of glycogen depletion, drinking only water places the
athlete at risk of water intoxication, a potentially fatal
condition in which the sodium lost through sweat is
not replaced and is followed by the rapid intake of a
large quantity of water. The resulting electrolyte
imbalance affects the brain and central nervous sys-
tem. Blood plasma sodium levels below 100 mmol/L
(2.3g/L) frequently result in swelling of the brain tis-
sue, coma, and even death.Assessment of energy needs
Athletes usually require a higher level of calorie
intake than nonathletes, although the amount varies
depending on the athlete’s sex, age, height, weight,
body composition, stage of growth, level of fitness,
and the intensity, frequency, and duration of physical
exercise. An appropriate diet for most athletes consists
of a minimum of 2000 calories per day; 55–65%
should come from carbohydrates, 15–20% frompro-
tein, and 20–30% fromfats.Assessment of weight and body composition
The use of thebody mass index(BMI) to evaluate
athletes’ weight is not recommended because many
have a high proportion of muscle tissue to fat and
may therefore be considered ‘‘overweight’’ by stand-
ard body mass charts. A better reference guide is to
check whether the athlete falls between the 25th and
the 75th percentile of weight for height by age, meas-
ured according to the National Center for Health
Statistics (NCHS) guidelines.
Well-nourished athletes should have a lean muscle
mass above the 25th percentile, although the ideal ratio
of lean muscle to body fat has not yet been established
for any sport. Male athletes, however, should not have
less than 7% body fat. There are several methods for
estimating the proportion of body fat on an athlete’s
body: underwater weighing (equipment is expensive and
limited in availability); skinfold measurements taken by
high-precision calipers on three to five sites on the right
side of the body (the right side is always used even if the
athlete is left-handed); bioelectrical impedance analysis
or BIA (a technique that measures body composition by
passing a small electrical current through the body and
measuring the resistance of various body tissues, as lean
muscle contains a higher proportion of water than fat);
and computerized calipers.Strategies for weight change
It is important for athletes in any age group need-
ing or desiring to lose or gain weight to be properly
supervised by a nutritionist as well as a physician,because unhealthful dietary practices can lead to
long-term mental as well as physical disorders. The
American Academy of Pediatrics (AAP) makes the
following recommendations for weight change in
young athletes:
The dietary program should be started in a timely
fashion to permit gradual weight gain or loss over a
reasonable time period.
The program should allow a gain or loss of no more
than 1.5% of body weight per week.
It should be designed to permit weight lost to be fat
and weight gained to be muscle.
It should be accompanied by appropriate strength
and conditioning training.
The diet should provide an appropriate balance of
carbohydrates, protein, and fats.
WEIGHT LOSS.Weight loss programs are some-
times recommended for athletes in weight-sensitive
sports, most often wrestling or judo for boys and figure
skating, gymnastics, long-distance running, rowing,
and swimming for girls. Unfortunately, many young
people go too far in adopting unhealthful eating or
exercise patterns in order to keep their weight down.
Because of this tendency, the AAP states that children
younger than the ninth grade should not be put on
weight-loss regimens to improve athletic performance.
Restricting food intake is the most common
method of weight loss among athletes, but a large
percentage of young athletes also engage in purging
(self-induced vomiting plus abuse of laxatives and
diuretics), fasting, or the use of stimulants, wet suits,
sauna baths, or compulsive exercising. Some studies
have shown that as many as 11% of wrestlers meet the
criteria foreating disorders, and 15% of swimmers.
Unhealthful weight loss practices are dangerous
because much of the weight lost will be lean muscle
rather than fat, which can affect athletic perform-
ance. Girls who develop eating disorders or body
dysmorphic disorder are at risk of developing the
so-called female athlete triad, which consists of
disordered eating, cessation of menstrual periods
(amenorrhea), andosteoporosisor brittle bones. A
common symptom associated with the triad is an
unusually high number of stress fractures during the
girl’s athletic career. The triad, which was first
described in 1993, may have long-term consequences
for a woman’s health. Female athletes in their fresh-
man year of college are reported to be at increased
risk of developing the triad, particularly if it is their
first experience of living away from home or they are
having academic difficulties.Sports nutrition