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Posted on : June 21, 2008
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Female and male athletes
respond to training in a fairly comparable way. As volume and intensity
of training increases, so does aerobic capacity and hence performance.
Body composition tends to change, whether male or female, indicating
that physiologically, we are all actually quite
similar.</p><p>Nutritionally speaking, fuelling of training is similar
too. Regardless of the sport in question, energy intake must match
energy output in order to fuel training and recovery. For endurance
athletes, carbohydrate intake needs to equate to approximately 7 10g per
kg/bwt (or 4g per lb/bwt). If it doesn``t performance tends to suffer,
and fatigue creeps in. It is important for any athlete, regardless of
gender, to train and compete with optimum fuel reserves, and, of course
be well hydrated.</p><p>Despite seemingly parallel training responses
and "fuel" requirements between males and females, women
engaged in regular exercise, and especially those with demanding
training and competition schedules have quite unique nutritional
needs.</p><p>These special needs often mirror a particular time in a
female``s sexual development, or during one of the many hormonal
changes, which govern a women``s life. Dramatic hormonal shifts initiate
quite unique metabolic and chemical changes within the body that demand
specific nutrients. Needs change as a female enters her pubertal years
(onset of menarche), during her reproductive years and during pregnancy,
and then at the stage that marks the end of reproduction (menopause).
Disruption in a female``s normal menstrual functioning (e.g. amenorrhoea)
may create increased requirements in macro and micronutrients (e.g.
calcium, magnesium, vitamin K, protein and essential fatty acids). The
BNF``s briefing paper, Nutrition and Sport, reports increased calcium
requirements in amenorrhoeic women, and advises all female athletes to
pay attention to energy, calcium and iron intakes (1). Vitamin K
supplementation has been shown to improve markers of bone metabolism in
a small group of amenorrhoeic female elite athletes (2). Vitamin K
functions in the synthesis of calcium binding proteins.</p><p>Iron and
calcium requirements of the female athlete The two main nutrients that
require most attention are the minerals iron and calcium.</p><p>Levels
of iron in the body are particularly important given iron``s role in
many enzyme functions and it``s fundamental role in the formation of
haemoglobin (75% of total body iron is in this form) and as a
constituent of myoglobin (the O2 carrying material that functions inside
the cells). Iron performs the overwhelming activity of transporting
oxygen from the lungs to the mitochondria within muscle cells ? vital
for the athlete. Females have a higher rate of iron loss than men mainly
via blood loss through menstruation, as well as during pregnancy and
childbirth. This creates a higher iron requirement in women
generally.</p><p>An athlete``s iron status (measured by levels of blood
haemoglobin, haematocrit concentration and plasma ferritin levels) may
further be compromised due to a number of factors directly related to
training. These have been identified as bleeding within the digestive
system, inadequate diet and poor iron absorption, loss of iron through
heavy sweating, red blood cell breakdown due to trauma created by
certain high impact activities (e.g. long distance running), and even
over frequent blood donation.</p><p>Iron deficiency anaemia (haemoglobin
levels below 12g/dl) has a major impact on performance and immune
status. It decreases aerobic capacity and endurance, induces fatigue,
and lowers resistance to infection. It has not yet been clearly
established whether iron depletion (low ferritin concentrations and
reduced bone marrow iron) negatively affects performance, but certainly
low ferritin is not something to be ignored. Many however, suggest
changes in plasma ferritin concentration are due to either heavy
training, or as a response to inflammation, and low blood haemoglobin in
some athletes is simply due to plasma volume expansion. Assessment of
iron status in athletes is clearly not straightforward. Taking into
account measured indices of iron status, individual dietary habits,
digestive function, menstruating patterns and other significant factors
should help determine the impact iron status may be having on a
particular individual``s performance. It is fair to say that in some
cases, borderline measurements or those at the lower end of "normal"
are often clinically significant, and iron supplementation produces
noticeable improvements in iron status and performance (3).</p><p>The
use of iron supplements at this point may also prevent the development
of full blown iron deficiency anaemia in some female athletes, which is
often when "re pletion" is most difficult, especially via diet
alone. Inorganic forms of iron (e.g. ferrous sulphate, ferrous gluconate)
are notoriously poorly absorbed, and often cause gastrointestinal
problems such as constipation. More importantly, they often fail to
raise Hb levels. Where iron supplementation is deemed appropriate (i.e.
anaemia), serious consideration should be given to using new "food form"
iron supplements. Food form iron is a version of iron that has been
grown into yeast cells, and the absorbability of yeast based iron is
much closer to haem iron. It also produces little or no uncomfortable
side effects.</p><p>Calcium</p><p>National surveys have consistently
reported low calcium intake is young and adult females (4, 5, 6), as
well as female athletes (2, 7). This is normally due to low energy
intakes, fad diets, or poorly planned vegetarian and vegan diets.
Inadequate calcium intake and consequently poor calcium status is
compounded by diets that contain high phosphorous, high salt and high
caffeine food and drink. These have a negative impact of calcium
balance, due to an increase in urinary calcium excretion
(8).</p><p>Calcium and bone health</p><p>About 60% of adult bone is laid
down during adolescence (9), when calcium deposition is at it``s highest
(10). This is due to increases in the hormones oestrogen, growth hormone
and calcitriol. |
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