Obesity and Weight Loss
Diagnosis and Assessment of Obesity
Obesity is typically diagnosed and defined by analysis of body size, weight, and composition. Body mass index (BMI) is the most commonly accepted metric for defining obesity; it is a surrogate measurement of adiposity, calculated as body mass (in kilograms) divided by height squared (in meters). Alternatively, it can be calculated in Imperial units as [weight (in pounds) / height2 (in inches)] x 703 (Expert Treatment Panel 1998). The World Health Organization (WHO) definitions of overweight and obese are BMIs of ≥25 and ≥30 kg/m2, respectively (World Health Organization 1998).
WHO Classification of weight status by BMI: (World Health Organization 2000)
|Obese class I
|Obese class II
|Obese class III/Morbid obesity
Although BMI is strongly correlated with total body fat, it is not without limitations. For example, there are significant racial considerations that can influence its interpretation (eg, Asians typically carry more body fat, and Africans less, than Caucasians at any particular BMI). BMI overestimates body fat content for individuals with high muscle mass (such as athletes). Additionally, BMI cannot measure some changes in body composition; for example, the concurrent loss of lean muscle and increase in body fat in aging individuals might not result in a change in their BMI (Prentice 2001). Alternative measurements (eg, skin-fold thickness and waist-to-hip ratio) have been suggested as more accurate methods for body fat estimation, but in terms of predicting clinical outcomes, BMI has shown similar accuracy to these techniques and remains an acceptable measurement despite its shortcomings (Thomas 2011). BMI can be combined with waist circumference measurements, which can estimate an individual’s abdominal fat content (abdominal or visceral fat is a greater risk factor for obesity-related diseases than total body fat). Waist circumference measurements of >102 cm (40 in.) for men, and >88 cm (35 in.) for women carry high risk of obesity-associated disease (eg, type 2 diabetes, cardiovascular disease, and hypertension) (Expert Treatment Panel 1998).