Dr. Sharma's Obesity Notes

Regular readers will be quite familiar with the limited utility of BMI in predicting health status. The same appears to be true regarding the use of BMI in patients with cancer cachexia.

In a paper just published in the Journal of Clinical Oncology, Lisa Martin and colleagues from the University of Alberta studied around 1,500 patients with various stages of lung or gastrointestinal cancer presenting with a wide range of BMI (17% obese, 35% overweight, 36% normal weight, and 12% underweight).

Patients in all BMI categories varied widely in weight loss, muscle index, and muscle attenuation (measured by CT).

Irrespective of BMI, high weight loss, low muscle index, and low muscle attenuation were independently prognostic of survival.

Compared to a survival model containing conventional covariates (cancer diagnosis, stage, age, performance status), a model ignoring these variables but including only BMI, weight loss, muscle index, and muscle attenuation proved a far better predictor of patient survival.

Patients who had higher weight loss and lower muscle indicators survived 8.4 months, regardless of whether they presented as obese, overweight, normal weight, or underweight, in contrast to patients who had none of these features, who survived 28.4 months.

From these finding the authors conclude that, regardless of BMI, cancer patients presenting with involuntary weight loss, muscle depletion and muscle attenuation share the poorest prognosis.

Thus, the authors note that,

“Our findings provide evidence in support of the proposed international consensus definition of cancer cachexia as a multifactorial syndrome defined by an ongoing loss of skeletal muscle mass with or without loss of fat mass.”

Once again, simply stepping on a scale appears to be a rather limited measure of health.

AMS
Edmonton, Alberta

Martin L, Birdsell L, Macdonald N, Reiman T, Clandinin MT, McCargar LJ, Murphy R, Ghosh S, Sawyer MB, & Baracos VE (2013). Cancer Cachexia in the Age of Obesity: Skeletal Muscle Depletion Is a Powerful Prognostic Factor, Independent of Body Mass Index. Journal of clinical oncology : official journal of the American Society of Clinical Oncology PMID: 23530101

According to a landmark paper in this week’s issue of JAMA, I now realize that I need to gain about 75 lbs to get the most out of my pension plan.

Indeed, that is just about how many extra pounds I would need to pack on to achieve a BMI of 33, which would finally put me squarely in the Class 1 obesity range. That, according to this extensive review of the literature, would bestow me with the longest life expectancy.

Unfortunately, this will not be easy – If I recall correctly, Morgan Spurlock (the fellow in Super Size Me) only managed to gain a measly 25 lbs – and I recall how hard he had to work at this.

Or, could it perhaps be that the results of this paper are so obviously nonsensical, because the researchers asked the wrong question?

After all, who still cares about BMI?

I can only assume that my US colleagues were far too busy running their analyses to have time to read the Canadian Medical Association Journal (CMAJ or Canada’s version of JAMA), which happened to publish our analysis of data from the US(!) National Health and Nutritional Education Survey (NHANES) on this issue.

As readers of these pages may recall, our analysis of applying the Edmonton Obesity Staging System (EOSS) to two independent NHANES datasets, essentially showed that when it comes to mortality, what matters is how “sick” your are and not how “big” you are.

If you have a weight-related health problem (i.e. EOSS 1+), you die, if not, you don’t – end of story!

Neither BMI nor waist circumference were much use in predicting mortality – but whether or not you had hypertension, diabetes, or sleep apnea was.

As we outline in our paper, not only would BMI overestimate health problems in millions of US citizens, it would also completely miss about 25 million Americans, who do have weight-related health issues, despite falling well below the BMI 30 obesity range.

Perhaps, after this paper, we can finally lay BMI to rest and stop trying to predict people’s health with just scales and measuring tapes.

Hopefully, the only landmark that this paper leaves behind is a tombstone – BMI – RIP!

Let us now get back to actually taking a good medical history, doing a thorough physical exam, and running some tests before declaring someone too light or too heavy for their health.

And in the meantime, let’s not forget that prevention best starts by not losing sleep over your weight unless you have to.

AMS
Edmonton, Alberta

Readers of these pages are probably well aware that increasing body size poses important challenges for many areas of health care. Not least, when it comes to diagnostic imaging.

A paper by Phyllis Glanc and colleagues from the University of Toronto, published in RadioGraphics provides a succinct overview of some of these challenges when it comes to radiographic imaging of the pelvis in obese women.

As the authors point out,

“Obesity can contribute to missed diagnoses, nondiagnostic results of imaging studies, imaging examination cancellation because of weight or girth restrictions, scheduling of inappropriate examinations, and increased radiation dose exposure.”

Furthermore,

“The utility of the clinical examination is often limited in the obese woman, which results in an even greater reliance on imaging.”

Thus,

“Recognition of equipment limitations, imaging artifacts, optimization techniques, and appropriateness of modality choices is critical to providing good patient care.”

Although quite technical (as one would expect), this article is probably a worthwhile read for anyone who orders or performs pelvic exams in obese women.

AMS
Edmonton, Alberta

photo credit: EUSKALANATO via photopin cc

Glanc P, O’Hayon BE, Singh DK, Bokhari SA, & Maxwell CV (2012). Challenges of pelvic imaging in obese women. Radiographics : a review publication of the Radiological Society of North America, Inc, 32 (6), 1839-62 PMID: 23065172

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In the continuing saga of putative metabolic or cardiovascular benefits of this or the other vitamin, the current attention appears to be largely on vitamin D (given that the effects of supplementing other vitamins on these parameters have either been found to be non-existant or even harmful).

Much of the rationale for vitamin D is based on the known biological action of this vitamin (in experimental settings) and on the rather widespread suboptimal vitamin D levels found in a substantial proportion of the population (especially in nordic countries like Canada).

This said, a new systematic review on the role of vit D on glycemic control by George and colleagues from the University of Dundee, UK, published in Diabetic Medicine, finds little effect of vitamin D (or analogues) on preventing or improving diabetes control.

Their review of 15 randomised controlled trials – all of rather moderate quality – showed no significant improvement in fasting glucose, HbA(1c) or insulin resistance in those treated with vitamin D compared with placebo.

For patients with diabetes or impaired glucose tolerance, meta-analysis showed a small effect (non-significant) effect on fasting glucose and a small improvement in insulin resistance but no effect on HbA(1c) levels.

As the authors also note, due to the rather short duration of these trials, there was insufficient data to draw conclusions regarding micro- or macrovascular events.

Furthermore, in the two trials that looked at this issue, there was no reduction in new cases of diabetes in patients treated with vitamin D.

Thus, despite the considerable hype about vitamin D in the popular literature, there is currently no evidence that recommending vitamin D supplementation as a means of preventing diabetes or improving glycaemia or insulin resistance in patients with diabetes is warranted.

Not that this is likely to stop anyone from still expecting wonders from this vitamin beyond its well-recognised benefits (largely on bone health) in patients who do have severe vitamin D deficiencies.

AMS
Edmonton, Alberta

photo credit: Treasure Tia via photo pin cc

George PS, Pearson ER, & Witham MD (2012). Effect of vitamin D supplementation on glycaemic control and insulin resistance: a systematic review and meta-analysis. Diabetic medicine : a journal of the British Diabetic Association, 29 (8) PMID: 22486204

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In 2005, I wrote an article for the Canadian Medical Association Journal (CMAJ), in which I highlighted that fact that in light of the obesity epidemic, physicians and other health care workers will be delivering health care to a growing number of obese and severely obese patients.

“Diagnosing many common medical conditions, although straightforward in nonobese patients, can be fraught with difficulty in morbidly obese people because little is known about the sensitivity and specificity of diagnostic tests in this population. …obtaining imaging studies such as CT or MRI is often impossible for morbidly obese patients because of the size and weight limitations of the machines. Oversized equipment is unavailable in most hospitals. These limitations call for more research into diagnostic algorithms, tests and reference ranges for morbidly obese patients, to avoid misdiagnoses and to ensure optimal care.”

I also noted that with the exception of ‘weight-loss studies’, people with obesity are generally underrepresented in clinical trials.

“As a result, the majority of clinical practice guidelines, even for conditions commonly found in obese patients (e.g., hypertension, diabetes mellitus, asthma, ischemic heart disease, venous thrombosis and neuropsychiatric disorders) fail to make specific recommendations for patients with morbid obesity that go beyond a rather general appeal for weight loss. This issue is far from trivial, as obesity significantly affects the pathophysiology and pharmacodynamic response in a multitude of medical conditions. For example….gastroesophageal reflux disease, where the pathophysiology in obese patients (increased intra-abdominal pressure, hiatal hernia, vagal abnormalities) may be distinctly different from that in nonobese patients. Responses to medications may be different, as metoclopramide may fail to decrease gastric volume or raise pH in obese patients. Similarly, although self-reported asthma is more frequent at higher BMI levels, obese individuals paradoxically are at lowest risk for significant airflow obstruction, and much of the respiratory symptoms may indeed be due to nocturnal aspiration of gastric reflux. Thus, asthma not only may be overdiagnosed in the obese population but, if present, may require a different approach to management.”

I also commented on the need for studies that examine the effects of excess weight on pharmacokinetics and pharmacodynamics of medications commonly used in obese patients.

“Virtually all existing diagnostic criteria and algorithms will need to be revalidated in the obese population, and where physical limitations hinder the use of diagnostic imaging technology, new strategies will have to be developed to deal with very obese people…. In short, most of what we know about medicine will need to be re-evaluated to ensure optimal medical care of obese patients.”

In the seven years that have passed since I wrote this article, we have seen a vast increase in the study of obesity, including studies specifically addressing many of the issues I highlighted in this commentary.

However, we are still far from fully appreciating the impact of the obesity epidemic on medical practice and in many instances, managing obese patients can be better likened to ‘muddling through’ than to a sound evidence-based approach to medical practice.

Training in obesity management or bariatric care is still not a mandatory requirement for graduating from medical school or obtaining your medical license. We are still graduating health professionals, who know more about calcium homeostasis than about energy homeostasis.

If you have experienced problems with diagnostic procedures or treatments because of your size, I’d certainly love to hear about them.

AMS
Vancouver, BC