One of the major issues that these three definitions failed to address was the inherent ethnic differences in measurements of obesity (body mass index and waist circumference). It was also uncertain which of the definitions best predicted those at risk of CVD and diabetes, although from a clinical perspective, the ATP III definition was probably the most practical for alerting healthcare professionals to those at highest risk   3   5 .

It was because of this confusion and the need to take into account ethnic differences that the International Diabetes Federation (IDF) embarked on the process of arriving at an urgently needed consensus on a new global definition of the metabolic syndrome (see Table 1). This has now been published on the web and in both The Lancet   3   5  and, in more detail, in Diabetic Medicine   6 .

The new IDF definition recognizes the mounting evidence that visceral adiposity is common to each of the components of the metabolic syndrome although it does not necessarily imply an aetiological link. Thus, an excessive waist circumference (demonstrated to be a good proxy measurement for visceral adiposity) is now a necessary requirement for the metabolic syndrome. This is based on the strong evidence linking waist circumference with cardiovascular disease and the other metabolic syndrome components, and the likelihood that central obesity is an early step in the aetiological cascade leading to the full metabolic syndrome   3 . The optimal technique for its measurement is shown in Figure 1.

Figure 1 | Guide to measuring waist circumference

Waist circumference should be measured in a horizontal plane, midway between the inferior margin of the ribs and the superior border of the iliac crest. Data show that if BMI is greater than 30 kg/m2, waist circumference is highly likely to be above the diagnostic cut-points for the metabolic syndrome, and measurement is not necessary.

The waist circumference cut-off selected was the same as that used by EGIR and lower than the main ATP III recommendations, because most available data suggest an increase in other cardiovascular disease risk factors in Europids when the waist circumference rises above 94 cm in men and 80 cm in women   3 . Since it is clear that the levels of obesity at which the risk of other morbidities begins to rise varies between population groups   3   7 , ethnic-specific waist circumference cut-offs have been incorporated into the definition (see Table 1). The cut-offs have been based on available data linking waist circumference to other components of the metabolic syndrome in different populations   8   9 .

The levels of the other variables were as described by ATP III, except that the most recent diagnostic level from the American Diabetes Association (ADA) for impaired fasting glucose (5.6 mmol/L [100 mg/dL]) was used   10 .

Although the new definition will still miss substantial numbers of people with impaired glucose tolerance (because an oral glucose tolerance test is not required), it retains the simplicity of the instrument, particularly in a primary healthcare setting. In the short time since the new definition has been made available, a number of publications have reported the prevalence, and these are shown in Table 2.

Table 2 | Prevalence of the metabolic syndrome, according to the IDF definition

The IDF consensus report   6  also includes recommendations for future research into components not currently included in the core definition of the metabolic syndrome. These factors should be combined with assessment of cardiovascular disease outcome and development of diabetes so better predictors can be developed.

The IDF consensus report also highlights strategies for the treatment of the metabolic syndrome and its components. It addresses both clinical and research needs and:

• provides a simple entry point for primary care physicians to diagnose the metabolic syndrome;
• provides an accessible, diagnostic tool suitable for worldwide use, taking into account ethnic differences in waist circumference and associated type 2 diabetes and CVD risk; and
• establishes a comprehensive ‘platinum standard’ list of additional criteria that should be included in epidemiological studies and other research into the metabolic syndrome.

The IDF definition should provide researchers with a common platform for investigating the syndrome and its consequences. It provides for the first time a useful practical global tool that will draw attention to healthcare professionals of the metabolic consequences of obesity. The definition serves a useful purpose to focus on people, in both the community and clinical settings, who are at high risk of developing CVD and type 2 diabetes, and are likely to benefit from (lifestyle) interventions.