Myth Buster #2: Bariatric Surgery Induces Weight Loss via Restriction and Malabsorption

This one got me at first, too. 

This was an interesting idea of a myth that has it's root in the perception of the actual problem with obesity, and how we traditionally have thought of the corresponding benefit of Bariatric Surgery.  Restricting the amount the patient eats, and inducing malabsorption have their part in the success of these procedures, but there is more at work than just that, owing to the uniquely high efficacy of these procedures for weight loss and metabolic benefit.

Restriction 
  
   So what about a patient that has had a jaw wiring?  Why do they remain hungry, and seek the means to override their mechanical restriction?

Malabsorption

   Other operations that create an isolated protein-calorie malabsorption cause an increase in hunger - is there a CNS modulation effect at work with Gastric Bypass and BilioPancreatic Diversion?

Physiological Changes

   Several additional clinical observations support a primarily physiological model for weight loss after Bariatric Surgery.  Few patients become underweight after surgery unless a complication ensues. It would be expected to "overshoot" on occasions if the effect of surgery was purely mechanical. Also, patients that become pregnant after surgery gain weight at an appropriate rate, suggesting that the physiological changes of pregnancy can overcome those as changed by the surgery. And lastly, reports of Bariatric surgery performed on relatively "thin" patients (BMI<30), or animal models, consistently show relatively minimal weight loss.

   Changes in several GI peptide hormones (GLP-1, PYY, CCK, Amylin) likely contribute to a changed physiology post-surgery.  In contrast, the opposite changes are observed after dietary restriction alone (medical models of weight loss), which suggests the body attempts to counter-regulate the induced weight loss physiologically, through increased hunger and decreased energy expenditure.

   Beyond altering gut hormones through surgery, there seems to be other factors that regulate energy balance and metabolic function.  There also seems to be a change in the set point (see last "Myth Buster's" Blog entry), whereby a lower set point for weight is defended as the higher one once was.

In summary, to the degree whereby Obesity is viewed primarily as a behavioral, rather than a physiologic disorder, so goes the thinking of how to respond to the disease state- medically (calorie reduction and increased energy expenditure) or surgically.  Thinking of surgery as a powerful medical therapy, a "pharmacology on steroids" may make the surgical option more acceptable.

From MythBusters

Adapted from L Kaplan, R Seeley, J Harris. "Myth #2:  Bariatric Surgery induces weight loss primarily by mechanical restriction and nutrient malabsorption"  MARS initiative publication, Bariatric Times Vol 9 No 9. C8-C11.