Bariatric surgery mechanisms, indications and outcomes

doi:10.1111/j.1440-1746.2010.06391.x

A D VA N C E S I N C L I N I C A L P R A C T I C E jgh_6391 1358..1365

Bariatric surgery: Mechanisms, indications and outcomes
Paul E O’Brien
Centre for Obesity Research and Education, Monash University, Melbourne, Victoria, Australia

Key words Abstract
Obesity, weight loss, bariatric surgery, gastric
banding, gastric bypass, satiety, appetite.
The rising problem of obesity is causing major health problems, reduced quality of life and
laparoscopic surgery. reduced life expectancy. It now generates approximately 10% of all health costs. The
progression of the problem indicates preventive measures have been unsuccessful so far.
Accepted for publication 7 May 2010. Only bariatric surgical treatments have been able to achieve substantial and durable weight
loss. Gastric banding and gastric bypass are used in more than 90% of bariatric operations.
Correspondence The proportion of each varies from greater than 95% bands in Australia, about 50/50 in
Professor Paul O’Brien, Centre for Obesity Europe and USA and nearly 100% bypass in South America. The availability of follow up
Research and Education, Monash Medical is a prime determinant of choice. Understanding the mechanisms of effect for the bariatric
School, The Alfred Hospital, Melbourne, procedures is central to optimizing their effect. The traditional narrow concepts of restric-
Vic. 3004, Australia. Email: tive (blocking the transit of food) and malabsorptive (preventing the absorption of food)
paul.obrien@monash.edu should be discarded and the importance of induction of satiety, change of taste, diversion
of chyme, neural and hormonal mediation and the effects of aversion need to be included.
The primary mechanism of effect for gastric banding is the generation of a background of
satiety and early post-prandial satiation via specifically structured vagal afferents at the
level of the band. At five years after banding or bypass, there is typically a loss of 30–35 kg
representing 50–60% of excess weight. This weight loss has been shown to be associated
with major improvement or complete resolution of multiple common and serious health
problems plus improvement in quality of life and in survival. Level 1 evidence supports the
use of the gastric band over optimal lifestyle therapy. Randomized controlled trials has
shown gastric banding to achieve better weight loss, health and quality of life than optimal
lifestyle therapies for adults above a BMI of 30 and adolescents above a BMI of 35. In
adults with mild to severe obesity and type 2 diabetes gastric banding leads to remission in
three out of four individuals. Perioperative risk is significant with gastric bypass and late
revisional procedures can be required after both procedures. Gastric banding is indicated in
any adult who has a BMI over 30, has problems with their obesity and has made substantial
effort to reduce their weight by lifestyle methods. Gastric bypass or biliopancreatic diver-
sion should be considered in those with BMI greater than 35 if banding is contraindicated
or has been unsuccessful.

are suffering the disease of obesity. A similar rate of growth is
The evolution of obesity occurring in Australia with a current prevalence of approximately
Obesity is likely to be the disease of the 21st century. The growth 22% or 2.9 million adults.5
of obesity is worldwide, a pandemic, with the World Health Orga-
nization (WHO) estimating more than 1.6 billion people are cur-
rently overweight and 400 million obese.1 The rapid increase has
been best demonstrated by the careful population measurements
Obesity and its treatment is becoming
by the Centers for Disease Control and Prevention (CDC) in the
an important part of gastroenterology
United States.2 They show the prevalence of obesity has acceler- Acknowledgment of the problem of obesity is the first step to
ated after 1980. Between 1960 and 1980 the percentage of adults dealing with it. This has come slowly as the traditional view that
who were obese increased only marginally, from 13.4% to 14.4%. weight control is a personal responsibility is strongly embedded.
In the next 20 years it doubled to 30.4%.2 It has continued to Increasingly, governments, healthcare managers and physicians
increase during the present decade. It had risen to 33.8% in 20083 have accepted that we now live in an obesigenic environment, that
and projected figures for 2010 and 2020 are 37.4% and 44.2%, the obesity is causing much illness, premature death and high
respectively.4 Currently, more than 77 million adults in the USA healthcare costs and that the medical community should seek to

1358 Journal of Gastroenterology and Hepatology 25 (2010) 1358–1365
© 2010 Journal of Gastroenterology and Hepatology Foundation and Blackwell Publishing Asia Pty Ltd

PE O’Brien Bariatric surgery—current status

address it as a disease. This attitude is growing strongly in gastro- bariatric surgery. In Australia, there were less than 400 bariatric
enterology. Obesity is a disease of overnutrition. It is driven in part procedures in 1993. In 2008 there were more than 14 000. World-
by gut hormones and liver-derived insulin resistance. It generates wide, it is estimated that a total of 344 000 procedures were per-
diseases such as non-alcoholic steatohepatitis, several common GI formed in that year.14 Roux Y gastric bypass, both laparoscopic and
cancers and gastro-oesophageal reflux disease. Endoscopic and open, was the most common (47%) followed by gastric banding
surgical procedures on the gut are leading the attempts to generate (42%), sleeve gastrectomy (5%) and BPD (2%).14 The trend in
substantial weight loss in the obese. Leading journals are encour- Europe is for RYGB to increase, although gastric banding remains
aging the GI physician and surgeon to be knowledgeable and dominant. The opposite trend is occurring in the USA with gastric
skilled in managing this disease.6 banding now moving ahead of RYGB in frequency. In Australia,
gastric banding is the method of choice in more than 95% of
bariatric procedures.
Increased recognition of the The major differences in surgical approaches across the world
co-morbidities and costs can be seen to be derived directly from the funding of the proce-
Obesity is a one of the most virulent of pathogens. It causes or dures and their follow up requirements. Gastric banding is unique
exacerbates numerous common and serious diseases. Type 2 dia- among surgical procedures in that the placement of the band is
betes is the paradigm of an obesity-derived disease. There are now simply the first step of a process of care that continues perma-
an estimated 285 million people with type 2 diabetes world-wide.7 nently. The adjustment of the band to achieve control of appetite is
Increased weight and diabetes has been directly and strongly the central component of effect and therefore the follow up
linked through two major epidemiological studies, the Nurses’ program is crucial. The uptake of gastric banding is directly related
Health study of 112 000 women8 and the Male Health Profession- to the healthcare support for this follow up process. In Australia,
als study of 51 000 males.9 From baseline BMI values in the low follow up is covered under Medicare and banding has become the
20s, they have shown a direct and substantial rise in diabetes with preferred approach. In Europe, there is generally little funding for
weight increase. For the Nurse’s Health study, from a baseline of follow up and banding struggles. In South America, there is no
BMI of 22, there is 5 times the risk at BMI 25, 27 times the risk at aftercare funding and almost no banding.
BMI 30 and 93 times at BMI 35. The central question is not which operation is best but when
Obesity contributes to ischaemic heart disease, stroke and the bariatric surgery becomes indicated. All current procedures
diseases that are linked to the metabolic syndrome, such as hyper- achieve substantial weight loss. The type of procedure is the detail.
tension, the dyslipidaemias, obstructive sleep apnoea, non- Given the prevalence and pathogenicity of obesity, weight loss is
alcoholic steatohepatitis and polycystic ovary syndrome. Cancer arguably the most powerful treatment in medicine today. Substan-
risk is markedly increased, particularly for colorectal cancer10 but tial weight loss has major benefits to health, survival and quality of
also oesophageal, pancreatic, renal, endometrial, breast and gall life. Type 2 diabetes is the paradigm of an obesity related disease.
bladder cancers.11 In addition, back pain, degenerative diseases of With sufficient weight loss many patients will have remission of
the hips and knees and depression are common. Mortality risk is their disease.15 Most will have improvement in control of blood
markedly increased with obesity, now competing with smoking as sugar levels. Hypertension, obstructive sleeps apnoea, dyslipi-
the most prevalent preventable cause of death.12 daemia, non-alcoholic steatohepatitis, polycystic ovary syndrome,
Costs of the obesity pandemic are large. The direct healthcare metabolic syndrome, gastro-oesophageal reflux disease, asthma
costs in the United States for obesity during 2010 are estimated to and depression have been shown to improve or disappear.16 Obese
be US$194 billion4 and the Americans themselves are spending people who lose weight live longer than a comparative group of
US$59 billion on all the options offered to fight fatness. The total obese without weight loss. Comparison of the long-term survival
annual direct health care cost of overweight and obesity for Aus- of patients after gastric banding with a community group who
tralia for the year 2005 has been estimated to be $21 billion.13 were obese showed a 72% reduction in the relative risk of dying.17

Evolution of bariatric surgery
The hierarchy of obesity therapies
Bariatric surgery began in the 1950s with jejuno-ileal bypass. It
was superseded in the 1970s by gastric stapling procedures, such Obesity is a chronic disease. Resolution of the disease of obesity
as Roux Y gastric bypass (RYGB), various forms of gastroplasty, requires substantial and durable weight loss. The therapeutic
and by the malabsorptive procedure of biliopancreatic diversion options available are listed in Table 1 in order of their risk, side
(BPD). All procedures were able to achieve substantial weight loss effects, invasiveness and costs. We should always begin with the
in the morbidly obese and yet bariatric surgery during this time simplest and safest and work down the list. Lifestyle therapies
really had no impact at a community level as it failed to attract (diet, exercise, behavioral change) should always be the first line
even 1% of those suffering the problem. Factors such invasiveness, of management. Multiple randomized controlled trials (RCTs)
risks of death or complications and unknown long term effects have shown that a modest weight loss of between 2 and 5 kg can
were discouraging this approach. be achieved at 12 months.18–21 This level of weight loss is associ-
In the last 15 years, the application of a laparoscopic approach ated with a clinically valuable reduction of metabolic risk22–24 but
to complex abdominal surgery including bariatric surgery, the generally will not solve the problems of obesity. Lifestyle thera-
development of the laparoscopic adjustable gastric banding proce- pies should be applied optimally and sought to be maintained
dure (gastric banding), improved safety and the better documen- permanently. If, however, they fail to resolve the obese patient’s
tation of clinical effectiveness has led a surge of interest in problems, the next level of therapy should be considered. Current

Journal of Gastroenterology and Hepatology 25 (2010) 1358–1365 1359

Bariatric surgery—current status PE O’Brien

Table 1 Weight loss approaches and their relative risks, side effects, Table 2 How do bariatric procedures work?
invasiveness and costs
Bariatric Surgery—Options for Weight Loss Effect
Ranking Approach Risk
1. Reduce appetite, induce satiety
by risk score
2. Alter the taste of food
1. Lifestyle changes—eat less, more activity and 1 3. Restrict intake
exercise, modify behaviour. 4. Divert nutrients from duodenum
2. Drugs and very low energy diets 2 5. Malabsorption of nutrients
3. Endoscopic approaches—intragastric balloon et al. 4 6. Increase energy expenditure
4. Gastric Banding 5 7. Aversion effect—dumping, steatorrhoea, vomiting
5. Sleeve gastrectomy 7
6. Roux en Y gastric bypass (RYGB) 8
7. Open biliopancreatic diversion (BPD) 9
8. Laparoscopic biliopancreatic diversion 10

drug therapies add little further benefit.25 Very low energy diets can
be effective if taken correctly but are inevitably short term. The
recent versions of the intragastric balloon have yet to show effec-
tiveness by RCT and remain short term options. In spite of vigor-
ous research effort, no additional endoscopic approaches are yet
available which can provide even medium term benefit.
The bariatric surgical procedure of gastric banding becomes the
next option to consider. It should be preferred ahead of other
bariatric procedures on the hierarchy of risk (Table 1) for three
reasons:
1 Safety profile.26,27 Mortality after gastric banding is rare. In
systematic reviews, mortality has occurred in 1 in 200026 or
1 in 3000,28 ten to fifteen times less than for RYGB in the
same reviews. At the Centre for Bariatric Surgery (CBS) in
Melbourne we have now treated over 5700 patients with
gastric banding without mortality.
2 Minimal invasiveness. It is truly minimally invasive, not Figure 1 The adjustable gastric band placed at the very top of the
just because of the laparoscopic approach but also the stomach with no significant gastric pouch above. It is proposed that
minimal dissection needed to place the band. Outpatient compression of vagal afferents within this area of gastric cardia mediate
the satiety effect.
placement is now standard practice for many groups in the
USA and Canada with the mean length of post operative stay
of 2 h.29 Thus it can be placed with less risk and less time in
being a key factor.30 Satiety is the background feeling of not being
hospital than a liver biopsy.
hungry, without relationship to eating. Satiation is the feeling of
3 Complete and easy reversibility. There is no intention of
satisfaction after eating. Both are induced by optimal setting of the
reversal of gastric banding. It has occurred in only 128 of
band adjustment.30 As a result the gastric banding patient can
5710 (2.2%) of CBS patients. However obesity is not a
follow the eating guidelines which center on eating a small amount
curable disease. Better treatments are inevitable and the
of good food slowly. They eat the amount of food that could be
option of reversibility allows the potential to change over to
compressed into half a cup (125 gm) three or less times per day.
newer therapies in the future.
Food must be chewed well. Swallowed food is squeezed across the
The other bariatric procedures are available for consideration
area of the band by oesphageal peristalsis. Between two and six
should gastric banding be contraindicated or has failed. Less than
peristaltic waves are needed to clear a single small bite of food.
1% of our patients at CBS have required conversion.
Feelings of satiation are generated with each squeeze.31–33 Eating
for a maximum period of 20 min and taking one bite per minute
generates enough signals to achieve satiation. Figure 1 shows the
How does bariatric surgery work? position of the band at the cardia of the stomach. Note that there is
A key requirement, not yet fulfilled for all bariatric procedures, is no ‘pouch’ of stomach above the band.
to understand better how the therapeutic effect is achieved. Table 2 At optimal adjustment, the band compresses the cardia of the
lists some of the likely mechanisms. There has been a major stomach to generate a sense of satiety, of reduced appetite through-
increase in our understanding of mechanisms for gastric banding out the day. With eating, multiple additional signals are generated.
and RYGB in recent years. Neural and hormonal mediators for this effect have been sought. A
The induction of satiety and satiation after gastric banding has number of gut peptides are known to influence appetite. Ghrelin
been demonstrated in a prospective blinded crossover study as is the only hormone that increases appetite (orexigenic).



Glucagon-like pepetide-1 (GLP-1), peptide YY (PYY), pancreatic tained for at least 24 months.37 However, this same cross-sectional
polypeptide (PP), gastric inhibitory peptide (GIP) and cholecysto- and prospective study did not confirm the previously reported
kinin (CCK) are known to decrease appetite (anti-orexigenic). postprandial rise of the incretin, GLP-138 which brings into question
None of these appear to change in either basal or post-prandial the proposed role of incretins in the effect of RYGB on type 2
circulating level with the gastric band. diabetes.39 Diet-induced thermogenesis is noted in the rat model of
The vagal afferents are most likely the key mediators of this RYGB40 but remains to be established as an effect in humans.
effect through activation of intraganglionic lamellar endings
(IGLEs).34,35 These are specifically structured vagal afferent
tension/distension receptors attached to the connective tissue
Comparison of bariatric surgery with
sheath of the myenteric ganglia. They are sensitive to distension
non-surgical therapies
and distortion and are slowly adapting. Additional possible vagal We have performed three RCTs in which we have compared
afferent mediators include the intramuscular arrays (IMAs)34 gastric banding with optimal non-surgical programs. The initial
which lie within the circular and longitudinal muscle, are long RCT was of mild to moderately obese adults (BMI 30–35). We
straight varicose axons running parallel to the muscle fibres. They compared optimal non-surgical therapy, including lifestyle mea-
are particular concentrated in the fundus of the stomach, have sures, drug therapy and very low energy diets with the gastric band
close proximity to the interstitial cells of Cajal, the pacemaker and showed significantly better weight loss, health and quality of
cells of the smooth muscle. Morphologically, they appear capable life for the banding group.41 Adverse events were similar between
of detecting distension or distortion of the gastric wall but elec- groups. The gastric band patients had lost 86% of their excess
trophysiological study does not support this role.36 weight (%EWL) compared to 21% EWL in the non-surgical group
The mechanisms involved in RYGB (Fig. 2) are less defined and (Fig. 3). This substantial weight loss effect has remained at 6 years
probably multiple. The traditional concept of distension of the small follow up. The gastric banding participants showed almost com-
gastric pouch and delayed emptying through a narrow stoma has plete resolution of the metabolic syndrome, from 38% to 3% (vs
been considered a central effect. There is an enhanced post-prandial 38% to 24%; a non-significant change) and markedly improved
rise of the satiety-inducing hormone, PYY, an effect that is sus- quality of life as measured by the SF-36. The second study was of
obese adults (BMI 30–40) with type 2 diabetes. There was 73%
remission rate of diabetes in the gastric band group and 13% in the
lifestyle group.42 Again, the metabolic syndrome was significantly
improved in the banding group alone. The third RCT was of obese
adolescents (BMI > 35; age 14–18 years).43 The gastric band
group lost 79% of their excess weight and showed a significant
improvement on the metabolic syndrome which reduced from
36% to zero. There was also an improved quality of life.

Comparison between bariatric
surgical procedures
Table 3 lists a range of comparators and the position of each
current option against these comparators. The key outcome com-
parators between procedures are weight loss, health benefit and

Figure 2 The RYGB involved complete separation of a small section of
upper stomach from the body of stomach, creation of a roux en Y length Figure 3 Weight loss, expressed as % of excess weight lost (%EWL)
of proximal jejunum which is anastomosed to the proximal gastric in a RCT of gastric banding versus optimal non-surgical therapy in mild
pouch. Intake is restricted by the small pouch, gastric emptying is to moderately obese patients (data derived from continued follow up of
restricted by the narrow gastrojejunostomy and food is diverted from gastric banding patients from the RCT41). The gastric banding group
the duodenum. show durability of the weight loss at 6 years follow up.



Table 3 Comparison of attributes of the principal bariatric procedures

Attribute Gastric band RYGB Sleeve gastrectomy BPD +/- DS

Safe +++ ++ ++ +
Effective ++ ++ ++ +++
Durable +++ +++ ? +++
Side effects + ++ + ++
Reversible easily Yes No No No
Minimally invasive +++ ++ ++ +
Controllable/adjustable Yes No No No
Low revision rate + + ? +
Requires follow up +++ ++ + ++

There have been multiple observational studies of the various
comorbidities of obesity and generally these have reported either
total remission or major improvement. Of particular relevance to
the gastroenterologist are the studies of gastro-esophageal reflux
disease45 and non-alcoholic steatohepatitis.46

What are reasonable expectations
of risks?
Death is worst thing that can happen to a bariatric surgical patient.
Mortality rates associated with gastric bypass of up to 2% were
common47–49 but appear to have improved in recent years. The
National Institutes of Health (NIH) in the USA has funded a
longitudinal assessment of bariatric surgery, known as the LABS
study, to provide careful evaluation of the outcomes from bariatric
surgery. The perioperative safety data have now been published.27
Figure 4 Systematic review of the weight loss achieved in the A total of 4776 patients were enrolled and treated at 10 sites,
medium term (3–10 years) by the principal bariatric surgical procedures specifically selected for their bariatric surgical expertise. RYGB
of gastric banding, gastric bypass (RYGB) and biliopancreatic diversion and gastric banding were used. There were 15 deaths in the RYGB
(BPD) (Modified from Reference 44). patients (0.44%) and no deaths in the gastric banding group, a
highly significant difference. These findings are consistent with
adverse events at the medium term (3–10 years). Short term data the systematic reviews.26,28
(<3 years) are largely irrelevant and long term data (>10 years)
would be preferable but are almost totally absent. Systematic
Gastric banding
review of the medium term weight loss outcomes for gastric band-
ing26,28,44 have shown no difference between RYGB and gastric This is my preferred option for the primary treatment of severe
banding but suggest there is a better weight loss with biliopancre- obesity. When applied properly, it is effective, safe and gentle.
atic diversion. Insufficient studies of the latter procedure preclude Adjustability permits maintenance of effect as long as the band is
definitive conclusion. Figure 4 shows the relative % EWL for the in place. Reversibility permits access to other therapeutic options
three principal procedures. that may be developed in the future. There is a need for long term
The effects of bariatric surgery on type 2 diabetes have been skilled aftercare and there is a maintenance requirement, with
subject of two systematic reviews.15,28 Buchwald reported 86% of approximately 10% needing some revisional procedure in
1835 patients from multiple case studies showed remission or 10 years. Removal and replacement of the band for abnormal
improved control.15 Maggard et al.28 reviewed 21 case series and proximal gastric enlargement is effective and revised patients have
reported a range of 64–100% showing remission or improvement. a weight loss equal to the total group.
Numerous methodological problems existed in most of the pub-
lished reports. RCTs constituted less than 5% of 618 studies, the
definition of diabetes and its remission were not adequately
Roux en Y gastric bypass
described and there was extensive but poorly reported loss to Roux en Y gastric bypass (RYGB) has been known to be the most
follow up. Nevertheless, there was a trend towards better outcomes effective of the stomach stapling procedures since the 1980s.50 It
for the RYGB patients than the gastric band patients with complete achieves good weight loss, particularly in the short term. However
remission reported in 70.1% (95% CI 59–83) at more than 2 years it carries significant risk, it is non-adjustable and essentially not
after RYGB and 58.3% (95% CI 42–74) after gastric banding. reversible. Its effectiveness tends to fade with time. In the first
There was a direct relationship between weight loss and remission 12 months after RYGB, a weight loss of 60–70% EWL can be
across the studies. expected. This effect is maintained for 12 months and then begins



a gentle fade to average 50% EWL for those still attending follow Needs and challenges
up at 5 years. It is very effective in resolving type 2 diabetes,
possibly through a post-prandial increase of the incretins GLP-1 Bariatric surgery is never a quick fix. It is a process of care that
and GIP. It is now commonly, but not universally, performed begins with a careful initial clinical evaluation and detailed patient
laparoscopically. The significant mortality of 0.44% seen in the education and it continues beyond the operative procedure through
LABS study involved expert bariatric surgeons.27 The community a permanent follow up. All procedures have the potential for perio-
mortality rate was reported as 1.9% for the 15 years between 1990 perative complications and death. Revisional surgery is relatively
and 2004 and is probably still at or above 1.0%.49 In the LABS common as maintenance of the correct anatomy is intrinsic to
study, 109 of the patients had further abdominal surgery. effectiveness. But bariatric surgery can provide a solution to the
problem of obesity. It achieves substantial weight loss, improved
health and quality of life and a longer life. We need to optimize
Biliopancreatic diversion these benefits and minimize the risks and the costs. The following
It is the most metabolically severe of the current options and are some of the areas for further research and development:
therefore hasn’t proved to be popular with patients or surgeons in 1 A better understanding of the mechanisms of action of each
spite of favorable published outcomes. Biliopancreatic diversion procedure is required to enable optimum surgery and follow
(BPD) has been available for 30 years51 and yet remains a very up.
minor part of bariatric surgery. Worldwide, it constitutes less than 2 We need careful data management for all patients. Bariatric
2% of bariatric surgery.14 However, it does generate good weight surgical procedures should be incorporated into national
loss and should be considered on occasions as a second line bari- clinical registries to enable objective assessment of the risks
atric surgical option. and benefits across the community.
3 There is a need for more randomised controlled trials to
define the benefits of weight loss on various comorbidities of
Sleeve gastrectomy obesity. More study is needed in particular for the patients
The sleeve is the first element of the duodenal switch procedure, a with metabolic diseases—type 2 diabetes, metabolic syn-
variant of the BPD. It has lately become popular as a single drome, non-alcoholic steatohepatitis, the dyslipdidaemias,
procedure because of ease of surgery, relative effectiveness and polycystic ovary syndrome and obstructive sleep apnoea.
perceived lack of need for close follow up. A systematic review of 4 We need to know more about who should be offered bariatric
the 36 studies available to mid-2009 showed 55% EWL at surgery, and define the most safe and efficient pathways for
3 years.52 There has been only one medium term study which assessment, surgery and aftercare.
reports a 40% weight regain by 5 years.53 There is a general expec- 5 We need better cost-effectiveness evaluation of the bariatric
tation that the sleeve will fail to maintain acceptable levels of surgical approach to disease management in comparison
weight loss in the medium term as the tube of residual stomach with existing options.
inevitably expands. Continuation to completion of the duodenal Bariatric surgery has the potential to be one of the most impor-
switch would then need to be considered. Leaks are relatively tant and powerful treatment approaches in medicine. High quality
frequent (>1%) and tend to persist for months generating morbid- of clinical care, good science and comprehensive data manage-
ity, anxiety and costs. ment will allow optimal application of this approach to be realized.
Disclosures: CORE receives unrestricted research grants from
Allergan and Applied Medical.
Who should be considered and who
should not?
There is level 1 evidence supporting a better outcome for using References
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