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BJSM reviews: A−Z of nutritional supplements:
dietary supplements, sports nutrition foods and
ergogenic aids for health and performance Part
4
L M Burke, L M Castell, S J Stear, et al.
Br J Sports Med 2009 43: 1088-1090
doi: 10.1136/bjsm.2009.068643
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Nutritional supplement series
BJSM reviews: A–Z of nutritional supplements:
dietary supplements, sports nutrition foods and
ergogenic aids for health and performance Part 4
L M Burke,1 L M Castell,2 S J Stear,3
P J Rogers,4 E Blomstrand,5 S Gurr,6 N Mitchell,7 F B Stephens,8 P L Greenhaff8
1
Australian Institute of Sport,
Canberra, Australia; 2 University
of Oxford, Oxford, UK; 3 English
Institute of Sport, London, UK; 4
ASPARTAME, BRANCHED CHAIN AMINO ACIDS,
BEE POLLEN, BORON, CARNITINE
4
Department of Experimental
Psychology, University of Bristol,
Bristol, UK; 5 Åstrand
Laboratory, Swedish School of
Sport and Health Sciences,
Stockholm, Sweden; 6 Sports
Nutrition, Australian Institute of
Sport, Belconnen, Australia;
7
British Cycling, English Institute
of Sport, Sheffield, UK; 8 School
of Biomedical Sciences, The
Medical School, The University
of Nottingham, Nottingham, UK
Correspondence to:
L M Castell, University of Oxford,
Green Templeton College,
Oxford OX2 6HG, UK; lindy.
[email protected]
LB, LC and SJ edited this series.
Accepted 9 October 2009
INTRODUCTORY REMARKS
Welcome to Part 4 in our A–Z of nutritional
supplement series. One of the enjoyable aspects of
reviewing the many supplements in a fairly logical
order from A to Z means that, every now and then,
a review comprises a real assortment of supplements, and Part 4 is certainly one of them!
In Part 4, the review takes us from aspartame, a
sweetening ingredient found in many foods and
drinks, to BCAA, the three branched chain
essential amino acids; then onto bee pollen,
marketed as a ‘‘superfood,’’ followed by the ultra
trace element boron, known more for its association with bone health, and finally to L-carnitine, a
supplement which is widely used in the sporting
arena and seems to be gaining in popularity. We are
grateful for the excellent contributions from our
invited reviewers, which facilitate the provision of
access to impartial advice on the value of these
individual ingredients and supplements. These
contributions are establishing that, for some, the
performance evidence is limited or simply does not
yet exist.
In the January 2010 issue, we will be turning our
attention to ‘‘buffers,’’ where we will be covering
the key ones used by many athletes, such as betaalanine and carnosine, together with the two more
established compounds of sodium bicarbonate and
sodium citrate.
ASPARTAME
PJ Rogers
Aspartame (C14H18N2O5) is an example of an
intense or non-nutritive sweetener and an ingredient of many thousands of drink and food
products consumed worldwide. It is a methyl ester
of a dipeptide composed of the amino acids aspartic
acid and phenylalanine, which are constituents of
all protein-containing foods. Aspartame is about
180 times sweeter than sucrose with, for most
individuals, minimal bitterness and a good quality
of sweet taste. Being composed of amino acids, it
has an energy value of 4 kcal/g; however, at the
concentrations needed to sweeten foods and
drinks, its nutritive value is negligible. In products
it may be blended with one or more other intense
sweeteners (eg, acesulfame K and sucralose) and/
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or with sugars, including sucrose, fructose and
glucose.
The safety of aspartame has been the subject of
much, often ill-informed, debate. After ingestion,
aspartame is broken down to its constituent amino
acids and methanol, and some further minor
products. Even at high dietary intakes of aspartame, the amount of methanol produced is too
small to be harmful. Because high intakes of
phenylalanine are undesirable for those born with
phenylketonuria,1 products with aspartame may
contain information such as ‘‘Contains a source of
phenylalanine.’’ A recent comprehensive review
concluded that ‘‘The weight of existing evidence is
that aspartame is safe at current levels of consumption as a non-nutritive sweetener.’’2
By replacing sugars in products, intense sweeteners can potentially aid control of energy intake
and weight, but the extent of any benefit would
appear to be dependent on the context of use.3
Additionally, aspartame reduces appetite independent of its sweet taste by a physiological action
which is currently unknown.4 Aspartame, and
other intense sweeteners, are used in sport drinks
to allow adjustment of nutrient profile and
tonicity, while maintaining a pleasant level of
sweetness. The flavour and sweetness of such
products are important for motivating consumption, and thereby achieving desired levels of
hydration and nutrient intake.
BRANCHED CHAIN AMINO ACIDS
E Blomstrand
The three branched chain amino acids (BCAA;
leucine, isoleucine and valine) cannot be synthesised by the human body and must therefore be
provided in the diet. Food sources containing
BCAA are dietary proteins such as meat, poultry,
fish, egg, milk and cheese, which contain 15–20 g
of BCAA per 100 g of protein. The BCAA are
metabolised mainly in skeletal muscle, which
means they escape the liver, and ingestion of
BCAA causes a rapid increase in the plasma level.
The anabolic effect of BCAA on human skeletal
muscle was first demonstrated under resting
conditions, followed by studies showing similar
effects in the recovery period after endurance and
resistance exercise.5 6 More recent data indicate
that the effect of BCAA, particularly leucine, is
mediated through activation of regulatory
enzymes in the protein synthesis machinery.7
Increasing the plasma level of BCAA during
exercise may reduce the transport of tryptophan
Br J Sports Med 2009;43:1088–1090. doi:10.1136/bjsm.2009.068643
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Nutritional supplement series
into the brain and the synthesis of 5-hydroxytryptamine (5HT). 5-HT has been suggested to be involved in central
fatigue, that is, fatigue emanating from the brain rather than
muscle.8 BCAA supplementation during sustained physical
activity has exerted positive effects on cognitive performance
and perceived exertion.8 9 Under certain conditions, BCAA
supplementation can also improve physical performance,
although the majority of studies have found no effect of
BCAA on performance when supplied together with carbohydrates.10
The amount of BCAA recommended is 0.03–0.05 g/kg body
weight per hour or 2–4 g per hour ingested repeatedly during
exercise and recovery, preferably taken as a drink. Large doses
(,30 g per day) are well tolerated; however, they may be
detrimental to performance due to increased production of
ammonia by the exercising muscle.
BEE POLLEN
S Gurr
Bee pollen is a mixture collected by bees of pollen granules from
the stamens of flowers and flower nectar. It is commercially
available in granule, capsule or tablet preparations. These
contain a wide and varying array of nutrients, including
saccharides, amino acids, vitamins and minerals, as well as
possible contaminants.
Despite a long history in traditional medicine as a ‘‘superfood,’’ there is little evidence to support the range of health
claims for bee pollen. Interest in its ergogenic properties stems
from anecdotal reports and testimonies from successful
athletes.11 However, the few available studies from the 1970s
and 1980s involving athletes and bee pollen supplementation
(3–12-week protocols following manufacturers’ recommended
doses) have found minimal effects on: haemoglobin concentrations,12 strength and aerobic capacity,13 perceived exertion,14
time trial performance12 or repeated high-intensity exercise.14
One study13 did note fewer days lost to respiratory infections in
swimmers supplementing with bee pollen.
Allergic reactions including anaphylaxis have been reported in
people taking bee pollen supplements.15 The limited empirical
research suggests that bee pollen supplementation affords no
additional benefit to athletic performance beyond that provided
by a balanced diet.
BORON
N Mitchell
Boron, an element with the atomic number 5, is an essential
nutrient for plants, but the physiological role in humans is not
fully understood. Boron can be considered as an ultra trace
element16 therefore requirements are micrograms per day.
Dietary daily human intake is estimated to range from 2.1 to
4.3 mg of boron per kilogram body weight per day.
Boron enters the food chain via its incorporation into plant
structure and subsequent consumption by humans. There is
little evidence of boron deficiency in humans, however, oral
boron supplementation is used in the general health and sports
markets.
Boron has been linked to increased endogenous testosterone
levels, but there is little evidence in the literature using an
athletic population to support this. Research17 investigating
boron supplementation in postmenopausal women (after a
boron-restricted diet) focused on mineral, estrogen and testosterone metabolism. A supplementation of 3 mg of boron per
day was associated with an increase in testosterone levels. No
Br J Sports Med 2009;43:1088–1090. doi:10.1136/bjsm.2009.068643
proposed mechanism for increased testosterone was reported;
however, the authors suggested that maintenance of adequate
boron levels in postmenopausal women might prevent calcium
loss and bone demineralisation.
Few studies have investigated the effects of boron supplementation on increasing testosterone levels in an athletic population.
Fernando and Green18 used a randomised placebo-controlled
design including participants who regularly weight-trained for
at least 1 year (however, no data were reported describing the
trained status of the participants). The volunteers were given
either 2.5 mg/day of boron (n = 10) or placebo (n = 9) for a 7week period. The results suggested an increase in strength (based
on one repetition maximum, squat and bench press), increases in
lean tissue and testosterone in both groups. However, there was
no evidence that the boron supplementation had any additional
effect. Therefore, the changes could be regarded as only due to a
training effect.
A 10-month boron supplementation study in young female
athletes,19 versus sedentary women, produced a modest effect
on mineral status. This included a decrease in serum phosphorus
and increased urinary calcium excretion which was greater in
athletes than in controls.
There is currently little evidence to support the use of boron
supplementation in the athletic population.
L-CARNITINE
FB Stephens, PL Greenhaff
Ninety-five per cent of the body’s carnitine (3-hydroxy-4N,N,N-trimethylaminobutyric acid; C7H15NO3) store (,25 g)
exists within skeletal muscle where it plays a central role in fat
and carbohydrate oxidation, particularly during exercise (for a
review, see Stephens et al20). The recommended upper limit of
21
L-carnitine supplementation is 2 g/day, but no adverse effects
were reported following feeding up to 6 g/day for 1 year.21 22
The main food source of carnitine is meat. Non-vegetarians
ingest 1 mg/kg of dietary carnitine per day, whereas strict
vegetarians ingest around 0.01 mg/kg.23 Research has been
directed towards supplementing dietary L-carnitine to improve
exercise performance. However, neither oral (2–6 g/day for
1 day to 4 months) nor intravenous (up to 65 mg/kg)
L-carnitine administration per se has been found to alter fuel
metabolism during exercise or, more importantly, increase
muscle carnitine content in humans.20 22 24 Despite this,
L-carnitine feeding as a tool to promote apparent fat loss
remains the foundation of a multimillion dollar dietary
supplement industry in the present day.
More recently, intravenous infusion of L-carnitine along
with insulin (to stimulate Na+-dependent muscle carnitine
transport) has been found to increase muscle total carnitine
content by ,15% in healthy volunteers, and to have a
measurable effect on muscle fuel metabolism at rest.20 This
stimulatory effect on muscle carnitine accumulation occurred
in the physiological range for serum insulin concentration
(50–90 mU/l).20 Furthermore, feeding L-carnitine (3 g/d)
together with carbohydrate (500 ml solution containing 94 g
of simple sugars) for 2 weeks increased whole-body carnitine
retention compared with ingestion of L-carnitine alone.25
However, because orally administered L-carnitine has a poor
bioavailability (,15% for a 2–6 g dose), it is likely that this
supplementation regimen would take ,100 days to increase
muscle carnitine content by ,10%.25 Further research is
required to determine the impact that an insulin-mediated
increase in muscle carnitine content has on muscle fuel
metabolism and performance during exercise.
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Nutritional supplement series
CONCLUDING REMARKS
Although aspartame is not a supplement per se, its wide use
in many sports foods and drinks warrants inclusion in the
review series. Non-nutritive sweeteners have been around a
long time, with saccharin first being introduced back in 1878
and becoming a household name as a substitute for sugar
during the sugar restrictions of World War I and World War
II. Aspartame, discovered in 1965, is now the most common
sweetener, and is also probably the most researched and
evaluated food additive in the world. There has been much
scare-mongering about the safety of using sweeteners including aspartame, in particular the association with cancer risk,
which has actually been disproved regularly. We hope this
brief review of the ingredient makes an important contribution towards addressing the issue. There is no doubt that
taste is down to preference, and that it is individual choice
which dictates whether products are selected with or without
sweeteners.
Despite the popularity of bee pollen supplements, this review
demonstrates the lack of evidence for a performance benefit,
and with the added complication of potential allergic reactions,
it may be a supplement to steer clear of. With regard to boron,
there is a small amount of evidence to suggest its usefulness in
bone health. However, there is currently limited evidence to
support the need to consume boron supplements on top of a
healthy, well-chosen diet, either for bones or for sports
performance.
From the review summaries presented here, there appears
to be some evidence of potential benefits of consuming
BCAA, and future work with L-carnitine may also find some
useful outcomes. Nevertheless, it is pertinent to stress again
that any athlete considering using a supplement is strongly
recommended to obtain advice from a sports nutrition
professional first. In particular, any potential clinical issues
should be discussed. Furthermore, in relation to supplement
contamination issues, as discussed in the introductory review
in the September issue, it must be reiterated that any athlete
who competes under the World Anti-Doping Agency (http://
www.wada-ama.org) code needs to be extremely cautious
about using supplements. Athletes should always work with
a qualified professional to minimise the risk of supplement
use.
Competing interests: None.
Provenance and peer review: Commissioned; not externally peer reviewed.
1090
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