A World View of the
W. PHILIP T. JAMES
A global perspective on obesity is now possible because all countries and the World Health Organization (WHO) have come to accept a general classification of normal weight, with different degrees of underweight, overweight, and obesity based on the body mass index (BMI) (see Chapter 68). The range of normal body weight is currently accepted internationally as a BMI of 18.5 to 24.9, the lower limit being determined on the basis of our classification of different degrees of underweight in adults, specifying increasing limitations in work capacity below a BMI of 18.5. The BMI of 25.0 was a compromise between the then-standard in North America based on U.S. analyses and an Asian concern that comorbidities emerged at lower BMIs. For reference purposes, BMIs of 25.0 and 30.0 will now allow estimates of regional and global overweight and obesity rates, respectively. Currently, WHO estimates that there are about 180 million obese adults, and the probability is that there are in addition at least twice as many adults who are overweight, with a BMI of 25.0 to 29.9.
Four issues of classification are important. First is the increasing recognition that waist circumference may be a particularly useful additional criterion for specifying comorbidity risks (see Chapters 68, 84, and 86). This is particularly important in the developing world where early poor growth in utero and postnatally could explain the increased propensity to abdominal obesity at modest increases in adult weight. Second, Latin American investigators highlight the spuriously enhanced BMIs of adults of short stature because they have short legs, having been “stunted” throughout childhood. By simply measuring sitting heights, however, it is possible to derive simple corrections for this feature. Short people (e.g., those living in Central America and Asia) need to accumulate substantially less total energy before their weight exceeds a BMI of 25.0, even with adjustments for sitting height. The smaller gain in energy is, however, sufficient to trigger similar comorbidities (e.g., with serum lipid changes, glucose intolerance, and hypertension) to those seen in taller Caucasians.
Third, many Asian experts consider lower cutoff points for both BMI and waist