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The Gut Microbiome Shifts Acutely and Independently From Hypocaloric Restriction Following the Vertical Sleeve Gastrectomy
Cyrus Jahansouz*1, Christopher Staley2, Hongliang Xu4, Michael J. Sadowsky2, Alexander Khoruts3, Sayeed Ikramuddin1
1Surgery, University of Minnesota, Minneapolis, MN; 2BioTechnology Institute, University of Minnesota, Minneapolis, MN; 3Medicine, University of Minnesota, Minneapolis, MN; 4Biochemistry, University of Minnesota, Minneapolis, MN
INTRODUCTION:
The Vertical Sleeve Gastrectomy (VSG) dramatically improves glucose homeostasis even before substantial weight loss. Mechanistic explanations may be related to the anatomic or dietary changes associated with bariatric surgery. Both factors can affect the gut microbiota, which is known to have important roles in energy metabolism. In order to dissect these contributors, we compared acute shifts in the composition of fecal microbiota in patients treated with either VSG or hypocaloric diet (HC Diet) prior to significant weight loss.
METHODS:
Eighteen obese patients with prediabetes or T2DM were recruited to either VSG (n=7) or a hypocaloric diet (HC Diet) (n=11) matching that which post-bariatric surgery patients adhere. Fecal samples were collected prior to and seven days following intervention and bacterial composition was characterized using 16S rRNA gene profiling.
RESULTS:
No baseline differences were present between VSG and HC Diet groups with regards to age, weight at intervention, BMI, HbA1c, and fasting glucose (Table 1). Prior to intervention, each patient exhibited a predominance of the phylum Firmicutes. After one week, both cohorts experienced similar weight loss. However, only VSG patients experienced a significant shift in community composition (beta-diversity) (ANOSIM p<0.001), favoring a decrease in Firmicutes and a near 2.5 fold increase in Bacteroidetes. Shifts in phyla abundances corresponded to shifts in the families Lachnospiraceae (Firmicutes), Ruminococcaceae (Firmicutes), Bacteroidiaceae (Bacteroidetes), and Porphyromonadaceae (Bacteroidetes). Only a minimal and non-significant shift occurred in the HC Diet cohort, as Firmicutes remained the dominant phylum in relation to Bacteroidetes at a ratio of 2:1.
CONCLUSIONS:
Microbiome changes associated with VSG fundamentally differ from those in hypocaloric restriction. We hypothesize that this difference is mechanistically linked to the sustained metabolic improvement that can be achieved with VSG. Longer-term studies that also include functional characterization of gut microbiota are needed to test this idea.
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