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Research Articles
CLA (conjugated linoleic acid)
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Br J Nutr 2002 Sep;88(3):243-51 |
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The effect of dietary supplementation using
isomeric blends of conjugated linoleic acid on lipid metabolism in
healthy human subjects.
Noone EJ, Roche HM, Nugent AP, Gibney MJ.
Unit of Nutrition, Department of Clinical Medicine, Trinity Centre
for Health Sciences, St James's Hospital, Dublin, Republic of
Ireland. enoone@tcd.ie
Conjugated linoleic acid (CLA) refers to a group of positional and
geometric isomers of linoleic acid. Studies using animal models have
shown that CLA reduces adiposity, improves plasma lipoprotein
metabolism and insulin sensitivity and reduces arteriosclerosis.
Whilst CLA may have therapeutic potential with regard to coronary
artery disease risk factors in human subjects, there has been little
investigation into its effects in human subjects. This current study
investigated the effects of dietary supplementation using two
isomeric blends of CLA on triacylglycerol (TAG)-rich lipoprotein
metabolism and reverse cholesterol transport in human subjects and
evaluates whether CLA modulated cardiovascular disease risk factors.
Fifty-one normolipidaemic subjects participated in this randomised
double-blind placebo-controlled intervention trial. Subjects were
randomly assigned to receive 3 g cis-9,trans-11-trans-10,cis-12
isomeric blend (50 : 50) or a cis-9,trans-11-trans-10,cis-12
isomeric blend (80 : 20) CLA or linoleic acid (control)/d for 8
weeks. The 50 : 50 CLA isomer blend significantly reduced
(P<or=0.005) fasting plasma TAG concentrations. The 80 : 20 CLA
isomer blend significantly reduced (P<or=0.05) VLDL-cholesterol
concentrations. CLA supplementation had no significant effect on LDL-cholesterol,
HDL-lipid-protein composition or reverse cholesterol transport. CLA
supplementation had no effect on body weight, plasma glucose and
insulin concentrations. Fatty acid analysis revealed that the
cis-9,trans-11 CLA isomer was incorporated into total plasma lipids
following supplementation with both isomeric blends of CLA. The
present study demonstrates that CLA supplementation significantly
improves plasma TAG and VLDL metabolism in human subjects. The study
confirms that some of the cardio-protective effects of CLA that were
shown in animal studies are relevant to man.
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J Strength Cond Res 2002 Aug;16(3):325-34 |
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Effects of conjugated linoleic acid
supplementation during resistance training on body composition, bone
density, strength, and selected hematological markers.
Kreider RB, Ferreira MP,
Greenwood M, Wilson M, Almada AL.
Exercise and Sport Nutrition Laboratory, Department of Human
Movement Sciences and Education,
University of Memphis,
Tennessee 38152, USA. richard_kreider@baylor.edu
Conjugated linoleic acids (CLA) are essential fatty acids that have
been reported in animal studies to decrease catabolism, promote fat
loss, increase bone density, enhance immunity, and serve as an
antiatherogenic and anticarcinogenic agent. For this reason, CLA has
been marketed as a supplement to promote weight loss and general
health. CLA has also been heavily marketed to resistance-trained
athletes as a supplement that may help lessen catabolism, decrease
body fat, and promote greater gains in strength and muscle mass
during training. Although basic research is promising, few studies
have examined whether CLA supplementation during training enhances
training adaptations and/or affects markers of health. This study
evaluated whether CLA supplementation during resistance training
affects body composition, strength, and/or general markers of
catabolism and immunity. In a double-blind and randomized manner, 23
experienced, resistance-trained subjects were matched according to
body mass and training volume and randomly assigned to supplement
their diet with 9 g;pdd(-1) of an olive oil placebo or 6 g;pdd(-1)
of CLA with 3 g;pdd(-1) of fatty acids for 28 days. Prior to and
following supplementation, fasting blood samples, total body mass,
and dual-energy X-ray absorptiometry (DEXA) determined body
composition, and isotonic bench press and leg press 1 repetition
maximums (1RMs) were determined. Results revealed that although some
statistical trends were observed with moderate to large effect
sizes, CLA supplementation did not significantly affect (p > 0.05)
changes in total body mass, fat-free mass, fat mass, percent body
fat, bone mass, strength, serum substrates, or general markers of
catabolism and immunity during training. These findings indicate
that CLA does not appear to possess significant ergogenic value for
experienced resistance-trained athletes.
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J Nutr Biochem 2001 Oct;12(10):585-594 |
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Effect of supplementation with conjugated
linoleic acid on human serum lipids and body fat.
Mougios V, Matsakas A, Petridou A, Ring S, Sagredos A,
Melissopoulou A, Tsigilis N, Nikolaidis M.
Department of Physical Education and Sport Science, Aristotle
University of Thessaloniki,
Thessaloniki,
Greece
Conjugated linoleic acid (CLA) is a natural component of meat and
dairy products with anticarcinogenic, fat lowering, antiatherogenic
and anticatabolic activity in animals. The purpose of this study was
to examine the effect of CLA supplementation to humans on body fat,
certain biochemical parameters of serum, and the CLA content of
serum lipids. Twenty-two volunteers were divided into a study group
and a control group in a doubly blind design. The study group
received 0.7 g of CLA for four weeks and 1.4 g of CLA for the next
four weeks, while the control group received placebo. Diet was
controlled and no significant differences in energy or macronutrient
intake were found between the two groups. Measurements were taken at
baseline, four weeks, and eight weeks. The sum of the thickness of
ten skinfolds, percentage body fat calculated from it and fat mass
was significantly reduced in the CLA group during the second period
(P < 0.004) but not overall during the study. Serum HDL-cholesterol
decreased significantly (P < 0.001) and triacylglycerols as well as
total cholesterol tended to decrease in the CLA group during the
first period. The CLA content of serum non-esterified fatty acids,
triacylglycerols, phospholipids, and cholesteryl esters increased
gradually with supplementation; the CLA content of total serum
lipids doubled at the end of the study compared to baseline.
Phospholipids had the highest CLA content regardless of
supplementation. These data indicate that supplementation with
0.7-1.4 g CLA daily for 4-8 weeks may modulate body fat and serum
lipids, as well as increase the CLA content of serum lipids in
humans.
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Lipids 2001 Aug;36(8):773-81 |
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Conjugated linoleic acid supplementation in
humans--metabolic effects.
Smedman A, Vessby B.
Department of Public Health and Caring Sciences/Geriatrics,
Uppsala
University, Sweden. annika.smedman@pubcare.uu.se
Supplementation with conjugated linoleic acid (CLA) induces a number
of physiological effects in experimental animals, including reduced
body fat content, decreased aortic lipid deposition, and improved
serum lipid profile. Controlled trials on the effects of CLA in
humans have hitherto been scarce. The aim of this study was to
evaluate the effects of supplementation with CLA in healthy humans
on anthropometric and metabolic variables and on the fatty acid
composition of serum lipids and thrombocytes. Fifty-three healthy
men and women, aged 23-63 yr, were randomly assigned to
supplementation with CLA (4.2 g/d) or the same amount of olive oil
during 12 wk in a double-blind fashion. The proportion of body fat
decreased (-3.8%, P< 0.001) in the CLA-treated group, with a
significant difference from the control group (P = 0.050). Body
weight, body mass index, and sagittal abdominal diameter were
unchanged. There were no major differences between the groups in
serum lipoproteins, nonesterified fatty acids, plasma insulin, blood
glucose, or plasminogen activator inhibitor 1 (PAI-1). In the CLA
group the proportions of stearic, docosatetraenoic, and
docosapentaenoic acids increased in serum lipids and thrombocytes,
while proportions of palmitic, oleic, and dihomo-gamma-linolenic
acids decreased, causing a decrease of the estimated delta-6 and
delta-9 and an increase in the delta-5 desaturase activities. These
results suggest that supplementation with CLA may reduce the
proportion of body fat in humans and that CLA affects fatty acid
metabolism. No effects on body weight, serum lipids, glucose
metabolism, or PAI-1 were seen.
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Lipids 2001 Mar;36(3):229-36 |
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The effect of conjugated linoleic acid on plasma lipoproteins and
tissue fatty acid composition in humans.
Benito P, Nelson GJ, Kelley DS, Bartolini G, Schmidt PC, Simon V.
Western Human Nutrition Research Center, USDA, One Shields Ave.,
University of California, Davis, CA 95616, USA.
Conjugated linoleic acid (CLA) has been suggested by some animal
studies to possess antiatherogenic properties. To determine, in
humans, the effect of dietary CLA on blood lipids, lipoproteins, and
tissue fatty acid composition, we conducted a 93-d study with 17
healthy female volunteers at the Metabolic Research Unit of the
Western
Human Nutrition Research Center. Throughout the study, subjects were
fed a low-fat diet [30 energy percent (en%) fat, 19 en% protein, and
51 en% carbohydrate] that consisted of natural foods with the
recommended dietary allowances for all known nutrients. After a 30-d
stabilization period, subjects were randomly assigned to either an
intervention group (n = 10) supplemented daily with capsules
containing 3.9 g of CLA or a control group (n = 7) that received an
equivalent amount of sunflower oil. The CLA capsules (CLA 65%)
contained four major cis/trans geometric isomers (11.4% 9 cis-,11
trans-18:2; 10.8% 8 trans-,10 cis-18:2; 15.3% 11 cis-,13 trans-18:2;
and 14.7% 10 trans-,12 cis-18:2) and their corresponding cis/cis
(6.74% total) and trans/trans (5.99% total) varieties in smaller
amounts. Fasting blood was drawn on study days 30 (end of the
stabilization period), 60 (midpoint of the intervention period), and
93 (end of the intervention period). Adipose tissue samples were
taken on days 30 and 93. CLA supplementation for 63 d did not change
the levels of plasma cholesterol, low density lipoprotein
cholesterol, high density lipoprotein cholesterol, and triglycerides.
The weight percentage of CLA in plasma increased from 0.28 +/- 0.06
to 1.09 +/- 0.31 (n = 10, P < 0.05) after the supplementation. The 9
cis-,11 trans-isomer was the most prominent variety followed by the
11 cis-,13 trans- and 10 trans-,12 cis-isomers in lesser amounts.
CLA in adipose tissue was not influenced by the supplementation
(0.79 +/- 0.18 to 0.83 +/- 0.19 wt%) (n = 10) and the 9 cis-,11
trans-variety was the only isomer present. Thus, contrary to
findings from some animal studies, CLA does not seem to offer health
benefits, in the short term, regarding the prevention of
atherosclerosis in humans. CLA supplementation for 2 mon did not
alter the blood cholesterol or lipoprotein levels of healthy,
normolipidemic subjects. The supplementation did increase CLA in the
plasma but only 4.23% of the ingested CLA was present in the plasma
at any given time. No adverse effect of CLA supplementation was
detected in this study.
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Lipids 2000 Jul;35(7):783-8 |
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Conjugated linoleic acid supplementation in
humans: effects on circulating leptin concentrations and appetite.
Medina
EA, Horn WF, Keim NL, Havel PJ, Benito P, Kelley DS, Nelson GJ,
Erickson KL.
Department of Cell Biology and Human Anatomy, School of Medicine,
University of California, Davis 95616, USA.
Conjugated linoleic acid (CLA) has been demonstrated to reduce body
fat in animals. However, the mechanism by which this reduction
occurs is unknown. Leptin may mediate the effect of CLA to decrease
body fat. We assessed the effects of 64 d of CLA supplementation (3
g/d) on circulating leptin, insulin, glucose, and lactate
concentrations in healthy women. Appetite was assessed as a
physiological correlate of changes in circulating leptin levels.
Analysis of plasma leptin concentrations adjusted for adiposity by
using fat mass as a covariate showed that CLA supplementation
significantly decreased circulating leptin concentrations in the
absence of any changes of fat mass. Mean leptin levels decreased
over the first 7 wk and then returned to baseline levels over the
last 2 wk of the study in the CLA-treated group. Appetite parameters
measured at around the time when the greatest decreases in leptin
levels were observed showed no significant differences between
supplementation and baseline determinations in the CLA-supplemented
group or between the CLA and placebo-supplemented groups. There was
a nonsignificant trend for mean insulin levels to increase toward
the end of the supplementation period in CLA-treated subjects. CLA
did not affect plasma glucose and lactate over the treatment period.
Thus, 64 d of CLA supplementation in women produced a transient
decrease in leptin levels but did not alter appetite. CLA did not
affect these parameters in a manner that promoted decreases of
adiposity.
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