Hunger and Eating
Hungry? The question "why do we feel hungry?" seems to be very
obvious to answer. It is because we need to get nutrients to
survive. Hunger is the motivation for us to be able to know that
we need to get the nutrients in our body. But how do we really
know that we are hungry? The answer can be analyzed by three
different components: biological, learned, and cognitive.
Hunger and Eating Based on Biology
Many theories of hunger are historically discussed from the
biological component. Cannon and Washburn (as cited in Coon, 1995)
came up with the stomach contraction theory which states that we
know we are hungry when our stomach contracts. In the notorious
balloon study, Washburn trained himself to swallow a balloon which
was attached to a tube, then the balloon was inflated inside of his
stomach. When the balloon was inflated, he did not feel hungry.
Later this theory was opposed by the fact that people whose stomach
was removed still felt hungry. Glucose theory states that we feel
hungry when our blood glucose level is low. Bash (as cited in
Franken, 1994) conducted an experiment transfusing blood from a
satiated dog to a starved dog. The transfusion resulted in
termination of stomach contraction in the starved dog, and
supported the glucose theory. But as LeMagnen (as cited in Kalat,
1995) suggests that blood glucose level does not change much under
normal conditions. Insulin theory states that we feel hungry when
our insulin level increases suddenly in our bodies (Heller, &
Heller, 1991). However, this theory seems to indicate that we have
to eat to increase our insulin level in order to feel hungry.
Fatty acid theory states that our bodies have receptors that detect
an increase in the level of fatty acid. Activation of the receptor
for fatty acid triggers hunger (Dole, 1956, Klein et al., 1960
cited in Franken, 1994). Heat-Production theory suggested by
Brobeck (as cited in Franken, 1994) states that we feel hungry when
our body temperature drops, and when it rises, the hunger
decreases. This might be explain that we tend to eat more during
Hunger and Eating Based on LearningHunger cannot truly be explained only by the biological
component. As human beings, we cannot ignore our psychological
part, the learned and cognitive components of hunger. Unlike any
other beings, we humans use an external clock in our daily routine,
including when to sleep and when to eat. This external time
triggers our hunger. For instance, when the clock says 12 pm,
lunch time, many people feel hungry just because it is lunch time.
This hunger is triggered by learned behavior.
In addition, the
smell, taste, or texture of food also triggers hunger. For
instance, if you like french fries, the smell of frying potatoes
may trigger your hunger. However, this preference of taste, smell,
or texture is a culturally learned preference. If one does not
like sushi, the smell of sushi does not trigger hunger.
Interestingly, people also feel hungry for a particular taste, more
specifically, the four basic tastes: sweet, sour, bitter, and
salty. For example, an often heard expression is "I am hungry for
something sweet." People keep feeling hungry until these four
tastes are satisfied.
Hunger and Eating Based on Cognition
Colors also contribute to hunger. Looking at a yellow banana
makes one to want to eat it, but a red banana does not. Similarly,
red or green can trigger hunger for an apple, but not blue. It is
hard to find natural food with blue color, because mother nature
does not produce blue food. Blue is said to be an appetite
suppressant. Color greatly affects our hunger.
Many people eat foods base on their knowledge of what foods are
good for them. For example, low fat, low sugar, and low sodium
food are said to be good. Eventually people learn to change their
preference and want to eat "good food" only (Franken, 1994).
The mechanism of hunger and satiety are not necessarily the
same. There are two mechanisms for satiety. One is at the brain
level, the other is at the gastrointestinal tract level. There are
two places in the hypothalamus, part of the brain, that controls
hunger and eating. The Ventromedial Nuclei gives a signal when to
stop eating, and the Lateral hypothalamus gives a signal to start
eating (e.g.,Coon 1995). We feel satiety at the brain level
because of the function of the Ventromedial Nuclei. On the other
hand, at the level of the gastrointestinal tract, Koopmans (1985)
states that satiety signals come from the stomach, which controls
Obesity is defined as exceeded the average weight for one's
height, bone structure, age, and sex by a given percentage, above
25% (Franken 1994). The question of why some people are obese can
be answered in different ways. Is it because obese people have a
different hunger and satiety mechanism from people who are not?
Obesity can be caused biologically. Many studies show that
twins who grew up apart still weigh about the same. Also, adopted
children's weights are similar to their biological parents, not
their adopted parents (Stunkard et al., 1986). But this does not
explain all cases of obesity.
Set point theory by Keesy and Powley (as cited in Franken, 1994)
states that we have a predetermined weight, set by the
hypothalamus, that the body attempts to maintain. According to
this theory, diet does not work because the individual has his or
her own set point weight, and the body works to maintain that set
point. Thus the more one tries to intake less calories, the more
the body wants to keep the weight that is set by the hypothalamus.
For obesity, this set point is too high due to damage to the
Stanley Schachter (1971) came up with the internal-external
theory of hunger and eating of the obese. They ran an experiment
in which subjects were measured by the amount of crackers eaten
during the time when the real time was manipulated by a faster
clock or a slower clock. They hypothesized that if the obese
person is more affected by the clock time than the real time, then,
he or she should eat more when the clock shows it is close to
dinner time. The results were consistent with the hypothesis.
Schachter concluded that obese people respond to external cues of
hunger, such as time, more than non-obese people who tend to
respond more to internal cues of hunger.
Rodin (1981) connected the external cues of hunger to insulin,
and hypothesized that people (whether obese or not) who respond to
external cues of hunger tend to increase the level of insulin in
the blood more than people who respond to internal cues. In
Rodin's experiment, hungry subjects who are external cue
respondents were gathered, around noon, where steaks were grilled.
After they smelt and heard the steak, their insulin levels were
measured. As expected, the smell and sound of cooking increased
the insulin level of those subjects.
The boundary theory of hunger (Herman & Polivy, 1984) has a
cognitive perspective about hunger of the obese. According to this
theory, there are boundary lines of hunger and satiety determined
biologically. The space between those two boundaries is determined
cognitively. In the space between those two boundaries, people set
how much they think they should eat, and if one sets a satiety
boundary cognitively lower (like diet) than one that is
biologically predetermined, the body tries to compensate food
intake to meet the biologically determined boundary level by
triggering hunger. For the obese, this biologically determined
satiety boundary is higher than for the non-obese.
Eating Disorders of Hunger and Eating
Many theories point out that obese people have a strong
biological component of hunger and eating. What about people with
eating disorders? What is the mechanism of hunger and eating for
people with eating disorders? There are mainly three kinds of
eating disorders; Binge Eating, Anorexia Nervosa, and Bulimia.
Binge eating is characterized by one's eating a very large amount
of food until she or he feels uncomfortably full. This binge
eating is done when one is not hungry. According to the DSM-VI,
Anorexia Nervosa has two types; restricting type, and
binge-eating/purging type (American Psychiatric Association, 1994).
Anorexia Nervosa restricting type is when one extremely restricts
food intake, and it is not followed by binge-eating or purging
behavior. On the other hand, Anorexia Nervosa binge-eating/purging
type was described as one engaged in purging and binge-eating
regularly. A common symptom of Anorexia is one's putting her or
himself on self-starvation to avoid feeling fat or gaining weight.
Although people with this disorder weigh far below normal, they
still think they are overweight. Eventually they are at risk of
losing their lives due to malnutrition.
People with this disorder still feel hungry, yet they cannot eat
because they are too afraid of gaining weight. Physiological
causes of this disease are not yet clear, although there are some
findings showing a connection with serotonin and norepinephrine.
The learned component of Anorexia cannot be ignored. Studies show
that there is more Anorexia in westernized cultures than other
cultures, (e.g., Suematsu, 1986), because the social value of
slimness pushes people to be thinner. Cognitively, these people
have a distorted body image of themselves, and dissatisfaction with
their own body image, which is influenced by the cultural value of
slimness, and leads to eating disorders (Mumford, Whitehouse, &
Bulimia Nervosa is a condition of binge eating followed by
purging and use of laxatives (American Psychiatric Association,
1994). Unlike Anorexia, people with this disorder are normal or
above weight. Psychologically, having quilt and shame are common
symptoms among people with Bulimia. Unlike anorexic people who put
absolute control over restricted eating, bulimic people cannot
control their eating. The physiological cause of Bulimia is still
unclear. Psychologically, Bulimia is said to be linked to
depression and anxiety, but clear evidence of causation has not yet
been found. Cognitively, people with Bulimia are said to be
motivated to escape from reality by binging. It is possible that
those people were given food by their caretakers to lift their mood
in their childhood. Like Anorexia, cultural learning that one
needs to be thin to be accepted may also contribute to the cause.
Mind and Body Connection of Hunger
Hunger is a primary motivation. Despite strong beliefs that
hunger is caused biologically, this motivation is controlled not
just by physiology, but also psychology as well. There are two
kinds of hungers; one is caused physiologically, and the other is
caused psychologically. What makes human beings different from
animals is we eat not only to feed our bodies to satiate
physiological hunger, but also to feed our minds to satiate
psychological hunger as well. Although these two kinds of hunger
interchangeably cause hunger by affecting one another, putting some
food in our mouth is not necessarily the right way to feed our
psychological hunger. Problems like eating disorders and obesity
could occur because we mistakenly keep tying to satiate our
psychological hunger by eating food. Until we realize that we need
to feed our mind with something, rather than eating, we can not
feel satiated. Until we recognize it is our mind, not our body
which needs food, we cannot be satisfied with what we put in our
mouth. Thus, hunger is not only about how the body changes
physiologically, it is about how our body and mind together are
well fed, not just by the food that one can put in their mouth, but
also by the whole environment around us.