Introduction
By virtue of its mass and unique potential
to increase metabolic rate, skeletal muscle is
man’s largest ‘metabolic organ’. Energy ex-
penditure is increased profoundly during ex-
ercise with the body’s large muscles and
individuals who engage regularly and fre-
quently in such exercise have enhanced energy
requirements. These are met through increased
nutrient intake, particularly of carbohydrate, so
that the relative contributions of macronutrients
to energy intake may be altered. This in itself
may constitute a more healthy diet but, in addi-
tion, the metabolic handling of dietary fats and
carbohydrates is improved, changes which help
reduce the risk of developing several chronic
diseases, specifically atherosclerotic vascular dis-
eases, non-insulin-dependent diabetes (NIDDM,
also known as adult-onset or type II diabetes)
and possibly some cancers (Bouchard et al.
1994).
An example of an association between disease
risk and energy turnover is given in Table 3.1,
which shows average daily energy intakes in
prospective studies of coronary heart disease
(CHD). Men who subsequently had fatal attacks
showed lower levels of energy intake than
survivors, an apparent paradox in the light of
the increase in CHD risk associated with
overweight, obesity and the deleterious meta-
bolic sequelae of these. One explanation is
that the men with higher energy intakes were
more physically active, and that their exercise
afforded a level of protection against CHD,
compared with more sedentary men who ate
less.
Thus, the transition from a sedentary to
an active state is associated with a higher
energy turnover, with important implications
for the transport, storage and utilization of the
body’s metabolic fuels. All of these are altered
in the trained state such that regular exercisers
experience a lower risk of what has been
called ‘metabolic, hypertensive cardiovascular
disease’. Higher energy turnover may also be
associated with improved weight regulation
because food intake appears to be more closely
coupled to energy expenditure with more
exercise.
Rather than prolonging life, regular exercise
protects against premature death, with an esti-
mated increase in longevity in men on average of
one or two years (Paffenbarger et al. 1986). More-
over, lower all-cause mortality has recently been
reported for physically active women (Blair et al.
1996), although evidence is much less extensive.
People who take exercise also maintain a better
quality of life into old age, being less likely
than sedentary individuals to develop functional
limitations.
This chapter will identify some of the health
gains which accrue from the biological inter-
actions between exercise and the body’s meta-
bolism of dietary carbohydrate and fats. For
discussion of the evidence for a specific role of
diet in promoting health, the reader is referred to
other sources (WHO 1990).