A blood pressure that is too high can kill you – so can a blood pressure that is too low.
A blood sugar that is too high can kill you – so can a blood sugar that is too low.
It turns out that BMI is no different – too high and too low both carry a risk – a risk, however, that is substantially confounded by actual body fat%, which is not reliably measured by BMI.
This is basically the message in a paper by my colleagues Raj Padwal and co from the University of Alberta in a paper published in the Annals of Internal Medicine.
The researchers looked at data from about 50,000 women and 5,000 men (mean age, 63.5 years; mean BMI, 27.0 kg/m2) referred for bone mineral density (BMD) testing with dual-energy x-ray absorptiometry (DXA), which they linked to administrative databases.
Given the size and demographics of the cohort, death occurred in almost 5000 women over a median of 6.7 years and 1000 men over a median of 4.5 years.
Women in the lowest BMI and body fat% quintiles had a 40% higher risk of dying (compared to quintile 3). Risk of dying were also about 20% greater in the highest body fat% quintile for women.
Similarly in men, both low BMI (HR, 1.45 for quintile 1) and high body fat percentage (HR, 1.59 for quintile 5) were associated with increased mortality.
The exciting bit about this study is that the researchers had both BMI and body fat% available to them and were able to show that both variables independently of each other contribute to mortality risk.
Thus, the worst possible combination in both men and women was low BMI and high body fat%.
Or, as the authors put it,
“Low BMI and high body fat percentage were both associated with increased all-cause mortality. Mortality increased as BMI decreased and body fat percentage increased…..Thus, our results suggest that BMI may be an inappropriate surrogate for adiposity, and this limitation may explain the presence of the obesity paradox in many studies.”
As the authors discuss, these finding should have clinical implications as they clearly demonstrate the limitations of BMI as a measure of health risk.
“..our findings underscore that the risk for all-cause mortality increases with both increasing adiposity and decreasing BMI in a general population of middle-aged and older adults. These findings also suggest the importance of using direct measures of adiposity when building prognostic or even exploratory models.”
There is no doubt that bariatric surgery is currently the most effective long-term treatment for severe obesity, however, there is also some evidence to suggest that patients seeking bariatric surgery (or for that matter any kind of weight loss) are more likely to have accompanying mental issues that individuals with obesity who don’t and that such issues may affect the outcomes of surgery.
Now, a paper by Aaron Dawes and colleagues from Los Angeles, CA, published in JAMA presents a meta-analysis of mental health conditions among patients seeking and undergoing bariatric surgery.
They identified 68 publications meeting inclusion criteria: 59 reporting the prevalence of preoperative mental health conditions (65,363 patients) and 27 reporting associations between preoperative mental health conditions and postoperative outcomes (50,182 patients).
Among patients seeking and undergoing bariatric surgery, the most common mental health conditions, each affecting about one-in-five patients were depression and binge eating disorder.
However, neither condition was consistently associated with differences in post-surgical weight outcomes. Nor was there a consistent relationship between other mental health conditions including PTSD or bipolar disease and post-surgical outcomes.
Interestingly, bariatric surgery was consistently associated with a significant decrease in the prevalence and/or severity of depressive symptoms.
So what do these findings mean for clinical practice?
As the authors note,
“Guidelines from the American Society for Metabolic and Bariatric Surgery and the Department of Veterans Affairs/Department of Defense recommend routine preoperative health assessments, including a review of patients’ mental health conditions. Other groups advocate for a more comprehensive, preoperative mental health examination in addition to the general evaluation currently performed by medical and surgical teams. The results of our study do not defend or rebut such a recommendation.”
So why are these data not clearer than they should be? Here is what the authors have to offer:
“Much of the difficulty in determining the effectiveness of preoperative mental health screening is due to the limitations of current screening strategies, which use a variety of scales and focus on mental health diagnoses rather than psychosocial factors. Previous reviews have suggested that self-esteem, mental image, cognitive function, temperament, support networks, and socioeconomic stability play major roles in determining outcomes after bariatric surgery. Future studies would benefit from including these characteristics as well as having clear eligibility criteria, standardized instruments, regular measurement intervals, and transparency with respect to time-specific follow-up rates. By addressing these methodological issues, future work can help to identify the optimal strategy for evaluating patients’ mental health prior to bariatric surgery.”
At this time, perhaps to err on the side of caution, our centre (like many others) continues to screen for and address any relevant mental health issues in patients wishing to undergo bariatric surgery.
One factor accounting for this may well be the lack of timely access to sleep testing.
Now, a study by Hirsch Allen and colleagues from the University of British Columbia Hospital Sleep Clinic, published in the Annals of the American Thoracic Society, examined the relationship between severity of sleep apnea and travel times to the clinic in 1275 patients referred for suspected sleep apnea.
After controlling for a number of confounders including gender, age, obesity and education, travel time was a significant predictor of OSA severity with each 10 minute increase in travel time associated with an apnea-hypopnea-index increase of 1.4 events per hour.
The most likely explanation for these findings is probably related to the fact that the more severe the symptoms, the more likely patients are to travel longer distances to undergo a sleep study.
Thus, travel distance may well be a significant barrier for many patients accounting for a large proportion of undiagnosed sleep apnea – at least for milder forms.
Given the often vast distances in Canada one can only wonder about just how much sleep apnea goes under diagnosed because of this issue.
This morning, I presented a keynote address at the 31st Scientific Meeting of the Deutsche Adipositas Gesellschaft (German Obesity Society) on the issue of risk stratification beyond BMI.
As regular readers will be well aware, I have long stated that our current definition of obesity based on BMI is problematic when applied to individuals presenting with excess weight.
We have therefore proposed the use of the Edmonton Obesity Staging System as a simple clinical tool for risk stratification that can guide clinical decision making.
Judging by the response from the audience, this concept met overwhelming approval, especially from the clinicians in the audience.
If, how, and when this concept will find its way into German obesity management guidelines remains to be seen.
As a clinician often dealing with patients presenting with binge-eating disorder (BED), I am quite aware of the often pathological cognitive and emotional relationship to food, eating, and body image presented by patients with this syndrome.
Whether or not this impairment in thinking and feeling also extends to other behavioural or emotional domains is the topic of a systematic review by Kittel and colleagues from the University of Leipzig, published in the International Journal of Eating Disorders.
The paper is based on the review of almost 60 studies and shows that, individuals with BED consistently demonstrate higher information processing biases compared to obese and normal-weight controls in the context of disorder-related stimuli (i.e., food and body cues) – in contrast, cognitive functioning in the context of neutral stimuli appear to be less affected.
With regard to emotional functioning, individuals with BED also report greater emotional deficits when compared to obese and normal-weight controls.
Thus, these findings confirm the clinical observation that patients with BED tend to have specific difficulties in cognitive and emotional functioning when it comes to food, eating or body image, however, appear to function adequately in other domains.
For clinicians these finding are relevant as they show that while people with BED may benefit from help in changing their cognitive and emotional response to food cues, such problems are indeed more often encountered in people with BED rather than in everyone living with obesity.
Screening for BED should be an essential element of workup in anyone presenting with excess weight gain.