increased energy expenditure and decreased
energy intake. The objective is to reach the
desired goal weight over a reasonable period of
time, minimizing the potential loss of fat-free
mass (Wilmore 1992).
It has been clearly established that for both
rapid and moderate rates of weight loss, a sub-
stantial percentage of the weight loss, i.e. 50% or
more of the weight, can be derived from the fat-
free mass, predominantly from the total body
water and protein stores. In fact, with very low
energy diets (i.e. 1680–3360 kJ · day–1, 400–
800 kcal · day–1) or low energy diets extended
over longer periods of time, water and protein
can still constitute a substantial percentage of the
weight lost. Keys et al. (1950), in their classic
series of studies on human starvation, fed non-
obese adult men a test diet of 6570 kJ · day–1(1570
kcal · day–1) for 24 weeks. The subjects’ diet
which maintained stable weight prior to going
on the low energy diet was 14.5 MJ · day–1(3468
kcal · day–1). Over the first 11 weeks, approxi-
mately 40% of the weight lost was from fat, 12%
from protein, and 48% from water, with an
average rate of weight loss of 0.15 kg per day. In a
study of obese subjects, Yang and Van Itallie
(1976) reported an average rate of weight loss of
0.45 kg per day in obese subjects on a 5020 kJ ·
day–1(1200 kcal · day–1) mixed diet over the first
5 days on the diet. Water comprised 66% of the
total weight loss. The relatively high contribu-
tion of water to initial weight losses is at least
partially the result of obligatory water loss
accompanying the metabolism of glycogen and
protein. Both glycogen and protein have hydra-
tion ratios of approximately 3–4 g water · g–1of
substrate, both for storage and degradation (Van
Itallie & Yang 1977). Thus, athletes must be very
careful when dieting to maximize weight loss
while minimizing loss of fat-free tissue. Again, it
is important to combine exercise with diet to
achieve a given energy deficit per day. Including
exercise as a component of the energy deficit
attenuates the loss of fat-free mass when com-
pared to diet alone (Ballor & Poehlman 1994;
Saris 1995).
Dehydration is the most widely used tech-
nique for rapid weight loss. Intentional dehydra-
tion is probably a better phrase to use since the
intent of the technique is specific to producing
body water loss, where unintentional dehydra-
tion is an unexpected consequence of negative
energy balance resulting from the obligatory
water loss associated with glycogen and protein
degradation. With intentional dehydration, both
metabolic and thermal techniques are intended
to induce water loss through sweating, although
an added bonus from exercise is the obligatory
water loss from depletion of the body’s glycogen
stores as discussed previously. Sweat losses,weight category sports 639
Fig. 49.1Rapid weight loss to
make weight for competition can
pose health risks and can impair
performance. However, as long as
competitors perceive an
advantage, the practice will
persist. Photo © Allsport / D.
Leah.