Metabolically obese normal weight (MONW) was first described in the 1980s, when Ruderman et al. ^[1] described a case of patients with symptoms indicative of the metabolic syndromes—reduced insulin sensitivity, hypertension, T2DM, and hypertriglyceridemia—despite normal body mass index (BMI). In 1989 Ruderman et al. ^[2] proposed a scoring system that assessed 22 features (Table 1) that were assigned a specific number of points. Obtaining at least 7 points was equivalent to the diagnosis of MONW.

Table 1. A point scale to identify people with MONW ^[2].

This system had its drawbacks, requiring the performance of biochemical tests not routinely performed in healthy people (including uric acid concentration). For this reason, the search for much simpler and more accessible diagnostic criteria was started.

2. A contemporary look at MONW

It is now known that in addition to metabolic disorders people with MONW are characterized by an increased content of adipose tissue—in particular, its visceral deposit ^[3]. The assessment of the fat depot is possible after measuring the body composition. This test allows for precise and accurate measurement of individual body components including muscle mass, lean mass and, most importantly, the percentage of adipose tissue (PBF,% BF), the knowledge of which, together with the BMI value, can be used as a screening tool. Among body compositions methods of body composition analysis, dual-energy X-ray absorptiometry  (DXA) is considered the “gold standard”.

Currently, the authors of the MONW diagnostics use the developed indicators:

1. the visceral adiposity index (VAI) - which is based on BMI, WC, triglycerides and HDL cholesterol:

2. the triglycerides–glucose index (TyG) - which is the product of fasting blood glucose and triglycerides:

3. lipid accumulation product (LAP) - which is based on the combination of waist circumference measurements and fasting triglycerides:

4. the cardiometabolic index (CMI) - which is based on the combination of triglycerides, HDL cholesterol and waist-to-height ratio:

5. metabolic syndrome (MetS) criteria according to the criteria of the National Cholesterol Education Program Adult Treatment Panel III (NCEPATP III) or proposed by the International Diabetes Federation (IDF):

Table 2. Diagnostic criteria for the Metabolic Syndrome.

Legend: WC—waist circumference; TG—concentration of triglycerides; BP—blood pressure; FG—fasting glucose; * in the European population.

3. Conclusions

MONW is undoubtedly a growing problem that should be the focus of further research. Due to the fact that it is a disease that does not show phenotypic signs, screening tests should be carried out, mainly including body composition analysis among young, theoretically healthy people. This will allow for early detection of MONW and appropriate reactions before the occurrence of undesirable consequences—including atherosclerosis or coronary artery disease.