50 Food Choice
Metabolic models of eating behaviorFrom a biological perspective, eating behavior is generally referred to as
ingestive behavior. The dominant model for understanding why and when
we eat emphasizes homeostasis and focuses on the role of negative feed-
back. At the beginning of the nineteenth century, Walter Cannon coined
the term homeostasisto refer to the mechanisms by which biological
variables, including eating, are regulated within defined limits. For example,
when we get hot we sweat, which cools us; when we become dehydrated
we experience thirst, which makes us drink more; and likewise when we
need food we experience hunger, which makes us eat. Homeostasis is main-
tained via a negative feedback loop which assumes that any given bodily
variable has a set point (or range) and that the actual value of this variable
is compared by the body to where it should be and adjusted accordingly.
In terms of body weight, it has been suggested that each person has a
set point and his or her weight is regulated around this point. In relation
to hunger, the body has a sense of what is acceptable and regulates eating
around this. Several different mechanisms have been proposed as the basis
for this negative feedback loop, including our fat stores (the lipostatic
hypothesis) and our glucose levels (the glucostatic hypothesis), which
suggests that either when our fat stores are depleted or when our blood
glucose levels are low, we feel hungry, which makes us eat.
More recently, researchers have emphasized the importance of cellular
energy in the regulation of food intake. In particular, research has high-
lighted a role for adenosine trisophate (ATP), which is a product of the
breakdown of macronutrients. It is suggested that fats, carbohydrates, and
proteins are initially broken down into small molecules and then eventually
into cellular energy and waste via a metabolic chain, called the citric acid
cycle. ATP is a form of cellular energy and is considered important for the
regulation and maintenance of homeostasis. Although these biological
models of eating behavior have been the basis of much research, most
approaches to eating behavior today regard biological factors as only the
starting point to an understanding of food intake, given what we know about
the role of learning and cognition.
The hypothalamus
Researchers working within a biological approach have attempted to
locate areas of the brain associated with feeding. Early clues to the role of
the brain came from patients with tumors of the basal hypothalamus