Key messages
– We do not know if nutritional supplements in addition to normal diet are better for people having surgery on the digestive system due to uncertainty in the evidence.
– There is some evidence that oral supplements reduce infections in people who have lost weight or are malnourished.
– More research is required in this area.
Background
People who will be undergoing surgery on the digestive tract often have malnutrition before the surgery (that is, they have a poor level of nourishment, possibly because their diet does not contain the right amount of nutrients or their bodies do not absorb nutrients well). This can increase the possibility of death, other illnesses or problems, and result in longer hospital stays. Research shows that malnutrition and weight loss are linked to infections and other complications after surgery on the digestive system, such as poor healing at the site of surgery, the heart not pumping blood around the body properly, blood clots or bleeding. We looked at the effects of providing extra nourishment to people before an operation.
What did we want to find out?
We wanted to know if giving people nutritional supplements orally, via a tube into the stomach (enterally) or via a tube into the veins (parenterally) in addition to normal food before an operation on the digestive tract would lead to fewer non-infectious complications (that is, complications other than an infection), infectious complications (that is, complications related to infections at the site of surgery or elsewhere in the body) and shorter stays in hospital. For the oral supplements, we looked at standard supplements and immune-enhancing supplements (which are enriched with ingredients to boost the body's immune system to help fight infections).
What did we do?
We searched scientific databases for relevant studies that compared additional nutritional therapy versus usual care in people undergoing surgery on the digestive tract.
Main findings
We identified 16 studies including 2164 participants. For parenteral and enteral feeding, we are uncertain if there was any effect on the number of people with a non-infectious complication, an infectious complication or length of hospital stay. For oral supplements with immune-enhancing ingredients, we were uncertain if there was any effect on the number of people with a non-infectious complication, an infectious complication or length of hospital stay. For standard oral supplements, we found little or no effect on the number of people with a non-infectious or infectious complication. Although in two studies that looked at people losing weight or those who were malnourished, standard oral supplements probably reduced infections. Standard oral supplements may reduce length of hospital stay compared to usual care.
What are the limitations of this evidence?
We had limited confidence in the results as, for example, some studies were old, methods and results varied between studies, and in some studies, participants and researchers knew which treatment they received so may have favoured one treatment over another.
How up to date is this evidence?
This was an update of a review first published in 2012. The latest search was 28 March 2023.
We were unable to determine if parenteral nutrition, enteral nutrition, immune-enhancing nutrition or standard oral nutrition supplements have any effect on the clinical outcomes due to very low-certainty evidence. There is some evidence that standard oral nutrition supplements may have no effect on complications. Sensitivity analysis showed standard oral nutrition supplements probably reduced infections in weight-losing or malnourished participants. Further high-quality multicentre research considering the ERAS programme is required and further research in low- and middle-income countries is needed.
Poor preoperative nutritional status has been consistently linked to an increase in postoperative complications and worse surgical outcomes. We updated a review first published in 2012.
To assess the effects of preoperative nutritional therapy compared to usual care in people undergoing gastrointestinal surgery.
We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, three other databases and two trial registries on 28 March 2023. We searched reference lists of included studies.
We included randomised controlled trials (RCTs) of people undergoing gastrointestinal surgery and receiving preoperative nutritional therapy, including parenteral nutrition, enteral nutrition or oral nutrition supplements, compared to usual care. We only included nutritional therapy that contained macronutrients (protein, carbohydrate and fat) and micronutrients, and excluded studies that evaluated single nutrients. We included studies regardless of the nutritional status of participants, that is, well-nourished participants, participants at risk of malnutrition, or mixed populations. We excluded studies in people undergoing pancreatic and liver surgery.
Our primary outcomes were non-infectious complications, infectious complications and length of hospital stay. Our secondary outcomes were nutritional aspects, quality of life, change in macronutrient intake, biochemical parameters, 30-day perioperative mortality and adverse effects.
We used standard Cochrane methodology. We assessed risk of bias using the RoB 1 tool and applied the GRADE criteria to assess the certainty of evidence.
We included 16 RCTs reporting 19 comparisons (2164 participants). Seven studies were new for this update. Participants' ages ranged from 21 to 79 years, and 62% were men. Three RCTs used parenteral nutrition, two used enteral nutrition, eight used immune-enhancing nutrition and six used standard oral nutrition supplements. All studies included mixed groups of well-nourished and malnourished participants; they used different methods to identify malnutrition and reported this in different ways. Not all the included studies were conducted within an Enhanced Recovery After Surgery (ERAS) programme, which is now current clinical practice in most hospitals undertaking GI surgery.
We were concerned about risk of bias in all the studies and 14 studies were at high risk of bias due to lack of blinding.
We are uncertain if parenteral nutrition has any effect on the number of participants who had a non-infectious complication (risk ratio (RR) 0.61, 95% confidence interval (CI) 0.36 to 1.02; 3 RCTs, 260 participants; very low-certainty evidence); infectious complication (RR 0.98, 95% CI 0.53 to 1.80; 3 RCTs, 260 participants; very low-certainty evidence) or length of hospital stay (mean difference (MD) 5.49 days, 95% CI 0.02 to 10.96; 2 RCTs, 135 participants; very low-certainty evidence).
None of the enteral nutrition studies reported non-infectious complications as an outcome. The evidence is very uncertain about the effect of enteral nutrition on the number of participants with infectious complications after surgery (RR 0.90, 95% CI 0.59 to 1.38; 2 RCTs, 126 participants; very low-certainty evidence) or length of hospital stay (MD 5.10 days, 95% CI −1.03 to 11.23; 2 RCTs, 126 participants; very low-certainty evidence).
Immune-enhancing nutrition compared to controls may result in little to no effect on the number of participants experiencing a non-infectious complication (RR 0.79, 95% CI 0.62 to 1.00; 8 RCTs, 1020 participants; low-certainty evidence), infectious complications (RR 0.74, 95% CI 0.53 to 1.04; 7 RCTs, 925 participants; low-certainty evidence) or length of hospital stay (MD −1.22 days, 95% CI −2.80 to 0.35; 6 RCTs, 688 participants; low-certainty evidence).
Standard oral nutrition supplements may result in little to no effect on number of participants with a non-infectious complication (RR 0.90, 95% CI 0.67 to 1.20; 5 RCTs, 473 participants; low-certainty evidence) or the length of hospital stay (MD −0.65 days, 95% CI −2.33 to 1.03; 3 RCTs, 299 participants; low-certainty evidence). The evidence is very uncertain about the effect of oral nutrition supplements on the number of participants with an infectious complication (RR 0.88, 95% CI 0.60 to 1.27; 5 RCTs, 473 participants; very low-certainty evidence). Sensitivity analysis based on malnourished and weight-losing participants found oral nutrition supplements may result in a slight reduction in infections (RR 0.58, 95% CI 0.40 to 0.85; 2 RCTs, 184 participants).
Studies reported some secondary outcomes, but not consistently.
Complications associated with central venous catheters occurred in RCTs involving parenteral nutrition. Adverse events in the enteral nutrition, immune-enhancing nutrition and standard oral nutrition supplements RCTs included nausea, vomiting, diarrhoea and abdominal pain.