Abstract: The search identified eight trials including 500 participants. Six trials were conducted in the USA and two in Europe. 1. Parenteral nutrition (PN) versus oral nutrition: based on one study with 157 participants, PN may increase postoperative complications within 30 days (risk ratio (RR) 1.40, 95% confidence interval (CI) 1.07 to 1.82; low-quality evidence). We downgraded the quality of evidence for serious study limitations (unclear risk of selection, performance and selective reporting bias) and serious imprecision. This corresponds to 198 more complications per 1000 participants (95% CI 35 more to 405 more). Length of hospital stay may be similar (mean difference (MD) 0.5 days higher, CI not reported; low-quality evidence). 2. Immuno-enhancing nutrition versus standard nutrition: based on one study including 29 participants, immuno-enhancing nutrition may reduce 90-day postoperative complications (RR 0.31, 95% CI 0.08 to 1.23; low-quality evidence). These findings correspond to 322 fewer complications per 1000 participants (95% CI 429 fewer to 107 more). Length of hospital stay may be similar (MD 0.20 days, 95% CI 1.69 lower to 2.09 higher; low-quality evidence). We downgraded the quality of evidence of both outcomes for very serious imprecision. 3. Preoperative oral nutritional support versus normal diet: based on one study including 28 participants, we are very uncertain if preoperative oral supplements reduces postoperative complications. We downgraded quality for serious study limitations (unclear risk of selection, performance, attrition and selective reporting bias) and very serious imprecision. The study did not report on length of hospital stay. 4. Early postoperative feeding versus standard postoperative management: based on one study with 102 participants, early postoperative feeding may increase postoperative complications (very low-quality evidence) but we are very uncertain of this finding. We downgraded the quality of evidence for serious study limitations (unclear risk of selection and performance bias) and very serious imprecision. Length of hospital stay may be similar (MD 0.95 days less, CI not reported; low-quality evidence). We downgraded the quality of evidence for serious study limitations (unclear risk of selection and performance bias) and serious imprecision. 5. Amino acid with dextrose versus dextrose: based on two studies with 104 participants, we are very uncertain whether amino acids reduce postoperative complications (very low-quality evidence). We are also very uncertain whether length of hospital stay is similar (very low-quality evidence). We downgraded the quality of evidence for both outcomes for serious study limitations (unclear and high risk of selection bias; unclear risk of performance, detection and selective reporting bias), serious indirectness related to the patient population and very serious imprecision. 6. Branch chain amino acids versus dextrose only: based on one study including 19 participants, we are very uncertain whether complication rates are similar (very low-quality evidence). We downgraded the quality of evidence for serious study limitations (unclear risk of selection, performance, detection, attrition and selective reporting bias), serious indirectness related to the patient population and very serious imprecision. The study did not report on length of hospital stay. 7. Perioperative oral nutritional supplements versus oral multivitamin and mineral supplement: based on one study with 61 participants, oral supplements compared to a multivitamin and mineral supplement may slightly decrease postoperative complications (low-quality evidence). These findings correspond to 135 fewer occurrences per 1000 participants (95% CI 256 fewer to 65 more). Length of hospital stay may be similar (low-quality evidence). We downgraded the quality of evidence of both outcomes for study limitations and imprecision. Based on few, small and dated studies, with serious methodological limitations, we found limited evidence for a benefit of perioperative nutrition interventions. We rated the quality of evidence as low or very low, which underscores the urgent need for high-quality research studies to better inform nutritional support interventions for people undergoing surgery for bladder cancer.

Plain-language summary: The evidence is current up to 22 February 2019. There were eight studies conducted including 500 people in hospital. There were seven different ways in which nutrition was given. 1. Feeding into a vein versus oral nutrition: based on one study that included 157 people, we found that feeding into a vein may increase complications after surgery. However, there may be little or no difference in length of hospital stay. 2. Immuno‐enhancing nutrition versus standard supplements: immuno‐enhancing nutrition has high levels of nutrients that are thought to improve the immune function and was given in one study that included 29 people. We found that this form of nutrition may decrease complications 90 days after surgery, but may have little effect on length of hospital stay. 3. Preoperative oral nutrition support versus diet: based on one study that included 28 people, we are uncertain if oral supplements before surgery improve complications after surgery. Length of hospital stay was not reported. 4. Early postoperative feeding versus standard care: based on one study that included 102 people, early postoperative feeding may increase postoperative complications after surgery, but we are very uncertain of this finding. Length of hospital stay may be similar. 5. Amino acids versus dextrose: amino acids are the building blocks of proteins and dextrose is sugary water. From two studies that included 104 people, we are uncertain whether complications may be reduced. Length of hospital stay may be similar. 6. Branch chain versus dextrose: branch chain are a type of amino acid. From one study that included 19 people, we are very uncertain whether complication rates are similar. Length of hospital stay was not reported. 7. Perioperative oral nutritional supplements versus multivitamin and mineral supplement: from one study that included 61 people, oral supplements compared to a multivitamin and mineral supplement may slightly decrease postoperative complications. Length of hospital stay may be similar. The certainty of the evidence for all outcomes in this review was low or very low, meaning that the true effect may be very different or is likely very different from what we found.