a0005 Eating, Psychology of

Jennifer S. Mills and Julie ColemanYork University, Toronto, Ontario, Canada

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E

1. Introduction

2. Cultural and Environmental Influences on Food Selection

3. Social Influences on Eating Behavior

4. The Role of Personality in Eating Behavior

5. Set Point Model of Weight Regulation

6. Obesity and the Problem of Eating Too Much

7. Overcoming Obstacles to Weight Control

Further Reading

GLOSSARY

basal metabolic rate The daily energy requirements for the

body to perform its basic functions, expressed in terms of

number of calories.

body mass index (BMI) An estimate of body fat or degree of

obesity (BMI = kg/m2).

dieting The attempt to limit food intake in terms of amount

or type of food for the purpose of weight control or

restrained eating.

food neophobia A fear of trying new or novel foods.

satiety The feeling of fullness after eating.

set point An internal sensor of body fat to which metabolic

processes will respond to achieve a balance of energy input

and expenditure so as to defend a specific weight range for

an individual.

Eating is a complex human behavior that is influenced

by cultural, social, personality, and biological factors.

Dieting, obesity, and overeating all are important social

and health problems within applied psychology. The

Encyclopedia of Applied Psychology, 655VOLUME 1

absence of demonstrably successful weight loss

programs, as well as controversy over the supposed

health benefits of weight loss in the long term, casts

doubt on the popular notion that dieting makes peoplehealthier.

1. INTRODUCTION

One might think that a behavior so essential to our

survival as eating would be fully explained through

biology. It might seem that, like other essential behav-

iors such as sleeping and breathing, one could neatly

explain the physiological mechanisms at work just

before we put food into our mouths. However, decades

of research into the biological mechanisms involved ineating have produced rather disappointing results. It

seems that humans just do not do a very good job of

eating in accordance with verifiable hunger and satiety

cues. The biological perspective of eating posits that we

should eat when our metabolic energy fuels are

expended. However, one problem with this explana-

tion of eating behavior is that humans often report

feeling ‘‘hunger’’ despite ample energy stores in theform of body fat. Furthermore, most of us eat much

more food than we require to remain alive. Another

problem with the biological explanation of eating is

that overall blood glucose levels (another index of

metabolic energy) do not correspond well with

reported hunger or (again) eating behavior. Finally,

the hormone and neurotransmitter involvement in

#2004 Elsevier Inc.

All rights reserved.

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656 Eat ing , Psycho logy o f

hunger and eating is especially complex and not yetcompletely understood, with several hormones poten-

tially involved (e.g., leptin, insulin, ghrelin, cholecyso-

kinin). Rather than being determined by iatrogenic

biological markers, humans’ eating behavior seems to

be largely determined by factors outside the individual.

This article examines the psychology of eating and

attempts to answer the question of why we generally

tend not to eat according to hunger and fullness.Culture and environment, sensory factors, social fac-

tors, and even personality can influence food choice

and eating behavior, and all of these factors take us

further away from eating according to our internal

hunger and satiety cues. The article also examines the

problems of eating too much and obesity as well as

what applied psychology can tell us about the solutions

to these complex health problems.

2. CULTURAL ANDENVIRONMENTAL INFLUENCES

ON FOOD SELECTION

In general, our diets are made up of what is readily

available for us to eat. To a large extent, our culture

decides for us the type of food we can eat as well as the

portion sizes we consider to be normative. In brief, wetend to eat what is put in front of us. For instance, the

North American diet, replete with an overabundance of

saturated fats and larger portion sizes as compared

with its international counterparts, can at least par-

tially explain North America’s relatively high obesity

rates. Experimental studies have confirmed that the

more we are served, the more we eat.

Humans and animals alike experience food neopho-bia, that is, an intrinsic fear of trying new or novel

foods. This fear is believed to serve a protective func-

tion in that it dissuades us from eating foods with

which we are not familiar and that might not be safe.

Factors that have been shown to increase food neopho-

bia include knowledge that the food is of animal origin

as well as trait and state anxiety. Factors that decrease

our unwillingness to try new foods include modelingby others trying the new food, information about the

nutritional value of the food, information about the

good taste of the food, and mere exposure to the food.

In addition to the role of culture in determining our

diets, personal learning experience dictates which

foods we will and will not tend to include in our

diets. Negative food associations are formed quite

readily. For example, a single episode of upper gastro-intestinal illness (i.e., vomiting) after eating a particu-

lar food can be enough to produce a strong and

resilient conditioned taste aversion. Presumably, this

aversion has a protective function by keeping us away

from a food that may make us sick again and endanger

our health. Interestingly, illness after ingesting foods of

animal origin is more likely to lead to the development

of a conditioned taste aversion than is illness aftereating fruits, grains, or vegetables.

Sensory qualities of foods themselves may override

our bodies’ hunger and satiety cues, resulting in our

eating either more or less of the foods. For instance, we

generally eat more as a function of the variety of foods

we are offered, with total food intake increasing with

greater variety. Even variety in the texture of a single

type of food we are offered (e.g., different pasta shapes,ice cream vs milkshake) can increase our total food

intake as compared with the presentation of a single

texture of that food alone. The taste of a food also

moderates our desire to eat more or less of it. Foods

that are high in sugar and fat are intrinsically more

appealing to the human palate, so it is not surprising

that we are more likely to consume more of these foods

when we are given the opportunity. According to theevolutionary perspective, this preference for sweet and

fatty foods is due to those foods’ scarcity during the

hunting-and-gathering phase of human evolution and

their energy content per gram of food as compared

with foods high in protein. We can also lose our

appetite for eating a specific food, a phenomenon

known as sensory specific satiety, but then begin eating

again when a new food is introduced. Most of us haveexperienced a resurgence of appetite for dessert,

despite feeling full after finishing dinner. It is as though

our bodies ‘‘get bored’’ of a particular food or taste after

a while, prompting us to seek out more variety in our

diets. This effect would presumably have a positive

impact on our health by increasing the number of

nutrients in our system.

Despite the cultural variations in cuisine and foodselection, research has shown that humans are gener-

ally good at self-selecting a nutritionally balanced

diet—at least they are as children. In a classic series

of studies by Davis, human toddlers were offered a

‘‘buffet-style’’ meal plan and were allowed to choose

the type and amount of food they ate. Her results

showed that the toddlers self-selected foods that

together made up a nutritionally balanced diet andresulted in a normal and stable pattern of weight

regulation.

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3. SOCIAL INFLUENCES ON EATINGBEHAVIOR

Although we may start out with an intrinsic appetite forfoods that will maximize our chances of being healthy as

well as a general reliance on internal hunger and fullness

cues, as we grow, our eating is more likely to be influ-

enced by non-nutrient-related variables. One social fac-

tor affecting how much we eat is the number of people

who are present in a given situation. We generally eat

more as a power function of the number of people

present. One proposed explanation for this social facil-itation of eating behavior is related to competition for

food resources; that is, we do not want to lose out on the

opportunity to eat by letting our companions get to the

food first. Another explanation is that the mere presence

of people may provide distraction from our satiety cues.

Of course, in real life, the presence of eating companions

is often confounded by other factors that stimulate eat-

ing such as the variety and quantity of foods available(e.g., the ‘‘dinner party’’ effect). There is some evidence

that the relationship between people who are eating

together also moderates this social facilitation effect;

that is, we are more likely to eat dessert when our eating

companions are friends than when they are strangers.

This suggests that the presence of others, particularly

others with whom we are socially close, reduces inhibi-

tions around eating. Interestingly, the idea that we eatmore with more people present does not appear to hold

true for obese and dieting individuals, who actually eat

less when eating with others and are prone to splurge

when eating alone. Presumably, for these individuals, an

impression management motive—the desire to present

themselves to others as being small eaters—overrides

the effect of social facilitation of eating.

In addition to the mere presence of other individuals,the eating behavior of those individuals affects our own

eating behavior. Modeling by others has a strong influ-

ence on eating behavior in that individuals tend to match

the amount eaten by those with whom they are eating.

For instance, even when we are very hungry, we will

tend to match a small amount eaten by our companions.

4. THE ROLE OF PERSONALITYIN EATING BEHAVIOR

Personality also influences diet and eating behavior.

The goal of weight loss or weight maintenance is the

most common reason for efforts to control one’s eating.

Herman and Polivy’s ‘‘restraint theory’’ of eating behav-ior emphasizes the importance of chronic attempts at

dieting as a predictor of food intake and has been very

influential in the study of eating behavior. In research

studies, restrained eaters (or chronic dieters) have

been shown to demonstrate several differences with

respect to their eating as compared with their unrest-

rained eating counterparts. Psychologically, restrained

eaters exhibit higher body dissatisfaction, lower self-esteem, and a higher drive for thinness. Although diet-

ers’ eating can be characterized essentially as an

attempt to reduce energy intake (calories, fat, and/or

portion size), they are especially prone to overeating.

Laboratory studies of eating often employ a taste test

methodology to demonstrate this effect. Participants

are allowed to ad lib eat as part of an ostensible taste

test during which they rate the different taste proper-ties of the food (e.g., sweetness, saltiness). Their total

food intake is measured by subtracting the weight of

the plate(s) (or, in some cases, counting the number of

food items eaten such as candies) after the experiment

from the preexperiment weight. Sometimes, partici-

pants are given a ‘‘preload’’ or snack to eat before the

taste test, and they are typically exposed to an inde-

pendent variable of interest before the eating task.Disinhibited eating or overeating among dieters has

been demonstrated to occur in response to ingestion

of a high-calorie preload (e.g., milkshake, chocolate

bar), stress, perceived weight gain, food cues, lowered

mood, positive mood, exposure to thin media images,

and even anticipated future overeating. With all of

these and more potentially disinhibiting factors, it is

not surprising that studies have shown that dieterstend to eat more overall, and also weigh more, than

do nondieters. As noted previously, humans are

inclined to select foods based on their sensory quali-

ties. Obese and dieting individuals are particularly

dependent on external and sensory cues in deciding

how much of a food to eat, showing a heightened

preference for good-tasting food over that of their

normal-weight or nondieting counterparts.Herman and Polivy’s ‘‘boundary model’’ of overeating

posits that restrained eaters have a cognitively deter-

mined ‘‘diet boundary’’ that exists before the experience

of satiety. This boundary represents what a dieter

believes he or she should eat. Under normal conditions,

food intake is expected to remain within the limits set

by the diet boundary. However, once eating has

surpassed the boundary limit (e.g., by ingesting a high-calorie preload such as a milkshake), eating will

continue until eventual fullness is achieved. Herman

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658 Eat ing , Psycho logy o f

and Polivy labeled this event the ‘‘what the hell’’ effect;given that the dieter’s self-imposed diet boundary has

already been surpassed, the dieter continues to eat until

satiety and sometimes even beyond. Therefore, intended

eating behavior for restrained eaters is cognitively deter-

mined by perceptions of what should be eaten in terms

of type or quantity of food. In contrast, unrestrained

eating is relatively more determined by an awareness of

hunger or satiety cues.

5. SET POINT MODEL OF WEIGHTREGULATION

There is solid evidence for a genetic factor in body

weight determination. In terms of weight, adopted

children tend to resemble their biological parents

more than they do their adoptive parents. Identical

twins, even when reared apart, are more similar interms of weight than are fraternal twins or siblings.

These examples suggest that genetics plays a role in

determining one’s ‘‘set point,’’ that is, a type of internal

sensor around which weight is regulated. When fat

levels fall below this set point, the body responds by

slowing metabolic processes so as to require fewer

calories, thereby making the body more efficient in its

energy expenditures and fighting against the depletionof fat stores. Keys and colleagues demonstrated this

scenario in an experimental study of human semistar-

vation during World War II. Participants in the study

were young men who agreed to lose 25% of their body

weights for the study for the purpose of determining

the best way in which to refeed starving people in war-

torn Europe. On rations of 50% of their original daily

caloric intake, the men initially lost weight quickly.However, over the 6-month starvation phase of the

experiment, the men’s rate of weight loss reached a

plateau, with many participants’ rations needing to be

cut even further to achieve the desired weight loss.

Keys’s starving participants exhibited a number of

symptoms characteristic of the body’s corrective action

of falling below its normal weight (and, presumably,

below its set point in this initially nondieting sample).The men became irritable, miserable, hungry, and

obsessed with thoughts of food. Their basal metabolic

rates decreased significantly, indicating their bodies’

desire to conserve as many calories as possible. They

became apathetic and lethargic, avoiding as much

physical activity and energy expenditure as possible.

They had very strong urges to overeat, and when they

were allowed to eat during the refeeding phase of theexperiment, they overate and demonstrated a prefer-

ence for high-calorie foods that would increase their fat

stores most quickly, a situation that is consistent with

the predictions of set point theory.

In another study of the effects of overeating that also

found evidence supporting the set point theory, Sims

and colleagues recruited prison inmate volunteers to

gain 25% of their body weights as part of an experi-ment. The men’s food intake was increased, and their

physical activity was decreased and controlled. At first,

the volunteers gained weight easily, but the rate of

weight gain soon slowed and their daily caloric intake

had to be increased for them to continue gaining. One

man did not reach his goal weight even though he

consumed more than 10,000 calories per day. Once

the men reached their goal weights, the men continuedto require extra calories to maintain their higher than

normal weights. During the experiment, these volun-

teers began to be repulsed by food and had to force

themselves to eat. Many considered dropping out of

the study due to the discomfort of overeating. Physical

responses included an increased basal metabolic rate

and profuse sweating, indications that their bodies

were eliminating the excess calories they were ingest-ing. After the experiment, there were differences in

how quickly the men returned to their preexperiment

weights, with two participants (both with family his-

tories of obesity) never reaching their original weights.

In sum, there is evidence that our body weights and

shapes have a genetic component, but changes in eating

behavior, hormones, or other variables can also produce

weight gain or loss. Because of this apparent contra-diction, some researchers have abandoned the set

point theory of weight regulation in favor of a ‘‘settling

zone’’ alternative. In 2002, Levitsky argued that within

the biologically determined range or zone of body

weight, actual body composition may ‘‘settle’’ at a value

determined by behavior. Furthermore, the width of

one’s settling zone may also depend on individual fac-

tors such that some individuals will naturally experiencegreater weight fluctuations over time than will others.

6. OBESITY AND THE PROBLEMOF EATING TOO MUCH

Although genetics can predispose individuals to higher

than average weights, there is no doubt that overeating

can contribute to obesity. Because of societal pressure

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Eat ing , Psycho logy o f 659

to be thin and the stigma against overweight persons inmany parts of the world, the obese and dieting popula-

tions overlap considerably. Therefore, many of the

disinhibiting factors discussed in the preceding section

operate regularly on the eating behavior of obese per-

sons, leading to frequent episodes of overeating. In the

preceding section, it was pointed out that overeating

can occur beyond the point of satiety and until stom-

ach capacity is eventually reached. Binge eating con-sists of eating episodes that involve consuming large

quantities of food (e.g., twice a normal serving) com-

bined with a feeling of being out of control. For binge

eaters, food intake may continue until they reach

capacity, and there is never really a sense of feeling as

if they have eaten enough to satisfy their hunger. Binge

eating combined with compensatory behaviors, such as

self-induced vomiting, excessive exercise, extremefood restriction, and laxative abuse, is the hallmark of

bulimia nervosa, an eating disorder. ‘‘Binge eating dis-

order,’’ although not currently a formal diagnostic

category, is characterized by regular binge eating epi-

sodes without attempts at compensation and is esti-

mated to be highly prevalent in the obese population.

There is little consensus on the technical definition

of obesity. Traditionally, charts that provide normalweight ranges for various heights and body frame

sizes were the standard tool for determining normal

weight and overweight. These charts were originally

published by the Metropolitan Life Insurance

Company in 1959, were based on associated mortality

rates, and have undergone revisions during more

recent years. Another method that gained popularity

during the 1990s is the body mass index (BMI), whichis defined as BMI = kg/m2. A BMI of 20 to 25 is

considered to be medically ideal, and obesity is defined

as a BMI of 30 or more. However, unlike the

Metropolitan Life Insurance charts, BMI does not take

into account gender, age, or body frame. Body fat

distribution can be estimated through one’s hip-to-

waist ratio. A low hip-to-waist ratio indicates that the

person is carrying fat around their midsection, whereasa high hip-to-waist ratio indicates a relatively small

waist and larger hips. The skinfold technique measures

the thickness of a pinch of skin, usually under the

upper arm. Despite the convenience and low cost of

all these techniques, none of them is very accurate at

measuring body fat. The most accurate method for

assessing body fat is the water displacement method,

whereby the individual is immersed in a tank of waterand the displaced amount of water is measured.

Obviously, this method has its practical drawbacks.

Obesity is unquestionably socially undesirable in manycultures today. But is it actually unhealthy?

Unfortunately, the research is unclear as to how much

weight gain is associated with increased health risks such

as hypertension and cardiovascular disease. Being obese

(BMI > 30) has reliably been shown to put people at a

significantly elevated risk for all-cause morbidity, prema-

ture death, type 2 diabetes, gallbladder disease, high blood

pressure, sleep apnea, respiratory problems, liver disease,osteoarthritis, reproductive problems (in women), and

colon cancer. However, those in the overweight category

(25 < BMI < 30) might not experience much more risk

than do those in the normal weight range. Furthermore,

weight loss itself can be a health risk for some. Most

experts agree that there is a U-shaped relationship

between weight and mortality and that a person’s optimal

weight range is uniquely determined by his or her ownbiology, varying with age and even ethnic background.

7. OVERCOMING OBSTACLESTO WEIGHT CONTROL

Of course, the most common method for weight loss is

caloric restriction through dieting. However, most nor-

mal-weight dieters would be healthier if they did not

diet at all. Dieting has psychological costs (e.g., irri-tability, hunger, food obsession), may be ineffective in

improving health, and can worsen body dissatisfaction.

Anorexia nervosa, another eating disorder, is charac-

terized by extreme food restriction despite very low

weight. The dieting of anorexics typically has a com-

pulsive quality to it, and anorexia nervosa is routinely a

difficult disorder to treat.

There are several obstacles to weight loss throughdieting. A person’s genetically influenced set point may

be higher than his or her desired weight, and efforts at

reducing caloric intake may be counterproductive and

result in decreased metabolism and increased fat stores.

Dieting individuals show an increased preference for

restricted or forbidden foods and are more sensitive to

sensory food cues, eating more good-tasting foods—

foods that are also likely to be higher in sugar and/or fatcontent. Emotional states may lead to overeating or binge

eating. Finally, calorically dense foods are all too avail-

able and convenient, leading to unbalanced food choices.

With an increasingly thin and lean physical ideal for

both men and women, it is not surprising that there has

been a rise in more drastic weight loss methods over

recent years. All of the drastic weight loss methods are

t0005TABLE I

Suggestions for Successful Weight Control

� Spread daily caloric intake evenly throughout the day. Do

not skip meals.

� Try to eat only in a regular place and at regular times.

� Observe suggested serving sizes.

� Avoid buffets and second helpings.

� Eat slowly.

� Eat in the company of others.

� Do not read or watch television while eating.

� Limit intake of high-calorie foods.

� Allow for variety. Do not label any foods as ‘‘forbidden.’’

� Do not try to lose weight too quickly.

� Find non-food-related ways in which to cope with negative

emotional states.

� Combine diet with exercise.

660 Eat ing , Psycho logy o f

personal, social, and/or professional realms. In reality,weight loss rarely brings about the type of happiness

that dieters anticipate. In addition, many chronic diet-

ers demonstrate ‘‘false hope beliefs’’ around dieting.

That is, despite numerous failed attempts in the past,

these dieters believe that the next diet will surely work.

Previous diet failures are frequently attributed to lack

of will power or perseverance on the part of the dieters

rather than to the intrinsically difficult nature of suc-cessful long-term weight loss. Not only is this belief

incorrect, but it can also be demoralizing, often exacer-

bating the poor self-image that precedes dieting efforts.

See Also the Following Articles

Health and Culture n Health Psychology, Cross-Cultural

Further Reading

De Castro, J. M., & Plunkett, S. (2002). A general model of

intake regulation. Neuroscience and Biobehavioral Reviews,

26, 581–595.

Drewnowski, A. (1995). Energy intake and sensory proper-

ties of food. American Journal of Clinical Nutrition, 62,

S1081–S1085.

Fairburn, C. G., & Brownell, K. D. (2003). Eating disorders

and obesity: A comprehensive handbook (2nd ed.). New York:

Guilford.

Hetherington, M. M. (1996). Sensory-specific satiety and

its importance in meal termination. Neuroscience and

Biobehavioral Reviews, 20, 113–117.

Levitsky, D. A. (2002). Putting behavior back into feeding

behavior. Appetite, 38, 143–148.

Martins, Y., Pelchat, M. L., & Pliner, P. (1997). ‘‘Try it; it’s good

and it’s good for you’’: Effects of taste and nutrition informa-

tion on willingness to try novel foods. Appetite, 28, 89–102.

Ogden, J. (2003). The psychology of eating. Oxford, UK:

Blackwell.

Polivy, J., & Herman, C. P. (2002). Causes of eating disor-

ders. Annual Review of Psychology, 53, 187–214.

Stunkard, A. J., Sorensen, T. I. A., Hanis, C., Teasdale, T. W.,

Chakraborty, R., Schull, W. J., & Schulsinger, F. (1986).

An adoption study of human obesity. New England Journal

of Medicine, 314, 193–198.

unhealthy. Extreme restriction and elimination of a

food category from an individual’s diet are nutrition-

ally ill advised. Fasting, surgery, and diet drugs have

significant and sometimes fatal health risks associated

with them. Even when weight loss is achieved (and

regardless of the method used), weight loss is very

difficult to maintain in the absence of permanent life-style changes and good nutritional habits.

However, despite the low success rates of weight loss

methods in general, most experts agree that the way in

which individuals select foods and eat can have a

positive impact on their weight and health. Table I

displays suggestions for achieving a healthy and stable

weight. The goal of these behaviors is to bring one’s

eating more in line with bodily cues of hunger andsatiety and to try to override many of the psychological

factors that can lead to overeating.

In addition to these practical ways in which to make

eating more in tune with the body’s needs, cognitive

factors can be modified to reduce a reliance on dieting.

Specifically, there is evidence that many dieters

demonstrate unrealistic expectations for weight loss.

They believe that profound and positive changes willresult from losing weight in terms of their success in