Our systematic review included a total of 15 clinical trials, which compiled information from 557 individuals with IBD, and who had an intervention with PN. All the studies had a broad reach, and within the diverse effects found, BW, albumin, COM, and CDAI were the most common, allowing us to conduct a meta-analysis to arrive at more complete conclusions.

PN implies the intravenous administration of a mix of macronutrients, micronutrients, and electrolytes [47], and its main objective for IBD is to achieve bowel rest, correct nutritional deficits, and the elimination of antigenic stimuli in the mucosa [48]. PN is commonly used during the acute inflammatory phase in patients who are experiencing malnutrition, such as undernourishment [49]. This undernourishment could be a factor that affects micronutrient deficiency [50,51]. The results from the systematic review show that the administration of PN significantly improved the levels of ESR [35,38], cholesterol [46], total phospholipids [46], and serum albumin [37,38,39,40,44,46], without producing clinical symptoms of hypoglycemia, independent of the method of interruption [43]. This improvement of the albumin is mirrored in the results of the meta-analysis. The meta-regression performed showed that the improvement could be greater a few days after the intervention.

The most common type of under-nourishment in patients with IBD was protein-energetic malnutrition, mainly shown with weight loss [52,53]. This malnutrition could worsen due to diverse surgical interventions that are necessary for emerging situations or when the medical treatment fails [54]. Therefore, the nutritional support should be carefully chosen during the treatment and before the surgery, based on a plan that is customized according to the patient [55]. Some authors declare that PN results in an increase in BMI, helping to correct the individual’s malnutrition [23,56]. We have not collected the BMI; however we have identified the BW, which are equivalent terms in adults, and the meta-analysis did not show the existence of a change in BW in patients with IBD when administering PN.

The CDAI, developed by Best et al. [57], measures the activity of the disease in patients with CD, with high values indicating a high activity of this pathology. Therefore, a reduction of this index indicates an improvement. The clinical trials conducted showed improvements in this index, but while these were significant in Jones [38], Greenberg et al. [39], Wright et al. [41], the results in Okenga [44] were not. The meta-analysis shows a significant reduction of the values found for the CDAI, and this decrease is accentuated days after the application of PN. These results are in agreement with diverse expert researchers, who declare that PN could provide, along with a possible administration of drugs such as infliximab, an improvement in this pathology [54,58,59].

Despite the accessibility to immunosuppressive drugs, antibiotic treatments, and fecal microbial transplantation, patients experience a high rate of relapse of malabsorption due to intestinal insufficiency [60]. In the case of individuals affected with CD, more than half are subjected to some surgery, such as bowel resection within 10 years after the diagnosis, and a third of them require a resection within the following five years [60]. This is the reason why PN could be fundamental with respect to the survival of the patient, as its management has drastically improved in the last 10 years, and the rate of related complications has notably decreased [60].

Likewise, the role of PN in postoperative complications is controversial. A recent meta-analysis has shown that the pre-surgery nutritional supplementation reduced posterior complications after the surgery in patients with CD, and more specifically, the TPN showed a tendency of being higher than the standard of care without nutritional support, but without statistical significance [61]. Hypoalbuminemia is associated with more postoperative complications, and it is sometimes a contraindication for surgery that requires anastomosis without a protective ileostomy [62]. In our qualitative synthesis with respect to the TPN, the results by Jacobson [46] concluded that it could be recommended for reducing the risk of suffering from postoperative complications until achieving clinical remission, and Yao et al. [45] declare that the perioperative PN may improve humoral immunity, reverse malnutrition and facilitate the rehabilitation of the patient. However, Fasth et al. [36] indicate that the administration of postoperative NPT does not result in a reduction of the complication rate after the surgery, although this difference could be due to the small sample utilized in this study. Our meta-analysis showed that the postoperative complications utilizing PN exist, although the proportion is low.

The term bowel rest has been frequently linked to the use of PN with active IBD or important complications such as the control of sepsis or imminent surgical procedures, and it is also theoretically attractive because of the expectation that it could improve bowel inflammation by alleviating mechanical trauma, bowel secretions, and antigenic challenge of the foods [35,63]. On the contrary, the results by Jones [38] and Dickinson et al. [33] show that there are no differences in patients with CD treated with either EN or TPN, and in patients with IBD treated solely with hydration or TPN. According to Abad-Lacruz et al. [40], and Wright et al. [41], Gonzalez-Huix et al. [42], and Greenberg et al. [39], EN results in significantly less frequent abnormalities in the LFT than TPN in patients with IBD, the PN with bowel rest does not show evidence of having a better impact on the remission than EN in patients with active CD, likewise, the EN is safer, cheaper and nutritionally effective in severe attacks as compared with TPN, and there were no differences in the remission and activity of patients with active CD.

All of this coincides with diverse studies and clinical practice guides, which indicate that bowel rest is not necessary when nutritional therapy is utilized for managing the patients [48,64,65]. Therefore, they should be allowed to eat “ad libitum” when medical therapy is prescribed and when different nutritional regimes exist through which clinical remission and repair of the mucosa can be achieved [15,48,64,65,66].

Also, it has recently been shown that there is a high load of underfeeding, orders of “nil per os” or a diet with clear liquids, which is unjustified for patients who are hospitalized with CU, especially for patients admitted without evidence of an objective flare of the disease that could be provoking iatrogenic malnutrition, so that bowel rest and the nutritional treatment should be given special attention [67].

Despite being the first systematic review that deals with the general effects of PN on adult patients with IBD, this article is not exempt from limitations. It is possible that the CONSORT questionnaire was not the best for evaluating the NRCCT, and UNRCT reviewed; however, this limitation has been tried to be avoided by adjusting the items of this tool to the type of study, as no questionnaire was found that evaluated the RCCT, the NRCCT and the UNRCT [26,68]. Also, most of the studies were somewhat old, with the most current one being from 2012, which could have reduced the score of this tool on the methodological quality due to the lack of standard criteria at the time the clinical trials were conducted. The UC and CD data have been combined to develop the meta-analysis for the variables BW, albumin, and postoperative complications due to the low number of studies that separated these diseases to elaborate their results. However, these clinical entities have different clinical courses.

The results derived from this work could help in clinical practice, to help the health professionals with the creation of a guide oriented towards evaluating the addition of TPN within the set of medical therapies for an adult patient diagnosed with IBD. However, as future lines of research, the use of TPN with the said patients should be addressed, having in mind their quality of life, the manner of administration, and the composition of the nutritional therapy in all the surgical procedures possible.

PN has shown to have efficacy for the treatment of IBD and is compatible with other medicines. The CDAI and albumin improve, although the effect of PN is greater after a while. However, the effect on the albumin could be less than the observed value in the meta-analysis, due to possible publication bias. The body weight does not change after intervention. Postoperative complications utilizing PN has been observed, although the proportion is low. More studies specifically referred to UC and CD are needed to develop more concrete clinical results.