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The efficacy of long-term conjugated linoleic acid (CLA) supplementation on body composition in overweight and obese individuals: A systematic review and meta-analysis of randomized clinical trials

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Numerous supplements containing conjugated linoleic acid (CLA) are presently being promoted for body weight reduction. The aim of this systematic review is to evaluate the evidence for or against the long-term efficacy of CLA. Electronic searches were conducted to identify relevant randomized clinical trials (RCTs). No restrictions in age, time, or language were imposed. Studies had to be at least 6 months in duration. Three reviewers independently determined the eligibility of studies. Two reviewers independently extracted data and assessed the reporting quality of all RCTs. Fifteen RCTs were identified, and seven were included. Four of the included RCTs had serious flaws in the reporting of their methodology. A meta-analysis revealed a statistically significant difference in weight loss favouring CLA over placebo (mean difference: -0.70 kg; 95% confidence interval: -1.09, -0.32). Our meta-analysis also revealed a small significant difference in fat loss favouring CLA over placebo (MD: -1.33 kg; 95% CI: -1.79, -0.86; I (2) = 54%). The magnitude of these effects is small, and the clinical relevance is uncertain. Adverse events included constipation, diarrhea, and soft stools. The evidence from RCTs does not convincingly show that CLA intake generates any clinically relevant effects on body composition on the long term.
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... [10][11][12] Apart from animal studies, several clinical trials of CLA have been conducted, and a few systematic reviews and metaanalyses of these trials have been published. Three of the meta-analyses investigated the effects of CLA on the general population [13][14][15] , 2 focused on overweight and obese individuals, 16,17 and 1 focused on people with metabolic syndrome. 18 CLA administration has been reported to result in decreases in body weight and fat mass and increases in lean body mass. ...
... 18 CLA administration has been reported to result in decreases in body weight and fat mass and increases in lean body mass. [14][15][16][17][18] However, CLA may not significantly affect insulin resistance, and its effect on lipid profiles has remained controversial. 13,18 Because of its potential benefits, several commercial CLA products have been made for physically active individuals and claim to improve their general health, to accelerate increases in muscle mass, and to indirectly enhance exercise performance. ...
... Heterogeneity: t 2 = 0.00; c 2 = 5.11, df = 10 (P = 0.88); I 2 = 0% Test for overall effect: Z = 1. 60 weight (range of mean difference, À0.51 to À0.70 kg), [16][17][18] this effect was not observed in this study. By contrast, in the present study, CLA combined with exercise was beneficial for body-fat reduction, a result that is in line with those of previous meta-analyses. ...
Article
Context Conjugated linoleic acid (CLA) has been reported to have anti-obesity and antidiabetic effects. However, the benefits of CLA combined with exercise remain unclear, and studies report conflicting results. Objective A systematic review and meta-analysis were performed to investigate the synergistic effect of CLA and exercise on body composition, exercise-related indices, insulin resistance, and lipid profiles; and of the safety of CLA supplements. Data sources In October 2021, the PubMed, Embase, and Cochrane Library databases were searched for reports on clinical trials of the combined intervention of CLA and exercise. Data extraction A total of 18 randomized controlled trials and 2 crossover trials were included. The methodological quality assessment was performed using the revised Cochrane risk-of-bias tool. Pooled effect sizes were reported as standardized mean difference (SMD) for continuous data and risk ratio for dichotomous data with their corresponding 95% confidence intervals (CIs). Heterogeneity was tested using the I2 statistic. Data analysis The combination of CLA and exercise resulted in significantly decreased body fat (SMD, –0.42 [95%CI, –0.70, –0.14]; P = 0.003; I2 = 65) and insulin resistance (SMD, –0.25 [95%CI, –0.44, –0.06]; P = 0.01; I2 = 0) than did exercise alone. In subgroup analysis, the following factors were associated with significant outcomes: (1) body mass index ≥25 kg/m2; (2) female sex; (3) follow-up time >4 weeks; and (4) intervention duration >4 weeks. Nevertheless, supplementation with CLA during exercise programs was not effective for body-weight control, exercise performance enhancement, or lipid-profile improvement. CLA in combination with exercise did not result in a higher risk of adverse events (risk ratio, 1.32 [95%CI, 0.94–1.84]; P > 0.05; I2 = 0). Conclusion CLA combined with exercise is generally safe and can lower body fat and insulin resistance but does not reduce body weight, enhance exercise performance, or improve lipid profiles.
... Of the widely available supplements, there is some evidence to support weight-loss claims for caffeine, (L-)carnitine, conjugated linoleic acid, green tea, and ephedrine. However, meta-analyses have concluded that ephedrine [352,353] and conjugated linoleic acid [354] can elicit weight loss of less than 1 kg, for which the clinical relevance is low. ...
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Metabolic demands of skeletal muscle are substantial and are characterized normally as highly flexible and with a large dynamic range. Skeletal muscle composition (e.g., fiber type and mitochondrial content) and metabolism (e.g., capacity to switch between fatty acid and glucose substrates) are altered in obesity, with some changes proceeding and some following the development of the disease. Nonetheless, there are marked interindividual differences in skeletal muscle composition and metabolism in obesity, some of which have been associated with obesity risk and weight loss capacity. In this review, we discuss related molecular mechanisms and how current and novel treatment strategies may enhance weight loss capacity, particularly in diet-resistant obesity.
... It can be speculated that the reasons for these differences may be due to differences in major dietary sources of n-6 PUFAs and linoleic acid. Considering the potential weight-reducing effect of LA (41), it may have long-term benefits in preventing T2DM risk, at least in part, by means of its effect on body fat. ...
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Background: Some evidence indicates a potential beneficial effect of omega-6 polyunsaturated fatty acids (n-6 PUFAs) on type 2 diabetes mellitus (T2DM); however, the findings to date remains inconclusive and little is known about whether sex modifies these associations. Therefore, this study aimed to investigate potential sex-specific differences in this associations among Chinese adults. Methods: We conducted a cross-sectional study in an area of Dalian city, China; Chinese men and women who attended the Department of Clinical Nutrition and Metabolism between January and December 2020 were invited to participate in this study. All participants were assessed for basic demographic characteristics, fasting blood glucose, HbA1c, and other serum biomarkers and serum phospholipid FAs. Results: In total, 575 Chinese adult participants (270 men and 305 women) were included in the analysis. Hypertension and dyslipidaemia were more common among men than women, but there were no significant differences between the sexes in fatty acid composition, except for eicosadienoic acid (EA; 20:2n-6) and total monounsaturated fatty acids (MUFA). The age-adjusted OR for having T2DM in the highest quartile of arachidonic acid (20:4n-6) level was 0.47 (95% CI, 0.22, 0.98) in men, and this association remained consistently significant in the fully adjusted multivariate models. In contrast, no significant associations between n-6 PUFAs and T2DM risk were observed in women, regardless of model adjustment. Conclusions: In conclusion, these results demonstrate a notable sex-specific differences in the associations between n-6 PUFAs and T2DM. Higher n-6 PUFA status may be protective against the risk of T2DM in men.
... Penelitian lain yang dilakukan oleh Almeida (2019) bahwa minyak ikan mengandung asam palmitat (C16:0) yang berfungsi sebagai penyuplai asam vaccenic yang merupakan prekursor utama CLA (conjugated linoleic acid) sebagai penyebab menurunnya kolesterol darah. CLA adalah grup isomer dari asam linoleat yang mempunyai kapasitas untuk melakukan beberapa manfaat terhadap metabolisme, seperti penghambatan lipogenesis, kolesterol darah dan pengurangan insiden kanker, serta perubahan pertumbuhan jaringan otot (Onakpoya et al., 2012;Rice et al., 2012). ...
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Conjugated linoleic acids (CLA) are believed to influence body composition, blood lipids and certain endocrine parameters in animals and humans. The aim of this study was to investigate the effects of a six months dietary supplementation of 7 g CLA-oil (containing 54% CLA) daily in two groups of male and female resistance-trained athletes who were at a different training stage. The volunteers were matched according to their previous training: 7 beginners (3♀/4♂) and 7 advanced athletes (2♀/5♂). During the intervention period they performed a standardized training routine three times per week. Blood samples were taken and body mass index, body composition (bioelectrical impedance assessment) and nutrient intake (7-day food record) were recorded at baseline as well as during and following dietary supplementation Results: Serum lipid concentrations, serum leptin, soluble leptin receptor and IGF-I levels or body composition were similar in the two categories of athletes after CLA supplementation. However, despite a higher energy intake, a significant reduction of body fat (P <0.05) was observed and both groups tended to increase their body cell mass (not significant). Total body water increased in the novice athletes (P <0.05). Furthermore, total cholesterol (P = 0.049) increased over baseline levels in the novice athletes. These levels remained within the physiological range. In all athletes there was a significant correlation between percentage body fat and leptin (baseline: r2 = 0.46, P = 0.01, CLA: r2 = 0.49, P = 0.011), as well as between fat mass and serum leptin levels (baseline: r2 = 0.35, P = 0.033, CLA: r2 = 0.60, P = 0.002). Conclusions: Over a period of six months no differences were observed in the effects of a commercial CLA-triacylglyceride (54% CLA, 7g/d) on selected endocrine parameters, blood lipids, food intake and body composition between advanced and novice resistance-trained athletes who take part in a regular training program.
Obesity and pattern of fat distribution are both important factors related to poor health outcomes. Many measures of obesity and fat distribution pattern have been employed by different authors and to facilitate interpopulation comparisons and interpretation of secular trends it is necessary that standardized methods for measurement and classification are set in place. The use of BMI as a measure of fatness for epidemiological studies is widely accepted, easily measured and BMI predicts morbidity and mortality in many populations. The most appropriate level at which to define obesity is a matter of debate but systems which use BMI ⩾ 25 and ⩽ 30 kg/m2 as overweight, and BMI > 30 kg/m2 as obese for all adults are simple, easily remembered, already widely used and BMIs above 30 kg/m2 are clearly associated with increased risk of morbidity and mortality. In some populations there may be a case for using a lower cut-off but not unless there is specific evidence to support this. For the present WHR is probably the best method for assessing fat distribution, although waist circumference on its own may be more useful in determining risk levels. Standard sites for measurement of both waist and hip girths have been described.There is a large variation in the prevalence of obesity across the populations for which data is available, with high prevalences of obesity and dramatic secular trends especially apparent in modernizing Pacific Island populations. The ‘thrifty genotype’ hypothesis has been invoked to try and explain this situation.The clustering of obesity, NIDDM and CVD risk factors has been recognized and various ‘syndromes’ have been described which group different factors together, with hyperinsulinaemia and insulin resistance proposed as the underlying problem.