Obesity 175study in the UK also provided support for the fat proportion theory of
obesity (Blundell and Macdiarmid, 1997). This study reported that high-fat
eaters who derived more than 45 percent of their energy from fat were 19
times more likely to be obese than those who derived less than 35 percent
of their energy from fat. These studies suggest that the obese may not eat
consistently more overall than the nonobese, or more calories, or carbo-
hydrate, or fat per se. But they eat more fat compared to the amount of
carbohydrate; the proportion of fat in their diet is higher. So how might
a relative increase in fat consumption relate to obesity?
As a possible explanation of these results research has examined the
role of fat and carbohydrates in appetite regulation. Three possible mech-
anisms have been proposed, as follows (Blundell et al., 1996; Blundell and
Macdiarmid, 1997):
- The benefits of complex carbohydrates to energy use: First, it has been
suggested that it takes more energy to burn carbohydrates than fat.
Further, while carbohydrate intake is accompanied by an increase of
carbohydrate oxidation, increased fat intake is not accompanied by an
increase in fat oxidation. Therefore, carbohydrates are burned, fat is stored. - The benefits of complex carbohydrates to hunger: Second, it has been
suggested that complex carbohydrates (such as bread, potatoes, pasta,
rice) reduce hunger, causing reduced food intake due to their bulk and
the amount of fiber in them. In addition, they switch off the desire to
eat. Therefore carbohydrates make you feel fuller faster. - The costs of fat to hunger: Third, it has been suggested that fat does
not switch off the desire to eat, making it easier to eat more and more
fat without feeling full.
How does dieting influence obesity?
Many people who are already obese diet in an attempt to lose weight. The
success of these attempts is reviewed in chapter 9. Dieting, however, may
not only be a consequence of obesity but also a cause. The research reviewed
in chapter 7 indicated that dieting is often characterized by periods of overeat-
ing which are precipitated by factors such as lowered mood, cognitive shifts,
and shifts in self-awareness. There is also some evidence that dieting is
reflected in weight variability. For example, Heatherton, Polivy, and Herman
(1991) weighed 24 restrained and unrestrained subjects daily for 6 weeks
and again after 6 months and concluded that restraint was a better predictor
of weight variability than relative body weight. This suggests that the