Metabolic Effects of Gastric Bypass Surgery - is it all about Calories?

Bariatric surgery is an efficient method to induce weight loss and frequently also remission of type 2 diabetes (T2D). Unpaired studies have shown bariatric surgery and dietary interventions to impact differentially on multiple hormonal and metabolic parameters, suggesting that bariatric surgery causes T2D remission at least partially via unique mechanisms.

In the present study, plasma metabolite profiling was conducted in patients with (n=10) and without T2D (n=9) subjected to Roux-en-Y gastric bypass surgery (RYGB). Mixed-meal tests were conducted at baseline, after the pre-surgical very low-calorie diet (VLCD) intervention, immediately after RYGB, and after a 6-weeks recovery period. Thereby, we could compare fasted and post-prandial metabolic consequences of RYGB and VLCD in the same patients.

VLCD yielded a pronounced increase in fasting acylcarnitine levels, whereas RYGB, both immediately and after a recovery period, resulted in a smaller, but opposite effect. Furthermore, we observed profound changes in lipid metabolism following VLCD, but not in response to RYGB.

Most changes previously associated with RYGB were found to be consequences of the pre-surgical dietary intervention. Overall, our results question previous findings of unique metabolic effects of RYGB and suggest that the effect of RYGB on the metabolite profile is mainly attributed to caloric restriction.