Abstract

CONTEXT 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. OBJECTIVES 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. DATA SOURCES 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. DATA EXTRACTION The studies that assessed energy, carbohydrate, protein, fat, fiber, and water intakes pre- and post-fasting were extracted. DATA ANALYSIS 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. CONCLUSIONS The change in meal timing rather than quantitative dietary intake may explain various physiological and health effects associated with RF.

Abstract

Background: The potential positive interaction between intermittent fasting (IF) and brain-derived neurotrophic factor (BDNF) on cognitive function has been widely discussed. This systematic review tried to assess the efficacy of interventions with different IF regimens on BDNF levels and their association with cognitive functions in humans. Interventions with different forms of IF such as caloric restriction (CR), alternate-day fasting (ADF), time-restricted eating (TRE), and the Ramadan model of intermittent fasting (RIF) were targeted. Methods: A systematic review was conducted for experimental and observational studies on healthy people and patients with diseases published in EMBASE, Scopus, PubMed, and Google Scholar databases from January 2000 to December 2023. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis statements (PRISMA) for writing this review. Results: Sixteen research works conducted on healthy people and patients with metabolic disorders met the inclusion criteria for this systematic review. Five studies showed a significant increase in BDNF after the intervention, while five studies reported a significant decrease in BDNF levels, and the other six studies showed no significant changes in BDNF levels due to IF regimens. Moreover, five studies examined the RIF protocol, of which, three studies showed a significant reduction, while two showed a significant increase in BDNF levels, along with an improvement in cognitive function after RIF. Conclusions: The current findings suggest that IF has varying effects on BDNF levels and cognitive functions in healthy, overweight/obese individuals and patients with metabolic conditions. However, few human studies have shown that IF increases BDNF levels, with controversial results. In humans, IF has yet to be fully investigated in terms of its long-term effect on BDNF and cognitive functions. Large-scale, well-controlled studies with high-quality data are warranted to elucidate the impact of the IF regimens on BDNF levels and cognitive functions.