On Tuesday, January 14th, the Lancet Diabetes and Endocrinology Global Commission released a report on the definition and diagnostic criteria of clinical obesity,. The report reflects the work of 58 commissioners over nearly 30 months. Remarkably, the commissioners achieved consensus on 37 consensus statements that included the clinical assessment, diagnosis, and goals of treatment of obesity. The report addressed many of the concerns we have had regarding the diagnosis of obesity. Their definition requires that in addition to BMI, there be a measure of body fat, such as waist circumference, waist-hip ratio, or waist-height ratio. One of the limitations of the measures of fat distribution is that standards exist for waist circumference in adults but not for children and adolescents. The Lancet’s new definition distinguishes between preclinical and clinical obesity. In addition to BMI and fat distribution, the diagnosis of clinical obesity requires at least 1 of 18 “obesity-related diseases” for adults or at least 1 of 13 organ, tissue or body systems for children and adolescents.
The Lancet posits that these measurements allow for a more comprehensive criteria and aid in more clear-cut decision making. As shown in the figure below from the report, what separates Patients 3 and 5 is their BMI (28.8 vs. 39.2), in which the old diagnosis would diagnose Patient 3 as overweight and Patient 5 with obesity. However, what distinguishes Patient 5 (preclinical obesity) and 6 (clinical obesity), is not their BMI and fat mass, but the presence of additional signs of organ dysfunction.
Several limitations exist in regarding the Commission’s criteria for the diagnosis of clinical obesity in the pediatric population. As indicated above, no standards exist for fat distribution in children. Furthermore, recent work has shown that BMI alone is a highly specific measure of fatness in children and adults. One of the remaining limitations of the Lancet criteria for the diagnosis of obesity in both adults and children is that measures of fatness fail to distinguish visceral from subcutaneous fat. Ideally, the anthropometric measures of fat distribution will be displaced by biomarkers that reflect the toxic effects of visceral fat.
The clinical burden of disease associated using the Lancet criteria remains uncertain. As the Commission acknowledges, no representative data exist on the prevalence of preclinical and clinical obesity in adults, nor is there sufficient research on the frequency of any of the 18 obesity related diseases in adults and the 13 measures in children. For example, in a study of the frequency of obesity-associated co-morbidities among children and adolescents, only elevated blood pressure and metabolic dysfunction steatohepatitis overlapped with the Lancet criteria. Among adults with obesity, 29% had at least one of 13 co-morbidities, but only a minority of these co-morbidities were included in the Commission's criteria. Finally, among children and adolescents, it is not clear whether the presence of an obesity-associated disease would prompt a different clinical approach from one based on BMI and risk factors, such as elevated blood pressure, hyperlipidemia, or elevated fasting hyperglycemia.
Many of these unanswered questions will require resolution before the Lancet criteria can be widely implemented. The research agenda required is certain to make epidemiologists very happy, but will increase clinician uncertainty about how to proceed.