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Conjugated linoleic acid supplementation, insulin sensitivity, and lipoprotein metabolism in patients with type 2 diabetes mellitus1-3


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Some animal studies have suggested that conjugated linoleic acid (CLA) supplementation may have therapeutic potential with respect to insulin sensitivity and lipid metabolism, which are important cardiovascular disease (CVD) risk factors associated with type 2 diabetes mellitus. We investigated the effect of CLA supplementation on markers of glucose and insulin metabolism, lipoprotein metabolism, and inflammatory markers of CVD in subjects with type 2 diabetes. The study was a randomized, double-blind, placebo-controlled trial. Thirty-two subjects with stable, diet-controlled type 2 diabetes received CLA (3.0 g/d; 50:50 blend of cis-9,trans-11 CLA and trans-10,cis-12 CLA) or control for 8 wk. A 3-h 75-g oral-glucose-tolerance test was performed, and fasting plasma lipid concentrations and inflammatory markers were measured before and after the intervention. CLA supplementation significantly increased fasting glucose concentrations (6.3%; P < 0.05) and reduced insulin sensitivity as measured by homeostasis model assessment, oral glucose insulin sensitivity, and the insulin sensitivity index (composite) (P = 0.05). Total HDL-cholesterol concentrations increased by 8% (P < 0.05), which was due to a significant increase in HDL(2)-cholesterol concentrations (P < 0.05). The ratio of LDL to HDL cholesterol was significantly reduced (P < 0.01). CLA supplementation reduced fibrinogen concentrations (P < 0.01) but had no effect on the inflammatory markers of CVD (C-reactive protein and interleukin 6). CLA supplementation had an adverse effect on insulin and glucose metabolism. Whereas CLA had positive effects on HDL metabolism and fibrinogen, a therapeutic nutrient should not be associated with potentially adverse effects on other clinical markers of type 2 diabetes.
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Conjugated linoleic acid supplementation, insulin sensitivity, and
lipoprotein metabolism in patients with type 2 diabetes mellitus
Fiona Moloney, Toh-Peng Yeow, Anne Mullen, John J Nolan, and Helen M Roche
Background: Some animal studies have suggested that conjugated
with respect to insulin sensitivity and lipid metabolism, which are
type 2 diabetes mellitus.
Objective: We investigated the effect of CLA supplementation on
and inflammatory markersof CVD in subjects with type 2 diabetes.
Design: The study was a randomized, double-blind, placebo-
controlledtrial. Thirty-two subjects withstable, diet-controlled type
and trans-10,cis-12 CLA) or control for 8 wk. A 3-h 75-g oral-
glucose-tolerance test was performed, and fasting plasma lipid con-
centrations and inflammatory markers were measured before and
after the intervention.
Results: CLA supplementation significantly increased fasting glu-
coseconcentrations(6.3%;P 0.05) andreducedinsulinsensitivity
as measured by homeostasis model assessment, oral glucose insulin
sensitivity, and the insulin sensitivity index (composite) (P ҃ 0.05).
Total HDL-cholesterol concentrations increased by 8% (P 0.05),
which was due to a significant increase in HDL
-cholesterol con-
centrations (P 0.05). The ratio of LDL to HDL cholesterol was
significantly reduced (P 0.01). CLA supplementation reduced
fibrinogen concentrations (P 0.01) but had no effect on the in-
flammatory markers of CVD (C-reactive protein and interleukin 6).
Conclusions: CLA supplementation had an adverse effect on insu-
lin and glucose metabolism. Whereas CLA had positive effects on
HDL metabolism and fibrinogen, a therapeutic nutrient should not
beassociatedwithpotentially adverse effectsonotherclinicalmark-
ers of type 2 diabetes. Am J Clin Nutr 2004;80:887–95.
KEY WORDS Conjugated linoleic acid, diabetes, type 2 dia-
betes mellitus, humans, metabolic syndrome, cardiovascular dis-
ease, glucose, insulin sensitivity, lipoprotein metabolism, inflam-
In parallel with the global epidemic of type 2 diabetes are
significant health and socioeconomic burdens (1). Thus, there is
a need to identify effective dietary strategies to attenuate the
effect of type 2 diabetes, which is a heterogeneous disease char-
acterized by target-tissue insulin resistance that cannot be over-
come by
cell hypersecretion (2). The World Health Organiza-
tion (WHO) defined the clustering of metabolic abnormalities
associated with type 2 diabetes as the metabolic syndrome. Fea-
diabetes mellitus coupled with 2 metabolic derangements, in-
cluding obesity, insulin resistance, hypertension, dyslipidemia
(increasedplasmatriacylglyceroland low HDL-cholesterolcon-
centrations); and microalbuminuria (3). Low-grade inflamma-
tion, also a feature of type 2 diabetes (4), has been implicated in
the development of atherosclerosis (5). Cardiovascular disease
(CVD) is the leading cause of morbidity and mortality among
type 2 diabetes patients, as a result of the presence of several
primary risk factors for CVD in this patient population (6).
Although little can be done to avert a genetic predisposition to
through dietary and lifestyle factors is important. Conjugated
linoleic acid (CLA) has received attention as a potential thera-
peutic nutrient with respect to insulin resistance and hyperlipid-
emia (7), which are key characteristics of type 2 diabetes. The
term CLA refers to the positional and geometric isomers of lino-
leic acid with a conjugated double-bond system (8). Animal
feeding studies showed that CLA reduced body fat, increased
lean body mass (9–11), improved plasma lipid metabolism, and
inhibited the progression and promoted the regression of athero-
sclerosis (12–14). There are relatively few human intervention
studies, and the results of those few are mixed. Most of the
evidence regarding body composition suggests that CLA sup-
LDL cholesterol (16, 17) and conflicting effects regarding HDL
cholesterol (16, 18, 19) have been observed after CLA supple-
mentation in humans. A recent study indicated that trans-
10,cis-12 CLA (t10,c12 CLA) supplementation had negative
effects on insulin resistance and biomarkers of oxidative stress
and inflammation in obese men who had signs of the metabolic
combining cis-9,trans-11 (c9,t11) and t10,c12 CLA improved
plasma triacylglycerol concentrations and VLDL metabolism,
without adverse effects on insulin and glucose metabolism, in
From the Nutrigenomics Research Group, Department of Clinical Med-
icine, Trinity Centre for Health Sciences, Dublin (FM, AM, and HMR), and
the Metabolic Research Unit, St James’s Hospital, Dublin (T-PY and JJN).
Supported by the Wellcome Trust, United Kingdom.
Address reprint requests to HM Roche,Trinity Centre for Health Sci-
ences, St James’s Hospital, James’s Street, Dublin 8, Ireland. E-mail:
Received February 2, 2004.
Accepted for publication April 7, 2004.
887Am J Clin Nutr 2004;80:887–95. Printed in USA. © 2004 American Society for Clinical Nutrition
by guest on June 13, 2013ajcn.nutrition.orgDownloaded from
healthy subjects (17). These conflicting results may reflect dif-
ferences in study duration, cohort composition, study settings,
and, most important, supplement composition. CLA is a very
heterogenous compound, and distinct isomer-specific effects
and t10,c12 CLA, have contrasting metabolic and molecular
effects. Feeding c9,t11 CLA improved lipid and glucose metab-
and dylipidemia in ob/ob mice (7, 22).
The objective of the present study was to determine the effect
of CLA supplementation (providing equal proportions of c9,t11
and t10,c12 CLA) in patients with stable, diet-controlled type 2
diabetes. To date no study hasinvestigated the metabolic effects
ofCLAsupplementationinthesepatients.Several key aspectsof
the metabolic syndrome, including insulin and glucose metabo-
lism, lipoprotein metabolism, and markers of coagulation and
inflammation, were measured to ascertain the effect of CLA in
persons with diet-controlled type 2 diabetes.
This study was approved by the Joint Ethics Committee of St
JamessHospital and theFederated Dublin VoluntaryHospitals,
explained before written informed consent was obtained from
a2030% change in triacylglycerol concentrations, assuming a
type I error of 0.05 and a power of 0.9. Thirty-two subjects with
type 2 diabetes who attended the Diabetic Day Care Centre at St
diet therapy alone completed the trial. All subjects had stable
metabolic control with a glycatedhemoglobin (HbA
) concen
tration of 6.83 0.18 mmol/L and a mean fasting blood glucose
concentration of 7.33 0.24 mmol/L. No subjects were receiv-
ing pharmacologic treatment for glucose control or lipid-
lowering purposes. Hypertension was present in approximately
one-half of the subjects. However, only subjects whose blood
pressurewasunderstablecontrolparticipatedin the study.There
was no difference in the prevelance of hypertension between the
2 groups. In addition, there was no documentation of macrovas-
culardisease in the medical notes of any participant. All subjects
hadstablebodyweight.Allwerefollowing healthy eatingguide-
lines as recommended by the American Diabetes Association
(23). The study subjects did notconsume fatty acid supplements
or other dietary products known to affect metabolic markers of
type 2 diabetes.
Study design
This randomized, double-blinded, placebo-controlled study
was conducted on a free-living, outpatient basis. Subjects re-
ceived 3.0 g CLA/d (six 0.5-g capsules; a 50:50 isomer blend of
c9,t11 and t10,c12 CLA) or placebo (blend of palm oil and soya
bean oil) for 8 wk. The placebo was designed to contain a blend
of fatty acids that was representative of a habitual Western diet
by Loders Crooklann (Wormeveer, Netherlands). Each volun-
wk 4. A capsule count was completed midway and at the end of
the supplementary period. All participants were asked to main-
tain their usual dietary and lifestyle habits. The effect of changes
in diet, weight, and physical activity was explained to the sub-
jects. There was no change in prescribed medication (ie, antihy-
pertensives) throughout the trial.
Dietary assessment
Mean daily dietary intake was assessed by using two 4-d food
records, one completed immediately before the study and the
other completed at the end of the supplementation period (26).
Household measures, standard food portions, and a food atlas
was analyzed for macronutrient composition with the use of
NETWISP software (version 2.0; Tinuviel Software, War-
rington, United Kingdom), which was modified to include the
composition of frequently consumed foods that were not part of
the database. This additional information was obtained from the
nutrient information panel supplied by the manufacturers.
Clinical investigations
Subjects attended the Metabolic Unit, Department of Endo-
crinology, St Jamess Hospital, for blood sampling after a 12-h
overnight fast before and after intervention (weeks 0 and 8).
Subjects abstained from strenuous exercise and alcohol intake
for 24 h before the examination and refrained from smoking on
the morning of the examination. No medications (eg, antihyper-
tensives) were taken before the clinical investigations. On the
morningofeachinvestigation,afastingblood sample wasdrawn
andastandard 3-h,75-g oral-glucose-tolerance test(OGTT) was
performed. The 75 g anhydrous glucose equivalent (Polycal;
Nutricia Clinical, Trowbridge, United Kingdom) was consumed
in 300 mL water within 5 min. Blood samples were collected at
0, 30, 60, 90, 120, and 180 min for the measurement of plasma
glucose and serum insulin and C-peptide concentrations.
Biochemical analysis
Blood for measurement of cholesterol, triacylglycerol, LDL,
interleukin 6 (IL-6), insulin, and C-peptide concentrations was
collected in serum tubes (Becton Dickinson, Oxford, United
Kingdom). Blood for HDL and VLDL analysis was collected in
EDTA-coated evacuated tubes (Becton Dickinson). Samples for
glucose analysis were collected in tubes containing sodium flu-
oride, and blood for fibrinogen, C-reactive protein (CRP), and
Fatty acid composition of the conjugated linoleic acid (CLA) supplement
and the control supplement
Control CLA
% by wt of total fatty acids
Fatty acid composition (%)
16:0 38.52 4.82
18:0 4.70 2.28
18:1 34.84 10.17
18:2nҀ6 17.89 1.73
Saturated fatty acids 44.97 8.16
CLA isomers (%)
Total CLA 0.06 73.83
cis-9, trans-11 CLA 0.06 35.62
trans-10, cis-12 CLA ND 38.21
Supplements were given as free fatty acid. ND, not detectable.
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ton Dickinson). Serum samples were allowed to clot for 1 h.
Samples for lipid, glucose, insulin, C-peptide, and IL-6 analyses
were centrifuged immediately at 1400 ҂ g for 10 min at room
temperature. Citrated samples for CRP and fibrinogen measure-
mentswerecollectedandthencentrifugedat2000҂ gfor20min
atroomtemperature.Bloodsamplescollectedfor fatty acidanal-
ysis were centrifuged at 200 ҂ g for 20 min at room temperature
to harvest the platelet pellet and platelet-poor plasma. All of the
samples listed above were frozen immediately and stored at
Ҁ70 °C for subsequent analysis.
Plasma samples were analyzed for triacylglycerol and choles-
terol concentrations with the use of enzymatic colorimetric as-
says supplied by Instrumentation Laboratory (Warrington,
United Kingdom) on an IL Monarch centrifugal analyzer (In-
strumentation Laboratory) as previously described (28). Total
-, and HDL
-cholesterol concentrations were de
termined after precipitation with Immuno Quantolip total HDL
reagent (both: Immuno Ag, Vienna) as previously described
(17). LDL-cholesterol concentrations were measured after pre-
cipitation of LDL by using a Randox precipitation reagent (Ran-
dox, Antrim, United Kingdom) according to the manufacturers
instructions. VLDL was isolated according to published labora-
tory methods (17). VLDL, LDL, and HDL lipid compositions
were determined according to published methods (28). VLDL
apolipoprotein B (apoB) was measured by using a turbidimetric
assay (Instrumentation Laboratory) on the IL Monarch centrif-
ugal analyzer (29).
Plasma glucose concentrations were measured by using enzy-
matic determination based on the glucose oxidase principle
(BioMerieux, Marcy-lEtoile, France). Serum insulin and
C-peptide concentrations were measured by using solid-phase,
two-site fluoroimmunometric assays (AutoDELFIA Insulin kit
and AutoDELFIA C-Peptide kit, respectively; Wallac Oy,
Turku, Finland) on a 1235 AutoDELFIA automatic immunoas-
say system (Wallac Oy). Hb A
was assessed by using a fully
automated HPLC analyzer (Menarini-Arkray HA 8140; Arkray
KDK, Kyoto, Japan).
IL-6 and CRP assays were performed by using human high-
sensitivity immunoassay test kits (Biosource, Camarillo, CA,
and BioCheck Inc, Burlingame, CA, respectively) according to
each manufacturers instructions. Fibrinogen clotting activity
described (30).
For each marker, both preintervention and postintervention
and 3.15%, respectively. The interassay CV for fibrinogen was
3.25%. Insulin, C-peptide, Hb A
, glucose, and microalbumin
concentrations were analyzed in the laboratory of St Jamess
Hospital and were acceptable according to the routine internal
and external standards applied.
Fatty acid compositional analysis
Protocol compliance was verified by conducting a capsule
theuse ofgas liquid chromatography (GLC). Totalplasma lipids
were isolated by using the method of Folch et al (31), as previ-
ously described (17). Methyl esters of total plasma lipid were
prepared by adding 0.5 mL of 0.01 mmol NaOH/L in dry meth-
anol and then adding 0.5 mL boron trifluoride as described
previously (17). Total plasma lipid fatty acid composition was
determined by using Shimadzu GC-14A GLC (Mason Technol-
ogies, Dublin) fitted with a Shimadzu C-16A integrator (Mason
Technologies) and a CP Sil 88 fused silica column (50 m ҂
0.22 mm, 0.2
m file thickness; Chrompack Ltd, Middelburg,
Netherlands). Conditions for GLC analysis were as follows: N
was the carrier gas, and the column initial temperature (180 °C)
was increased (at a rate of 5 °C/min) to 195 °C, held for 40 min,
and then increased (by 2 °C/min) to 220 °C and held for 20 min.
Plasma fatty acids were identified according to their retention
times in comparison with a fatty acid methyl ester standard
(Sigma-Aldrich, Dublin) spiked with known concentrations of
transmethylated c9,t11 and t10,c12 CLA isomers (Cayman
Chemical, Ann Arbor, MI). Plasma fatty acid composition was
calculated as a percentage of total fatty acids.
Anthropometric measurements
Body weight was measured on an electronic balance (to the
nearest0.1 kg) with subjects wearing light clothing but no shoes.
Height was assessed by using a stadiometer that measured to the
nearest 0.1 cm. Waist girth was measured at the minimum cir-
measured at the maximum width over the greater trochanters.
Waist-to-hip ratio (WHR) was calculated from these measure-
ments (32). Bioelectric impedance analysis was measured in
subjects in the erect position by using a body fat analyzer (TBF-
300; Tanita Corporation, Arlington Heights, IL). Percentage
body fat was calculated by using the manufacturers pro-
grammed equations.
Data preparation and statistical analysis
All statistical analysis was conducted by using DATA DESK
are presented as mean ( SEM). When necessary, values were
transformed to give a normal Gaussian distribution. The post-
prandial data were expressed in summary formie, area under
the postprandial curve (AUC), incremental area under the post-
prandial curve (IAUC), maximum postprandial concentration
), and time to maximal postprandial concentration (T
These data were used to investigate postprandial variations be-
tween the supplement groups. AUC was calculated by using the
trapezium rule (33), and IAUC was calculated as the total incre-
mental AUC according to Le Floch (34). Homeostasis model
assessment (HOMA) was calculated as fasting glucose (mg/dL)
multiplied by fasting insulin (
U/mL) divided by 22.5 (35). Quan-
titative insulinsensitivity check index (QUICKI) was calculated as
)ѿ log(G
)], where I ҃ insulin and G ҃ glucose (36).The
by Matsuda et al (37). Oral glucose insulin sensitivity (OGIS) was
calculated by using the published formula (38).
line value of the outcome variable, was used to identify signifi-
cant changes in biochemical values after the supplementation
concentrations because baseline values differed between the
groups. Three-way analysis of variance (ANOVA) with subject,
treatment, and intervention as independent variables and a
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treatment-by-intervention interaction was used to identify sig-
nificant changes in plasma fatty acid composition. Repeated-
measures ANOVA with a treatment-by-time interaction was
used to investigate significant differences in postprandial re-
sponses between the study groups. Post hoc statistical analysis
was conducted by using Scheffes test. A P value 0.05 was
considered significant.
Subject characteristics and intervention details
Baseline characteristics of the 2 study groups are summarized
in Table 2. The mean age, weight, body mass index (BMI; in
),waist circumference, hip circumference, WHR, percent
age body fat, and duration of diabetes did not differ significantly
between groups. The anthropometric measurements did not
change after either the CLA or control supplements (data not
shown). Study compliance was assessed by a pill count, total
plasma fatty acid composition, and dietary assessment. The sub-
jects consumed 96.16% of the prescribed supplements. Compli-
ance did not differ significantly between the study groups:
CLA groups, respectively. The fatty acid compositions of total
plasma lipids are shown in Table 3. The c9,t11 CLA concentra-
tions increased by 89% after CLA supplementation (P 0.001).
The t10,c12 CLA isomer was undetectable in most samples and
was not affected by CLA supplementation. Linoleic acid (18:
2nҀ6) concentrations increased significantly in the CLA group
(P 0.01). Dietary analysis, based on two 4-d food records, one
completed before and the other completed after the intervention,
showed that mean daily energy, macronutrient, dietary fiber,
cholesterol, alcohol intake, and percentage contributions to total
or food energy did not differ significantly after CLA or placebo
supplementation (data not shown). In addition, mean daily nu-
trient intakes did not differ significantly between groups before
or after intervention (data not shown).
Insulin and glucose metabolism
The effect of CLA supplementation on a range of measures of
insulin sensitivity and glycemic control is shown in Table 4.
CLAsupplementation(P 0.05). HOMAwasalsosignificantly
higherafter CLAsupplementation thanafter controlsupplemen-
tation (P ҃ 0.05). Both OGIS and the ISI (composite) were
significantlylowerafterCLA supplementation thanaftercontrol
supplementation (P ҃ 0.05 and P 0.05, respectively). The
QUICKI measure of insulin sensitivity and the Hb A
and mi
croalbumin concentrations were not significantly altered by
CLA supplementation. The postprandial glucose, insulin, and
C-peptide concentrations in response to the OGTT are shown in
Figure1. Repeated-measures ANOVA showed that plasma glu-
cose, serum insulin, and C-peptide concentrations increased sig-
nificantly (P 0.001) during the OGTT. Both before and after
Baseline characteristics of the study population by treatment group
Control group
(n ҃ 16)
CLA group
(n ҃ 16)
Age (y) 58.1 2.7 63.8 2.2
Weight (kg) 88.2 3.8 84.37 3.1
BMI (kg/m
30.7 1.2 29.1 1.0
Waist circumference (cm) 101.1 2.6 102.7 2.5
Hip circumference (cm) 110.0 2.8 108.2 1.9
WHR 0.92 0.02 0.95 0.02
Percentage body fat (%) 33.2 2.3 32.9 2.5
Duration of diabetes (mo) 32.9 7.4 34.5 5.74
All values are x SEM. CLA, conjugated linoleic acid; WHR,waist-
to-hipratio. Therewere nosignificantdifferencesinbaselinevaluesbetween
the 2 groups (one-way ANOVA).
Fatty acid composition of total plasma lipids before and after conjugated linoleic acid (CLA) supplementation or placebo for 8 wk
Fatty acid
Control group
(n ҃ 16)
CLA group
(n ҃ 16)
Week 0 Week 8 Week 0 Week 8
% by wt of total fatty acids
16:0 24.80 0.55 25.52 0.58 25.75 0.57 26.3 0.50
16:1 2.16 0.22 1.79 0.13 2.17 0.22 2.24 0.19
18:0 9.96 0.40 10.97 0.55 10.3 0.40 10.78 0.40
18:1 18.58 0.85 17.66 0.80 18.46 0.88 19.66 0.96
18:2nҀ6 20.73 0.72 21.26 0.91 19.21 0.74 21.90 1.18
18:3nҀ6 0.26 0.02 0.23 0.01 0.20 0.02 0.24 0.01
18:3nҀ3 0.49 0.08 0.57 0.1 0.44 0.06 0.32 0.05
CLA 0.28 0.04 0.32 0.05 0.37 0.06 0.7 0.08
20:2 0.27 0.02 0.29 0.02 0.30 0.01 0.29 0.02
20:3nҀ6 2.52 0.15 2.59 0.24 2.31 0.25 2.30 0.14
20:4nҀ6 8.58 0.37 9.06 0.53 9.36 0.56 8.66 0.46
20:5nҀ3 1.30 0.16 1.24 0.24 1.67 0.32 1.18 0.14
22:4nҀ6 0.41 0.03 0.43 0.06 0.70 0.18 0.40 0.03
22:6nҀ3 2.94 0.25 2.47 0.23 3.15 0.29 3.16 0.26
All values are x SEM.
Significantly different from week 0, P 0.01 (three-way ANOVA).
Significant difference between groups after 8 wk of supplementation (treatment ҂ intervention interaction), P 0.001 (three-way ANOVA).
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the intervention, postprandial glucose concentrations were sig-
nificantly higher in the CLA group, whereas postprandial
C-peptideconcentrationsweresignificantly higher inthecontrol
group (P 0.01). Fasting glucose concentrations were signifi-
cantly higher after CLA supplementation than after control sup-
plementation (P 0.05). Postprandial glucose concentrations
neither supplement had a significant effect on fasting or post-
response after the OGTT were not significantly altered by CLA
or control supplementation (data not shown).
Lipoprotein metabolism
Fasting serum and lipoprotein lipid concentrations before and
after supplementation are shown in Table 5. There was no sig-
nificant effect of either CLA or control supplementation on total
or LDL-cholesterol concentrations. Total HDL-cholesterol con-
centrations were significantly increased after CLA supplemen-
tation (P 0.05). The 7.9% increase in total HDL-cholesterol
concentration was due to a significant increase in HDL
trations after CLA supplementation (P 0.05). LDL:HDL cho-
lesterol was significantly reduced after CLA supplementation
(P 0.01). Serum and VLDL triacylglycerol and VLDL-
cholesterol concentrations were not significantly altered by ei-
ther supplement. VLDL apoB concentrations were significantly
higherafter CLAsupplementation thanafter controlsupplemen-
tation (P 0.05). Triacylglycerol-poor lipoprotein triacylglyc-
by the CLA or placebo supplements (data not shown).
Markers of inflammation and coagulation
The effect of CLA and control supplementation on inflamma-
tion and coagulation was also determined. Plasma fibrinogen
concentrations were significantly lower after CLA supplemen-
tationthanaftercontrol supplementation (315.11 7.34,317.36
5.56, 310.15 5.84, and 294.30 5.87 mg/dL for control
week 0, control week 8, CLA week 0, and CLA week 8, respec-
tively)significantly more than did control supplementation (P
0.01). Serum IL-6 and plasma CRP concentrations were not
altered by CLA or control supplements (data not shown).
This study determined the effect of CLA supplementation on
several key CVD risk factors in a group of healthy subjects with
well-controlled type 2 diabetes that was treated by diet therapy
alone. In view of the increased risk of CVD associated with
diabetes, it is important to investigate the ability of nutritional
therapies to attenuate the effect of modifiable risk factors asso-
ciated with CVD in this high-risk patient group. Glucose toler-
ance and insulin sensitivity are central to type 2 diabetes, and
therefore an OGTT was performed, and a number of fasting and
postprandial indexes were investigated. CLA supplementation
had a negative effect on fasting glucose concentrations. HOMA
is a common measure of insulin resistance, derived from fasting
insulin and glucose concentrations. In our study, CLA supple-
mentation had an adverse effect on insulin resistance, increasing
HOMA by 19%. Postprandial plasma glucose concentration has
been cited as an independent risk factor for CVD in persons with
type 2 diabetes (39). Hepatic and peripheral insulin sensitivities
differ considerably within subjects, and a combination of fasting
andpostprandialmeasuresprovides a morecomprehensivemea-
sure of insulin sensitivity than does either measure alone (37).
Postprandial glucose and insulin concentrations did not increase
significantly after CLA supplementation, but the ISI (compos-
ite), which was derived from both fasting and postprandial mea-
sures, decreased significantly after CLA supplementation. In
addition, OGIS, which is also based on both fasting and post-
prandial data, was significantly reduced by CLA supplementa-
tion. It has been proposed that OGIS represents a better index of
insulin sensitivity because it has a more physiologic basis than
the empirical formulas have (38). Moreover, OGIS strongly cor-
relates with the hyperinsulinemic-euglycemic glucose clamp
measures of insulin sensitivity in diabetic subjects, whereas
HOMA and ISI (composite) do not (38).
This study investigated the effect of a CLA supplement that
provides equal proportions of the c9,t11 and t10,c12 CLA iso-
mers, the composition of which reflects most commercially
availableCLAsupplements. Itisinteresting thatthis supplement
did not adversely affect insulin and glucose metabolism in
healthy subjects (17). The present study confirms work that
showed that t10,c12 CLA supplementation had a negative effect
on insulin resistance in obese men with signs of the metabolic
Measurements of insulin sensitivity and glycemic control before and after conjugated linoleic acid (CLA) supplementation or placebo for 8 wk
Control group
(n ҃ 16)
CLA group
(n ҃ 16)
Week 0 Week 8 Week 0 Week 8
Fasting glucose (mmol/L) 7.33 0.40 7.09 0.35 7.34 0.27 7.8 0.28
Fasting insulin (pmol/L) 54.94 5.10 50.68 7.60 52.13 7.90 57.87 8.86
HOMA 3.00 0.35 2.59 0.42 2.81 0.42 3.35 0.54
QUICKI 0.33 0.005 0.36 0.025 0.34 0.007 0.33 0.007
ISI (composite) 3.98 0.40 6.26 1.89 4.58 0.64 4.11 0.54
OGIS 353.63 19.0 362.40 16.41 341.08 15.89 329.84 16.38
Hb A
6.73 0.12 6.59 0.18 6.93 0.33 6.63 0.16
Microalbumin 3.22 0.77 3.32 0.72 1.61 0.31 1.49 0.21
All values are x SEM. HOMA, homeostasis model assessment; QUICKI, quantitative insulin sensitivity check index; ISI (composite), insulin
sensitivity index (composite); OGIS, oral glucose insulin sensitivity; Hb A
, hemoglobin A
Significant difference between groups after 8 wk of supplementation (analysis of covariance):
P 0.05,
P ҃ 0.05.
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FIGURE1.Mean( SEM) plasmaglucose,serum insulin,and C-peptideconcentrationsin responseto theadministrationof 75g anhydrousglucosebefore
and after conjugated linoleic acid (CLA) supplementation (3 g/d) or placebo for 8 wk in the control group (week 0, ; week 8, ) and the CLA group (week
0, F; week 8, ). By repeated-measures ANOVA, there was a significant time effect for glucose, insulin, and C-peptide (P 0.001) and a treatment-by-time
effect for plasma glucose and serum C-peptide (P 0.01). Fasting plasma glucose concentrations were significantly higher after CLA supplementation, P
0.05 (analysis of covariance).
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syndrome (20). The discrepancy between studies reflects the
Our group found that feeding a t10,c12 CLArich diet induced a
profound prodiabetic effect, whereas feeding the c9,t11 CLA
isomerimproved lipid and glucose metabolism in ob/ob mice (7,
22). Other groups have shown that feeding a blend of CLA
isomers induced marked lipodystrophic insulin resistance and
glucose intolerance in the C57BL/6J mouse model of diabetes
(40). In contrast, another group showed that feeding a 50:50
blend of c9,t11 and t10,c12 CLA reduced glucose and insulin
concentrations in male ZDF rats (41, 42). Clearly the effect of
CLA supplementation is isomer-specific and dependent on the
diabetic risk of the experimental model. In the case of subjects
with type 2 diabetes, a CLA blend containing equal quantities of
c9,t11 and t10,c12 CLA does not improve insulin and glucose
CLA supplementation had a positive effect on HDL-
cholesterolconcentrationsinthis study. Ithasbeen reported that,
for each increase of 0.03 mmol/L in HDL-cholesterol concen-
tration, there is a 23% reduction in coronary heart disease
(CHD) risk (43). Thus, the increase in HDL cholesterol after
CLA supplementation could represent a 7.311% reduction in
promote reverse cholesterol transport (RCT; 44). Because RCT
is impaired in persons with type 2 diabetes (45), the potential
ability of CLA to restore RCT would be favorable.CLA supple-
mentation reduced LDL-cholesterol concentrations (8.8%), al-
beit not significantly, but that reduction contributed to a greater
reduction (14.5%) in LDL:HDL cholesterol. The Helsinki Heart
Study showed that LDL:HDL cholesterol was the single best
predictor of cardiac events (46). Therefore, the effect of CLA
supplementation on LDL:HDL cholesterol in type 2 diabetes
may be of clinical benefit.
The lack of effect on CLA on triacylglycerol metabolism con-
trasts with our previous findings (17). It is possible that this
triacylglycerol metabolism, an effect that may be linked to the
adverse effects of CLA on glucose and insulin metabolism.
VLDL apoB concentrations increased after CLA supplementa-
concentrations after CLA supplementation. Increased intrahe-
patic lipid substrate (triacylglycerol and cholesterol) delivery is
a critical factor regulating hepatic VLDL apoB secretion. How-
ever, neither triacylglycerol nor cholesterol concentrations were
significantly altered after CLA supplementation. Increased
VLDL apoB concentrations are associated with insulin resis-
in this study may be related to increased insulin resistance.
Elevated plasma concentrations of fibrinogen, CRP, and IL-6
are associated with increased risk of CHD and the severity of
atherosclerosis (49). Both low-grade inflammation (4) and a
prothrombotic risk profile have been reported in persons with
type 2 diabetes (50). CLA supplementation reduced plasma fi-
brinogen concentrations, which have a key role in coagulation
(51). CRP concentrations showed a nonsignificant reduction
CLA supplementation had no effect on markers of blood coag-
ulation and platelet function in a small group of healthy women
who were given a CLA supplement containing a mixture of 10
CLA isomers for 63 d (18). This isomeric blend is in contrast to
our supplement. CRP concentrations were significantly in-
creasedin obese men with signs of the metabolic syndrome (21).
The latter result may reflect the isomer-specific effect of t10,c12
CLA.CRP stimulates tissue factor production,which isthe main
stimulus for initiating coagulation (49). Therefore, reduced
plasma fibrinogen and CRP concentrations indicate that CLA
may attenuate thrombosis.
Baseline plasma concentrations of c9,t11 CLA and the per-
centage increase after CLA supplementation are comparable to
those in previous supplementation studies (17, 52, 53). In con-
trast, there were negligible concentrations of t10,c12 CLA in
baseline samples, and they did not increase after CLA supple-
mentation, despite the fact that the supplement providedt10,c12
CLA. The difficulty in detecting the t10,c12 CLA isomer has
been documented previously (17). Two hypotheses for this ob-
servation have been suggested. First, the t10,c12 CLA may be
Mean fasting plasma and lipoprotein cholesterol and triacylglycerol concentrations before and after conjugated linoleic acid (CLA) supplementation or
placebo for 8 wk
Control group
(n ҃ 16)
CLA group
(n ҃ 16)
Week 0 Week 8 Week 0 Week 8
Plasma Cholesterol (mmol/L) 4.73 0.26 4.78 0.23 5.16 0.17
5.06 0.14
Cholesterol (mmol/L)
LDL 3.10 0.22 3.18 0.20 3.63 0.18 3.31 0.19
Total HDL 1.50 0.10 1.54 0.08 1.44 0.07 1.55 0.08
0.23 0.03 0.25 0.03 0.23 0.04 0.34 0.05
1.26 0.08 1.29 0.07 1.21 0.05 1.21 0.05
0.20 0.03 0.21 0.03 0.19 0.03 0.28 0.05
LDL:HDL 2.15 0.17 2.13 0.16 2.63 0.21 2.26 0.21
Plasma triacylglycerol (mmol/L) 1.60 0.16 1.51 0.18 1.62 0.12 1.64 0.13
VLDL triacylglycerol (mmol/L) 0.66 0.08 0.56 0.07 0.76 0.09 0.78 0.7
VLDL cholesterol (mmol/L) 0.28 0.05 0.24 0.03 0.30 0.04 0.33 0.04
VLDL apolipoprotein B (
g/mL) 43.91 6.36 39.93 5.0 42.03 3.57 49.09 4.64
All values are x SEM. VLDL, very-low-density lipoprotein.
Significant difference within group after 8-wk supplementation (three-way ANOVA):
P 0.05,
P 0.01.
Significant difference between groups after 8 wk of supplementation, P 0.05 (analysis of covariance).
by guest on June 13, 2013ajcn.nutrition.orgDownloaded from
more easily oxidized because of its structure, and this would
allow it to bypass a number of rate-limiting steps in the peroxi-
-oxidation pathway (54). Alternatively, Sebedio et al
(55) showed that the t10,c12 CLA isomer is metabolized into
20:4 5,8,12,14 and 20:3 8,12,14 via desaturation and elon-
gation pathways. Consequently, t10,c12 CLA is not efficiently
incorporated into plasma lipids.
In conclusion, CLA supplementation did not have a positive
effecton insulin andglucose concentrations in persons with type
2 diabetes. Whereas we did show positive effects of CLA on
HDL-cholesterol and fibrinogen concentrations, the relative im-
portance of one CVD risk factor over another is unknown. Com-
in total plasma lipid fraction, which was comparable with pre-
viously reported data (17, 52). Any truly effective dietary strat-
egywouldimproveCVD risk factorswithoutany negative effect
on other components of the metabolic syndrome.
We are indebted to the study participants for their enthusiasm and com-
FMprepared themanuscriptand conductedmostoftheexperiments. TPY
conducted the clinicalinvestigations.AMassistedin the experimental work.
JJNwas involvedin theformulation ofthescientifichypothesisforthisstudy
and provided significant advice. HMR formulated the scientific hypothesis
and experimental design and prepared the manuscript. None of the authors
have any commercial interest in CLA, and noneof the authors hadany other
conflict of interest.
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... Men with abdominal obesity who received treatment with trans-10cis12 conjugated linoleic acid saw a decrease in high density lipoprotein cholesterol but not in body weight (RISerus et al., 2002). Although the treatment group decreased fibrinogen concentrations, there were negative effects on insulin and glucose metabolism, according to a different study of a conjugated linoleic acid intervention in T2DM patients (Moloney et al., 2004). ...
... Unfortunately, the natural products now reported in the literature are largely weak PPAR agonists, with small sample sizes a combined with species and gender differences. Also, there are clinical trials indicating adverse effects of natural products (Moloney et al., 2004). At present, the mechanisms of natural PPAR agonists have not been thoroughly investigated and their metabolites and their possible use as dietary supplements will require further study in the future. ...
Background: Peroxisome proliferator-activated receptors (PPARs) are a class of ligand-activated nuclear transcription factors, members of the type nuclear receptor superfamily, with three subtypes, namely PPARα, PPARβ/δ, and PPARγ, which play a key role in the metabolic syndrome. In the past decades, a large number of studies have shown that natural products can act by regulating metabolic pathways mediated by PPARs. Purpose: This work summarizes the physiological importance and clinical significance of PPARs and reviews the experimental evidence that natural products mediate metabolic syndrome via PPARs. Methods: This study reviews relevant literature on clinical trials, epidemiology, animals, and cell cultures published in NCBI PubMed, Scopus, Web of Science, Google Scholar, and other databases from 2001 to October 2022. Search keywords were "natural product" OR "botanical" OR "phytochemical" AND "PPAR" as well as free text words. Results: The modulatory involvement of PPARs in the metabolic syndrome has been supported by prior research. It has been observed that many natural products can treat metabolic syndrome by altering PPARs. The majority of currently described natural compounds are mild PPAR-selective agonists with therapeutic effects that are equivalent to synthetic medicines but less harmful adverse effects. Conclusion: PPAR agonists can be combined with natural products to treat and prevent metabolic syndrome. Further human investigations are required because it is unknown how natural products cause harm and how they might have negative impacts.
... Importantly, conjugated linoleic acid supplementation adversely affects insulin and glucose metabolism in T2DM patients. 36 The study supports our metabolomics data and suggests linoleic acid as an indicator of IR development. ...
High-fat-diet (HFD)-induced obesity is associated with an elevated risk of insulin resistance (IR), which may precede the onset of type 2 diabetes mellitus and associated metabolic complications. Being a heterogeneous metabolic condition, it is pertinent to understand the metabolites and metabolic pathways that are altered during the development and progression of IR toward T2DM. Serum samples were collected from C57BL/6J mice fed with HFD or chow diet (CD) for 16 weeks. Collected samples were analyzed by gas chromatography-tandem mass spectrometry (GC-MS/MS). Data on the identified raw metabolites were evaluated using a combination of univariate and multivariate statistical methods. Mice fed with HFD had glucose and insulin intolerance associated with impairment of insulin signaling in key metabolic tissues. From the GC-MS/MS analysis of serum samples, a total of 75 common annotated metabolites were identified between HFD- and CD-fed mice. In the t-test, 22 significantly altered metabolites were identified. Out of these, 16 metabolites were up-accumulated, whereas 6 metabolites were down-accumulated. Pathway analysis identified 4 significantly altered metabolic pathways. In particular, primary bile acid biosynthesis and linoleic acid metabolism were upregulated, whereas the TCA cycle and pentose and glucuronate interconversion were downregulated in HFD-fed mice in comparison to CD-fed mice. These results show the distinct metabolic profiles associated with the onset of IR that could provide promising metabolic biomarkers for diagnostic and clinical applications.
... However, CLA has been shown to exhibit some adverse effects [112], including reduction in insulin sensitivity in subjects with type 2 diabetes [113] and augmentation of the pre-existing insulin resistance [114,115]. Additionally, longterm studies in rodents have demonstrated a lipodystrophic effect of CLA [116] that is associated with decreased plasma adiponectin and leptin levels and increased insulin resistance [117]. ...
... GO enrichment analysis of these modules showed that the metabolomic profiles were implicated in Sphingolipid signaling pathway, Glycerophospholipid metabolism, Choline metabolism in cancer, Linoleic acid metabolism, Fatty acid degradation, Primary bile acid biosynthesis, Nicotinate and nicotinamide metabolism, and Glycine in both TAMG (+) and TAMG (−). Extensive studies have shown that linoleic acid supplementation might have therapeutic potential concerning insulin sensitivity and lipid metabolism [22]. Furthermore, linoleic acid is an efficient mediator in constraining the progression of hyperinsulinemia [23]. ...
Full-text available
Background: Thymoma-associated myasthenia gravis (TAMG) is a well-described subtype of Myasthenia gravis (MG). Nevertheless, the detailed proteins and bioprocess differentiating TAMG from TAMG (-) thymoma have remained unclear. Methods: The proteomics and metabolomics were carried out on serum samples from thymoma group (n = 60, TNMG), TAMG (+) thymoma group (n = 70, TAMG (+)), and TAMG (-) thymomas group (n = 62, TAMG (-)), and controls (n = 159). groups. Proteomics and metabolomics analyses, including weighted gene co-expression network analysis (WGCNA), was conducted to detect the hub proteins and metabolomics processes that could differentiate TAMG (+) from TAMG (-) thymomas. MetaboAnalyst was used to examine the integration of proteomic and metabolomic analysis to differentiate TAMG (+) from TAMG (-) thymomas. Results: The of module-trait correlation of WGCNA analysis identified KRT1, GSN, COL6A1, KRT10, FOLR2, KRT9, KRT2, TPI1, ARF3, LYZ, ADIPOQ, SEMA4B, IGKV1-27, MASP2, IGF2R was associated with TAMG (+) thymomas. In addition, organismal systems-immune system and metabolism-biosynthesis of other secondary metabolites were closely related to the mechanism of TAMG (+) pathogenesis. Conclusion: Our integrated proteomics and metabolomics analysis supply a systems-level view of proteome changes in TAMG (+), TAMG (-) thymomas and exposes disease-associated protein network alterations involved in.
... The content of c9,t11-CLA in suckling lamb meat is in line with those reported in other studies on suckling [26] and weaned lambs [38]. Clinical and animal studies have suggested anti-inflammatory and immunomodulatory antiatherogenic activities of c9,t11-CLA [57][58][59], as well as lowering cholesterol [60][61][62] and hyperinsulinemia prevention [63,64] effects. The anticarcinogenic effect of c9,t11-CLA has been widely observed in several studies on cell cancer lines and laboratory animals [58], but these results need to be confirmed in humans. ...
Full-text available
The effects of the dams and suckling lamb feeding systems on the fatty acid (FA) profile of lamb meat are reviewed in this article. The suckling lamb can be considered a functional monogastric, and therefore, its meat FA composition is strongly influenced by the FA composition of maternal milk. The major source of variation for ewe milk FA composition is represented by pasture amount and type. In the traditional sheep breeding system of the Mediterranean area, the main lambing period occurs in late autumn–early winter, and ewes are able to exploit the seasonal availability of the natural pastures at their best. Therefore, lambs start suckling when maternal milk concentrations of vaccenic, rumenic, and n-3 long-chain polyunsaturated FA in maternal milk are the highest. When maternal diet is mainly based on hay and concentrates, the use of vegetable oils can be considered a good strategy to improve the meat FA profile of suckling lambs.
Conjugated linoleic acid (CLA) is a collective term for the octadecadienoic acid isomers containing conjugated double bonds. This article reviewed CLA isomers from biological activities, biosynthesis mechanisms and analytical methods. The biological activities of CLA isomers in anti-obesity, cardiovascular protection, diabetes management and anti-cancer in vitro and in vivo were mainly reviewed. More attention has been paid to the production of the specific CLA isomer due to its biological activity. The biosynthesis methods of CLA isomers, such as dietary modification in ruminants and fermentation by microorganisms & enzymes, were systematically introduced. A rapid, accurate and economic analysis method will promote the research in both biological activities and biosynthesis mechanisms of CLA isomers. The merits of UV spectrometry, GC, HPLC, MS and CE used in the analysis of CLA isomers were also compared in detail. This paper aims to put into perspective the current status and future trends on CLA isomers.
Full-text available
Background The findings of trials investigating the effect of conjugated linoleic acid (CLA) administration on lipid profile are controversial. This meta-analysis of randomized controlled trials (RCTs) was performed to explore the effects of CLA supplementation on lipid profile. Methods Two authors independently searched electronic databases including PubMed, Web of Science, and Scopus until March 2022, in order to find relevant RCTs. The random effects model was used to evaluate the mean and standard deviation. Results In total, 56 RCTs with 73 effect sizes met the inclusion criteria and were eligible for the meta-analysis. CLA supplementation significantly alter triglycerides (TG) (WMD: 1.76; 95% CI: −1.65, 5.19), total cholesterols (TC) (WMD: 0.86; 95% CI: −0.42, 2.26), low-density lipoprotein cholesterols (LDL-C) (WMD: 0.49; 95% CI: −0.75, 2.74), apolipoprotein A (WMD: −3.15; 95% CI: −16.12, 9.81), and apolipoprotein B (WMD: −0.73; 95% CI: −9.87, 8.41) concentrations. However, CLA supplementation significantly increased the density lipoprotein cholesterol (HDL-C) (WMD: −0.40; 95% CI: −0.72, −0.07) concentrations. Conclusion CLA supplementation significantly improved HDL-C concentrations, however, increased concentrations of TG, TC, LDL-C, apolipoprotein A, and apolipoprotein B.
Diabetes is a metabolic disorder in which lack of insulin production or disturbances in the utilization of insulin lead to high concentrations of glucose in the blood and urine. In recent years, diabetes has reached almost epidemic proportions, possibly because of the changes in human lifestyle, which include dietary habits and a more sedentary form of living. Scientists are taking a closer look at both plants and animals, including marine entities, as sources of compounds for more efficacious and safer antidiabetic drugs at a cheaper cost. A number of promising leads have emerged and are covered in this chapter. The chapter also discusses two important factors that are now recognized in the pathophysiology of diabetes and diabetes-induced loss of vision, kidney function, and dementia, namely oxidative stress and gut dysbiosis. It is possible that a fresh approach towards diabetes in the breaking of the diabetes-oxidative stress/dysbiosis-diabetes cycle with the aid of better glucose-lowering drugs, antioxidants, and probiotic symbionts may enable us to finally conquer this dread disease.
This systematic review and meta-analysis assessed the antidiabetic effect of pharmaconutrients as an add-on in type 2 diabetes mellitus patients by pooling data from currently available randomized controlled trials (RCTs). Data sources included the PubMed and EMBASE, Cochrane Central Register of Controlled Trials. RCTs reporting changes in glycosylated hemoglobin (HbA1c), fasting blood glucose (FBG), or homeostasis model assessment of insulin resistance (HOMA-IR) levels following add-on pharmaconutritional therapies for T2DM patients consuming antidiabetic drugs were targeted. Using random-effects meta-analyses, we identified pharmaconutrients with effects on glycemic outcomes. Heterogeneity among studies was presented using I2 values. Among 9537 articles, 119 RCTs with nine pharmaconutrients (chromium; coenzyme Q10; omega-3 fatty acids; vitamins C, D, and E; alpha-lipoic acid; selenium; and zinc) were included. Chromium (HbA1c, FBG, and HOMA-IR), coenzyme Q10 (HbA1c and FBG), vitamin C (HbA1c and FBG), and vitamin E (HbA1c and HOMA-IR) significantly improved glycemic control. Baseline HbA1c level and study duration influenced the effects of chromium and vitamin E on HbA1c level. Sensitivity analyses did not modify the pooled effects of pharmaconutrients on glycemic control. Administration of chromium, coenzyme Q10, and vitamins C and E for T2DM significantly improved glycemic control. This study has been registered in PROSPERO (CRD42018115229).
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Conjugated linoleic acid (CLA) is a heterogeneous group of positional and geometric isomers of linoleic acid. This study demonstrates the divergent effects of the cis-9 trans-11 (c9,t11-CLA) and trans-10 cis-12 (t10,c12-CLA) isomers of CLA on lipid metabolism and nutrient regulation of gene expression in ob/ob mice. The c9, t11-CLA diet decreased serum triacylglycerol (P = 0.01) and nonesterified fatty acid (NEFA) (P = 0.05) concentrations, and this was associated with reduced hepatic sterol regulatory element-binding protein-1c (SREBP-1c; P = 0.0045) mRNA expression, coupled with reduced levels of both the membrane-bound precursor and the nuclear forms of the SREBP-1 protein. C9,t11-CLA significantly reduced hepatic LXRalpha (P = 0.019) mRNA expression, a novel regulator of SREBP-1c. In contrast, c9,t11-CLA increased adipose tissue SREBP-1c mRNA expression (P = 0.0162) proportionally to the degree of reduction of tumor necrosis factor alpha (TNF-alpha) mRNA (P = 0.012). Recombinant TNF-alpha almost completely abolished adipose tissue SREBP-1c mRNA expression in vivo. The t10,c12-CLA diet promoted insulin resistance and increased serum glucose (P = 0.025) and insulin (P = 0.01) concentrations. T10, c12-CLA induced profound weight loss (P = 0.0001) and increased brown and white adipose tissue UCP-2 (P = 0.001) and skeletal muscle UCP-3 (P = 0.008) mRNA expression. This study highlights the contrasting molecular and metabolic effect of two isomers of the same fatty acids. The ameliorative effect of c9,t11-CLA on lipid metabolism may be ascribed to reduced synthesis and cleavage of hepatic SREBP-1, which in turn may be regulated by hepatic LXRalpha expression.
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We report the effect of an atherogenic diet supplemented with cis-9, trans-11-octadecadienoic acid (c9t11), linoleic acid (LA) or an isomeric mixture of conjugated linoleic acids (CLA) on plasma lipids, weight gain and food intake of male Golden Syrian hamsters. Animals were assigned to three diet groups (n = 10), and fed nonpurified diet, supplemented with 10% hydrogenated coconut oil and 0.05% cholesterol for 6 wk. The first diet group was further supplemented with 1% CLA (CLA group), the second diet group with 0.2% c9t11 (c9t11 group) and the third group with 0.2% LA (LA group). The diets were designed to have equivalent levels of c9t11 in the CLA and c9t11 groups. At 2 and 6 wk of feeding, the CLA group had significantly lower plasma triglyceride and total cholesterol concentrations than either the c9t11 or the LA groups. HDL-cholesterol did not differ among diet groups. The CLA group had significantly lower weight gain but greater food intake than either the c9t11 or the LA groups. There were no significant differences between the c9t11 and the LA groups in any of the variables measured. We conclude that under our experimental conditions of short-term feeding, c9t11, thought to be the active compound in CLA, does not produce the same effect as the isomer mixture.
We report the effect of an atherogenic diet supplemented with cis-9,trans-11-octadecadienoic acid (c9t11), linoleic acid (LA) or an isomeric mixture of conjugated linoleic acids (CLA) on plasma lipids, weight gain and food intake of male Golden Syrian hamsters. Animals were assigned to three diet groups (n = 10), and fed nonpurified diet, supplemented with 10% hydrogenated coconut oil and 0.05% cholesterol for 6 wk. The first diet group was further supplemented with 1% CLA (CLA group), the second diet group with 0.2% c9t11 (c9t11 group) and the third group with 0.2% LA (LA group). The diets were designed to have equivalent levels of c9t11 in the CLA and c9t11 groups. At 2 and 6 wk of feeding, the CLA group had significantly lower plasma triglyceride and total cholesterol concentrations than either the c9t11 or the LA groups. HDL-cholesterol did not differ among diet groups. The CLA group had significantly lower weight gain but greater food intake than either the c9t11 or the LA groups. There were no significant differences between the c9t11 and the LA groups in any of the variables measured. We conclude that under our experimental conditions of short-term feeding, c9t11, thought to be the active compound in CLA, does not produce the same effect as the isomer mixture.
Conjugated linoleic acid (CLA) is a naturally occurring group of dienoic derivatives of linoleic acid found in the fat of beef and other ruminants. CLA is reported to have effects on both tumor development and body fat in animal models. To further characterize the metabolic effects of CLA, male AKR/J mice were fed a high-fat (45 kcal%) or low-fat (15 kcal%) diet with or without CLA (2.46 mg/kcal; 1.2 and 1.0% by weight in high- and low-fat diets, respectively) for 6 wk. CLA. significantly reduced energy intake, growth rate, adipose depot weight, and carcass lipid and protein content independent of diet composition. Overall, the reduction of adipose depot weight ranged from 43 to 88%, with the retroperitoneal depot most sensitive to CLA. CLA significantly increased metabolic rate and decreased the nighttime respiratory quotient. These findings demonstrate that CLA reduces body fat by several mechanisms, including a reduced energy intake, increased metabolic rate, and a shift in the nocturnal fuel mix.
Thirty-six male F1B hamsters, 10 weeks of age, were divided into 3 groups of 12 based on similar body weights. The experimental diets comprised of a chow-based hypercholesterolemic diet supplemented with 20% coconut oil, 2% safflower oil, and 0.12% cholesterol (HCD); the HCD plus either 1% CLA as the free fatty acid (CLA), or 1% LA as the free fatty acid (LA) and were fed for 12 weeks. Plasma total cholesterol (TC) and nonHDL-C (very low- and low-density lipoprotein cholesterol) were significantly lower in the CLA and LA relative to the HCD (P < 0.05). The CLA had significantly less maximum number of dienes formed relative to the LA and HCD (P < 0.05). The CLA developed significantly less early aortic atherosclerosis relative to both the HCD and LA (P < 0.05). Thus it appears CLA reduces the development of early aortic atherosclerosis to a greater degree than LA possibly through changes in LDL oxidative susceptibility in hypercholesterolemic hamsters.
GREAT progress has been made over the past 30 years in identifying cardiovascular risk factors and in developing and implementing measures to correct them. The Adult Treatment Panel of the National Cholesterol Education Program developed guidelines in 1988 that identified low-density lipoprotein (LDL) as the major atherogenic lipoprotein and high levels of LDL cholesterol (LDL-C) as the primary target for cholesterol-lowering therapy. Since these guidelines were developed, the scientific database has significantly expanded. Genetic investigations into familial dyslipidemias, advances in molecular biology, animal experiments, human observational studies, lipid metabolic studies, epidemiologic data, and the results of interventional clinical trials looking at mortality, cardiovascular end points, and angiographic changes in atheromatous lesions have created interest in further examination of the role of high-density lipoprotein cholesterol (HDL-C) and triglycerides (TGs) in the pathogenesis of coronary artery disease. To address these questions, the National Heart, Lung, and Blood Institute and the Office of
Conjugated linoleic acid (CLA) is a naturally occurring fatty acid which has anti-carcinogenic and anti-atherogenic properties. CLA activates PPAR alpha in liver, and shares functional similarities to ligands of PPAR gamma, the thiazolidinediones, which are potent insulin sensitizers. We provide the first evidence that CLA is able to normalize impaired glucose tolerance and improve hyperinsulinemia in the pre-diabetic ZDF rat. Additionally, dietary CLA increased steady state levels of aP2 mRNA in adipose tissue of fatty ZDF rats compared to controls, consistent with activation of PPAR gamma. The insulin sensitizing effects of CLA are due, at least in part, to activation of PPAR gamma since increasing levels of CLA induced a dose-dependent transactivation of PPAR gamma in CV-1 cells cotransfected with PPAR gamma and PPRE X 3-luciferase reporter construct. CLA effects on glucose tolerance and glucose homeostasis indicate that dietary CLA may prove to be an important therapy for the prevention and treatment of NIDDM.
1. Diene-conjugated fatty acids are one of the products of free-radical attack upon lipids and therefore have been used as markers of such attack. The major diene-conjugated fatty acid in human tissue and serum is an isomer of linoleic acid (9,12-octadecadienoic acid), namely 9,11-octadecadienoic acid. Diet may be another source of this isomer, raising questions as to its value as a free-radical marker. The aim of this study was to determine the importance of diet as a source of 9,11-octadecadienoic acid in phospholipid esterified fatty acids in human serum. 2. Foodstuffs rich in 9,11-octadecadienoic acid were identified. Fourteen subjects volunteered to alter their diets, either increasing ('high diet') or decreasing ('low diet') their intake of these foodstuffs for 3 weeks. Where subjects undertook both diets, a washout period of at least 3 weeks was allowed between phases. 3. Seven-day diet histories were kept and scored with respect to their content of 9,11-octadecadienoic acid. The concentrations of 9,11-octadecadienoic acid and linoleic acid in serum phospholipids were measured by h.p.l.c. with u.v. detection. 4. The percentage molar ratio of 9,11-octadecadienoic acid to linoleic acid was calculated. The percentage molar ratio rose significantly on the ‘high diet’ [1.3(0.4) versus 1.9(0.7), P=0.01, mean (SD)] and fell significantly on the ‘low diet’ [1.6(0.4) versus 1.1(0.4), P=0.004, means (SD)]. There was a significant correlation between the change in dietary intake of 9,11-octadecadienoic acid and the change in the percentage molar ratio (r= 0.829, P = 0.001). 5. The concentration of 9,11-octadecadienoic acid in serum phospholipids is influenced by diet. Its use as a marker of free-radical activity is questionable and at least in need of careful interpretation.