Paul Zimmet
International Diabetes Institute, Melbourne, Australia

The term diabesity was coined by a world expert of animal models of diabetes, Prof. Elias Shafrir from Israel. E. Shafrir used an excellent animal model of obesity and type 2 diabetes, the Israeli sand rat (Psammomys obesus). When given a high-energy diet, this animal becomes obese and develops type 2 diabetes. In terms of body weight, percentage of body fat, blood glucose and plasma insulin concentration, Psammomys obesus exhibits a phenotypic pattern closely resembling that observed in human population studies.

Hence, the term diabesity seems particularly relevant to describe the twin epidemic of obesity and diabetes that we are facing throughout the world. Just like instead of using the terms impaired glucose tolerance and impaired fasting glucose, we talk of pre-diabetes to communicate to the lay public, the term diabesity can be useful to popularise the notion of twin epidemic. In addition, we know that a linkage exists between the increase in obesity observed in many communities around the world, particularly in the US, and the increased number of people with type 2 diabetes.

To explain the worldwide increase in obesity, the adoption of sedentary lifestyles is probably more to blame than changes in nutritional habits. That increase in obesity is associated with the development of insulin resistance, which precedes type 2 diabetes in many instances. Since there is a definite epidemiological link and a probable pathophysiological link between obesity and type 2 diabetes, some common genetic determinant for both conditions can be suspected.

Another feature shared by obesity and type 2 diabetes is that both are associated with an increased frequency of the metabolic syndrome. There are two possible interpretations of this association. The metabolic syndrome can be seen as secondary to both obesity and type 2 diabetes. Alternatively, obese individuals and type 2 diabetic patients can be viewed as exhibiting a first manifestation of the metabolic syndrome: with time, those persons are likely to develop other cardiovascular risk factors such as high blood pressure, a prothrombotic state, and dyslipidemia, which are as many features of the metabolic syndrome.

Similar diagnostic criteria for type 2 diabetes have been used in many epidemiological studies, thus enabling comparisons between different populations. Although the rates of diabetes are less than 6-7% in European adults, rates up to 30-40% have been reported in populations of developing countries where rapid modernization has occurred, for example in the Pacific area. Comparable high rates in adults have been described in the native populations of the US and Canada as well as in the Australian indigenous community. It should be emphasized that type 2 diabetes was rare in those communities as long as they adhered to their traditional lifestyles. We also see an evolving major epidemic of diabetes in the Arab nations, in India, and progressively in China where lifestyle habits are changing as this country becomes more open to the outside world.

Because different sets of criteria have been proposed to identify people with the metabolic syndrome, comparing rates of this condition between countries has been more difficult. However, the set of criteria proposed by the NCEP-ATP III has shown a prevalence of the metabolic syndrome around 12-15% in European adults whereas approximately 40% of US adults are affected.

A major health concern is that, due to their expected impact on cardiovascular disease incidence, diabesity and the associated metabolic syndrome are likely to represent the biggest epidemic ever seen in human history. Primary care physicians should be aware that every patient who presents with obesity, diabetes, dyslipidemia or high blood pressure is a candidate for the metabolic syndrome. In patients presenting with only one of those features, all other risk factors must be assessed. Indeed, it is quite likely that such patients already have or will develop other features of the metabolic syndrome, thereby markedly increasing their cardiovascular risk.