Obesity Surgery

Twenty-five percent of the adult Australian population are obese (body mass-index (BMI) greater than 30 kg/m2). Obesity is a significant risk factor for the metabolic syndrome and other diseases.  Weight-loss (bariatric) surgery provides durable reduction in weight and remission of obesity related co-morbidities.  Current debate centres on the application of bariatric surgery in the non-morbidly obese population and the choice of operation.

Bariatric surgery is indicated for morbidly obese patients (BMI>40) who have failed non-surgical weight loss.  In this patient group there is good evidence that it improves quality of life and prolongs survival.  Surgery is also indicated in those with a BMI>35 with significant obesity related co-morbidities.  There is some evidence to recommend bariatric surgery to any obese non-insulin dependent diabetic, but this has yet to be tested in large prospective trials.

There are three bariatric procedures commonly performed in Australia: the adjustable gastric band (AGB), the roux-en-Y gastric bypass (RYGBP), and the sleeve gastrectomy (SG).  These procedures are generally performed laparoscopically, although open surgery is sometimes used in the revisional setting.  All three operations act primarily by restricting the volume that can be eaten.  Primarily malabsorptive operations, such as the bilio-pancreatic diversion, have been associated with significant morbidity and mortality and are not routinely performed in this country.  The vertical banded gastroplasty (“stomach stapling”) is now obsolete.

The AGB accounts for 95% of bariatric surgery in Australia.  This popularity relates to its perceived safety.  There is no doubt that the AGB is the safest weight-loss operation (Table 1), but revisional surgery is required at a rate of 1-2% per year.  This is mostly for slippage of the stomach under the band, erosion of the band into the stomach or inadequate weight-loss.  Revisional bariatric surgery is more complex than primary surgery and there is a four-fold increase in morbidity and mortality.

Predicted weight-loss with the AGB is 50% of excess body weight (EBW) over three years.  This is achieved with careful follow-up to ensure that the degree of restriction is appropriate. The AGB works by transiently obstructing the passage of solid foods, which stretches the gastric wall above the band thereby signaling satiety.  An AGB that is too tight leads to maladaptive eating: softer textured foods are favoured as solids precipitate pain, reflux or regurgitation.  This bypasses the satiety mechanism leading to inadequate weight-loss, and probably increases the rate of AGB slippage due to recurrent vomiting.  Regular dietetic review is mandatory to monitor nutritional intake and help facilitate changes in eating behaviours (e.g. avoiding grazing, eating slowly, eating to satiety rather than fullness).

Four percent of the Australian population currently have diabetes and this number is predicted to rise significantly. Bariatric surgery cures a significant proportion of type two diabetes.  A randomized controlled trial (RCT) by Dixon et al (10) compared the AGB to conventional therapy in 60 obese patients (BMI 30-40).  Over a two year follow-up period 73% of the surgically treated group achieved remission compared to 13% of the conventionally treated group.  The same group have published the cost-effectiveness of surgery as a treatment for type two diabetes and concluded that it is a dominant intervention: one that saves money ($2400) and prolongs life (1.2 quality-adjusted life-years).

The RYGBP is the most established bariatric procedure; gastric bypass for weight loss has been performed since the 1960s.  Predicted weight loss averages 65% EBW, mostly by 18 months post-op and there is a sustained reduction of 30% of total body-weight at 10 years.  A small gastric reservoir is created and a roux limb of jejunum is anastomosed to it.  While the primary effect of surgery is to restrict the volume of food eaten, undigested food entering the roux limb can lead to a dumping syndrome which acts as a deterrent to over-eating calorie rich foods. Bypass of the proximal small bowel leads to a reduction in putative diabetogenic factors which leads to rapid resolution of type two diabetes, even before significant weight-loss occurs.  Remission of diabetes is seen in 75-95% of patients.

Laparoscopic RYGBP is technically more demanding than AGB, and the complications of surgery (anastomotic leak, stomal ulceration, internal hernia) are potentially life threatening.  Nutritional sequelae such as iron deficiency, vitamin B12 deficiency, osteoporosis and gallstone formation occur with greater frequency than with the AGB, and mandate careful follow-up.

Laparoscopic SG is a relatively new procedure.  It originated as the first stage of a two stage procedure in the super-obese, but is now increasingly performed as a definitive bariatric operation.  It is the only non-reversible bariatric operation: it involves removal of the greater curvature of the stomach leaving a narrow gastric tube.  The fundus of the stomach is the primary site for ghrelin secretion.  Ghrelin is the only identified orexigenic hormone (“hunger hormone”) and SG has been shown to lead to sustained reduction in ghrelin levels and reduced hunger compared to other bariatric operations.  Karamanakos et al enlisted 32 patients in a double blind RCT comparing SG with RYGBP and found better weight loss in the SG group at one year (70% vs 60%).  Himpens et al compared SG with AGB (80 patients) and found better weight loss at three years (66% vs 48%).  The long term results of the SG are yet to be published: gastric reflux and dilatation of the sleeve have been reported, and the incidence of weight regain is not yet known.  The SG sits between the AGB and RYGBP in terms of operative morbidity: anastomotic leak from the long gastric staple line has been reported in up to 1% of cases, however there is no potential for procedure-related complications once convalescence is complete (cf. RYGBP where there is up to a 5% lifetime incidence of internal hernia requiring re-operation).  This may make the SG an appropriate choice for people living remotely.

Bariatric surgery in Australia is still dominated by the AGB, and with good reason, as Australia’s published results for weight-loss with the AGB are the best in the world.  The AGB is a prosthetic device and a certain proportion will require revision.  As the cohort of patients requiring revisional surgery grows, so will the prevalence of RYGBP.  There are no large multi-centre trials comparing the various operations as primary procedures, and these are unlikely to happen until the surgery becomes widely available in the public sector.  A tailored approach to the choice of primary operation based upon patients’ expectations of weight loss, ability to attend follow-up, co-morbidities, presence of reflux and initial BMI may lead to a reduction in the need for revisional surgery (table 2).

Table 1. Efficacy and risk of bariatric surgery

  AGB SG RYGBP
EBW loss 50% at 3 years 65% at 2 years 65% at 2 years
Failure rate 20% 10% 10%
Mortality 0.1% 0.2% 0.4%
Morbidity 2% 5% 5%
Revisional surgery 10% at 10 years ? 5%

Failure rate refers to failure to achieve loss of 50% EBW.

Table 2. Factors influencing choice of operation

  AGB SG RYGBP
BMI>50 + + -
Patient goal BMI<30 - + ++
Remote or difficulty with follow-up - + -
GORD + - +
NIDDM + + ++