The problem of obesity has reached epidemic proportions in the United States (see also other chapters by Boan and McMahon), and evidence of its negative impact on health is rapidly accumulating. Excessive body mass, defined as a body-mass index (BMI) over 25 kg/m2 (overweight; OW) and > 30 kg/m2 (obese; OB) is linked with an increased risk for a number of serious chronic diseases, including cardiovascular disease (CVD), hypertension, and some cancers, as well as type 2 diabetes (1-3). The relationship between OW/OB and diabetes is exceedingly strong, with the prevalence of type 2 diabetes increasing along with OW/OB in a dose-dependent manner (3). In fact, as many as 90 percent of all type 2 diabetic individuals fit the OW/OB BMI criteria (4). Thus, OW/OB and type 2 diabetes are "inextricably linked" (5), the term "diabesity" having been coined by Astrup and Finer (6) to emphasize the close connection between the two disorders.
The need to deal with the obesity problem by restoring optimal body mass and composition is well recognized for all segments of the adult population, but it is particularly critical for individuals with type 2 diabetes. The risk to mortality posed by obesity is greatly enhanced by the coexistence of diabetes; moreover, diabetes treatment can interfere with the ability to achieve and maintain a healthy body mass. OW/OB may also directly impact glycemic control. Due to greater hepatic or peripheral insulin resistance, type 2 diabetic patients who are OW/OB can have a reduced response to antidiabetic therapy compared with normal-weight patients, necessitating higher doses of antihyperglycemia medications (7). In addition, the risk of CVD — a major cause of mortality and morbidity in individuals with diabetes — is heightened due to OW/OB-linked hypertension and dyslipidemia.
Recognizing the need for prompt, effective interventions to disrupt the cycle of OW/OB and diabetes, the American Diabetes Association, the North American Association for the Study of Obesity, and the American Society for Clinical Nutrition have jointly developed and recently released a statement on the use of lifestyle modification to prevent and manage type 2 diabetes (8). The statement emphasizes the importance of lifestyle intervention as the principal therapy for OW and OB patients. In this chapter, we focus on the lifestyle modifications (diet and exercise) recommended in the statement. The utilization of weight-loss medications and bar-iatric surgery to aid weight loss in type 2 diabetes is discussed separately elsewhere in the book, and comprehensive reviews on the subject are available (9-10).
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