Bariatric Surgeries and Glucose Homeostasis During a Mixed Meal Test
Condition: Obesity
MeSH terms: Obesity
Study type: Observational

Summary: 
      Bariatric surgery can lead to improvement or even resolution of type 2 diabetes Mellitus
      (T2DM) with the spectrum of responses depending also on operation procedures. However, many
      mechanisms of metabolic action of different surgical techniques still are unclear.

      The aim of this study is to provide a better understanding of the effects of three types of
      bariatric surgery (lap banding, gastric bypass and sleeve gastrectomy) on beta-cell function
      and incretin secretion. A mixed meal tolerance (MMT) test will be performed before and 1 and
      12 months after surgery to assess beta cell adequacy and glucagon-like-peptide-1
      (GLP1)/glucose-dependent insulinotropic polypeptide (GIP) bioavailability.
    

Detailed description: 
      The effects of different kind of bariatric surgery on glucose homeostasis and its primary
      determinants (insulin sensitivity and secretion) may differ from one procedure to another. In
      spite being able to promote improvement/resolution of T2DM, many mechanisms of metabolic
      action of weight-loss surgery are still unclear. It has been hypothesized that changing the
      nutrient route through the gut may be a key factor in changing beta cell function and/or
      insulin sensitivity.

      In this study a mixed meal test will be used to assess changes in glucose regulation, beta
      cell function and incretin bioavailability brought about by different bariatric surgeries in
      obese patients.

      All participants will ingest a standardized mixed meal (163 Kcal; 57% carbohydrate, 33% fat,
      22% prot) and will be monitored for 300 minutes thereafter.

      Baseline (-20', -10', 0') blood samples will be collected to measure plasma glucose, insulin,
      C-peptide, incretins and the 13-Carbon-glucose/12-Carbon-glucose (13C-/12C-glucose) ratio
      (the last one by isotope ratio mass spectrometry).

      At time 0', subjects will ingest a standardized mixed meal containing 30 g corn flour and 20
      g cheese (parmesan) over 20 minutes. Plasma glucose, insulin, C-peptide, GLP1/GIP and the
      13C-/12C-glucose ratio will be assessed at +10', +20', +30', +45', +60', +75', +90', +105',
      +120', +140', +160', +180', +200', +220', +240', +270', +300'.

      Blood samples will be quickly spun at 1500 g at +4°C, plasma/serum will be collected and
      stored at -80°C.

      The 13-Carbon content of maize starch is higher than most of non maize derived sugars. Thus,
      in individuals on maize and cane sugar free diets, the 13-Carbon/12-Carbon (13C/12C) maize
      starch ratio is higher (about 10:1000) than the 13C/12C ratio of endogenous glucose derived
      from glycogenolysis/gluconeogenesis. When these individuals ingest maize starch, the glucose
      molecules appearing in the systemic circulation which are derived from maize starch will
      display a 13C-/12C ratio which is identical to maize starch and higher than endogenous
      glucose. Thus, by measuring the time course of plasma 13C-/12C-glucose ratio, it will be
      possible to distinguish meal derived glucose from endogenous glucose output (glycogenolysis
      and gluconeogenesis).

      This mixed meal test will be performed before and 1 and 12 months after bariatric surgery.
      The same tests with the same timing will be performed in a control group of obese patients
      not undergoing bariatric surgery, being treated with diet only.
    

Intervention name(s): Roux-en-Y-gastric bypass; laparoscopic adjustable gastric banding; laparoscopic sleeve gastrectomy; diet treatment
Intervention type(s): Procedure; Procedure; Procedure; Other
Intervention description(s): Gastric bypass consisted of creation of a 15-20 ml gastric pouch, a 150 cm Roux limb, and a 50 cm biliopancreatic limb; Gastric banding functions by limiting food intake after the placement of an inflatable tube around the stomach just below the gastroesophageal junction, which allows for adjustment of the size of the outlet via the addition or removal of saline through a subcutaneous port.; Sleeve gastrectomy involved a gastric reduction of 75 to 80% by resecting the stomach alongside a 30-French endoscope beginning 3 cm from pylorus and ending at the angle of His; Hypocaloric diet providing a 1000 Kcal/d deficit from total energy expenditure assessed by indirect calorimetry and physical activity determination
Other intervention name(s): RYGB; LAGB; SG; diet
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        A total of 64 morbidly obese patients will be studied, composed of:

          -  16 subjects scheduled for Roux-en-Y-gastric bypass;

          -  16 subjects scheduled for laparoscopic adjustable gastric banding;

          -  16 subjects scheduled for laparoscopic sleeve gastrectomy;

          -  16 subjects not undergoing bariatric surgery, on diet treatment (control group)
      
Biospecimen description: 
      serum, plasma
    
Keywords: bariatric surgery; gastric bypass; gastric banding; sleeve gastrectomy; weight loss; Type 2 Diabetes mellitus; GLP1; obesity; mixed meal test