Conjugated Linoleic Acid (CLA) is a free fatty
acid that is naturally occurring in most dairy products as well
as a wide variety of meats. In fact, close to 60% of naturally
occurring CLA is found in dairy products, about 37% is found
in meats and the rest is found in processed foods (66). CLA was
first discovered by accident in 1978 by Michael Pariza at the
University of Wisconsin. Although it took several years for scientists
to begin looking at the free fatty acid, the first true studies
on CLA were performed in the mid 1980's specifically by Ha et
al (67). Most of the research and scientific studies on the effects
of CLA were done on animals for nearly ten years. As a result,
CLA proved to have many benefits on the tested animals such as:
improved body composition, enhanced immune function, reduction
of atherosclerosis, decrease in cancerous cells, improved food
and energy intake, anti-catabolic and anabolic effects as well
as many other positive attributes (68).
In two similar studies performed by Blankson et al (69) and Thome
et al (70), there is evidence that the use of CLA had a significant
reduction in body fat in human subjects although there was no
significant decrease in bodyweight. Although this stagnation
of bodyweight was not addressed to a thorough degree, the only
reasonable explanation for the reduction of body fat accompanied
with no decrease in bodyweight would be due to a gain of muscle
mass. One of the only disputes that other researchers have with
both of these studies is the fact that in both experiments, the
use of CLA was combined with a light to strenuous training regime
which may have accounted for some of the improved body composition.
In other words, both of these studies would suggest that the
use of CLA causes a decrease in body fat in obese humans and
in healthy exercising individuals currently partaking in an exercise
Another large area of study on CLA in humans deals with the obese
and overweight population. This may be due to the belief that
CLA can cause a considerable decrease in fat mass and in bodyweight.
In two very similar studies, the effects of CLA were observed
in the overweight population for 1 year (71) and for 2 years
(72). Both studies have almost identical findings. The main difference
in the two experiments is that the 2 year study not only examined
physical benefits achieved through the use of CLA but also examined
the safety, tolerance level, and long term effects of the individuals
who used the product. It appears as though CLA had a very significant
impact on subjects from both studies.
Subjects who participated in the 12 month study experienced a
6.9% - 8.7% reduction in body fat mass while participants of
the 24 month study experienced an average loss of >4.5% in
body fat mass. There were no negative side effects or adverse
effects experienced in either study which is of significant importance
due to the length of the study and the long term use of the supplement.
Participants of the 24 month study also had a decrease of plasma
total cholesterol and LDL cholesterol although, there was no
change in HDL. These findings help to support the claim that
CLA can have a positive effect on individuals with atherosclerosis
and other coronary issues. Further study is needed to determine
its effect on blood triglycerides in humans. It should be noted
that both of these studies only involved overweight and obese
individuals. So although it is quite clear from the literature
that CLA reduces body fat mass in this population, these two
studies do not satisfy claims made in regard to a decrease in
body fat mass in normal weight individuals and athletes.
Knowing that CLA can have a positive effect on health and body
composition in the overweight population is of great importance,
especially due to the rapid increase of obesity in society. However,
there has been far less research done on the normal-weight and
athletic population. Two studies of great relevance to this specific
issue were recently performed by Pinkoski et al (73) and Kreider
et al (74) and deal with the effects of CLA during resistance
In the study performed by Pinkoski et al (73), participants engaged
in a consistent three days per week intensive weightlifting routine.
Although there were numerous measurements taken of various markers
in this study, most of which had no significant change, the most
striking results can be seen by looking at the body composition
and anabolic/anti-catabolic effects associated with the experiment.
At the end of the study, there was a reported lean tissue mass
gain of 1.4 kg for the CLA group compared to the placebo group
which gained only .2 kg. Also, the CLA group had an average loss
of -.8 kg of fat mass compared to the placebo group of -.4 kg.
Although these findings seem quite small and almost insignificant,
it is of great importance to note that this study only lasted
for seven weeks. Many individuals who participate in vigorous
lifting workouts often see little to no results after only seven
weeks. Had the study gone on much longer, the results may have
been far greater. In other words, the CLA group gained close
to one half a pound of lean body mass per week while the placebo
group gained almost none.
There is valid reasoning that had this study gone on for a longer
duration, the results would have been even better, mainly due
to other markers of anti-catabolic effects found in this study.
The most noteworthy finding here showed that the urinary marker
of myofibrillar degradation which directly results in a decrease
in the catabolic effect of training on muscle protein and protein
synthesis was significantly improved in the CLA group. In simple
terms, this would create a more anabolic environment for the
body to build muscle while at the same time losing body fat.
This could be of significant importance to athletes or bodybuilders
looking to shed body fat while maintaining or even gaining muscle
mass. The last measurement in this study that had any change
in comparison with the placebo group and CLA group was the strength
measurements. Almost all strength measurements stayed the same,
except for a significant increase in bench press strength only
seen in the male subjects of the CLA group. Although there may
be several explanations for this occurrence, the details involved
with this increased neuromuscular change goes beyond the scope
of this paper.
The study performed by Kreider et al (74) is one of the other
few CLA experiments performed on experienced exercisers and fit
individuals while undergoing an exercise regime. There are some
very intriguing results obtained from this study. At first glance,
this study would appear to negate any benefits formerly thought
to be associated with the supplementation of CLA, especially
in the fit or athletic population. In fact, the actual results
from this study clearly indicate that there was no significant
change in body composition, strength gains, and muscle mass,
or bone density when comparing the CLA and placebo groups. However,
if one examines the study more closely, there are two very interesting
factors to consider in regards to CLA and this particular experiment.
First of all, when the hematological analysis was conducted,
it showed that although there were certain significant markers
that did not change, there were others that did. The most notable
was lessening in the ratio of blood urea nitrogen to creatinine.
The experimenters themselves noted that the analysis revealed
moderate to large effects for changes in the ratio of blood urea
nitrogen to creatinine. This finding may have significance since
it is an important marker and indicator for catabolism. In other
words, according to this study, this hematological marker may
imply that CLA causes a lessening of a catabolic response in
the body. It may also promote an anabolic state, thus, resulting
in a gain of lean body mass over time. However, the key here
may be time itself.
As previously mentioned, there were two factors in this study
that may have profound significance as to the implications of
CLA when used with fit or athletic population. The second one
deals with the length of the study. This study was only conducted
for 4 weeks. This brief time period is simply not long enough
to determine the effectiveness of CLA supplementation, especially
in the fit and athletic population. To say that there was no
change in body mass, strength, and muscle gains during the study
is somewhat deceiving. In fact, there are very few aids or exercise
programs themselves that produce changes and measurable benefits
after only 4 weeks. Had the study been prolonged for at least
another month or two, the findings may have indicated a direct
change in body composition and strength gains. In fact, the decrease
of blood urea nitrogen to creatinine as mentioned earlier may
produce measurable gains of lean body mass and strength if this
process were to take place for a longer period of time. In other
words, for physiological and biochemical shifts to have a significant
effect on the body, it may take much longer to occur than just
As with much research done on supplements and ergogenic aids,
a great deal of it is performed on animals. This is done to test
out a new product where negative side effects and possible harm
to humans is unknown as well as for issues of practicality. Simply
put, it is much easier to use fifty rats than it is to recruit
fifty human participants. In regards to CLA, there have now been
hundreds of studies conducted on animals such as rodents and
cows. Unlike most studies conducted on an individual product
or substance, the results for CLA usage on animals are very conclusive
and similar throughout. Quite simply, CLA has a positive effect
on lean body mass, fat mass, and other markers of health.
Rather than endlessly listing hundreds of similar studies performed
on animals fed with CLA, simply describing the results of several
prominent and more recent experiments should be sufficient. A
study performed by Bhattacharya et al (75) showed that CLA decreased
body weight and fat mass in mice while at the same time being
fed a high fat diet. Yet, another similar study conducted by
several of the same scientists, Bhattacharya et al (76) concluded
that mice fed with CLA decreased their fat mass, had an increase
in muscle mass, a decrease in serum leptin levels, and an increase
in energy expenditure. Quite simply both of these studies show
that CLA has a very positive effect on body composition, decreases
appetite as seen from serum leptin levels, and increases the
metabolism as seen from the increased energy expenditure. Again,
these results are in regards only to mice. These studies did
not involve human subjects.
Another very profound study performed on mice while being fed
CLA was conducted by Banu et al (77). This experiment not only
showed a decrease in body weight, but also showed an increase
in bone mass and bone density. This is of great significance
due to the fact that weight loss in general is often associated
with a decrease in bone mass and bone density. Another similar
study performed by Viswanadha et al (78), showed that CLA caused
mice to decrease their total fat mass while increasing their
total weight. Although not all physiological markers were measured,
the scientists concluded that this increase in weight was from
either an increase in muscle mass or bone mass, or perhaps both.
Summary and Recommendation
Although there is a significant amount of positive research
surrounding CLA, there is still great debate on how CLA affects
the physiology and biochemistry of the body to induce the above
mentioned results. Some researchers believe that it helps keep
the adipose tissues small by possibly blocking certain enzymes
that are responsible for the enlargement of fat cells. Some feel
it is directly involved in fat metabolism by helping the body
use its own fat cells as its primary source of fuel. Others believe
that CLA's most notable influence is the effect it may have on
corticosteroids. It is theorized that CLA may help counteract
corticosteroids such as cortisol which is responsible for muscle
breakdown and body fat storage. Hopefully, further research will
give greater insight not only into the effectiveness of CLA,
but also to the specific physiological and biochemical pathways
that are responsible for understanding how it works in the human
All in all, it appears as though CLA is a beneficial supplement
and has the potential to assist many individuals with their health
and fitness goals. Although it appears to be beneficial to most
populations, the studies support its greatest benefits in the
overweight and obese population. This is not to say that CLA
will not aid athletes and fit individuals in their goals for
lean body mass and strength, they simply will not have as great
of changes in their bodies as would a population of lower fitness
levels. They will, however, receive many of the same benefits,
just to lesser degree. Some of these known benefits that humans
can gain from supplementing with CLA include a decrease in fat
mass, increase in muscle mass, increase in strength, possible
increase in muscular and cardiovascular endurance, increased
bone mass and bone density, increased immune system function,
decrease in overall body weight, increased metabolism, and increase
in energy expenditure and metabolism (73).
Other possible benefits that have been witnessed in animals,
but have yet to be seen with human studies include a decrease
in total cholesterol as well as a decrease in LDL and an increase
in HDL, improved levels of blood glucose levels, and a decrease
in blood triglyceride levels . If these benefits were to eventually
be reported in human studies, then this would prove that CLA
not only helps with physical appearance and fitness levels but
it may also play a role in decreasing obesity, cancer, heart
disease, and diabetes (73). Time will tell whether or not the
same benefits produced in animal studies will have as significant
of an impact on humans. If it does, then CLA may be a huge key
to the future for health and fitness supplementation.
There appear to be no toxicity issues or related concerns
when CLA is taken by healthy populations. However, as reported
by consumerlab.com, there is some information suggesting that
CLA may worsen blood sugar control in diabetics and obese individuals
without diabetes. For those who are willing to give CLA a try,
it is important to utilize CLA correctly as well as consume the
best brand names in order to receive the full benefits of the
supplement. A safe and effective dosage would range anywhere
between 1500-3000mg per day depending on overall body size (71,
72, 73, 74). Dosages should be evenly spread out three times
a day and should be consumed with meals.
Some of the better and more reliable CLA brand name products
as reported by consumerlab.com include: AST Sports Science CLA,
Metagenics Ultra CLA, Natrol Tonalin CLA, Natural Max Ultra Supertone
CLA, Nature's Sunshine CLA, Nutrilite CLA, Ultimate Nutrition
Patented CLA, and Vitamin World CLA.
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