The Psychology of Eating: From Healthy to Disordered Behavior

Obesity 159

Metabolic rate theory

The body uses energy to carry out the chemical and biological processes
which are essential to being alive (e.g., respiration, heart rate, and blood
pressure). The rate of this energy use is called the resting metabolic rate,
which has been found to be highly heritable (Bouchard et al., 1990). One
theory of obesity has argued that the obese may have lower metabolic rates,
that they burn up fewer calories when they are resting, and therefore that
they require less food intake to carry on living.
There is some tentative support for this suggestion. For example, research
in the US evaluated the relationship between metabolic rate and weight gain.
A group in Phoenix assessed the metabolic rates of 126 Pima Indians by
monitoring their breathing for a 40-minute period. The study was carried
out using Pima Indians because they have an abnormally high rate of obesity

• about 80 to 85 percent – and were considered an interesting population.
  The subjects remained stationary and the levels of oxygen consumed and
  carbon dioxide produced were measured. The researchers then followed any
  changes in weight and metabolic rate for a 4-year period and found that the
  people who gained a substantial amount of weight were the ones with the
  lowest metabolic rates at the beginning of the study. In a further study, 95
  subjects spent 24 hours in a respiratory chamber and the amount of energy
  used was measured. The subjects were followed up 2 years later, and the
  researchers found that those who had originally shown a low level of energy
  use were four times more likely to also show a substantial weight increase
  (Ravussin et al., 1988; Ravussin, 1993). Tataranni et al. (2003) used state-of-
  the art methods to assess energy intake and energy expenditure in 92 free-
  living, adult Pima Indians in Arizona. These methods allowed the researchers
  to measure energy intake and total energy expenditure accurately outside the
  laboratory in order to test their role in the etiology of obesity prospectively.
  The results demonstrate for the first time that baseline total energy intake is
  a key determinant of long-term changes in body weight in Pima Indians,
  and also confirm that a low resting metabolic rate is a risk factor for weight
  gain in this population. In addition, baseline energy expenditure, due to
  physical activity, was not found to be associated with changes in body weight.
  These results indicate a possible relationship between metabolic rate and
  the tendency for weight gain. If this is the case, then some individuals are
  predisposed to become obese because they require fewer calories to survive
  than thinner individuals. A genetic tendency to be obese may therefore express
  itself in lowered metabolic rates. However, most research does not support