embarrassment and stigma and that exercise plays a part in the maintenance of obesity
but not in its cause.
What effect does exercise have on food intake? The relationship between
exercise and food intake is complex, with research suggesting that exercise may increase,
decrease or have no effect on eating behaviour. For example, a study of middle-aged male
joggers who ran approximately 65km per week, suggested that increased calorie intake
was related to increased exercise with the joggers eating more than the sedentary control
group (Blair et al. 1981). However, another study of military cadets reported that
decreased food intake was related to increased exercise (Edholm et al. 1955). Much
research has also been carried out on rats, which shows a more consistent relationship
between increased exercise and decreased food intake. However, the extent to which such
results can be generalized to humans is questionable.
What effect does exercise have on energy expenditure? Exercise burns up
calories. For example, 10 minutes of sleeping uses up to 16 kcals, standing uses 19 kcals,
running uses 142 kcals, walking downstairs uses 88 kcals and walking upstairs uses
229 kcals (Brownell 1989). In addition, the amount of calories used increases with the
individual’s body weight. Therefore, exercise has long been recommended as a weight
loss method. However, the number of calories exercise burns up is relatively few com-
pared with those in an average meal. In addition, exercise is recommended as a means
to increase metabolic rate. However, only intense and prolonged exercise appears to have
an effect on metabolic rate.
Therefore, the role of exercise in obesity is still unclear. There appears to be an
association between population decreases in activity and increases in obesity. In addition,
prospective data support this association and highlight lower levels of activity as an
important risk factor. Further, cross-sectional data indicate that the obese appear to
exercise less than the non-obese. However, whether inactivity is a cause or consequence
of obesity is questionable. It is possible that an unidentified third factor may be creating
this association, and it is also debatable whether exercise has a role in reducing food
intake and promoting energy expenditure. However, exercise may have psychological
effects, which could benefit the obese either in terms of promoting weight loss or simply
by making them feel better about themselves (see Chapter 7 for the effects of exercise
on mood).
Eating behaviour
In an alternative approach to understanding the causes of obesity, research has exam-
ined eating behaviour. Research has asked ‘Are changes in food intake associated with
changes in obesity?’, ‘Do the obese eat for different reasons than the non-obese?’ and ‘Do
the obese eat more than the non-obese?’ These questions will now be examined.
Are changes in food intake associated with changes in obesity? The UK
National Food Survey collects data on food intake in the home, which can be analysed
OBESITY AND CORONARY HEART DISEASE 361