In the first post of this series we introduced the concept of the metabolically-healthy obese phenotype, and yesterday we discussed evidence regarding the risk of diabetes and cardiovascular disease among these individuals. In the third part of this series, we focus on research into the mortality risk among obese, but metabolically healthy people.
In yesterday’s post, after finding out that diabetes and cardiovascular disease risk among metabolically healthy obese individuals is no greater than that of healthy lean individuals, I posed the following question:
Is there more to health than the level of triglycerides in one’s blood, or their risk of diabetes or cardiovascular disease? And if we consider other, potentially more telling outcomes – such as mortality – will metabolically-healthy obese individuals still be considered healthy?
This question brings us to today’s post in which we discuss a landmark study published in the journal Diabetes Care, which was conducted by friends and colleagues of ours: Dr. Jennifer Kuk and Dr. Christopher Ardern. But rather than personally writing about the study, I figured I’d interview Dr. Kuk and get the details of their findings directly from the primary author.
OP: If you were to sum up the main findings of your study to a non-scientist at a dinner party, what would you say?
Dr. Kuk: I’d say that “My study shows that individuals who are obese and do not have common diabetes and heart disease risk factors die at the same rate as those who do. This means being overweight alone puts you at higher risk for dying, even though you do not high blood pressure, high cholesterol or high blood sugar. This highlights the negative health impact of body weight alone”.
OP: Why do you think the prevalence of metabolically-healthy obesity in your study was so much lower than previously reported in others (6% vs 20-30%)?
Dr. Kuk: The prevalence was lower in our study as compared to others simply because we used a more strict definition of metabolically normal. Other studies used insulin resistance or the metabolic syndrome (3+ risk factors) alone, but we defined ‘metabolically healthy’ as the absence of insulin resistance or any metabolic syndrome criteria. We felt this would be a more accurate definition of ‘metabolically healthy’ as each of the metabolic syndrome criteria are associated with morbidity and mortality alone.
OP: How do you reconcile the findings from the current study with those of prior studies suggesting that metabolically-health obese individuals are at no greater risk for developing type-2 diabetes or cardiovascular disease than normal weight individuals?
Dr. Kuk: Although I don’t know which studies you are referring to exactly, but in our study, 80% of the deaths in the metabolically-healthy obese were due to cancer and ‘other’ causes. Other causes are likely traumatic injuries, which highlights an important point. Obese individuals are less likely to survive a trauma as compared to normal weight individuals despite similar injuries. This is related to longer transport times due to their higher body weight, and difficulty assessing and treating the injuries due to their increased size. Further, they are less likely to see their physicians regularly, which may be in part why cancer is generally diagnosed in obese individuals at later stages. Thus, this study fits in line with the idea that these individuals are not more likely to develop these metabolic diseases, but still die from other causes.
OP: Recently, Drs. Sharma and Kushner proposed a new staging system for obesity treatment suggesting that obese individuals without established metabolic risk should be counseled to maintain current weight, rather than lose weight (Read about this on Dr. Sharma’s Obesity Notes blog). Do the results of your study agree or disagree with these recommendations?
Dr. Kuk: One can examine this question from a theoretical or practical standpoint. From a theoretical stand, weight loss improves metabolic factors, functionality and several psychological and social factors, and thus it would be intuitive to recommend that all obese lose weight. However, from a practical perspective it may be unethical to recommend an individual who is not presenting with overt disease to try to lose weight as most individuals fail to maintain their weight loss over the long term. Repeatedly failed attempts to maintain weight loss has been shown to elevate one’s risk for diabetes, cardiovascular and cancer for a given BMI. In other words, it may be better to recommend maintenance of weight rather than prescribing weight loss, knowing that they are likely to fail and be worse off because of it. Though we did not examine this issue, Sharma and Kushner’s staging system examines non-metabolic consequences as well, and it is reasonable to assume that these are equally important to examine as they are also important aspects of health, and inclusions of these factors may alter the associations observed.
OP: Are metabolically-healthy obese individuals actually healthy?
Dr. Kuk: I think that whether metabolically-healthy obese are actually healthy is dependent upon the accuracy of the definition. As we see that obese without cardiovascular disease or diabetes risk factors are at elevated cancer risk implies that our definition of metabolically healthy is not capturing cancer metabolic risk factors. Similarly, risk for trauma events may also reflect aspects of health that may or may not be captured by metabolic risk factors, but are crucial aspects of health. For example, musculoskeletal fitness would be a predictor of risk of falling or functionality.
Thus, if we used a more encompassing definition, we would likely see that these metabolically-healthy obese may be at lower risk for mortality and are healthy. However, as our definition only identified 6% metabolically healthy obese, I would suspect that an all encompassing definition for healthy obese would be a very minuscule proportion of the population.
OP: Thanks very much Dr. Kuk!
So, despite a healthy metabolic profile, no greater risk of diabetes or cardiovascular disease, metabolically-health obese individuals may still be at greater risk of dying early.
Maybe, they’re not so healthy after all.
This work would certainly suggest that all obese individuals – even those with a healthy metabolic profile – should attempt to lose weight.
But what if losing weight actually makes these, otherwise healthy, but obese individuals less healthy?
Tune in tomorrow to find out.
NOTE: Thanks very much to Dr. Jennifer Kuk, Assistant Professor at the School of Kinesiology and Health Science at York University. Before Dr. Kuk was at York University, she did her PhD in the same lab that I did mine (Queen’s university). Dr. Kuk has been instrumental in shaping my research interests while at Queen’s and beyond, and over the years has provided tremendous guidance in many areas. I could not be happier to showcase some of her pioneering research on Obesity Panacea.
Make sure to read other parts of this series:
Part 1: Metabolically-Healthy Obesity: an Oxymoron?
Part 2: Metabolically-Healthy Obese: Prospective Risk of Disease
Kuk, J., & Ardern, C. (2009). Are Metabolically Normal but Obese Individuals at Lower Risk for All-Cause Mortality? Diabetes Care, 32 (12), 2297-2299 DOI: 10.2337/dc09-0574