American journal of physiology. Gastrointestinal and liver physiologyJun 24, 2026

Weight loss surgery changes daily gut bacteria rhythms linked to better metabolism

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Jun 25, 2026

Abstract

Roux-en-Y gastric bypass (RYGB) significantly alters gut microbial composition and function in diet-induced obese mice.

Cecal gut microbial composition showed significant differences at multiple circadian time points in lean and sham-operated mice.
RYGB mice exhibited a notable difference only between the ZT9 and ZT21 time points.
Microbial gene counts and pathways differed between RYGB and sham-operated mice, correlating with liver gene expression.
Certain gut microbial taxa were associated with glucose homeostasis, regardless of the surgical intervention.
RYGB may influence host circadian rhythms alongside gut microbiome changes, potentially contributing to metabolic improvement.

Simplified

The circadian clock and gut microbiome are integral regulators of metabolic homeostasis, with disruptions in either system contributing to obesity pathogenesis. Roux-en-Y gastric bypass (RYGB) effectively treats severe obesity, yet the mechanisms underlying its benefits remain incompletely characterized. We investigated the impact of RYGB on cecal gut microbial composition and function using 16S rRNA sequencing in relation to host circadian gene expression and metabolic parameters in diet-induced obese mice. Diet-induced obese mice underwent RYGB or sham surgery and were compared with lean controls across multiple circadian Zeitgeber time (ZT) points (ZT3, ZT9, ZT15, ZT21). Principal component analysis at the ASV level revealed significant differences in all ZT points (ZT3, ZT9, ZT15, and ZT21) in the lean and sham-operated mice; however, only a significant difference between ZT9 and ZT21 was observed in RYGB mice. Microbial gene counts and microbial pathways were also different between RYGB and sham-operated mice, with several correlating with hepatic Clock and Bmal1 gene expression. Notably, specific taxa showed differential associations with glucose homeostasis, independent of surgical intervention. These findings demonstrate that RYGB alters the gut microbiome and host circadian rhythms, suggesting an association between microbial remodeling, circadian gene expression, and metabolic improvement following bariatric surgery.

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Weight loss surgery changes daily gut bacteria rhythms linked to better metabolism

Abstract

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