Effect of Gastric Bypass Surgery on Energy Metabolism

ERGEM: Effect of Roux-en-Y Gastric Bypass Surgery on Energy Metabolism.

The purpose of this study is to investigate the short term and long term effects of Roux-en-Y gastric bypass (RYGB) surgery on energy expenditure, gastrointestinal and appetite regulating hormone levels, and appetite sensation. We hypothesize that following RYGB surgery, metabolism will be elevated in comparison to patients who have not yet had RYGB but who are losing weight simultaneously using a low calorie diet. We further hypothesize that this higher metabolism will be associated with alterations in fasting and postmeal levels of gastrointestinal and appetite regulating hormones. Long term (1.5 years after RYGB), we hypothesize that differences in metabolism, body composition, and hormone levels will distinguish between patients who have maintained their weight loss after RYGB vs those who have regained weight.

Inclusion Criteria:

• Age 18-65
• BMI ≥40, or ≥35 with concomitant obstructive sleep apnea, or hypertension
• scheduled for RYGB surgery at Hvidovre Hospital, Copenhagen, Denmark
• Must have lost between 1-4% body weight after 3 months of dietary counselling

Exclusion Criteria:

• Deemed ineligible for RYGB surgery by patient's own physician(s)

• Diabetes Mellitus

• Non Caucasian

• Weight >160kg (due to DEXA scanner limitations), or morphologically unable to accommodate in DEXA scanner (>40cm in maximum supine anterior-posterior dimension, or >60cm in maximum supine body width)

• Hemoglobin <7.0 mmol/L

• Psychiatric illness under the care of a psychiatrist

• Eating disorder such as bulimia

• Patients on special diets (eg vegetarian, Atkins)

• Any history of thyroid dysfunction, or use of thyroid medication (with the exception of transient thyroiditis)

• Hypothalamic or genetic etiology of obesity

• A current diagnosis of cancer

• Any surgery other than RYGB planned in the ensuing 3 months

• Substance abuse or smoking

• Use of prescription medications or over-the-counter drugs affecting metabolism

• Excessive intake of alcohol (>7 drinks/week)

• Excessive intake of caffeine (>300 mg/day)

• Presence of any contraindication to use of a low calorie powder diet, including:

  • Past history of ventricular arrhythmias (even if treated)
  • Renal dysfunction (creatinine clearance <60 mL/min)
  • Liver enzymes (ALT or AST) >3x upper limit of normal
  • Milk protein allergy, or lactose intolerance
  • Porphyria or phenylketonuria
  • History of gout
  • Breastfeeding
  • Concomitant use of monoamine oxidase inhibitors or non potassium sparing diuretics
  • Inability or unwillingness to comply with a low calorie diet protocol
  • Patients who find the powder diet products to be unpalatable

• Do not enjoy yogurt, carrots, or milk (as these are essential elements of the low calorie diet)