Impact of Replacement of Individual Dietary SFAs on Circulating Lipids and Other Biomarkers of Cardiometabolic Health: A Systematic Review and Meta-Analysis of Randomized Controlled Trials in Humans

Little is known of the impact of individual saturated fatty acids (SFAs) and their isoenergetic substitution with other SFAs or unsaturated fatty acids (UFAs) on the prevention of cardiometabolic disease (CMD). This systematic literature review (POSPERO registration: CRD42020084241) assessed the impact of such dietary substitutions on a range of fasting CMD risk markers, including lipid profile, markers of glycemic control and inflammation, and metabolic hormone concentrations. Eligible randomized controlled trials (RCTs) investigated the effect of isoenergetic replacements of individual dietary SFAs for at least 14 days on one or more CMD risk markers in humans. Searches of PubMed, Embase, Scopus and Cochrane CENTRAL databases on 14th February 2021 identified 44 RCTs conducted in participants aged 39.9y (SD 15.2). Studies' risk of bias was assessed using the Cochrane Risk of Bias tool 2.0 for RCTs. Random-effect meta-analyses assessed the effect of at least three similar dietary substitutions on the same CMD risk marker. Other dietary interventions were described in qualitative syntheses. We observed reductions in low-density lipoprotein cholesterol concentrations after the replacement of palmitic acid (C16:0) with UFA (-0.36 mmol/L, 95%CI [-0.50, -0.21], I2 = 96.0%, n = 18 RCTs) or oleic acid (C18:1) (-0.16 mmol/L, 95% CI [-0.28, -0.03], I2 = 89.6%, n = 9 RCTs), with a similar impact on total cholesterol and apolipoprotein B concentrations. No effects on other CMD risk markers, including high-density lipoprotein cholesterol, triacylglycerol, glucose, insulin, or C-reactive protein concentrations, were evident. Similarly, we found no evidence of a benefit from replacing dietary stearic acid with UFA on CMD risk markers (n = 4 RCTs). In conclusion, the impact of replacing dietary palmitic acid with UFA on lipid biomarkers is aligned with current public health recommendations. However, due to the high heterogeneity and limited studies, relationships between all individual SFAs and biomarkers of cardiometabolic health need further confirmation from RCTs.