Fasting During Chemotherapy and Hematologic, Metabolic, and Quality of Life Outcomes: A Systematic Review and Meta-Analysis

Background/Objectives: Fasting has been proposed as a non-pharmacologic method of reducing chemotherapy toxicity. However, its effects across outcome domains have not been well-quantified. Methods: In line with PRISMA 2020 guidelines (PROSPERO: CRD420261296778), we searched PubMed, Embase, Web of Science, and CENTRAL from January 2015 through April 2026 for randomized or prospective comparative trials evaluating fasting during chemotherapy. Risk of bias was assessed using RoB 2 and criteria aligned with ROBINS-I. Standardized mean differences (Hedges’ g) and risk ratios (RRs) were pooled using three-level random-effects models. Results: Seven publications reporting six trials (268 participants) were included. The pooled estimate did not reach statistical significance (g = 0.21, 95% CI: −0.02–0.43, p = 0.064). Hematologic parameters (g = 0.11, 95% CI: −0.23–0.45) and quality of life (QoL) and patient-reported outcomes from one trial (g = 0.32, 95% CI: −0.03–0.66) did not differ significantly between groups. Adverse events also did not differ significantly (RR = 0.86, 95% CI: 0.55–1.36). Conclusions: Across six small trials, fasting during chemotherapy did not significantly affect hematologic parameters, QoL, or adverse events. However, it is worth nothing that point estimates generally favored fasting. Hence, a small benefit can neither be confirmed nor ruled out at this time. Adequately powered trials assessing patient-important outcomes and incorporating nutritional monitoring are needed before fasting can be recommended or ruled out.