Defining Physiological Ketosis Following Very-Low-Calorie Diets

Introduction: Very low-calorie diets (VLCDs) are used preoperatively in bariatric-metabolic surgery; however, this can lead to physiological ketosis. Euglycemic ketoacidosis is an increasingly recognized complication in diabetic patients on sodium-glucose-cotransporter-2 inhibitors (SGLT2i) undergoing surgery and requires assessment of ketones for diagnosis and monitoring. VLCD induced ketosis may confound monitoring in this group. We aimed to evaluate the influence of VLCD, compared to standard fasting, on perioperative ketone levels and acid-base balance.

Materials and methods: Twenty-seven patients were prospectively recruited to the intervention group and 26 to the control group from two tertiary referral centres in Melbourne, Australia. Intervention group patients were severely obese (body mass index) (BMI) (≥35), undergoing bariatric-metabolic surgery, and prescribed 2 wk of VLCD preoperatively. Control group patients underwent general surgical procedures and prescribed standard procedural fasting only. Patients were excluded if diabetic or prescribed SGLT2i. Ketone and acid-base measurements were taken at regular intervals. Univariate and multivariate regression was utilised with significance defined as P < 0.005.

Clinicaltrials: gov ID: NCT05442918.

Results: Patients on VLCD, compared to standard fasting, had an increased median preoperative (0.60 versus 0.21 mmol/L), immediate postoperative (0.99 versus 0.34 mmol/L) and day 1 postoperative (0.69 versus 0.21 mmol/L) ketone level (P < 0.001). Preoperative acid-base balance was normal in both groups, however VLCD patients were found to have a metabolic acidosis immediately postoperatively (pH 7.29 versus pH 7.35) (P = 0.019). Acid-base balance had normalized in VLCD patients on postoperative day 1.

Conclusions: Preoperative VLCD resulted in increased pre- and postoperative ketone levels with immediate postoperative values consistent with metabolic ketoacidosis. This should be considered particularly when monitoring diabetic patients prescribed SGLT2i.