The Concept of Normal Weight Obesity
Section snippets
Historic perspective of the concept of obesity
Measurement of height and weight was the initial step in the clinical assessment of overweight and obesity. In 1908, Symonds reported the results of a large prospective study of weight and mortality in New Jersey. He registered weight for a given height and age, and the influence of excess weight on vitality.6 Subsequently, obesity was defined in relation to desirable weight, taking in consideration the actuarial tables from the Metropolitan Life Insurance Company.7 The concept used was percent
Pitfalls of current BF mass measurements
BMI as a measure of BF became popular and widely used because of its simplicity and validation in multiple epidemiologic studies. Surprisingly, even though obesity is defined as excessive adiposity, there is no consensus on how to define obesity using fat mass calculation or fat percentage, other than the effort by the American Society of Endocrinologists who defined obesity by BF percent as > 35% in women and > 25% in men.16 Direct measurement of adipose tissue using methods like
Challenging the simplistic concept of obesity as defined by BMI
Over the last 30 years, there have been several new concepts challenging the simplistic concept that obesity can be diagnosed based on weight and height. Numerous studies have proposed definitions of the obesity subtypes (Table 1).
Firstly, Ruderman et al21 challenged the notion that standard weight–height tables were the proper way to determine high-risk groups for obesity associated disorders. They observed normal weight individuals suffering from type 2 DM, premature CHD, HTN and
Normal weight obesity: a distinct phenotype linked to metabolic dysregulation and inflammation
In 2006, De Lorenzo et al29 described the association between normal weight and high fat content with metabolic abnormalities. The term “NWO” described those individuals with normal body weight and BMI (< 25 kg/m2) with increased BF % (> 30%). Despite the fact that obesity is defined as excessive body adiposity according to the etymology of the word, there is no consensus about how to define obesity based on BF content or %. Some investigators have proposed sex- and age-adjusted cut-off values
Relationship between NWO, metabolic dysregulation and inflammation
There is strong evidence linking NWO and metabolic dysregulation. De Lorenzo et al29 evaluated 74 women and analyzed anthropometric variables, body composition, resting metabolic rate and biohumoral variables. They found significant differences in high-density lipoprotein (HDL) between normal weight obese and pre-obese-obese individuals. There were significant correlations among CVD risk indexes, lean of the right part of the trunk and total cholesterol/HDL (R = − 0.69, p < 0.001) and LDL/HDL (R = −
Relationship between NWO and metabolic syndrome(MetS)
There is increased risk for MetS and each one of its components with NWO. Romero-Corral et al20 demonstrated that individuals classified as NWO had a prevalence of MetS 4-fold higher than people also with normal BMI but normal BF %. NWO adults also had an increased prevalence of dyslipidemia, DM, hyperglycemia without DM, central obesity and HTN. When divided by sex, women were particularly affected, as women in the highest tertile were about 8 times more likely to have MetS than those in the
Normal weight with central obesity and prognosis in coronary artery disease
Increasing central obesity is linked to higher mortality in adults with or without CHD, even in those with normal BMI.41 Normal weight with central obesity as determined by WC or WHR in adults with CHD is associated with the highest risk of mortality,41., 42. compared with subjects with normal BMI and no central obesity and with obese patients by BMI regardless of their central obesity status. Furthermore, the obesity paradox, where people with CHD and obesity by BMI have shown better prognosis
NWO and mortality.
We have demonstrated that NWO has been associated with increased CVD and all-cause mortality.20 Women with NWO were 2.2 times more likely to die from CVDs compared with those with low BF. When women were classified by tertiles of BF %, the mortality risk increased as the BF %increased. The increased mortality risk was independent from HTN, DM and dyslipidemia, suggesting that the increased mortality risk implicates pathways beyond the traditional obesity-related comorbidities.
Future directions
NWO may be present in approximately 30 million Americans.20 The prevalence of NWO varies from 2% to 28% in women and less than 3% in men.32., 38. We have scarce information regarding the determinants of NWO in the general population. Although environmental factors are probably implicated in the origin of normal weight central obesity, genetic factors cannot be excluded. There is a need for epidemiologic studies assessing the prevalence of NWO among different ethnic groups and studies with
Conclusions
The diagnosis of obesity has been evolving over time. The current definition of obesity by weight and height has been challenged with recent evidence showing that BMI-defined obesity may not accurately identify all the obesity-related CVD risk. People with normal BMI and high BF content are at increased risk for metabolic dysregulation, systemic inflammation and mortality. The concept of metabolic obese normal weight overlaps with the NWO. It is possible that the metabolic dysregulation seen in
Statement of Conflict of Interest
All authors declare that there are no conflicts of interest.
Acknowledgments
Supported in part by the European Regional Development Fund, project FNUSA-ICRC (Z.1.05/1.1.00/02.0123) and Czech Ministry of Health (NT13434-4/2012).
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Statement of Conflict of Interest: see page 432.