NUTRITION IN SPORT

not associated with changes in body fatness over
3–6 months (Haskell 1991). Above this amount of
exercise, there tends to be a consistent loss of
body fat, 0.12 kg · week–1for men (a little less for
women), total exercise energy expenditure being
the variable most strongly related to the body
mass change. Thus, the natural adjustments to
increased exercise levels reduce, but do not elimi-
nate, the theoretical energy deficit. For example,
in a study where sedentary men followed a pro-
gramme of jogging for 2 years with no instruc-
tions about dietary intake, energy intake rose
over the first 6 months by about 1.3 MJ · day–1
(310 kcal · day–1). This compensation, however,
did not increase further, remaining less than the
energy expenditure of exercise so that a gradual
loss of body fat occurred.
Physical activity is increasingly viewed as an
important adjunct to restriction of dietary
energy. For example, the addition of exercise to a
low energy diet has been reported to enhance
weight and fat loss and prevent a fall in resting
metabolic rate and it may also help with the
intractable problem of weight maintenance after
weight loss. The most important role for activity
is probably that which is least well explored, i.e.
prevention of weight gain. Some information
on the relationship of activity with longer-term
weight change in the general population is avail-
able from the NHANES-I Epidemiologic Follow-

50 nutrition and exercise

up Study in the USA; this found that the risk of

major weight gain (>13 kg) over a 10-year period

was twice as high among inactive men and

sevenfold higher among inactive women, com-

pared with men and women of high activity level

(Williamson et al. 1993).

Exercise may influence the distribution of

body fat as well as the amount. In population

studies, individuals practising vigorous activi-

ties on a regular basis have lower waist-to-hip

ratios than others, even after the effect of subcu-

taneous fat is adjusted for. Training has some-

times been reported to decrease this ratio even in

the absence of a reduction in body weight. One

reason may be that the metabolic state of the vis-

ceral fat depot is such that it should be readily

mobilized during weight loss.

For individuals who are overweight, the

health gains from increased physical activity

should not be judged solely by the extent of

change in body fatness; several prospective

studies have shown that overweight men and

women who are physically active have lower

rates of morbidity and mortality than compara-

ble sedentary people.

Fat balance

The energy balance equation (change in energy

stores =energy intake – energy expenditure) has

Fig. 3.3Sport offers an

opportunity to people who wish

to take exercise for health reasons

rather than as a competitive

outlet. Photo courtesy of Ron

Maughan.