Pre-Operative Dietary Restriction: Influences on the Intestinal Microbiome

Keywords: Dietary Restriction, Pre-Operative Diet, Intestinal Microbiome, Surgical Stress

Synopsis: A hyperacute inflammatory response in the early days following surgery is associated with enhanced morbidity and mortality and reduced durability of operative interventions. Opportunities to modulate this response and improve surgical outcomes have been elusive. With established roles in attenuating insulin resistance, oxidative stress, and ischemia-reperfusion injury, short-term (<1 week) caloric and protein restriction is being investigated as a pre-operative conditioning strategy to mitigate surgical stress and improve outcomes. Based on an evolving linkage between the intestinal microbiome and the systemic milieu, we sought to examine the temporal dynamics of the intestinal microbiome during short-term dietary restriction.

Methods: 10 healthy individuals participated in a 4-day diet, individualized to achieve 30% calorie restriction and 70% protein restriction. Participants were permitted to resume an unrestricted diet from days 5-7, and stool samples were collected at baseline, day 4, and day 7. Taxonomic analysis included shotgun metagenomic sequencing (ZymoBIOMICS) followed by prevalence filtering and differential abundance analysis using PIME and ALDEx2 software packages. Functional profiling was performed using HUMAnN 2.0.

Results: Four days of dietary restriction caused distinct species variation in the intestine, which quickly returned to baseline after resuming an unrestricted diet (Fig 1). Day 4 clustering on network analysis of prevalent species confirmed the unique community composition after dietary intervention (Fig 2). 44 species were found to significantly differ (FDR p<.05) between baseline and Day 4, particularly notable for decreases in butyrate-producing Firmicutes and increases in mucin-degrading Ruminococcus torques. Despite community variations, alpha diversity between conditions failed to show significant changes (Shannon index p=0.24). Accompany the shift in composition, pathway analysis revealed notable changes in metabolic activity between conditions. Unlike the species composition, however, marked differences in metabolic pathway activity persisted following resumption of an unrestricted diet (Fig 3). 62 unique MetaCyc pathways changes were identified (FDR p<0.05). Reductions in amino acid and lipid biosynthesis pathways, as well as upregulation of catabolic pathways, were the primary functional changes seen on day 4. Figure 4 is an unsupervised hierarchical clustering heatmap of degradation pathways with obvious grouping between days. Notable process changes after dietary restriction included breakdown of organic compounds for use as energy and nutrients as well as decreased utilization of secondary metabolites.

Conclusions: Short-term caloric and protein restriction causes taxonomic diversity changes in as few as four days. Interestingly, a relative dysbiosis is present on day 4 with compositional and functional pathway similarities to inflammatory conditions such as Crohn's disease, suggesting a stressed state within the intestinal microbiome. Similarities in relative abundance before and after dietary intervention reveal a rapid return to baseline. Metabolic characteristics, however, do not fully match this species normalization. Further investigation into the impact of this microbial imbalance is warranted, especially as it relates to systemic stress response pathways and purported benefits of the preoperative conditioning strategy.