title: Roux-en-Y gastric bypass versus calorie restriction: support for surgery per se as the direct contributor to altered responses of insulin and incretins to a mixed meal.
abstract: OBJECTIVE
  To study the immediate effects of Roux-en-Y gastric bypass (RYGB) on glucose homeostasis, insulin, and incretin responses to mixed-meal tests compared with the effects of calorie restriction (CR).
  
  
  METHODS
  University-affiliated bariatric surgery clinic.
  
  
  BACKGROUND
  RYGB induces remission of type 2 diabetes (T2D) long before significant weight loss occurs. The time course and underlying mechanisms of this remission remain enigmatic. A prevailing theory is that secretory patterns of incretin hormones are altered due to rearrangement of the gastrointestinal tract. To what extent reduced calorie intake contributes to the remission of T2D is unknown.
  
  
  METHODS
  Nine normoglycemic patients and 10 T2D patients were subjected to mixed-meal tests (MMT) 4 weeks before surgery before initiation of a very low calorie diet regimen (MMT-4 w), 1 day before surgery on a very low calorie diet regimen (MMT-1 d), on the morning of the first day after surgery (MMT+1 d; first postsurgical meal), and 6 weeks after surgery (MMT+6 w). Insulin, glucose, active glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured.
  
  
  RESULTS
  CR lowered insulin in T2D patients, whereas glucose, GIP, and GLP-1 were unaffected. RYGB immediately increased plasma insulin and GIP. The GLP-1 response was delayed compared with the GIP response. T2D patients exhibited lower insulin responses after RYGB compared with normoglycemic patients. GIP responses were similar in both groups at all occasions, whereas T2D patients displayed markedly elevated GLP-1 responses 6 weeks after RYGB. Glucose was unaffected by CR and RYGB in both groups. Insulin sensitivity was unaffected by CR but improved with RYGB.
  
  
  CONCLUSIONS
  RYGB exerts powerful and immediate effects on insulin and incretin responses to food, independently of changes caused by CR.
authors.affiliation: Department of Surgery, Kalmar County Hospital, Kalmar, Sweden; Lund University Diabetes Centre, Lund University, Malmö, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Berggren
authors.affiliation: Lund University Diabetes Centre, Lund University, Malmö, Sweden.
authors.forename: Andreas
authors.initials: A
authors.lastname: Lindqvist
authors.affiliation: Lund University Diabetes Centre, Lund University, Malmö, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Hedenbro
authors.affiliation: Lund University Diabetes Centre, Lund University, Malmö, Sweden.
authors.forename: Leif
authors.initials: L
authors.lastname: Groop
authors.affiliation: Lund University Diabetes Centre, Lund University, Malmö, Sweden. Electronic address: Nils.wierup@med.lu.se.
authors.forename: Nils
authors.initials: N
authors.lastname: Wierup
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D031204:Caloric Restriction; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism / Q000628:therapy*; D005260:Female; D015390:Gastric Bypass; D005749:Gastric Inhibitory Polypeptide / Q000378:metabolism; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use; D054795:Incretins / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D061385:Insulins / Q000627:therapeutic use; D062407:Meals; D009765:Obesity / Q000601:surgery
chemical_list: D001786:Blood Glucose; D007004:Hypoglycemic Agents; D054795:Incretins; D007328:Insulin; D061385:Insulins; D005749:Gastric Inhibitory Polypeptide; D052216:Glucagon-Like Peptide 1
keywords: Bariatric surgery; Calorie restriction; Gastric bypass; Incretins