The Psychology of Eating: From Healthy to Disordered Behavior

Obesity 157

not always have a negative impact upon an individual’s psychological state.
Therefore, although some obese people may be depressed, be anxious, and
show poor body image and self-esteem, the relationship between body size
and psychological problems is not a simple one.

What Are the Causes of Obesity?

There are many theories about the causes of obesity and it is generally believed
that the variation in body fat relates to a complex interplay of genetic, nutri-
tional, energy expenditure, psychological, and social factors. This chapter
explores physiological theories, and environmental perspectives and beha-
vioral theories, which focus on physical activity and eating behavior.

Physiological Theories

Physiological theories are concerned with a number of different mecha-
nisms which emphasize aspects of an individual’s biology. This section will
explore the role of genetics, metabolic rate, fat cells, appetite regulation,
neural mechanisms, and an evolutionary approach.

Genetic theories

Size appears to run in families and the probability that a child will be
overweight is related to their parents’ weight. For example, having one obese
parent in a family results in a 40 percent chance of producing an obese
child, and having two obese parents results in an 80 percent chance. In con-
trast, the probability that thin parents will produce overweight children is
very small, about 7 percent (Garn et al., 1981). This observation has been
repeated in studies exploring populations from different countries and liv-
ing in different environments (Maes, Neale, and Eaves, 1997). Parents and
children share both environment and genetic constitution, so this likeness
could be due to either factor. To address this problem, research has exam-
ined twins and adoptees.

Twin studies
Twin studies examine the weight of identical twins reared apart, who have
identical genes but different environments. Studies also examine the weights