(grams per day) matched their oxidation rates,
while fat oxidation rates did not change signifi-
cantly even though fat intake increased (fat
intake was 150 g · day–1while fat oxidation was
only 59 g · day–1). The result was a 2.9-kg weight
gain in 12 days. Thus, excess energy eaten as
dietary fat is stored as triglycerides in adipose
tissue with little loss of energy (Acheson et al.
1984; Swinburn & Ravussin 1993).
Alcohol balance
When athletes ingest alcohol, it becomes a prior-
ity fuel, with a rapid rise in alcohol oxidation
occurring until all the alcohol is cleared from the
body. Alcohol also suppresses the oxidation of fat
and, to a lesser degree, that of protein and carbo-
hydrate (Shelmet et al. 1988). Alcohol is not
stored as fat nor can it contribute to the formation
of muscle or liver glycogen. It may, however,
indirectly divert fat to storage by providing an
alternative and preferred energy source for
the body (Sonko et al. 1994). Thus, alcohol, at
29.4 kJ · g–1(7 kcal · g–1), can contribute signifi-
cantly to total energy intake. Athletes who
consume alcohol must reduce their intake of
energy from other sources to maintain energy
balance.
Energy balance
Determination of energy balance requires the
measurement or estimation of both energy intake
and energy expenditure. Energy balance is then
estimated by subtracting energy expenditure
from energy intake. This section will briefly
review the various components of energy intake
and expenditure, how these components are
measured, and the many factors that may influ-
ence them.
Components of energy expenditure
The components of total daily energy expendi-
ture (TDEE) are generally divided into three
main categories: (i) resting metabolic rate (RMR),
(ii) the thermic effect of food (TEF), and (iii) the
472 practical issues
thermic effect of activity (TEA) (Fig. 35.3). RMR is
the energy required to maintain the systems of
the body and to regulate body temperature at
rest. In most sedentary healthy adults, RMR
accounts for approximately 60–80% of TDEE
(Bogardus et al. 1986; Ravussin et al. 1986).
However, in an active individual this percentage
can vary greatly. It is not unusual for some
athletes to expend 4.2–8.4 MJ (1000–2000 kcal)
per day in sport-related activities. For example,
Thompson et al. (1993) determined energy
balance in 24 elite male endurance athletes over a
3–7-day period and found that RMR represented
only 38–47% of TDEE. Similar results are
reported in female runners (Beidleman et al.
1995).
The TEF is the increase in energy expenditure
above RMR that results from the consumption of
food throughout the day. It includes the energy
cost of food digestion, absorption, transport,
metabolism and storage within the body, and
the energy expended due to sympathetic
nervous system activity brought about by seeing,
smelling and eating food. TEF is usually
expressed as a percentage of the energy content
of the foods consumed and accounts for 6–10%
of TDEE, with women usually having a lower
value (approximately 6–7%) (Poehlman 1989).
However, this value will vary depending on the
energy density and size of the meal and types of
foods consumed. In addition, if the absolute
amount of energy intake is decreased, then it
follows that the absolute amount of energy
expended in TEF will decrease.
TEA is the most variable component of energy
expenditure in humans. It includes the energy
cost of daily activities above RMR and TEF, such
as purposeful activities of daily living (making
dinner, dressing, cleaning house) and planned
exercise (running, weight training, cycling). It
also includes the energy cost of involuntary mus-
cular activity such as shivering and fidgeting.
This type of movement is called spontaneous
physical activity. TEA may be only 10–15% of
TDEE in sedentary individuals, but may be as
high as 50% in active individuals. The addition of
RMR, TEF and TEA should account for 100% of