Role of obesity and body fat distribution in cardiometabolic risk

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Obesity can be simply defined as an excessive amount of body fat which increases the risk of medical illness and premature death. For clinical purposes, assessments that are routinely used to define obesity include body weight and body mass index (BMI)1. The BMI assessment represents the relationship between weight and height, and is derived by calculating either the weight (in kg) divided by the height (in meters squared), or the weight (in pounds) multiplied by 704 divided by the height in inches squared1. Using the BMI as the main criteria, classification of obesity into risk categories have been proposed (Table 3.1). The BMI classification is based on data that has been collected from large epidemiological studies that evaluated body weight and mortality2-4. This classification provides clinicians with a mechanism for identifying patients at high risk for complications associated with obesity. It has been well established that those individuals considered obese, i.e. BMI a 30, are at much higher risk for cardiovascular mortality than those considered overweight, i.e. BMI between 25 and 29.91 (Figure 3.1).

The prevalence of obesity has reached epidemic proportions around the world and the rate continues to increase. According to the World Health Organization (WHO), it has been estimated that over 1 billion adults worldwide are overweight and at least 300 million are considered obese5. Many factors contribute to this rise, but among the major factors are sedentary lifestyles, consumption of high-fat caloric-dense diets, and increased urbanization. In the US alone, data from the National Health and Nutrition Examination Surveys obtained since l960 have suggested that over

Table 3.1 BMI-associated disease risk. Reproduced from reference 1, with permission

Obesity class

BMI (kg/m2)

Risk

Underweight

< 18.5

Increased

Normal

18.5-24.9

Normal

Overweight

25.0-29.9

Increased

Obesity

I

30.0-34.9

High

II

35.0-39.9

Very high

Extreme obesity

III

> 40

Extremely high

Additional risks: (1) waist circumference > 40 inches in men and > 35 inches in women; (2) weight gain of > 5 kg since age 18-20 years; (3) poor aerobic fitness; and (4) Southeast Asian descent

Additional risks: (1) waist circumference > 40 inches in men and > 35 inches in women; (2) weight gain of > 5 kg since age 18-20 years; (3) poor aerobic fitness; and (4) Southeast Asian descent

64% of the US adult population is classified as either overweight or obese (BMI > 25)5. Whereas the prevalence of overweight adults has increased slightly, from approximately 30.5% to 34.0%, the prevalence of obesity (BMI > 30) has more than doubled from approximately 13% in 1960 to over 30% in the year 20005. Furthermore, the prevalence of individuals with extreme obesity as defined by a BMI > 40 has increased over 6-fold in the same 40-year period (0.8% vs. 4.7%)5. Most of the increase in body weight has occurred since 1980 and, unfortunately, this trend is not expected to change (Figure 3.26). Thus, we will have to address the economic, medical, and psychosocial consequences of this epidemic for years to come.

Obviously, the major concern associated with the obesity epidemic centers around the associated

Body mass index (kg/m2)

Figure 3.1 Relationship between body mass index (BMI) and cardiovascular mortality in 302 233 adult men and women who had never smoked and had no pre-existing illness. Vertical lines indicate cut-off values for over-weight and obese of BMI 25.0-29.9 kg/m2 and obese BMI > 30 kg/m2, respectively. From reference 3, with permission

NHANES I (I97I-74) I NHANES II (I976-

NHANES III (I988-94) I NHANES I999

NHANES I (I97I-74) I NHANES II (I976-

NHANES III (I988-94) I NHANES I999

Overweight or obese

Overweight

Obese

Overweight or obese

Overweight

Obese

Figure 3.2 Age adjusted prevalence of overweight (BMI 25-29 kg/m2) and obesity (BMI > 30 kg/m2) in adults aged 20-74 years in the US since 1960. Data were obtained from the four National Health and Nutrition Examination surveys conducted between 1960 and 2000. As shown, the prevalence of overweight individuals has increased slightly, but the prevalence of obesity has more than doubled. From reference 1, with permission. Data from reference 6 and National Center for Health Statistics, Centers for Disease Control and Prevention website www.cdc.gov/nchs/products/pubs/pubd/hestats/obese/obse99.htm

complications which seem to affect every major organ system (Table 3.2). Specifically, obesity increases an individual's risk for cancer, gastrointestinal diseases, arthritis, and adversely affects psychological well-being. However, the major concern, as described in detail in this Atlas, is the markedly increased risk to develop diabetes and cardiovascular disease in those individuals who are obese. Specifically, obesity is significantly associated with both the traditional risk factors, i.e. hypertension, dyslipidemia, diabetes, and the non-traditional risk factors, i.e. fibrinogen and inflammatory markers, of cardiovascular disease. In addition, as the presence of insulin resistance is considered as the hallmark for the presence of the cardiometabolic risk syndrome, it is clear that obesity and insulin resistance are integrally related (Figure 3.3).

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