Does four-week consecutive, dawn-to-sunset intermittent fasting during Ramadan affect cardiometabolic risk factors in healthy adults? A systematic review, meta-analysis, and meta-regression

Aims: This study aimed to evaluate the effects of Ramadan diurnal intermittent fasting (RDIF; 29–30 days) on cardiometabolic risk factors (CMRF) in healthy adults, and examine the effect of various cofactors on the outcomes using sub-group meta-regression. Data synthesis: We conducted a systematic review and meta-analysis to measure the effect sizes of changes in CMRF in healthy adult Muslims observing RDIF. Ten scientific databases (EBSCOhost, CINAHL, Cochrane, EMBASE, PubMed/MEDLINE, Scopus, Google Scholar, ProQuest Medical, ScienceDirect, and Web of Science) were searched from the date of inception (1950) to the end of November 2020. The CMRF searched and analyzed were total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), very low-density lipoprotein cholesterol (VLDL-C), diastolic blood pressure (DBP), and heart rate (HR). We identified 91 studies (4431 adults aged 18–85 years) conducted between 1982 and 2020 in 23 countries distributed over four continents. RDIF-induced effect sizes for CMRF were: TC (no. of studies K = 77, number of subjects N = 3705, Hedge's g = −0.092, 95% confidence interval (CI): −0.168, 0.016); TG (K = 74, N = 3591, Hedge's g = −0.127, 95% CI: −0.203, 0.051); HDL-C (K = 68, N = 3528, Hedge's g = 0.138, 95% CI: 0.051, 0.224); LDL-C (K = 65, N = 3354, Hedge's g = −0.115, 95% CI: −0.197, −0.034); VLDL-C (K = 13, N = 648, Hedge's g = −0.252, 95% CI: −0.431, 0.073), DBP (K = 32, N = 1716, Hedge's g = −0.255, 95% CI: −0.363, 0.147), and HR (K = 12, N = 674, Hedge's g = −0.082, 95% CI: −0.300, 0.136). Meta-regression revealed that the age of fasting people was a significant moderator of changes in both HDL-C (P = 0.02) and VLDL-C (P = 0.01). Male sex was the only significant moderator of changes in LDL-C (P = 0.055). Fasting time duration was the only significant moderator of HDL-C (P = 0.001) at the end of Ramadan. Conclusions: RDIF positively impacts CMRF, which may confer short-term transient protection against cardiovascular disease among healthy people.