450 CHAPTER 10
In addition, some researchers suggest that eating less actually reduces anxiety, in
part, by reducing serotonin levels. This reduction may be a result of lower levels of tryp-
tophan in the diet, which occurs when food intake is reduced; tryptophan is a building
block of serotonin. When young rats are fed severely restricted diets, their serotonin
activity is reduced (Huether et al., 1997). Thus, the effects of reduced eating can affect
the functioning of the serotonin system.
Researchers have also found that people with bulimia are not as responsive to
serotonin as is typical (Kaye et al., 2000; Smith, Fairburn, & Cowen, 1999). In fact, the
worse the symptoms of bulimia, the less responsive to serotonin the patient generally is
(Jimerson et al., 1992). As with anorexia, tryptophan levels are related to symptoms of
bulimia (Smith, Fairburn, & Cowen, 1999), and, as noted above, reduced tryptophan
levels have the effect of reducing serotonin activity, which in turn can reduce anxiety.
The precise mechanism that underlies the dysregulation of serotonin and the ab-
normal behaviors found in eating disorders remains unknown, as do the reasons for its
differing manifestations in anorexia and bulimia.Genetics
When Marya Hornbacher told her parents that she had been making herself throw
up, her mother said, “I used to do that.” Did Hornbacher’s genes predispose her to
developing bulimia? If so, to what degree would genes play a role? As is true for
those with mood disorders and anxiety disorders, people with an eating disorder
are more likely than average to have family members with an eating disorder, but
not necessarily the same one (Lilenfeld & Kaye, 1998; Strober et al., 2000).
Like genetic studies of other types of disorders, such studies of eating disorders
compare identical twins to fraternal twins (see Chapter 2). The research fi ndings
indicate that anorexia has a substantial heritability, but estimates range from as
little as 33% to as much as 88% (Bulik, 2005; Jacobi et al., 2004), depending on
how the study was carried out. Twin studies of bulimia also indicate that the disor-
der in infl uenced by genes, and also yield a wide range of estimates of heritability,
from 28% to 83% (Bulik 2005; Jacobi et al., 2004). Given that many people with
bulimia previously had anorexia, it isn’t surprising that both disorders have the same
wide range of heritabilities—there is signifi cant overlap in the two populations.
The large variation in heritabilities may simply indicate, once again, that genes
aren’t destiny; the way the environment interacts with the genes is also important.
However, studies have shown that the shared family environment (such as how
many books are in the house or how many meals a family eats all together) may
not be as infl uential as the nonshared, unique environment (such as different re-
lationships between each child and her father, the extent to which an individual is
teased about weight, or unique peer group experiences) (Agliata, Tantleff-Dunn,
& renk, 2007; Bulik, 2004; Klump et al., 2002). We’ll examine such nonshared
environmental factors in more detail in the next two sections.Psychological Factors:
Thoughts of and Feelings About Food
Eating and breathing are both essential to life, but eating provides more than suste-
nance. It can evoke powerful feelings, memories, and thoughts. Hornbacher recalls
her associations to eating:
My memories of childhood are almost all related to food.... I was my father’s
darling, and the way he showed love was through food. I would give away my lunch
at school, then hop in my father’s car, and we’d drive to a fast-food place and, essen-
tially, binge.
My mother was another story altogether. She ate, some. She would pick at cottage
cheese, nibble at cucumbers, scarf down See’s Candies. But she, like my father, and like
me, associated food with love, and love with need.
(1998, p. 27)