The Cooper Institute
 

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH

 
 
 

The ‘Metabolically Healthy but Obese’ Body Type

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Move more

Monday, Dec 10, 2012

Are all obese individuals at high risk for adverse health outcomes? Well, it is well-established that obesity is a major risk factor for cardiovascular disease and many other serious health problems such as metabolic syndrome, type 2 diabetes, and some forms of cancer. It would be hard to find a health and fitness professional that is unaware that current rates of obesity in the U.S. are at an all-time high; with a current prevalence of ~35% in both men and women. However, not everyone is aware that a subset of obese individuals exist who seem to have protection against many of the complications of obesity. Such individuals have been described as being ‘metabolically healthy but obese’.

In most published papers which examine its’ health risks, obesity is defined as a body mass index (BMI) of >30 kg/m2. However, the use of BMI exclusively to identify obesity has limitations. For example, because BMI cannot discriminate between lean mass and fat mass, it can falsely identify extremely muscular individuals as being obese. Thus, it is helpful to have additional measures of obesity such as percent body fat in order to truly determine who is obese and who is not. Additionally, the overwhelming majority of ‘obesity and health risk’ papers do not measure the physical fitness level of study participants; failing to do so can further muddy the waters.  If your curious as to what your BMI is, you can calculate it on our Weigh Your Risk Tool but remember the points I made above when you receive your result. It also asks for waist circumference which helps to increase the strength of the tool.

A recent paper in the European Heart Journal1 helped shed some light on this interesting ‘metabolically healthy but obese’ population. A total of 33,882 apparently healthy adult men and women who underwent a comprehensive physical exam at the Cooper Clinic were included in the study.  Participants underwent measurement of cardiorespiratory fitness (via a maximal treadmill exercise test), BMI, waist circumference, percent body fat, resting blood pressure, and fasting blood chemistry. Participants were identified as being obese if they had a BMI >30 kg/m2 or a percent body fat >25% (males) or >30% (females). Participants were identified as having the metabolic syndrome if they had more than one of the following at baseline:

  • Resting blood pressure >130/85 mmHg or history of physician-diagnosed hypertension
  • Fasting blood triglyceride level >150 mg/dl
  • HDL cholesterol <40 mg/dl (males) or <50 mg/dl (females)
  • Fasting blood glucose level >100 mg/dl or history of physician-diagnosed diabetes
Obese participants were identified as ‘metabolically healthy but obese’ if they had none or just one of the four criteria listed above. Normal weight participants were defined as those with a BMI between 18-5-24.9 kg/m2 or percent body fat <25% (males) or <30% (females), and were identified as being ‘metabolically healthy’ in the same manner just described.

A comparison was then made between three groups at baseline and after an average follow-up period of 14.3 years. For simplicity sake, I will refer to Group number in the rest of this article.

  • Group 1: Metabolically healthy and normal percent body fat
  • Group 2: Metabolically healthy but obese
  • Group 3: Metabolic syndrome and obese
At baseline, it was found that 46.3% of the percent body fat-defined obese individuals were in Group 2. Regardless of whether BMI or percent body fat was used to identify obesity, Group 2 had a significantly higher level of cardiorespiratory fitness than Group 3, while Group 1 had a significantly higher fitness level than both Groups 2 and 3.

During the 14 year follow-up period, 1779 of the study participants died. Not surprisingly, the majority of deaths were from cardiovascular disease (n=546) and cancer (n=698). Because percent body fat is a more accurate measure of adiposity than BMI, the paper focused mostly on percent body fat when examining mortality rates between the three groups. Rates of all-cause, cardiovascular, and cancer mortality in Group 2 were significantly lower than in Group 3, and were actually very similar to rates in Group 1 (see Figure below).

The authors of this paper have shown convincingly not only that Group 2 had a significantly higher level of cardiorespiratory fitness than Group 3, but also that Group 2  had significantly less all-cause, cardiovascular, and cancer mortality than Group 3.  Thus, the ‘metabolically healthy but obese’ individual seems to have a relatively benign form of obesity. Because regular physical activity has a beneficial effect not only on fitness level, but also on the components of metabolic syndrome, it is imperative that Group 3 individuals meet public health guidelines for physical activity* with the goal of moving to the Group 2 category. Doing so will presumably significantly reduce their risk of mortality even though they remain obese. 

*Perform at least 150 minutes per week of moderate intensity aerobic activity and at least 2 days per week of strength activity.

Reference:

Ortega FB, et. al. The intriguing metabolically healthy but obese phenotype: cardiovascular prognosis and role of fitness. European Heart Journal. 2012. September 4 (e-pub, ahead of print).