Plain language summary
Elevated fats circulating in the blood has been shown to be a predictor for heart disease. Conjugated linoleic acid (CLA) is a type of fat that is found in the milk and meat of animals such as cows, sheep and goats. Although classed as a fat, when taken in a supplemental form, some studies have shown it to decrease circulating fats whereas others have shown no beneficial effects. This systematic review and meta-analysis of 56 randomised control trials aimed to explore the effects of CLA on circulating blood profiles. The results showed that CLA increased levels of cholesterols, which may contribute to heart disease, but also increased cholesterol which may help to prevent heart disease. It was concluded that CLA supplementation has little effect on fats in the blood. This study could be used by healthcare professionals to understand that there may be little utility in recommending a supplemental CLA for the management of heart disease.
Abstract
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. SYSTEMATIC REVIEW REGISTRATION https://www.crd.york.ac.uk/prospero/#recordDetails, identifier: CRD42022331100.
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