Ramadan fasting (RF) is associated with various physiological and metabolic changes among fasting Muslims. However, it remains unclear whether these effects are attributable to changes in meal timing or changes in dietary energy and macronutrient intakes. Furthermore, the literature on the associations between RF, meal timing, and energy and macronutrient intakes is inconclusive.
This systematic review aimed to estimate the effect sizes of RF on energy and macronutrient intakes (carbohydrates, protein, fats, dietary fiber, and water) and determine the effect of different moderators on the examined outcomes.
The Cochrane, CINAHL, EMBASE, EBSCOhost, Google Scholar, PubMed/MEDLINE, ProQuest Medical, Scopus, ScienceDirect, and Web of Science databases were searched from inception to January 31, 2022.
The studies that assessed energy, carbohydrate, protein, fat, fiber, and water intakes pre- and post-fasting were extracted.
Of the 4776 identified studies, 85 relevant studies (n = 4594 participants aged 9–85 y) were selected. The effect sizes for the studied variables were as follows: energy (number of studies [K] = 80, n = 3343 participants; mean difference [MD]: −142.45; 95% confidence interval [CI]: −215.19, −69.71), carbohydrates (K = 75, n = 3111; MD: −23.90; 95% CI: −36.42, −11.38), protein (K = 74, n = 3108; MD: −4.21; 95% CI: −7.34, −1.07), fats (K = 73, n = 3058; MD: −2.03; 95% CI: −5.73, 1.67), fiber (K = 16, n = 1198; MD: 0.47; 95% CI: −1.44, 2.39), and water (K = 17, n = 772; MD: −350.80; 95% CI: −618.09, 83.50). Subgroup analyses showed age significantly moderated the 6 dietary outcomes, and physical activity significantly moderated water intake. There were significant reductions in energy, carbohydrate, and protein intakes during RF.
The change in meal timing rather than quantitative dietary intake may explain various physiological and health effects associated with RF.