Arya M. Sharma, MD

As regular readers will be well aware, our recent publications on the Edmonton Obesity Staging System clearly show that BMI alone is a rather poor measure of mortality risk associated with excess weight.

Thus, according to our analyses of the NHANES population, 20-30% of obese individuals (Stage 0/1) had virtually no increased mortality risk even over the almost 20 year observation period, compared to Stage 2/3 individuals, who had substantially increased risk. Conversely, even in the ‘overweight’ category (BMI 25-30), almost 50% of individuals had a mortality risk as high of that of obese Stage 2/3 individuals.

This means that indications for obesity treatment based on BMI alone will overtreat a substantial number of obese individuals, who may have little benefit in terms of mortality, and miss an even greater number of individuals, who may well benefit from such treatments.

These observations are directly relevant to yesterday’s post on the findings of the SOS study.

As readers will recall, not only was there no relationship between BMI levels and cardiovascular outcomes in the SOS population but the overall cardiovascular risk of these participants - despite the majority being ’severely’ obese - was surprisingly low. In fact, the annual risk for experiencing an adverse cardiovascular outcome for SOS participants was well under 1% per year!

This risk level is highly reminiscent of the overall risk of Stage 0 obese individuals in our NHANES analyses.

Thus, it is readily apparent why it took almost 15 years to demonstrate any cardiovascular benefit of bariatric surgery in the SOS study - clearly this was a very ‘low-risk’ obese population.

Contrast this to the almost 3% annual cardiovascular event rate for the participants in the SCOUT trial, which, by definition, consisted exclusively of Stage 2/3 individuals. In this population, it took less than 3.5 years of even very modest weight-loss (3 to 10 kg) to significantly reduce cardiovascular outcomes.

But did surgery prove more beneficial in higher-risk participants in the SOS trial? It certainly did!

In fact, the only predictor of greater benefit of having bariatric surgery in the SOS paper proved to be having an elevated plasma insulin level - a rather crude marker of insulin resistance. It is fair to assume that these participants were in fact those with higher obesity Stages (elevated fasting insulin levels alone, would already suggest at least Stage 1 obesity).

The importance of this difference is reflected in the numbers-needed-to-treat (NNT): as low as 21 in participants with baseline plasma insulin concentrations above the median (>17.0 mU/L) and as high as 173 in individuals below or at the median (≤17.0 mU/L) insulin concentration.

This essentially means that you would need to operate only 21 patients with Stage 1+ obesity to ’save’ one life (over 15 years) but 173 Stage 0 patients for the same benefit. It does not take a financial genius to figure out that from a ‘cost-per-life-saved’ perspective, operating on Stage 1+ patients is a ‘no-brainer’ whereas operating on Stage 0 patients would (and should) probably raise some eyebrows (especially in a publicly funded healthcare system).

Thus, as we have argued before (and argued by Livingstone in an editorial accompanying the SOS paper in JAMA), it is high time we fully appreciate the “inadequacy of BMI as an indication for bariatric surgery” and begin adopting more sophisticated criteria (such as those of the Edmonton Obesity Staging System) to ensure that this treatment is available to those who are likely to benefit the most.

AMS
London, UK

Padwal RS, Pajewski NM, Allison DB, & Sharma AM (2011). Using the Edmonton obesity staging system to predict mortality in a population-representative cohort of people with overweight and obesity. CMAJ : Canadian Medical Association journal = journal de l’Association medicale canadienne, 183 (14) PMID: 21844111

Livingston EH (2012). Inadequacy of BMI as an indicator for bariatric surgery. JAMA : the journal of the American Medical Association, 307 (1), 88-9 PMID: 22215170

Earlier this week, I posted on an analysis of the SCOUT trial, in which we found a clear and significant ‘dose-response’ relationship between moderate weight loss (3-10 Kg) and reduced cardiovascular outcomes (including death) in the over 10,000 high-risk participants in this trial.

So far, the only data showing a reduction in overall mortality with weight loss comes from studies looking at the effects of bariatric surgery, such as the ongoing Swedish Obese Subjects (SOS) study, which just published its latest findings in the Journal of the American Medical Association (JAMA).

In this paper, Lars Sjöström and colleagues from the University of Gothenburg, Sweden, specifically examine the relationship between bariatric surgery, weight loss, and cardiovascular events in the SOS study.

Some readers may recall that the SOS study is an ongoing, nonrandomized, prospective, controlled study conducted at 25 public surgical departments and 480 primary health care centers in Sweden of 2010 obese participants who underwent bariatric surgery and 2037 contemporaneously matched obese controls who received usual care. Inclusion criteria were age 37 to 60 years and a body mass index of at least 34 in men and at least 38 in women. Surgery patients underwent gastric bypass (13.2%), banding (18.7%), or vertical banded gastroplasty (68.1%), and controls received usual care in the Swedish primary health care system.

In the present analysis, bariatric surgery was associated with an almost 50% reduction in the number of cardiovascular deaths (28 events among 2010 patients in the surgery group vs 49 events among 2037 patients in the control group) over the almost 15 years of follow-up. Similarly, there was an almost 35% reduction in the number of total first time (fatal or non-fatal) cardiovascular events (myocardial infarction or stroke, whichever came first) in the surgery group (199 vs. 234 events).

Notably, however, the investigators found no significant relationship between cardiovascular outcomes and baseline BMI or the magnitude of weight loss. This is in contrast to the SCOUT study, where we found a clear ‘dose-response’ relationship between the amount of weight lost and the reduction in cardiovascular outcomes.

Several factors may explain this lack of ‘dose-response’ relationship in the SOS study.

For one, the SOS population, despite being far more obese than the participants in the SCOUT trial, were at a much lower risk for cardiovascular complications. Thus, the annualised event rate per 1000 participants in the SCOUT trial population was more than four times that of the SOS trial (30 vs. 7). Thus, the SOS study, despite its size, duration, and heavier BMI of participants, may simply be underpowered to demonstrate a ‘dose-response’ relationship between the magnitude of weight loss and reduction in cardiovascular outcomes.

Another explanation for the lack of ‘dose response’ in the SOS vs. SCOUT trial could be related to the overall magnitude of weight loss. Thus, while average weight loss in the SCOUT trial was just under 5%, the average weight loss in SOS was about 20%. if, as many suspect, a moderate 5-10% weight loss is all it takes to significantly reduce cardiovascular risk, the average weight loss of 20% in SOS would obscure any ‘dose-response’ relationship, as all participants in SOS, so to say, were already on the highest effective ‘dose’ of weight loss.

Thus, by no means is it clear from the SOS study that losing 20% of your body weight through bariatric surgery is any better than losing just 5% of your body weight as far as cardiovascular outcomes are concerned (this is not denying any other potential benefits of bariatric surgery on diabetes, cancer, arthritis, sleep apnea, or quality of life).

Thus, in light of the recent SCOUT findings, the superiority of bariatric surgery to medical obesity treatment in reducing cardiovascular outcomes would indeed need to be demonstrated in a ‘head-to-head’ trial  - a study that is unlikely to be done anytime soon.

interestingly, the lack of relationship between baseline BMI and cardiovascular outcomes and the remarkably low overall incidence of cardiovascular complications in the SOS patients raises a number of other important issues regarding indications for surgery - a topic that I will save for tomorrow’s post.

AMS
Berlin, Germany

Sjöström L, Peltonen M, Jacobson P, Sjöström CD, Karason K, Wedel H, Ahlin S, Anveden Å, Bengtsson C, Bergmark G, Bouchard C, Carlsson B, Dahlgren S, Karlsson J, Lindroos AK, Lönroth H, Narbro K, Näslund I, Olbers T, Svensson PA, & Carlsson LM (2012). Bariatric surgery and long-term cardiovascular events. JAMA : the journal of the American Medical Association, 307 (1), 56-65 PMID: 22215166

Regular readers are by now quite familiar with the Edmonton Obesity Staging System (EOSS), which describes how ’sick’ rather than just how ‘big’ patients are.

In a paper just published in OBESITY SURGERY, we discuss how EOSS could be applied to better determine indications for bariatric surgery.

As we point out:

“…health technology assessments specify that bariatric surgery is cost-effective in patients with diabetes (EOSS stage 2). In contrast, the cost-effectiveness of bariatric surgery in patients without comorbidities (EOSS <2) is far less clear. Thus, it is likely that a formal health economics analysis based on the EOSS criteria will support the cost-effectiveness of bariatric surgery for EOSS 2/3 patients, with minimal (if any) cost-effectiveness (even in the long-term) in EOSS 0/1 individuals.”

We also note that:

“It may be argued that bariatric surgery prioritized to EOSS scores 2 and 3, who have increased severity of obesity-related comorbidities, rather than scores 0/1 may miss the opportunity to apply bariatric surgery as a preventative measure. However, in a public-funded health-care system, with limited access and resources, it is prudent to prioritize these resources to those in greatest need. In addition, there is little known about the natural history of obesity, and thus, it remains challenging to predict who will indeed progress to higher EOSS stages and who will remain stable.”

Clearly, our recent publications on EOSS have made it evident that BMI criteria alone are neither a good measure of health nor an adequate predictor of mortality.

Whatever the utility of BMI in population surveys may be, it’s use in clinical decision making is clearly limited - this will need to be reflected in future guidelines and practice recommendations.

AMS
Edmonton, Alberta

Gill RS, Karmali S, & Sharma AM (2011). The Potential Role of the Edmonton Obesity Staging System in Determining Indications for Bariatric Surgery. Obesity surgery PMID: 22002510

Readers may recall previous posts on how the risk of obesity in offspring of mothers, who undergo surgery prior to conception, is dramatically reduced.

That is not what this post is about.

Rather, a study by Woodard and colleagues from Stanford University, just published in the Archives of Surgery, suggests that there may be a positive ‘collateral’ effect on body weight and lifestyle in family members of patients undergoing bariatric surgery.

Thus, an analysis of 35 adult family members (60% of who were obese) and 15 children (73% of who were obese) of 35 patients who underwent Roux-en-Y gastric bypass surgery, showed significant weight loss or less weight gain than expected in the adult family members and kids, respectively.

This weight loss in family members was associated with increased daily physical activity levels, improved eating habits, less emotional eating and reduced alcohol consumption.

Thus, it appears that undergoing bariatric surgery well may have substantial beneficial effects on the health of other family members - both partners and kids.

Although I have heard this anecdotally from some of my patients, I wonder if others have made similar observations in their patients.

I also wonder how such findings would be reflected in health-economic assessments of bariatric surgery.

AMS
Edmonton, Alberta

Woodard GA, Encarnacion B, Peraza J, Hernandez-Boussard T, & Morton J (2011). Halo effect for bariatric surgery: collateral weight loss in patients’ family members. Archives of surgery (Chicago, Ill. : 1960), 146 (10), 1185-90 PMID: 22006878

Early this year, as part of the Alberta-Saxony Obesity Research and Training Alliance (ASORTA), we hosted the first International School on Obesity Research and Management (ISORAM).

This event was attended by over 50 faculty and trainees from Alberta and Germany.

In a follow-up to this immensely successful event, we are now planning ISORAM ‘12, which will be held from March 25-30, 2012, at the Chateau Lake Louise, in Alberta, Canada.

This time the focus will be on all aspects of metabolic and bariatric research as well as medical and surgical management of patients with severe obesity.

The course is open to all health professionals from around the world, who would like to hone their expertise in bariatric medicine and metabolic surgery.

The program, which will offer more than 40 hrs of teaching and interactive workshops, will also include ample time for informal networking and scientific exchange with the international faculty in the unique picturesque surroundings of one of Canada’s premier ski resorts.

Specifically, ISORAM ‘12 has the following objectives:

• To provide participants with a sound understanding of the scientific and methodological issues in bariatric medicine and surgical practices.

• To build participants knowledge in the areas of:

a. Clinical assessment and management of bariatric patients
b. Current best practices in dietary, psychological and behavioural management of bariatric patients
c. Current best practices in patient selection and preparation
d. Current understanding of the biology of metabolic and bariatric surgery patients
e. Interdisciplinary obesity research and practice.

• To educate participants in new developments in:

a. Medical and behavioural management of severe obesity
b. Nutritional and psychosocial complications in bariatric patients
c. Emerging devices in obesity management
d. Rehabilitation issues in bariatric care

• To give participants an understanding of health services/health systems impact on issues related to bariatric care

More information on this event can be here.

Please indicate your interest in learning more about and perhaps participating in this event here.

AMS
Edmonton, Alberta