Metabolically Healthy Obesity

Metabolically healthy obesity is a very complicated concept, but I'll just cover the basics here because it's the end of the semester and I haven't been able to read as much into the hormonal and cellular changes as I would like to include them. Also, I prefer to not make essays out of blog posts.

While reading various reviews and studies for this post, I noticed that no one really knows how to define "metabolically healthy obesity" and a lot of people like to talk about that. I went over a few large-scale literature reviews that lamented the lack of a definition but also failed to provide one, despite having amassed all of the literature over a decade or two on the subject. 

So, unfortunately, I will be going with the bare-bones idea of metabolically healthy obesity:  

Simply put, a metabolically healthy but obese (MHO) person is someone who would be classified as obese based on body fat percentage but is "resistant to the metabolic disturbances associated with obesity"⁽¹⁾. The metabolic disturbances primarily include low insulin sensitivity, high LDL cholesterol, low HDL cholesterol, and high plasma triglycerides. Some authors include inflammation and cardiovascular risk but there is quite a bit of disagreement on whether or not MHO individuals are protected against CVD.

Karelis et al. (2004) Primeau et al. (2011) and Stefan et al. (2013)^{(1, 2, 3)} conducted large-scale literature reviews to determine criteria or common characteristics of MHO individuals compared normal weight or metabolically abnormal obese (MAO) individiuals. Although neither proposed specific guidelines, it  was clear that MHO have identifiable differences from their metabolically abnormal counterparts.

MHO individuals were much more likely to have less visceral and ectopic (out of place) fat in the liver and skeletal muscle, and an overall healthier metabolic profile. In addition, there were interesting differences between effects of exercise and restrictive diets, such that MAO individuals were more likely to see a reduction in metabolic and cardiovascular risk factors but MHO tended to maintain their profiles. 

Although both reviews mentioned the effects of diet and exercise, both also mentioned the need for more studies on the differences between MHO and MAO individuals regarding energy intake and use. In addition, I think we need more information regarding the effects of body mass itself on joint and respiratory health in MHO.

If that is the research/biomedical side of things, what does the social/anthropological side have to say?

Honestly, when I look at the headlines for Google searches like "healthy obesity," "metabolically healthy obesity," and "fat but fit" and read some of the articles, I really think I'm looking at people who know they have something really cool on their hands but don't know what to do with it. They don't know the science well enough to understand the difference between being completely healthy and metabolically healthy or they don't want to come down on the wrong side of what is clearly a new thing in science. 

Any kind of "good" obesity is going to be a bit much for the average person to wrap their head around. Even people I've spoken to who understand human anatomy and cell biology and whatnot tend to have trouble with it. Heck, I had trouble with it when the matter was first brought to my attention, and even now I read the research looking for clues that something isn't quite right just because I have spent all my life being told obesity is basically an early death. 

Can we take a minute to recognize how interesting that is? The average American's (or Westerner's) view of obesity is largely a product of a culture which both promotes consumption of excess and sanctions some of those who participate. Never mind the idea that being metabolically obese could be a huge evolutionary advantage (although, the evolutionary aspect of this might not be relevant until the mechanism is better understood, which is sad because I really wanted to talk about that). 

I think what this comes down to is a simple acceptance of human variation. If we accept that human variation exists across all phenotypes, then we can research, write and talk about obesity with reduced bias in scholarly articles and the public sphere. It wouldn’t be so difficult to understand that obesity does not equate with complete health deterioration, nor does it indicate personality traits. Sometimes that variation is "bad" from an evolutionary standpoint because it decreases the chances of reproduction and sometimes it is "good" for the opposite reason. 

In sum, I have glossed over metabolically healthy obesity because it is very complicated and fun to read about. People don't know how to talk about it because of our culture. Human variation is a fantastic thing. 

See you next Monday!

Cheers,
JG

1: Karelis, A. D., St-Pierre, D. H., Conus, F., Rabasa-Lhoret, R., & Poehlman, E. T. (2004). Metabolic and body composition factors in subgroups of obesity: what do we know?. Journal of clinical endocrinology & metabolism, 89(6), 2569-2575.

2: Primeau, V., Coderre, L., Karelis, A. D., Brochu, M., Lavoie, M. E., Messier, V., ... & Rabasa-Lhoret, R. (2010). Characterizing the profile of obese patients who are metabolically healthy. International Journal of Obesity, 35(7), 971-981.

3: Stefan, N., Häring, H. U., Hu, F. B., & Schulze, M. B. (2013). Metabolically healthy obesity: epidemiology, mechanisms, and clinical implications. The Lancet Diabetes & Endocrinology, 1(2), 152-162.

 NOTE: The literature reviews I have cited include data from multiple decades and, to avoid making this post 90% citations, I have decided to cite the reviews themselves, which summarize the information. Credit for the work goes to the original authors (and if I were publishing in a journal, every single one would be properly cited). Please refer to these articles for further reading.