The limited, low-level evidence available on refeeding syndrome (RFS) is likely a result of there being no universally accepted definition of RFS. Cautious feeding is typically recommended to prevent RFS-related adverse outcomes; however, these recommendations are outdated. This systematic review aimed to summarize the RFS literature, describe feeding methods used, and determine whether higher or lower energy rates at commencement of feeding were associated with RFS or RFS-related adverse outcomes. Databases were searched for interventional and observational studies examining feeding and RFS-related adverse events in adult patients. Data extracted included study design, participant descriptions, energy intake, and incidence of RFS-related adverse outcomes. Studies were compared based on assertive (>20 kcal/kg/d) or conservative (≤20 kcal/kg/d) feeding initiation rates. Of 2803 abstracts, 24 studies were included (1 randomized control trial, 23 observational studies). Fifteen studies were classified as assertive. Feeding methods varied greatly, making interpretations difficult. Incidence of hypophosphatemia varied widely and was reported at rates of up to 74% for assertive studies and 72% for conservative studies. Similarly, diagnosed RFS was reported at rates of up to 20% for both types of studies. Time to achieve goal feeding rate appeared to have no influence on incidence of RFS-related adverse outcomes. No consensus was found regarding the best method of feeding, energy initiation, or the time to achieve goal feeding rate that minimizes risk of RFS. There is currently limited evidence to suggest that higher-energy feeding initiation rates have detrimental impacts on those at risk of RFS; however, further research is necessary. © 2020 American Society for Parenteral and Enteral Nutrition.