Metabolically Healthy Obesity

Fact or Fiction? 

It is generally thought that getting overweight, obese, or simply excessively fat, is harmful for health. In recent years, this idea has been challenged, which brought about the concept of "Metabolically Healthy Obesity". Early on, it had been suggested that up to 30-50% of obese individuals can actually be classified as metabolically healthy, which would cause us to reconsider whether or not these individuals are at risk by virtue of their excess body fat.

Image: Kubow & Iskandor 2022

Unfortunately, it seems that, even in the case where someone has “good metabolic health” when assessed by standard metrics (low high-density lipoprotein cholesterol, elevated blood pressure, triglycerides, and fasting plasma glucose), the incidence of Ischemic Heart Disease (IHD) events is still elevated, as well as risk of coronary heart disease, cerebrovascular disease and heart failure, and hence the term “metabolically-healthy-obesity” (MHO) may be quite misleading (Caleyachetty et al. 2017; Hansen et al. 2017). This is especially true for men, as the risk of an IHD event in that study for those with MHO was much higher, and while the risk was still elevated for MHO women, the authors note that it failed to reach statistical significance. The authors also note the impermanence of the MHO phenotype, as a large proportion of those with an MHO profile at the beginning of the study were no longer considered metabolically healthy at 5 years of follow-up.

This is consistent with other research following those classified as MHO over time, especially in those with visceral abdominal fat accumulation (Flint et al. 2010; Soriguer et al. 2013; Hwang et al. 2015; Kang et al. 2017; Fantin et al. 2019; Lonardo et al. 2020).

Stricter criteria for metabolic health (0 components of metabolic syndrome + absence of insulin resistance) tend to reduce the initial estimate of ~1/3 being MHO to as low as 5-6% (even in children), although this is quite a high bar to set. On average, true rates are likely to be lower than those often reported given the tendency for some studies to exclude those with pre-existing T2DM, CVD and other established diseases, as well as the acute effect of weight loss attempts (negative energy balance) on metabolic health parameters in those currently trying to lose weight.

Statistically, it’s not unreasonable to at least suspect that someone with obesity might have compromised metabolic health, or that this is likely to be the case in future, particularly when looking at rates of progression to a state of poorer metabolic health over 3-10 year follow-up.