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There is no consensus regarding energy content or duration of hypocaloric diets used for preoperative optimization of patients before metabolic bariatric surgery. In this systematic review, we aimed to compare the effect of different hypocaloric diets on reductions in total body weight, liver volume, glucose and insulin concentrations, and side effects. Six databases were searched for articles including adults with BMI ≥35 kg/m² treated with hypocaloric diets before metabolic bariatric surgery. Hypocaloric diets were categorized as (1) low-energy diet containing 800–1200 kcal/day for 2–4 weeks, (2) very low-energy diet containing 450–<800 kcal/day for 2–4 weeks, and (3) low-energy diet containing 800–1200 kcal/day for >4 weeks. Thirty-three articles (1868 patients) were included, and if data were sufficient, synthesis without meta-analysis was conducted. A low-energy diet and very low-energy diet for 2–4 weeks resulted in similar reductions in total body weight, but longer treatment correlated to a more pronounced weight reduction. In addition, a low-energy diet for 2–4 weeks led to decreased liver volume, which might facilitate the surgical procedure. Insulin resistance was generally reduced after a low-energy diet for 2–4 weeks. However, most studies were within-group control, and since more than 60% of the studies lacked variance measures for our outcomes, we did not perform a meta-analysis. Accordingly, our results should be interpreted carefully. The protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) with registration number: CRD42022295757; available at: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=295757.

This is an observational study of interstitial glucose (IG) concentrations, IG variability and dietary intake under free-living conditions in 46 females with obesity but without diabetes. We used continuous glucose monitoring, open-ended food recording and step monitoring during regular dietary intake followed by a low-energy diet (LED). Thirty-nine participants completed both study periods. The mean BMI at baseline was 43.6 ± 6.2 kg/m². Three weeks of LED resulted in a mean weight loss of 5.2% with a significant reduction in diurnal IG concentration but with greater glycemic variability observed during LED. The mean 24 h IG concentration decreased from 5.8 ± 0.5 mmol/L during the regular diet period to 5.4 ± 0.5 mmol/L (p < 0.001) during LED, while the mean amplitude of glycemic excursion increased from 1.5 ± 0.7 to 1.7 ± 0.7 mmol/L (p = 0.031). The positive incremental area under the curve at breakfast was significantly larger for LED compared to regular diet. The daily fiber intake and the glycemic index of breakfast meals were significantly associated with the glycemic variability during regular dietary intake. In conclusion, the 24 h mean IG concentration was lower but with more pronounced glycemic variability during LED compared to a regular diet. 

BACKGROUND: Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) lead to lower fasting glucose concentrations, but might cause higher glycemic variability (GV) and increased risk of hypoglycemia. However, it has been sparsely studied in patients without preoperative diabetes under normal living conditions.

OBJECTIVES: To study 24-hour interstitial glucose (IG) concentrations, GV, the occurrence of hypoglycemia and dietary intake before and after laparoscopic RYGB and SG in females without diabetes.

SETTING: Outpatient bariatric units at a community and a university hospital.

METHODS: Continuous glucose monitoring and open-ended food recording over 4 days in 4 study periods: at baseline, during the preoperative low-energy diet (LED) regimen, and at 6 and 12 months postoperatively.

RESULTS: Of 47 patients included at baseline, 83%, 81%, and 79% completed the remaining 3 study periods. The mean 24-hour IG concentration was similar during the preoperative LED regimen and after surgery and significantly lower compared to baseline in both surgical groups. GV was significantly increased 6 and 12 months after surgery compared to baseline. The self-reported carbohydrate intake was positively associated with GV after surgery. IG concentrations below 3.9 mmol/L were observed in 14/25 (56%) of RYGB- and 9/12 (75%) of SG-treated patients 12 months after surgery. About 70% of patients with low IG concentrations also reported hypoglycemic symptoms.

CONCLUSIONS: The lower IG concentration in combination with the higher GV after surgery, might create a lower margin to hypoglycemia. This could help explain the increased occurrence of hypoglycemic episodes after RYGB and SG.

Background: Bariatric surgery improves glucose homeostasis; however, side effects such as hypoglycemia can occur. We investigated the effects of meals on interstitial glucose (IG) response in biliopancreatic diversion with duodenal switch (BPD-DS) and Roux-en-Y gastric bypass (RYGBP)-operated patients at least 1 year after surgery.

Methods: Thirty patients treated with BPD-DS or RYGBP were recruited at the outpatient Obesity Unit, Uppsala University Hospital. IG was measured by continuous glucose monitoring (CGM) for 3 consecutive days, and postprandial IG levels from 5 to 120 min were analyzed for 2 of these days. All intake of food and beverages was simultaneously registered in a food diary, which was processed using The Meal Pattern Questionnaire.

Results: Postprandial IG levels were significantly lower in BPD-DS (n = 14) compared to RYGBP (n = 15)-treated patients, with mean concentrations of 5.0 (+/- 1.0) and 6.3 (+/- 1.8) mmol/L respectively (p < 0.001). The mean postprandial IG increment was lower in BPD-DS than in RYGBP patients, 0.2 (+/- 0.6) vs. 0.4 (+/- 1.4) mmol/L (p < 0.001). Furthermore, the postprandial IG variability was less pronounced in BPD-DS than in RYGBP patients. The mean number of daily meals did not differ between the two groups, 7.8 (+/- 2.6) in BPD-DS and 7.2 (+/- 1.7) in the RYGBP (p = 0.56).

Conclusion: BPD-DS patients demonstrated lower postprandial IG concentrations, with smaller postprandial IG increments and less pronounced postprandial IG variability compared to RYGBP patients. The two groups had similar meal pattern and the postprandial IG responses is probably associated with differences in postoperative physiology.