Effects of Bariatric Surgery on Diabetes

Bariatric procedures differ in their ability to ameliorate T2DM, with intestinal bypass procedures generally associated with greater glycemic control and remission rates than purely restrictive procedures. There has been until now a paucity of data from RCTs comparing the efficacy of various bariatric procedures to treat diabetes. The recently published RCT by Schauer et al. also indicates superior efficacy of RYGB over sleeve gastrectomy in the treatment of diabetes in obese individuals. On the other hand, BPD produced greater remission of diabetes in morbidly obese patients compared to RYGB (95 % versus 75 %) in the RCT reported by Mingrone et al.

Sleeve Gastrectomy as Metabolic Surgery

Karamanakos et al. showed that LSG suppressed fasting and postprandial ghrelin levels and attributed this decrease in ghrelin to improved postoperative satiety and greater weight loss at 1year compared to LRYGB. The LRYGB group in this study had an initial decrease in ghrelin levels after surgery, but these levels returned to normal levels within 3 months. Lee et al. studied the treatment of patients with a low body mass index and type 2 diabetes mellitus between the two groups. LRYGB is reportedly more effective than LSG; they conclude that both procedures have strong hindgut effects after surgery, but LRYGB has a significant duodenal exclusion effect on cholecystokinin. The LSG group had lower acylated ghrelin and des-acylated ghrelin levels but greater concentrations of resistin than the LRYGB group. In addition to evaluations of ghrelin, there are now several small studies demonstrating that gastric emptying is increased after sleeve gastrectomy. The loss of a large reservoir in the gastric fundus and body and preservation of the antral pump provide a reasonable explanation for this finding. A secondary effect of earlier distal bowel stimulation with nutrients after meals due to increased gastric emptying time may be similar to the effects seen after gastric bypass.

Several mechanistic studies have demonstrated early and exaggerated postprandial peak levels of Peptide YY3–36 and GLP-1 after LSG. GLP-1 is an incretin that stimulates insulin production and releases from pancreatic islet cells, and the increased PYY3–36 results in satiety and reduced food intake. Karamanakos et al. have independently shown that the sleeve gastrectomy does have the effect of increasing the transit time of chyme despite an intact pylorus as measured by increased postprandial PYY levels.

Peterli et al. performed a randomized prospective trial with 13 LRYGB and 14 LSG patients to investigate the potential mechanism of LSG focusing on foregut and hindgut mechanisms. They found marked improvement in glucose homeostasis 1 week after surgery in both groups. This improvement was associated with early, exaggerated increases in GLP-1 secretion at 1 week, 3 months, and 1 year postoperatively in both groups. In addition to changes in GLP-1, PYY3–36 increased significantly and ghrelin was suppressed in both groups. It is unclear whether PYY3–36 has a direct effect on glucose homeostasis or if its effects are exhibited via appetite reduction and concomitant weight loss. Preoperatively, some patients had a blunted PYY3–36 and GLP-1 response suggesting some “resistance” to these gut hormones in obese patients. These findings suggest that the LSG should not be viewed merely as a restrictive procedure but also as a procedure that has neurohormonal and incretin effects.

Gastric Bypass versus Laparoscopic Sleeve Gastrectomy

Ramon et al. compared the effects of LRYGB and LSG on glucose metabolism and levels of gastrointestinal hormones such as ghrelin, leptin, GLP-1, peptide YY (PYY), and pancreatic polypeptide (PP) in morbid obese patients. This prospective, randomized study confirmed that the postprandial response of ghrelin, GLP-1, and PYY was maintained in patients undergoing LSG for 12 months after surgery and was similar to the LRYGB group results. A prospective, randomized study by Woelnerhanssen et al. compared the 1-year results of LRYGB and LSG for weight loss, metabolic control, and fasting adipokine levels. The authors confirmed a close association of specific adipokines with obesity and with the changes observed with weight loss after two different bariatric surgical procedures. The concentrations of circulating leptin levels decreased by almost 50 % as early as 1 week postoperatively and continued to decrease until 12 months postoperatively and adiponectin increased progressively. No differences were found between the LRYGB and LSG groups regarding adipokine changes.

How to choice a procedure?

The choice of procedure is an important determinant of outcome with a decreasing gradient of efficacy predicted from BPD, RYGB to SG and then
LAGB. Other factors that have been positively correlated with diabetes remission are percentage of excess weight loss (% EWL), younger age, lower preop HbA1c, and shorter duration of diabetes (less than 5 years). Severity of diabetes, as judged by preop treatment modality, has also been noted to be a significant factor.

Schauer et al. have reported in their series of 191 obese diabetic patients (the majority of whom were on oral agents or insulin) a diabetes remission rate of 97 % in diet-controlled, 87 % in oral agent treated, and 62 % in insulin-treated subjects. This was also confirmed by a recent retrospective analysis of 505 morbidly obese diabetic patients who underwent RYGB. In this study, a more recent diagnosis of T2DM and the absence of preoperative insulin therapy were significant predictors of remission, independent of the percentage of EWL.

Dixon et al. have recently identified diabetes duration < 4 years, BMI > 35 kg/m2, and fasting c-peptide concentration > 2.9 ng/ mL as three clinically useful cutoffs and independent preoperative predictors of remission after analyzing the outcomes of 154 ethnic Chinese subjects after gastric bypass. C-peptide > 3 ng/mL has also previously been shown to be an important predictor of diabetes resolution after sleeve gastrectomy in non-morbidly obese diabetic subjects by Lee et al.

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