Myth Buster #5: Patient Behavior is the Primary Determinant of Outcomes After Bariatric Surgery

From MythBusters, Discovery Channel

I found this to be one of the most interesting Myths to be Busted so far.

The idea that there really were other significant determinants of outcomes, more than behavior, piqued my interest.  I know how many times we have discussed results of the various procedures (and various patients) and wondered what the various factors were, but we always seem to start and end with behavior.  Admittedly, that does seem to be such a huge part of the result of the surgery for an individual patient, but is there more...?

Studies have been done demonstrating the wide variability of results from patient to patient, albeit in a moderately narrow range.  This is exemplified by one study of Gastric Bypass patients who fell within a standard deviation of 20% Excess Weight Loss (EWL) amongst a studied group of 150 patients.

Furthermore, the variability of results also extends to other outcomes of surgery, including the magnitude of weight regain, DM2 improvement, lipid levels, HTN, and occurrence of adverse metabolic and nutritional effects.

Coming to an understanding of the basis of this variability would likely improve the overall utility of surgery, in a couple of ways.  With improved predictive value in terms of patient-specific beneficial and adverse outcomes, there would be an overall improvement in risk-benefit (and cost-benefit) profiles to Bariatric surgical procedures.  Also, that same information could be used to increase the understanding regarding how to improve results in patients that would be thought of as at higher risk of complications or not faring as well as others.  That latter group may still be a patient (DM2) that stands to gain a significant benefit from the surgery, or one that has no other real non-surgical option left.

The factors associated with weight loss surgery success vary from clinical to non-clinical components.

Clinical contributors that have been studied to reveal significantly better weight loss after Gastric Bypass are lower preoperative BMI, absence of DM2, higher capacity for physical exertion, higher education level, and greater participation in postoperative care.

Non-Clinical factors fall into mostly the description of genetics.  A few studies have looked at identical twins, genetically-related adults, and non-related cohorts of patients, and have shown repetitively that there is a strong genetic contribution to weight loss after Gastric Bypass.  In the identical twin group, the weight loss only varied by an average of 1.5% between the 2 pairs of twins. Yikes.  This is likely the start of a new field in medicine-"Surgicogenomics".

So, in summary, there is increasing recognition of multiple aspects to success after Bariatric Surgery- behavioral, physiological and genetic.  I still would have to say that behavior is the main determinant for success after surgery, but there are a few other factors at work as well that need further exploration.   With more information will come more insight into patient selection, procedure selection, improved results, and diminished untoward effects.


Adapted from Kaplan, Seeley, Harris.  "Patient behavior is the primary determinant of outcomes after bariatric surgery".  The Metabolic Applied Research Strategy, a supplement to Bariatric Times Vol 9 No 9.  C18-21.