Proteins are composed of various combinations of amino acids, and all
dietary proteins are eventually converted into amino acids. The amino
acids, which number about 22, are classified as either essential or
nonessential. Essential amino acids are so-named because your body can’t
synthesize them and so it’s essential that you get them in your diet.
The balance of essential amino acids in any particular protein
determines its biological value. Since animal protein sources are higher
in essential amino acids and more closely duplicate the amino acid
pattern found in the human body, they’re considered superior to
plant-derived proteins, which often have either low or no amounts of
essential aminos.
Recent research proves that from the perspective of muscle protein
synthesis, essential aminos are extremely important. In fact, some
studies show that getting as little as six grams a day of an essential
amino acid mixture promotes muscle protein synthesis following
resistance exercise, such as weight training. But watch out: Information
on the importance of essential amino acids may lead you to conclude
that the so-called nonessential amino acids are not very important.
That would be incorrect. Some nonessential amino acids have been
reclassified as “conditionally” essential because under certain
circumstances, such as high-stress conditions, the body cannot
sufficiently synthesize them and their status changes from unessential
to essential.
Examples of conditionally essential amino acids include glutamine
and arginine. Normally, the body can synthesize them if you’ve taken in a
sufficient supply of essential aminos. Sometimes, however, that
synthesis can’t take place rapidly enough.
Glutamine and arginine are among the most popular amino acid
supplements with athletes and bodybuilders today. Research on glutamine
was originally derived from hospitalized patients, especially burn
patients, who lose vast amounts of protein as a result of their
injuries. Giving them glutamine reversed or halted the cascading
catabolic effects on muscle that can result in death. Thanks to the
anticatabolic effect, glutamine earned a place in the supplement regimen
of intensely training athletes. Later studies showed that it also
appeared to prevent the immune-suppression effects of extended
exercise—endurance events, for instance.
Arginine was initially promoted as a growth hormone releaser because
doctors gave it intravenously to patients to treat growth hormone
deficiency. Forms of arginine used for other purposes have also turned
up in various food supplements, notably those that increase nitric
oxide.
Many of the food supplements that contain glutamine and/or arginine
also contain another amino acid,
taurine—particularly creatine
supplements. That’s because creatine is thought to encourage the
cellular hydration that signals increased muscle protein synthesis.
Glutamine and taurine also appear to promote cellular hydration, which
makes them synergistic with creatine.
If taurine did nothing more than promote cellular hydration, it would
likely still be considered a useful supplement. But
taurine—conditionally essential like glutamine and arginine—is far more
essential to those engaged in exercise.
What Is Taurine?
Taurine was discovered in 1827 as a component of ox bile, which
explains its name; taurus is Latin for bull. Taurine is not incorporated
into muscle and other tissues of the body like other amino acids but
instead is found as a free, or unbound, amino acid or as part of short
chains of aminos known as peptides. The significance of taurine wasn’t
recognized until studies in the 1970s found that it was an essential
nutrient for cats. Without it, cats develop retinal degeneration leading
to blindness and serious heart problems, which explains why cat food
labels prominently display the taurine content.
Research on cats led some scientists to investigate whether taurine
had any use for human nutrition. Initial studies found that babies fed
on formula instead of mother’s milk often developed taurine deficiency,
since their bodies lacked the enzymes needed to synthesize it. Normally,
taurine is synthesized from two other amino acids—the essential
methionine and the nonessential cysteine—both of which contain sulfur.
In fact, some scientists suggest that taurine isn’t a true amino
acid, since it contains a sulfonic acid group; other aminos contain a
carboxylic acid group. Taurine is found abundantly in the body, in
brain, skeletal and heart muscle tissue. In muscle, it’s the second most
abundant free amino acid, behind glutamine. Taurine’s presence in
muscle suggests that it must be there for a reason.
The body can synthesize taurine from methionine and cysteine but not
without the presence of the activated form of vitamin B6, or pyridoxine.
So a lack of B6 in the diet can impair taurine synthesis. Controversy
exists about just how well the body is able to make taurine. The main
enzyme involved is not that active in either humans or cats. That’s why
some theories suggest that many people can benefit from taking
supplemental taurine.
The most recognized function of taurine is its role in the production
of bile salts. Bile, composed mainly of cholesterol, is a substance
manufactured in the liver and stored in the gallbladder. In fact, the
primary way the body rids itself of excess cholesterol is by shunting it into bile production. Bile itself promotes
the digestion of fat by reducing its surface area, which makes it more
digestible by lipases, or fat-digesting enzymes.
Even so, bile isn’t soluble enough to work unless it’s conjugated, or
combined with other substances. When that happens, bile becomes bile
salts, and the two main conjugating agents are the amino acids glycine
and taurine. So taurine helps create bile salts and lower blood
cholesterol, keeping it from floating through the bloodstream as
low-density lipoprotein (the bad kind of cholesterol). High levels of
LDL are a major risk factor for cardiovascular disease, especially
oxidized LDL. The less LDL in the blood, the less chance of
cardiovascular disease.
Taurine accelerates bile salt synthesis by boosting the genes
responsible for making an enzyme called 7-alpha hydroxylase. The
increased use of cholesterol for bile synthesis lowers blood levels of
cholesterol, which in turn opens up LDL receptors on cells, also
lowering cholesterol levels.
One study examined the effects of providing either three grams a day
of taurine or a placebo to 30 overweight college students for seven
weeks.1 Those in the taurine group had lower triglyceride levels in the
blood, along with a reduced atherogenic index, a measure of the ratio of
HDL cholesterol (the good kind) to triglycerides in the blood. Taurine
increases HDL production by boosting the activity of the protein carrier
of HDL, apolipoprotein A-1.
A beneficial side effect also occurred in the students who took the
taurine supplements:
They all lost bodyfat. Studies done with diabetic
rats show that taurine
prevents buildup of abdominal fat, which is
considered the most dangerous to health, being linked to insulin
resistance, heart disease and diabetes.
Taurine also functions as an antioxidant, which protects against such
diseases as cardiovascular disease and cancer. When certain immune
cells destroy invading organisms, they release a stream of free
radicals, which are unstable oxygen by-products that destroy the
invading organism’s cellular membrane, killing it. Free radicals can
also damage normal tissue. When the body has sufficient taurine,
however, the taurine soaks up the excess free radicals, rendering them
neutral.
Smoking damages arterial linings and leads to cardiovascular disease. A
2003 study, however, found that in smokers who took taurine, the
function of the lining, or endothelium, rapidly improved to the point
where it worked similarly to that of nonsmokers. That occurred after
only five days on a 1.5-gram dose of taurine, about the same amount
found in a 100-gram serving of fish.
Although omega-3 fats are considered the health-promoting component
in fish, its high taurine content also offers protective benefits that
are frequently overlooked. Some studies show that the taurine content of
fish helps lower blood pressure and reduce the negative effects of a
high salt intake.2 Stress also increases blood pressure by increasing
the release of such hormones as epinephrine and norepinephrine, which
constrict blood vessels. Taurine counteracts that effect, leading to
lower blood pressure. Interestingly, the populations with the lowest
rates of cardiovascular disease in the world, those of Japan and the
Mediterranean countries, also get the greatest amounts of taurine in
their diets.
Still another way that taurine protects the heart is by modulating
electrolyte function. Excess calcium can rapidly lead to cellular death,
but taurine prevents that. It also favorably affects the balance of
sodium and potassium in heart tissue, thus maintaining proper heart
function.
Highly refined sugars, such as
in high-fructose corn syrup, are thought to be responsible for the
rising epidemic of obesity, especially in younger people.While HFCS is chemically the same as sucrose, or table sugar, the fact that it is ubiquitous in so many processed foods leads to overconsumption.Eating excess
fructose causes sugar to be deposited into protein tissues, an effect
called glycation that’s considered a major cause of aging and the prime
cause of the stiffness and lack of mobility many people experience as
they get older.
In a recent experiment rats were put on a 60 percent fructose diet
but also got a 2 percent taurine solution for 30 days. That prevented
the formation of glycation end products while also enhancing the use of
glucose.3 Taurine worked with insulin to affect glucose, although it
worked independently of insulin in promoting glucose use. Some studies
show that taurine may help prevent some serious diabetic complications,
including neuropathy (nerve degeneration) and retinopathy (blindness).
Can Taurine Help Your Workouts?
Slow-twitch muscles have higher levels of taurine than fast-twitch
muscles. That’s likely because slow-twitch fibers have a greater
oxidative capacity, and taurine has antioxidative properties. Studies
show that the body loses the greatest amount of taurine after
intense anaerobic exercise, such as weight training.
Experiments done with rats demonstrate that taurine increases
exercise capacity, especially in older animals.4 Another study found
that taking taurine may help protect against exercise-induced muscle
injuries.5 The authors of that study observed that taurine supplementation reversed “certain types of functional deficits in skeletal muscle.
Our results suggest that taurine supplementation may facilitate exercise
performance and reduce some limited aspects of muscle injury caused by
exercise.”
A later study that used human subjects confirmed the protective
effects of taurine during exercise.6 Because of the increased oxygen
intake that occurs, exercise also ups the production of dangerous free
radicals, and rampant free-radical release can damage DNA in cells,
leading to mutations that may cause cancer and other diseases. In this
study, however, giving men supplemental taurine before exercise
significantly prevented DNA strand breakage, an effect attributed to
taurine’s antioxidative properties. In addition, the subjects who took
taurine also showed increased VO2-max, an indicator of increased
endurance, increased time to exercise exhaustion and increased maximal
workload. That effect could come from taurine’s role in increasing the
pumping power of the heart and improving the electrical and contractile
properties of skeletal muscle.
In muscle, taurine stabilizes cell membranes, including the
sarcolemma, the membrane that surrounds muscle fibers. By controlling
calcium entry into muscle, it promotes muscle contraction as well.
Taurine’s effect on electrolyte functions in muscle may also explain
why it helps prevent severe muscle cramps. One theory suggests that
exercise-induced loss of sodium and calcium may precipitate such cramps.
By stabilizing those minerals during exercise, taurine may help prevent
postworkout muscle cramps. The transport of taurine into muscle is
promoted by sodium and chloride and decreased by lactate and
beta-alanine.
A recent study found that taurine content in fast-twitch muscle
significantly decreased during extended exercise sessions and noted that
it enhances the enzymes in muscle that regulate energy production and
fat oxidation.7 Taurine also stimulates cyclic AMP, which leads to a
greater release of catecholamines, such as epinephrine and
norepinephrine. The latter two substances activate the enzyme
hormone-sensitive lipase in fat cells, which leads to the release of fat
for use as energy during exercise.
Words of Caution
For those considering supplementing taurine, several caveats are in
order. The precise optimal dose of taurine for increasing exercise
performance has been calculated—in rats.8 It’s between 100 and 500
milligrams per kilogram (2.2 pounds) of bodyweight. The dose depends on
body size and would be considerably lower in a human. Good food sources
of taurine include most animal protein foods, particularly fish. Oysters
are a superior source.
Those who use the drug clenbuterol should be aware that it causes a
rapid and severe depletion of taurine from muscle and heart tissue. That
could explain the heart damage and muscle cramps that can occur with
its use.9 Ephedrine and mahuang supplements also reduce taurine muscle
content.
The amino acid beta-alanine is now being added to various food
supplements because it’s the precursor of L-carnosine synthesis in the
body. Beta-alanine and taurine compete for the same uptake carrier into
the body, and beta-alanine can block taurine uptake by 50 percent or
more. Best to use the two amino acids at different times. While the beta alanine and taurine conflict is possible, it almost never occurs, since you would need to ingest relatively massive amounts of beta-alanine to cause this interference with taurine uptake.
Finally, be aware that taurine functions in the brain as an
inhibitory neurotransmitter—meaning that it has a depressant action on
brain function. So taking too much taurine in a single dose can lead to
feelings of fatigue and lack of energy. Smaller doses of taurine, less
than a gram, have a reverse effect: providing energy. That’s ostensibly
why taurine is a major ingredient of a popular energy drink that
includes the word bull in its name. But since the drink also contains
caffeine, the taurine addition could indeed represent a lot of bull.
Cats deficient in taurine can go blind
References
1 Zhang, M., et al. (2004). Beneficial effects of taurine on serum
lipids in overweight or obese non-diabetic subjects. Amino Acids.
26:267-71.
2 Nara, Y., et al. (1978). Effects of dietary taurine on blood
pressure in spontaneously hypertensive rats. Biochem Pharmacol.
27:2689-92.
3 Nandhini, A.T., et al. (2004). Stimulation of glucose utilization
and inhibition of protein glycation and AGE products by taurine. Acta
Physiol Scand. 181:297-303.
4 Pierno, S., et al. (1998). Chronic administration of taurine to
aged rats improves the electrical and contractile properties of skeletal
muscle. J Pharmacol Exp Therap. 286:1183-90.
5 Dawson R, et al. (2002). The cytoprotective role of taurine in exercise-induced muscle injury. Amino Acids. 22:309-24.
6 Zhang, M. et al. (2004). Role of taurine supplementation to prevent
exercise-induced oxidative stress in healthy young men. Amino Acids.
26:203-7.
7 Matsuzaki, Y., et al. (2002). Decreased taurine concentration in
skeletal muscles after exercise for various durations. Med Sci Sports
Exer. 34:793-97.
8 Miyazaki, T., et al. (2004). Optimal and effective oral dose of
taurine to prolong exercise performance in rat. Amino Acids. 27:291-98.
9 Doheny, M.H., et al. (1998). The effects of the beta-2 agonist drug
clenbuterol on taurine in heart and other tissues in the rat. Amino
Acids. 15:13-25.
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