energy deficits clearly increase hunger and eating, they are not a common factor in the eating behavior of people like us, who live in food-replete societies. Although you may believe that your body is short of energy just before a meal, it is not. This misconception is one that is addressed in this section. Also, notice how research on nonhumans has played an important role in furthering understanding of human eating. Factors That Determine What We Eat Certain tastes have a high positive-incentive value for virtually all members of a species. For example, most humans have a special fondness for sweet, fatty, and salty tastes.
This species-typical pattern of human taste preferences is adaptive because in nature sweet and fatty tastes Evolutionary are typically characteristic of high-energy Evolutiona Perspective foods that are rich in vitamins and minerals, and salty tastes are characteristic of sodium-rich foods. In contrast, bitter tastes, for which most humans have an aversion, are often associated with toxins. Superimposed on our species-typical taste preferences and aversions, each of us has the ability to learn specific taste preferences and aversions (see Rozin & Shulkin, 1990).
Learned Taste Preferences and Aversions Animals learn to prefer tastes that are followed by an infusion of calories, and they learn to avoid tastes that are followed by illness (e. g. , Baker & Booth, 1989; Lucas & Sclafani, 1989; Sclafani, 1990). In addition, humans and other animals learn what to eat from their conspecifics. For example, ISBN 0-558-78571-9 Biopsychology, Eighth Edition, by John P. J. Pinel. Published by Allyn & Bacon. Copyright © 2011 by Pearson Education, Inc. 306 Chapter 12 ¦ Hunger, Eating, and Health
Thinking Creatively positive effect on your health: Some popular books on nutrition are dangerous, and even governments, inordinately influenced by economic considerations and special-interest groups, often do not provide the best nutritional advice (see Nestle, 2003). For sound research-based advice on nutrition, check out an article by Willett and Stampfer (2003) and the book on which it is based, Eat, Drink, and Be Healthy by Willett, Skerrett, and Giovannucci (2001). about nutrition that could have a hunger is caused by the expectation of food, not by an energy deficit.
As a high school student, I ate lunch at exactly 12:05 every day and was overwhelmed by hunger as the time approached. Now, my eating schedule is different, and I never experience Thinking Creatively noontime hunger pangs; I now get hungry just before the time at which I usually eat. Have you had a similar experience? Pavlovian Conditioning of Hunger In a classic series of Pavlovian conditioning experiments on laboratory rats, Weingarten (1983, 1984, 1985) provided strong support for the view that hunger is often caused by the expectation of food, not by an energy deficit.
During the conditioning phase of one