The Female Athlete

Chapter 31
The Female Athlete
KATHE A. GABEL
Introduction
As increasing numbers of women participate
in sport and exercise, recommendations for
their dietary intake to enhance general health
and performance become important. Unfortunately, physical and metabolic differences
between men and women generally have
not been considered in the development of
current dietary guidelines, except for calcium
and iron. However, gender differences exist
that could potentially affect a woman’s energy
and nutrient needs: upper body muscle mass
and strength (Miller et al. 1993), endurance
capacity in isometric and dynamic exercise at
relatively low intensities (Maughan et al.
1986), resting metabolic rate (Arciero et al. 1993)
and heart rate measured during different
exercise modalities (Kravitz et al. 1997). Rather
than deriving recommendations from research
involving mixed-gender or female populations,
dietary guidelines for protein (Lemon 1995)
and carbohydrate (CHO) (Williams 1989) intakes have been developed from studies using male subjects. In consideration of dietary
guidelines for the female athlete, this chapter
will address limitations of the use of current
recommendations for athletes, present evidence
for gender differences related to lipid and substrate metabolism and provide discussion
regarding macro- and micronutrient recommendations. A brief clarification of terms used to
define nutrient needs and recommendations
for intake to meet these needs in populations
and in individuals will precede these topics of
discussion.
Clarification of dietary
guideline nomenclature
Terms that reflect estimates of nutrient requirements vary among countries. In the United
Kingdom, nomenclature consists of dietary reference values (DRV), estimated average requirement
(EAR), lower reference nutrient intake (LRNI) and
reference nutrient intake (RNI) (Department of
Health 1991). The term recommended dietary
allowance (RDA) (National Research Council
1989) has traditionally been used in the United
States, but is expected to change in the next
edition of guidelines to terminology similar to
that currently used in the UK. In Canada, recommended intakes of energy and certain nutrients
are called recommended nutrient intakes (RNI)
(Health and Welfare Canada 1983). To simplify
reading, dietary guideline will be used in this
chapter when referring to RNI, RDA or terms
used by other countries.
Limitations of the use of current
dietary guidelines for athletes
Dietary guidelines used in the US are expressed
as quantities of a nutrient for a reference individual per day, a term that should be interpreted as
an average intake over time (National Research
Council 1989). For dietary assessments of athletes, food intake should be recorded for a
417
418
special considerations
Fig. 31.1 Performances of elite
female athletes have improved
rapidly with increased
opportunities for participation
and increased training loads.
Photo © Allsport / John Gichigi.
minimum of 3 days. Dietary guidelines of most
nutrients are intended to be intakes averaged
over at least 3 days and over several months for
those nutrients stored by the body, e.g. vitamin
A.
Physical activity levels, climate and other
factors can change dietary requirements. Anyone
who exercises and/or is exposed to cold or
hot environments may require different levels of
some nutrients as compared to levels listed in
current guidelines. As the reader evaluates
dietary assessments of physically active populations, these limitations of the dietary guidelines
should be considered.
Requirement for energy
Energy needs are related to body mass. In the
UK, median weights and heights of the population, recorded in 1980, are used to calculate
energy needs (MJ · day–1). Total energy expenditure (TEE) is expressed as a multiple of the basal
metabolic rate (BMR) and is affected by the
physical activity level. Examples of TEE calculations for men and women can be found in the UK
Report on Dietary Reference Values (Department of
Health 1991). Current US energy calculations are
based on median heights and weights found
in the second National Health and Nutrition
Examination Survey with empirically derived
equations developed by the World Health
Organization (WHO 1985) specifically used to
estimate resting energy expenditure (REE). To
estimate total energy expenditure (TEE), REE is
multiplied by a factor that represents an activity
level which needs to be recorded over a sufficiently long time accounting for weekdays
and weekends to increase validity of the estimate
of energy expenditure. Examples of this calculation can be found in the US reference (National
Research Council 1989).
Agreement regarding which equation to use
for TEE estimation does not exist. As published
in the WHO’s Report on Energy and Protein
Requirements, BMR forms the basis of the factorial
method to estimate TEE (WHO 1985). However,
examination of the calculations indicates that the
equations overestimate BMR of some population
groups (Piers et al. 1997). Carpenter et al. (1995),
in a meta-analysis of 13 studies that utilized
doubly labelled water technique as the method
to measure TEE in free-living humans, concluded that there are insufficient published
data to permit development of practical models
to predict TEE in adults.
Acknowledgement of potential limitations of
TEE calculations and of the derivation of energy
recommendations is necessary to prevent inappropriate energy-related conclusions made in
sports nutrition research or recommendations
the female athlete
given to athletes. It is also expected that most
female athletes will have a different weight/
height ratio as compared to the women in the UK
or US surveys. This difference is illustrated by
comparing estimates of body fat and weights for
national-level competitive female rhythmic gymnasts to controls of the same age and height.
Female gymnasts averaged 10% body fat (range,
6–17%) as compared to controls, whose mean
percentage body fat was 19% (range, 14–27%).
An average weight of the gymnasts was reported
to be 42 kg as opposed to 54 kg average weight
for the controls (Sundgot-Borgen 1996).
Depending upon desired level for accuracy of
energy estimates and in spite of the identified
limitations, TEE equations may still be useful to
calculate an estimate of energy expenditure for
the female athlete. Additional research is needed
to better predict TEE for athletic populations and
understand the influence of exercise on TEE, particularly in relation to the female athlete. Gender
differences in substrate metabolism as discussed
in the next section also support this need.
Substrate metabolism
Levels of triacylglycerol, total cholesterol (TC),
high-density lipoprotein cholesterol (HDL-C)
and low-density lipoprotein (LDL-C) can be
affected by the presence of oestrogen. Major
proteins for HDL and LDL are apo A-1 and apo
B, respectively, and were investigated in 25
female runners and 36 age-matched nonexercising women (controls) (Lamon-Fava et al.
1989). Lower concentrations of TC, apo B, triacylglycerol and higher apo A-1 to apo B ratios were
observed in the eumenorrhoeic female runners
(n = 16) as compared with nonexercising controls.
All blood parameters in the amenorrhoeic
runners (n = 9) were similar to levels in the controls, except that apo B-values were 20% lower.
Except for the effect on apo B levels, the positive
effects of exercise on serum lipids were negated
in those females with decreased oestrogen, i.e.
amenorrhoeic runners.
In considering oestrogen’s effect on lipid
metabolism, one may ask whether there is a
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difference between men and women in the
substrates used for energy during exercise.
Tarnopolsky et al. (1990) matched subjects for
maximal oxygen consumption, training status,
and competition histories; tested females during
the midfollicular phase of their menstrual cycles;
and controlled the macronutrient content of the
diet to prevent confounding effects of these
factors on results. Subjects ran 15.5 km on a treadmill at a velocity requiring oxygen consumption
of about 65% of maximal. Glycogen utilization
was estimated from muscle biopsies, with respiratory exchange ratio (RER) used to determine
substrate utilization during the exercise. Females
demonstrated greater lipid utilization based on
RER values, less muscle glycogen use and less
urea nitrogen excretion than males during
moderate-intensity, long-duration exercise.
Given that a female athlete could oxidize greater
fat stores while preserving CHO and protein,
females would have an advantage in endurance
and ultra-endurance events in which fat oxidation becomes metabolically more important.
However, one may also argue that controlling for
training level and substrate availability between
genders is unlikely. This presents researchers
with a challenging task in answering the question of gender-related substrate use.
Hormonal status of the female may need consideration by the researcher and sport nutritionist when evaluating energy intake of the female
athlete. Barr et al. (1995) provide evidence that
energy intakes of normally ovulating women are
higher during the luteal phase of their menstrual
cycles. While it is possible to ignore differences
when conducting cross-sectional studies, it
would be necessary to consider these energy
intake differences in longitudinal studies.
Whether a dietary assessment is taken over time
or for 1 day, inquiry about the athlete’s menstrual
cycle may provide useful information related to
energy intake, as well as nutritional and health
status.
Carbohydrate recommendations
Recommended percentages of energy from CHO
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special considerations
in the total diet have been listed as 55–70% for
those engaged in exercise and training (Williams
1995). The percentage of energy (E%) derived
from CHO may be helpful in comparison of
dietary intakes, but has limited value for counselling athletes and, if used alone, can be misleading. For example, an endurance cyclist could
consume a diet of 63% energy from CHO which
would normally be considered less than the
recommended level of 70% for the intake of an
athlete engaged in endurance-type exercise. Yet,
when the actual daily intake of approximately
18 g CHO · kg–1 body weight (BW) is considered
(Gabel et al. 1995), intake of the athlete cycling
14–16 h · day–1 is greater than current recommendations. To obtain a greater understanding of
an athlete’s food intake, the optimal analysis
would include values for g CHO · kg–1 BW, E%
from CHO and total amount of CHO.
Reports of dietary intakes for female athletes
illustrate a lower than expected energy and CHO
intake in relation to current dietary recommendations for those engaged in exercise and
training. Review of CHO and energy intake in
female athletes (Walberg-Rankin 1995) revealed
consumption of 3.2–5.4 g CHO · kg–1 BW · day–1
and energy intakes of 6.4–9.6 MJ · day-1
(1540–2300 kcal · day-1) for female athletes
involved in anaerobic sports (bodybuilding,
gymnastics, basketball). Ranges of 4.4–6.2 g
CHO · kg–1 BW · day–1 and 7–10 MJ · day-1 (1660–
2400 kcal) were reported for those participating in aerobic sports (running, cycling,
triathlons). In preparation for a 90-km ultramarathon, 23 South African female runners consumed an average of 49.5% of their energy intake
(7.5 MJ) from CHO or 4 g CHO · kg–1 BW · day–1 as
part of their training diet (Peters & Goetzsche
1997). The female athletes reported running an
average of 73.4 (± 12.1) km · week–1. Dietary
assessments included two 24-h food records
obtained 4 weeks prior to the race and no associations were found among energy, macro- and
micronutrient intake and performance in the
event. The use of 24-h records limits interpretation of these results.
Steen et al. (1995) reported average energy and
CHO intakes of female heavyweight collegiate
rowers below those expected for athletes
engaged in training for 12 h and 2 h of weight
training per week. Average intakes of 11 MJ
(2630 kcal; range, 2025–3858 kcal) and 51% of
energy from CHO (4.9 g · kg–1 BW) were estimated from 5-day food records (3 weekdays
and 2 weekend days). Simonsen et al. (1991)
investigated energy needs of 24 collegiate
rowers during 4 weeks of twice daily training
6 days per week. A high-CHO diet providing 10 g
CHO · kg–1 BW promoted greater muscle glycogen content and greater power output than a
diet containing 5 g CHO · kg–1 BW. However, the
moderate-CHO diet provided a constant level
of muscle glycogen (119 mmol · kg–1) and did
not lead to glycogen depletion or performance
impairment.
Dietary recommendations for CHO intake do
not differentiate for gender nor are the current
CHO dietary recommendations derived from
female athletic populations. Current recommendations include a minimum CHO intake of 5 g ·
kg–1 · day–1 that has been suggested for a recreational athlete (Clark 1990) and increased levels
for a more competitive athlete. For counselling
women who participate in endurance and
ultra-endurance events, sports nutritionists are
encouraged to use recommendations of more
than 6 g CHO · kg–1 BW currently suggested to
athletes involved in endurance sports and a
minimum of 5 g CHO · kg–1 BW for other female
athletes. Researchers are encouraged to pursue
the question of macro-nutrient needs of female
athletes at all levels of exercise intensity and
related performance.
It is worth repeating the advice for analysing
the female athlete’s food intake using values of g
CHO · kg–1 BW, E% from CHO and total amount
of CHO. The findings from Simonsen et al. (1991)
suggested that 10 g CHO · kg–1 BW will promote greater muscle glycogen content and
power output. If this CHO recommendation was
used for a female rower who weighed 60 kg,
consider the ramifications.
the female athlete
10 g CHO kg BW ¥ 60 kg BW = 600 g CHO
¥ 16.7 kJ (or 4 kcal) g CHO
= 10 MJ (or 2400 kcal)
If perchance the athlete consumed a total of
10.9 MJ · day-1 (2600 kcal · day-1) (Steen et al.
1995), only 840 kJ (200 kcal) would remain for
protein and fat needs. This yields an impossible
task not only in providing adequate levels of
protein and fat, but in a practical sense as well.
Another CHO recommendation comes in the
form of total amount of CHO per day. The currently used 500–600 g CHO · day–1 recommendation was derived from four trained male runners
whose average weight was 80 kg (Costill et al.
1981). As illustrated and reflected in current
intakes of females, these higher recommended
levels of CHO are not practical for the typically
lower weight female athlete.
Protein recommendations
When compared with CHO and fat, protein is a
nutrient with greater biological diversity in the
body, greater methodological challenges in its
study and with corresponding controversy in the
findings. The reader can find in-depth reviews
of amino acid metabolism in Chapter 9 and of
protein requirements in Chapter 10.
Recognized as important for the athlete,
protein is an energy nutrient that has a dietary
guideline of about 0.75 g · kg–1 · day–1 in the UK
(Department of Health 1991) and US (National
Research Council 1989). As previously mentioned, these recommendations are not set with
consideration for the effects of physical activity
or climate. Rationale for using the recommended
level of protein for both sexes stems from limited
evidence found during a nitrogen balance study
of six young women that requirement values,
when expressed per kilogram of body weight,
are not substantially different from those for
young adult men. Calloway and Kurzer (1982)
also noted in their study the importance of hormonal influences on the gain and loss of nitrogen
and cautioned others that failure to consider the
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effect of the menstrual cycle could lead to inaccurate estimates of nitrogen/protein requirements.
Endurance athletes have greater protein
requirements than those of sedentary persons
(Tarnopolsky et al. 1988; Meredith et al. 1989).
Phillips et al. (1993) considered protein needs for
individuals engaged in habitual physical exercise and concluded that 0.86 g · kg–1 · day–1 was
inadequate for endurance athletes. Females in
the study were eumenorrhoeic, not taking oral
contraceptives and matched to training levels of
males with the use of training and performance
histories. Male athletes exhibited higher absolute
leucine oxidation than females, yet an increase in
oxidation with exercise was proportionally
greater in the females. This was not explained
by the authors. In respect to methodology, a
15N-glycine isotope revealed a higher protein
turnover in elderly women (n = 6) after they consumed 20% of their total energy as protein than
after a 10% protein diet and no difference was
observed when a [1-13C] leucine method was
used (Pannemans et al. 1997). Care must therefore be taken in choosing the stable isotope tracer
to measure protein turnover. The age of these
subjects and small sample size limit the application of this research to female athletes, yet may
pose questions for researchers who investigate
protein utilizing leucine as a tracer.
While investigations of the most appropriate
isotope tracer may redirect protein research, the
more traditional nitrogen balance studies still
support increased protein needs for active individuals. Without support for a specific protein
requirement for the female athlete, reliance on a
thorough dietary assessment of protein quality
and energy intake followed with the provision
of current recommendations for protein is suggested. Lemon (1995) suggests that endurance
athletes consume protein levels of 1.2–1.4 g · kg–1 ·
day–1 and increased amounts for the strength
athlete, 1.4–1.8 g protein · kg–1 · day–1. Unfortunately, these recommendations are based on data
derived from male subjects aged 20–40 years. In
consideration of recent data suggesting gender
differences in substrate utilization, the protein
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special considerations
levels may be excessive for the female; however,
Lemon (1995) suggests that any adverse effect of
excessive protein intake is minimal for individuals with normal kidney function.
Concern regarding protein intake for the
female athlete stems from whether or not the
individual consumes a low-energy intake or a
strict vegetarian diet. Negative nitrogen balance
can result in situations when energy intake is
insufficient or consumed protein is of lesser
biological quality. In these situations, heightened
attention to the protein quality and adequate
energy levels is warranted in the dietary
assessment.
Fat
Dietary fat guidelines promoted by different
countries and agencies (James et al. 1988; Committee on Diet and Health 1989) vary from 20 to
35 E%. Developed for the general public, these
levels stem from research that associates high fat
intake with a variety of chronic diseases. Some
have proposed the use of high-fat diets or fat
loading to improve endurance capability of
athletes. In their review of studies testing the
fat-loading hypothesis, Sherman and Leenders
(1995) concluded that the use of high-fat diets to
improve endurance is not supported by a sufficient number of valid, credible and replicated
studies. See Chapter 14 for more support of this
conclusion.
Concern for a lower weight and percentage of
body fat, as indicated by a score on the Eating
Attitudes Test, motivates amenorrhoeic female
athletes to consume less fat (11 E%) than eumenorrhoeic athletes (17 E%) (Perry et al. 1996), while
other female athletes could benefit from counselling to reduce fat content in their diets (Steen et
al. 1995). Consideration for the female athlete’s
weight history, appropriate goals for body
composition and weight, current eating habits
and serum lipid chemistries, family history of
disease, and factors that influence energy and fat
intake is important in the development of appropriate recommendations for fat intake. For the
sport nutritionist, a thorough dietary and health
assessment will provide the best basis for any
recommendation that can be made for fat intake
by female athletes.
Vitamins
It is generally supported that vitamin supplementation is not needed for those athletes
consuming a variety of foods and that vitamin
supplementation in athletes with an adequate
vitamin status has no effect on performance (van
der Beek 1991). For further discussion of vitamins, see Chapters 20 and 21. For the female
athlete, research on vitamin B6 and the antioxidant vitamins requires further discussion in this
chapter.
Vitamin B6
Energy metabolism during exercise relies on
several biological functions of vitamin B6. The six
biologically active forms of vitamin B6 may function as a cofactor for enzymes used in metabolic
transformation of amino acids, in gluconeogenesis and glycogenolysis. Other functions related to
exercise include serotonin formation and synthesis of haemoglobin and carnitine. With the possibility of an increased need for this vitamin in
young women, it may be beneficial to consider
vitamin B6 intake of the female athlete.
Female athletes tend to report vitamin B6
intakes that are less than two thirds of the dietary
guideline. However, it is important to note
the possible influences of underreporting, low
energy intakes or inadequate vitamin B6 data in
dietary computer software programs as possible
contributors to the reported lower than expected
intakes of vitamin B6.
Manore (1994) summarized post-1985 studies
reporting average dietary intakes of vitamin
B6 for female athletes. With the majority of
researchers using a 3-day record to record
intakes, 10–60% of the subjects reported consumption of less than two thirds of the dietary
guideline for vitamin B6. However, levels of the
vitamin expressed as milligrams of vitamin B6
per gram of protein were not below the currently
the female athlete
recommended level of 0.016. The results of a
study by Huang et al. (1998) provide recent evidence that the level of 0.016 mg vitamin B6 · g–1
protein is inadequate for young women. Their
study of eight women residing in a metabolic
unit for 92 days suggests that 0.019 mg vitamin
B6 · g–1 protein is needed to normalize vitamin
B6 measures to controlled baseline values. If
vitamin B6 needs are indeed higher than current
guidelines for young women, more attention to
an adequate intake of this vitamin is needed for
female athletes.
It is advisable for those working with athletes
who typically report low energy intakes, i.e.
gymnasts, figure skaters, and runners, to appropriately assess food intakes while noting completeness of the nutrient data bank used to
estimate vitamin B6 intake. Based on a thorough
assessment, one may potentially proceed to recommend consumption of additional vitamin B6rich foods.
Antioxidant vitamins
Exercise-induced oxidative stress may be a
concern for an athlete. Oxidative stress occurs
at submaximal levels of exercise (Leaf et al.
.
1997), and at peak Vo2max. (Viguie et al. 1990). The
human body constantly forms free radicals and
other oxygen-derived species that can damage
DNA, lipids and proteins. When exposed to
mild oxidative stress, the body can respond by
increasing its defensive antioxidant enzymes
and proteins; however, severe damage may lead
to cell transformation and the increased oxidative damage has been associated with human
disease, specifically cardiovascular disease and
cancer (Halliwell 1994).
To diminish the effect of naturally occurring
oxidative damage, it has been suggested that
antioxidant nutrients should be added to the diet
(Jacob & Burri 1996). Carotenoids, ascorbic acid,
a-tocopherol, flavonoids, and other plant phenolics are a few of those suggested as important in
protecting against oxidative damage. In other
words, inclusion of fruits and vegetables in the
athlete’s diet can partially provide a solution to
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the concern for increased oxidative stress from
exercise.
Some reports suggest that supplementation
with antioxidant nutrients, such as vitamin E,
can attenuate the exercise-induced lipid peroxidation (Sumida et al. 1989). A daily combination
of 294 mg vitamin E, 1000 mg ascorbic acid and
60 mg ubiquinone was found to be effective in
preventing LDL oxidation in male endurance
athletes; however, 4 weeks’ supplementation
with the antioxidant nutrients did not reduce
LDL oxidation products, i.e. conjugated dienes
(Vasankari et al. 1997). Limited data specifically
on female athletes are again noted in the area of
antioxidant research.
For possible increased antioxidant vitamin
requirements for those who exercise, the recommendation for an increased fruit and vegetable
intake is worthy of emphasis. Dietary guidelines
from several US organizations recommend five
or more daily servings of fruits and vegetables to
help reduce the risk of heart disease and certain
kinds of cancer (Jacob & Burri 1996). For the
female athlete, increased intake of fruits and vegetables can provide additional CHO and several
essential nutrients. For those athletes limiting
energy intake to reduce body fat, these foods will
provide a higher nutrient to calorie ratio known
to be beneficial for consuming a more nutrient
adequate food intake.
Minerals
Macrominerals: calcium
A nutrient worthy of consideration for supplementation to the female athlete’s diet is calcium.
For detailed discussion of this mineral’s roles in
the body, calcium intake and its relationship to
exercise, refer to Chapter 23. Discussion supporting the concern for adequate intake of this
mineral and of practical ways to increase calcium
intake in female athletes follows.
Peak bone mass development depends upon
adequate calcium intake during skeletal growth
(Matkovic 1991; Johnston et al. 1992) as well as for
gain in bone mass until the third decade of life
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special considerations
(Recker et al. 1992). The combination of suboptimal calcium intakes by female athletes (Chen
et al. 1989; Steen et al. 1995; Peters & Goetzsche
1997) and differences of opinion regarding recommended dietary guidelines for this mineral
(Health and Welfare Canada 1983; National
Research Council 1989; Department of Health
1991) prompts some concern and questions
among those who care for, work with or feed
female athletes.
Why should one have concern? Since physical
activity, particularly high impact, is associated
with greater bone density (Dook et al. 1997), one
might expect that female athletes need not worry
about the possibility of bone loss. However, identification of a syndrome of disordered eating,
amenorrhoea and reduced bone density (Loucks
1987) overshadows this positive aspect of physical activity and may contribute to a greater consideration for adequate calcium intakes in female
athletes.
The important questions regarding calcium
are:
1 What is an optimal calcium intake to promote
and support adequate bone density in a female
athlete?
2 How can suboptimal calcium intakes be
improved?
The answer to the first question is currently
unknown. Differences of opinion regarding
optimal calcium intakes for adults exist among
countries, agencies and researchers. Even though
physical activity has been identified as a positive
factor in promoting greater bone density, no one
has identified either the optimal level of exercise
or calcium intake to support adequate bone
density in the female athlete. To recommend an
appropriate level of calcium intake, one needs to
rely on a thorough nutritional, exercise and
medical history of the athlete. Answers to questions about the following will provide added
perspective on whether to recommend the
dietary guideline for calcium or potentially a
higher level.
• Family history of osteoporosis
• Typical intake of calcium, fluoride, other bonerelated minerals, protein and energy
• Training intensity and type of sport
• Menstrual history and current status
• Supplement and/or drug use and any malabsorption conditions
For the athlete who avoids calcium-rich foods
or is restricting energy intake to lose weight,
discussion of low-fat calcium-rich foods, food
choices not normally recognized as calcium-rich
or those that are fortified with calcium, e.g.
calcium-fortified orange juice, is recommended.
Consumption of a mineral water that has a high
calcium content may also be appropriate for a
possible source of dietary calcium (Couzy et al.
1995).
The second choice would be that for supplementation of the female athlete’s diet with
calcium tablets. Determination of the typical
calcium intake from food will help determine the
appropriate level of supplement to recommend.
However, supplementation with minerals is
not without potential adverse effects. Wood and
Zheng (1997) report that high dietary calcium
intakes during a 36-day study reduced zinc
absorption in healthy postmenopausal women.
Limitations of the study include that activity
level was not reported for the subjects and
that differences will exist in nutrient absorption
between a postmenopausal female and a young
female. Cook et al. (1991) reported calcium supplements could inhibit the absorption of ferrous
sulphate when consumed with food, although
Reddy and Cook (1997) found no significant
influence of calcium intake on non-haem iron
absorption when varying levels of calcium
(280–1281 mg · day–1) were consumed as part of
the diet.
In general, most experts agree that a calciumrich diet is the most appropriate dietary prescription to promote and support optimal bone
density. If this is not possible, consideration for
low to moderate levels of a calcium supplement
in addition to the dietary calcium intake to meet
optimal levels is reserved for an alternative
action.
The relationship between the macrominerals
and microminerals warrants more attention as
athletes look to supplementation as solutions to
their possible dietary inadequacies. Lukaski
(1995) has expressed concern for the adverse
the female athlete
effects of trace mineral supplementation, particularly magnesium, zinc, and copper; while
Clarkson and Haymes (1994) recommend a
multivitamin/mineral supplement containing
no more than the dietary guideline to athletes
whose diets may be less than optimal.
Microminerals: iron
Iron is another mineral worthy of consideration
for supplementation. Deficiency of this mineral
has the distinction of being common in female
athletes and is frequently reported in physically
active populations. In a comparison of 111 adult
female habitual runners with 65 inactive females
of comparable age, Pate et al. (1993) found
serum ferritin levels, indicative of iron status,
28% lower in the runners than controls.
However, frank iron deficiency indicated by suboptimal haemoglobin levels was rare in both
groups. Dr Eichner provides insight into the
reasons for iron depletion and expanded discussion of the effect of exercise on this mineral (see
Chapter 24).
Challenges in maintaining adequate iron
stores in the female athlete include the complexity of the mineral’s absorption, lower intakes of
energy by females, low levels of iron in food,
avoidance of meat products, and monthly menstrual losses. More challenge is added to understanding this issue when one needs to decide
which haematological assessment to use for iron
status determination. Lack of standardization of
the blood parameters and values used to classify
the stages of iron depletion lends to the variability reported for the incidence of iron depletion in
athletic populations.
However, most agree that iron supplements
are appropriately given to those athletes who
are diagnosed with iron deficiency anaemia
(Haymes 1987). This is related to reports by some
researchers that aerobic capacity in female
athletes with mild anaemia can be improved
with iron supplementation (Fogelholm 1995).
Supplement use by athletes
Sobal and Marquart (1994) reviewed 51 studies
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in which 10 274 athletes were investigated
regarding the prevalence, patterns and explanations for their vitamin/mineral supplement
use. Mean percentage of supplement use among
female athletes was 57% (33 study groups).
Several reasons were noted by the athletes for
their supplement use: performance enhancement, prevention of illness, substitute for inadequate diet, provision of additional energy, and
the meeting of specific nutrient demands for
exercise. It was also noted that vitamin and
mineral supplements were more frequently used
by female athletes consuming low energy diets.
Small sample sizes (< 50 athletes) of most of the
reviewed studies (56%) and the minor focus on
supplements in the studies limits our understanding of supplement use by athletes. The
authors recommended that those who study
dietary intake of athletes consider vitamin/
mineral supplement use as an important part
of their study designs and sport nutritionists
include a vitamin/mineral supplement history
as part of their dietary assessment.
If the female athlete consumes adequate
amounts of a variety of foods, she does not
require vitamin/mineral supplementation to her
food intake. However, for those athletes who
consistently restrict energy intake, a one-a-day
multiple vitamin/mineral supplement can
provide some insurance in meeting nutrient
needs for overall good health and exercise.
Fluid intake and recommendations
Due to the wide variation in individual fluid
losses during exercise, it is not reasonable to differentiate hydration recommendations for the
female athlete. In spite of the physical, physiological and hormonal differences between
males and females, individual variations in
fluid balance surpass any gender differences (R.J.
Maughan, personal communication).
Conclusion
Dietary guidelines based on data from sedentary
or male populations pose challenges, as well as
opportunities, for the sports nutritionist and
426
special considerations
researcher who are interested in the nutritional
needs of the female athlete. Since macronutrient
dietary guidelines for athletes have been
based on male subjects and micronutrient needs
derived from non-athletic populations, the
researcher has the opportunity to explore these
needs of the female athlete, while faced with
the challenge of understanding and controlling
for the hormonal influences on metabolism. The
sports nutritionist is presented with opportunities to systematically collect food intakes and
supplementation information from female athletes, yet challenged with the lack of dietary
guidelines specifically designed for the female
athlete.
Presently, information obtained from a thorough diet, supplement and health history,
3–5-day food record, and training schedule; estimation of energy expenditure during exercise;
plus anthropometric and biochemical data can
provide a good basis for providing appropriate
nutritional advice. Observation of the female
athlete while training and competing, as well as
during meal times, can also help to understand
better the energy and nutrient requirements of
the individual.
References
Arciero, P.J., Goran, M.I. & Poehlman, E.T. (1993)
Resting metabolic rate is lower in women than in
men. Journal of Applied Physiology 75, 2514–2520.
Barr, S.I., Janelle, K.C. & Prior, J.C. (1995) Energy
intakes are higher during the luteal phase of ovulatory menstrual cycles. American Journal of Clinical
Nutrition 61, 39–43.
Calloway, D.H. & Kurzer, M.S. (1982) Menstrual cycle
and protein requirements of women. Journal of
Nutrition 112, 356–366.
Carpenter, W.H., Poehlman, E.T., O’Connell, M. &
Goran, M.I. (1995) Influence of body composition
and resting metabolic rate on variation in total
energy expenditure: a meta-analysis. American
Journal of Clinical Nutrition 61, 4–10.
Chen, J.D., Wang, J.F., Li, K.J. et al. (1989) Nutritional
problems and measures in elite and amateur
athletes. American Journal of Clinical Nutrition 49,
1084–1089.
Clark, N. (1990) Sport Nutrition Guide: Eating to Fuel
Your Lifestyle. Leisure Press, Champaign, IL.
Clarkson, P.M. & Haymes, E.M. (1994) Trace mineral
requirements for athletes. International Journal of
Sport Nutrition 4, 104–119.
Committee on Diet and Health, National Research
Council (1989) Diet and Health: Implications for Reducing Chronic Disease Risk. National Academy Press,
Washington, DC.
Cook, J.D., Dassenko, S.A. & Whittaker, P. (1991)
Calcium supplementation: effect on iron absorption. American Journal of Clinical Nutrition 53, 106–
111.
Costill, D.L., Sherman, W.M., Fink, W.J., Maresh, C.,
Witten, M. & Miller, J.M. (1981) The role of dietary
carbohydrates in muscle glycogen resynthesis after
strenuous running. American Journal of Clinical Nutrition 34, 1831–1836.
Couzy, F., Kastenmayer, P., Vigo, M., Clough, J.,
Munoz-Box, R. & Barclay, D.V. (1995) Calcium
bioavailability from a calcium- and sulfate-rich
mineral water, compared with milk, in young adult
women. American Journal of Clinical Nutrition 62,
1239–1244.
Department of Health (1991) Dietary Reference Values for
Food Energy and Nutrients for the United Kingdom.
HMSO, London.
Dook, J.E., James, C., Henderson, N.K. & Price, R.I.
(1997) Exercise and bone mineral density in mature
female athletes. Medicine and Science in Sports and
Exercise 29, 291–296.
Fogelholm, M. (1995) Indicators of vitamin and mineral
status in athletes’ blood: a review. International
Journal of Sport Nutrition 5, 267–284.
Gabel, K., Aldous, A. & Edgington, C. (1995) Dietary
intake of two elite male cyclists during 10-day, 2,050mile ride. International Journal of Sport Nutrition 5,
56–61.
Halliwell, B. (1994) Free radicals, antioxidants, and
human disease: curiosity, cause, or consequence?
Lancet 334, 721–724.
Haymes, E.M. (1987) Nutritional concerns: need for
iron. Medicine and Science in Sports and Exercise 19,
S197–S200.
Health and Welfare Canada (1983) Recommended Nutrient Intakes for Canadians. Bureau of Nutritional
Sciences, Health Protection Branch, Health and
Welfare, Ottawa.
Huang, Y.-C., Chen, W., Evans, M.A., Mitchell, M.E. &
Shultz, T.D. (1998) Vitamin B-6 requirement and
status assessment of young women fed a highprotein diet with various levels of vitamin B-6.
American Journal of Clinical Nutrition 67, 208–220.
Jacob, R.A. & Burri, B.J. (1996) Oxidative damage and
defense. American Journal of Clinical Nutrition 63,
985S–990S.
James, W.P.T., Ferro-Luzzi, A., Isaksson, B. & Szostak,
W.B. (1988) Healthy Nutrition: Preventing Nutrition-
the female athlete
Related Diseases in Europe. WHO Regular Publication,
European Series, no. 24, WHO, Copenhagen.
Johnston, C.C., Miller, J.Z., Slemenda, C.W. et al. (1992)
Calcium supplementation and increases in bone
mineral density in children. New England Journal of
Medicine 327, 82–87.
Kravitz, L., Robergs, R.A., Heyward, V.H., Wagner,
D.R. & Powers, K. (1997) Exercise mode and gender
comparisons of energy expenditure at self-selected
intensities. Medicine and Science in Sports and Exercise
29, 1028–1035.
Lamon-Fava, S., Fisher, E.C., Nelson, M.E., Evans, W.J.,
Millar, J.S., Ordovas, J.M. & Schaefer, E.J. (1989)
Effect of exercise and menstrual cycle status on
plasma lipids, low density lipoprotein particle size,
and apolipoproteins. Journal of Clinical Endocrinology
and Metabolism 68, 17–21.
Leaf, D.A., Kleinman, M.T., Hamilton, M. & Barstow,
T.J. (1997) The effect of exercise intensity on lipid peroxidation. Medicine and Science in Sports and Exercise
29, 1036–1039.
Lemon, P.W.R. (1995) Do athletes need more dietary
protein and amino acids? International Journal of Sport
Nutrition 5, S39–S61.
Loucks, A.B. (1987) Skeletal demineralisation in the
amenorrheic athlete. In Exercise: Benefits, Limits
and Adaptations (ed. D. Macleod, R. Maughan, M.
Nimmo, T. Reilly & C. Williams), pp. 255–269. E. &
F.M. Spon, London.
Lukaski, H.C. (1995) Micronutrients (magnesium, zinc,
and copper): are mineral supplements needed for
athletes? International Journal of Sport Nutrition 5,
S74–S83.
Manore, M.M. (1994) Vitamin B6 and exercise. International Journal of Sport Nutrition 4, 89–103.
Matkovic, V. (1991) Calcium metabolism, and calcium
requirements during skeletal modeling and consolidation of bone mass. American Journal of Clinical
Nutrition 54, 245S–260S.
Maughan, R.J., Harmon, M., Leiper, J.B., Sale, D. &
Delman, A. (1986) Endurance capacity of untrained
males and females in isometric and dynamic muscular contractions. European Journal of Applied Physiology 55, 395–400.
Meredith, C.N., Zackin, M.J., Frontera, W.R. & Evans,
W.J. (1989) Dietary protein requirements and body
protein metabolism in endurance-trained men.
Journal of Applied Physiology 66, 2850–2856.
Miller, A.E.J., MacDougall, J.D., Tarnopolsky, M.A. &
Sale, D.G. (1993) Gender differences in strength and
muscle fiber characteristics. European Journal of
Applied Physiology 66, 254–262.
National Research Council (1989) Recommended Dietary
Allowances, 10th edn. National Academy of Science,
Washington, DC.
Pannemans, D.L.E., Wagenmakers, A.J.M., Westerterp,
427
K.R., Schaafsma, G. & Halliday, D. (1997) The effect
of an increase of protein intake on whole-body
protein turnover in elderly women is tracer dependent. Journal of Nutrition 127, 1788–1794.
Pate, R.R., Miller, B.J., Davis, J.M., Slentz, C.A. & Klingshirn, L.A. (1993) Iron status of female runners. International Journal of Sport Nutrition 3, 222–231.
Perry, A.C., Crane, L.S., Applegate, B., MarquezSterling, S., Signorile, J.F. & Miller, P.C. (1996) Nutrient intake and psychological and physiological
assessment in eumenorrheic and amenorrheic
female athletes: a preliminary study. International
Journal of Sport Nutrition 6, 3–13.
Peters, E.M. & Goetzsche, J.M. (1997) Dietary practices
of South African ultradistance runners. International
Journal of Sport Nutrition 7, 90–103.
Phillips, S.M., Atkinson, S.A., Tarnopolsky, M.A. &
MacDougall, J.D. (1993) Gender differences in
leucine kinetics and nitrogen balance in endurance
athletes. Journal of Applied Physiology 75, 2134–2141.
Piers, L.S., Diffey, B., Soares, M.J., Frandsen, S.L.,
McCormack, L.M., Lutschini, M.J. & O’Dea, K. (1997)
The validity of predicting the basal metabolic rate of
young Australian men and women. European Journal
of Clinical Nutrition 51, 333–337.
Recker, R.R., Davies, K.M., Hinders, S.M., Heaney, R.P.,
Stegman, M.R. & Kimmel, D.B. (1992) Bone gain in
young adult women. Journal of the American Medical
Association 268, 2403–2408.
Reddy, M.B. & Cook, J.D. (1997) Effect of calcium intake
on nonheme-iron absorption from a complete diet.
American Journal of Clinical Nutrition 65, 1820–1825.
Sherman, W.M. & Leenders, N. (1995) Fat loading: the
next magic bullet? International Journal of Sport Nutrition 5, S1–S12.
Simonsen, J.C., Sherman, W.M., Lamb, D.R., Dernbach,
A.R., Doyle, J.A. & Strauss, R. (1991) Dietary carbohydrate, muscle glycogen, and power output during
rowing training. Journal of Applied Physiology 70,
1500–1505.
Sobal, J. & Marquart, L.F. (1994) Vitamin/mineral supplement use among athletes: a review of the literature. International Journal of Sport Nutrition 4, 320–334.
Steen, S.N., Mayer, K., Brownell, K.D. & Wadden, T.A.
(1995) Dietary intake of female collegiate heavyweight rowers. International Journal of Sport Nutrition
5, 225–231.
Sumida, S., Tanaka, K., Kitao, H. & Nakadomo, F. (1989)
Exercise-induced lipid peroxidation and leakage of
enzymes, before and after vitamin E supplementation. International Journal of Biochemistry 21, 835–
838.
Sundgot-Borgen, J. (1996) Eating disorders, energy
intake, training volume, and menstrual function in
high-level modern rhythmic gymnasts. International
Journal of Sport Nutrition 6, 100–109.
428
special considerations
Tarnopolsky, L.J., MacDougall, J.D., Atkinson, S.A.,
Tarnopolsky, M.A. & Sutton, J.R. (1990) Gender differences in substrate for endurance exercise. Journal
of Applied Physiology 68, 302–308.
Tarnopolsky, M.A., MacDougall, J.D. & Atkinson, S.A.
(1988) Influence of protein intake and training status
on nitrogen balance and lean body mass. Journal of
Applied Physiology 64, 187–193.
van der Beek, E.J. (1991) Vitamin supplementation and
physical exercise performance. Journal of Sports
Science 9, 77–89.
Vasankari, T.J., Kujala, U.M., Vasankari, T.M.,
Vuorimaa, T. & Ahotupa, M. (1997) Increased serum
and low-density lipoprotein antioxidant potential
after antioxidant supplementation in endurance athletes. American Journal of Clinical Nutrition 65,
1052–1056.
Viguie, C.A., Frei, B., Shigenanga, M.K., Ames, B.N.,
Packer, L. & Brooks, G.A. (1990) Oxidant stress in
human beings during consecutive days of exercise
(Abstract). Medicine and Science in Sports and Exercise
22, 86S.
Walberg-Rankin, J. (1995) Dietary carbohydrate as an
ergogenic aid for prolonged and brief competitions
in sport. International Journal of Sport Nutrition 5,
S13–S28.
WHO (1985) Energy and Protein Requirements: Report of
a Joint FAO/WHO/UNU Expert Consultation. Technical Report Series 724, World Health Organization,
Geneva.
Williams, C. (1989) Diet and endurance fitness.
American Journal of Clinical Nutrition 49, 1077–1083.
Williams, M. (1995) Nutrition Related to Fitness and
Sport. Brown and Benchmark, Dubuque, IA.
Wood, R.J. & Zheng, J.J. (1997) High dietary calcium
intakes reduce zinc absorption and balance in
humans. American Journal of Clinical Nutrition 65,
1803–1809.