Purpose: Studies on the effect of Ramadan diurnal intermittent fasting (RDIF) on body weight have yielded conflicting results. Therefore, we conducted a systematic review and meta-analysis to estimate the effect size of body weight changes in healthy, non-athletic Muslims practicing Ramadan fasting, and to assess the effect of covariates such as age, sex, fasting time duration, season, and country, using subgroup analysis, and meta-regression. Covariate adjustments were performed to explain the variability of weight change in response to Ramadan fasting.
Methods: CINAHL, Cochrane, EBSCOhost, EMBASE, Google Scholar, ProQuest Medical, PubMed/MEDLINE, ScienceDirect, Scopus, and Web of Science databases were searched from date of inception in 1950 to the end of August 2019.
Results: Eighty-five studies, conducted in 25 countries during 1982-2019, were identified. RDIF yielded a significant, but small reduction in body weight (K = 85, number of subjects, N = 4176 (aged 16-80 years), Hedges' g =- 0.360, 95% confidence interval (CI) - 0.405 to - 0.315, I2 = 45.6%), this effect size translates into difference in means of - 1.022 kg (95% CI - 1.164 kg to - 0.880 kg). Regression analysis for moderator covariates revealed that fasting time (min/day) is a significant (P < 0.05) moderator for weight change at the end of Ramadan, while age and sex are not. Variable effects for the season and country were found.
Conclusion: RDIF may confer a significant small reduction in body weight in non-athletic healthy people aged 16 years and above, directly associated with fasting time and variably correlated with the season, and country.
Keywords: Body weight; Caloric restriction; Diurnal intermittent fasting; Meta-analysis; Obesity; Ramadan; Systematic review.