Obesity and Type 2 Diabetes

• Changes in human behaviour and lifestyle over the last century have spurred a dramatic increase in the incidence of obesity and type 2 diabetes worldwide.
• Because obesity and diabetes are closely linked, the term “diabesity” has been coined to illustrate the interdependence of these two diseases.
• Obesity and type 2 diabetes frequently occur together and the majority of patients with type 2 diabetes are or have been obese.
• Besides genetic susceptibility, obesity is the most important risk factor for type 2 diabetes.
• Lifestyle changes are the best way to prevent obesity and slow this worldwide epidemic.

Developed societies face two crucial health problems: overweight and obesity. Obesity is the most common metabolic disease, and the number of individuals who are overweight or obese is fast increasing worldwide [1]. Increased body fat has been linked to numerous co-morbidities such as dyslipidemia, cardiovascular disease (CVD), and type 2 diabetes [2]. The rapid, global increase in obesity has also sparked an increase in cases of type 2 diabetes [3]. Lifestyle and environment changes have sent the rates of both obesity and diabetes soaring [4]. The end result is that, over the past two decades, the number of individuals with diabetes has skyrocketed worldwide [5,6]. All signs indicate that the diabetes epidemic will continue to escalate. It has been suggested that there will be more than 700 million individuals with diabetes by the year 2045 [7].

The term “diabesity” has been coined to illustrate the close relationship between obesity and diabetes [8,9]. Obesity and type 2 diabetes frequently occur together and the vast majority of type 2 diabetic individuals are obese [10,11]. In combination with genetic susceptibility, obesity is the most important type 2 diabetes risk factor [12,13]. The relative risk of developing type 2 diabetes increases tenfold in obese women and elevenfold in obese men [14]. Obesity is therefore a major risk factor for type 2 diabetes.

Environmental and behavioural factors (sedentary lifestyle and poor nutrition) have contributed to the worldwide epidemic of obesity and type 2 diabetes. However, one of the major debates in diabetes etiology is the notion of “thrifty genotype” versus “thrifty phenotype” [7]. The “thrifty genotype” concept suggests that a predisposition to type 2 diabetes may result from a genotype that promotes fat storage during famine periods—a possible evolutionary advantage. This hypothesis partly explains the high prevalence of type 2 diabetes in Pima Indians, a population genetically prone to type 2 diabetes. When this specific genotype is exposed to an obesogenic environment (a diet high in simple refined carbohydrates and saturated fat, combined with a sedentary lifestyle), obesity and type 2 diabetes soon follow. The “thrifty phenotype” hypothesis—which is based on the observation that low birth weight is an important risk factor for type 2 diabetes [21]— suggests that type 2 diabetes is mainly caused by early environmental factors and by genetic factors to a much lesser extent. However, given the compelling evidence in support of the role of genetic factors in type 2 diabetes, it is likely that both hypotheses may modulate type 2 diabetes risk, although some believe that the “thrifty genotype” theory will prevail over the “thrifty phenotype” theory.

Overweight and obesity are critical health problems in our modern society. Both conditions significantly increase the risk of type 2 diabetes and CVD. Yet obesity does not occur in a vacuum. It is a complex disorder in which environmental and behavioural factors interact with genetic susceptibility. All these factors combined have contributed to the worldwide obesity and type 2 diabetes epidemic.