Background: Nutritional interventions play a critical role in bone marrow transplant (BMT) patients. This review evaluates the effectiveness of nutritional strategies in mitigating post-transplant malnutrition and improving clinical outcomes. Methods: A systematic review was conducted using PubMed, CINAHL, Cochrane Library, and Embase. The search terms included “bone marrow transplant”, “malnutrition”, and “preoperative nutritional interventions”. The quality of studies and risk of bias were assessed using the JBI framework, while evidence certainty was evaluated with the Oxford OCEBM. Results: Six studies were included (n = 3545 screened). The studies demonstrated predominantly high methodological quality and a low risk of bias, although heterogeneity in the treatments investigated and small sample sizes limited the evidence. Nutritional interventions significantly increased energy intake (26 vs. 24 kcal/kg/day, p = 0.038) and improved body weight (25% vs. 9%) with protein supplementation. Clinical complications decreased, including severe acute graft-versus-host disease (17.1% vs. 43.4%, p = 0.001) and pneumonia (27.6% vs. 52.7%, p = 0.002). The length of hospital stay (27 vs. 32 days, p = 0.006) and the need for parenteral nutrition (53% vs. 62%, p = 0.03) were also reduced. Overall survival improved with ≥50% adherence to prescribed TGF-beta2 intake (33 vs. 25.1 months, p = 0.03). Conclusions: Nutritional prehabilitation shows promise in improving BMT outcomes. Standardized nutritional programs could optimize care, although limitations in current evidence are clearly present. Larger randomized studies are needed to confirm findings and refine pre-transplant protocols.