nutritional disorders
Obesity
Diagnosis of Obesity
Body mass index (BMI) Waist circumference Body composition analysis In adults, BMI, defined as weight (kg) divided by the square of the height (m2), is used to screen for overweight or obesity: Overweight = 25 to 29.9 kg/m2 Class I obesity = 30 to 34.9 kg/m2 Class II obesity = 35 to 39.9 kg/m2 Class II obesity = ≥ 40 kg/m2 BMI is a commonly used tool that can be easily calculated and correlates with metabolic and fat mass disease in human population studies. However, BMI is a crude screening tool and has limitations in many subpopulations. It tends to overdiagnose overweight and obesity in muscular patients and underdiagnose them in patients with sarcopenia. Some experts think that BMI cutoffs should vary based on ethnicity, sex, and age. The World Health Organization (WHO) and International Diabetes Federation suggest lower cutoff points for people of Asian descent compared with those of other ethnicities ( Diagnosis references ). Waist circumference and the presence of Metabolic Syndrome appear to predict risk of metabolic and cardiovascular complications better than BMI does ( Body composition—the percentage of body fat and muscle—is also considered when obesity is diagnosed. Although probably unnecessary in routine clinical practice, body composition analysis can be helpful if clinicians question whether elevated BMI is due to muscle or excessive fat. Men are considered to have obesity when body fat levels are > 25%. In women, the cutoff is > 32%. The percentage of body fat can be estimated by measuring skinfold thickness (usually over the triceps) or determining Physical examination . Bioelectrical impedance analysis(BIA) can estimate percentage of body fat simply and noninvasively. BIA estimates percentage of total body water directly; percentage of body fat is derived indirectly. BIA is most reliable in healthy people and in people with only a few chronic disorders that do not change the percentage of total body water (eg, moderate obesity, diabetes mellitus). Whether measuring BIA poses risks in people with implanted defibrillators is unclear. Underwater (hydrostatic) weighingis the most accurate method for measuring percentage of body fat. Costly and time-consuming, it is used more often in research than in clinical care. To be weighed accurately while submerged, people must fully exhale beforehand. Imaging procedures, including CT, MRI, and dual-energy x-ray absorptiometry (DXA), can also estimate the percentage and distribution of body fat but are usually used only for research. Patients with obesity should be screened for common comorbid disorders, such as Obstructive Sleep Apnea (OSA) , 1.WHO Expert Consultation: Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies.Lancet. 363 (9403):157–163, 2004. doi: 10.1016/S0140-6736(03)15268-3 Erratum inLancet363 (9412):902, 2004. 3.Ross R, Neeland IJ, Yamashita S, et al: Waist circumference as a vital sign in clinical practice: A Consensus Statement from the IAS [International Atherosclerosis Society] and ICCR [International Chair on Cardiometabolic Risk] Working Group on Visceral Obesity.Nat Rev Endocrinol16 (3):177–189, 2020. doi: 10.1038/s41574-019-0310-7 Epub 2020 Feb 4. 3.Luo J, Hendryx M, Laddu D, et al: Racial and ethnic differences in anthropometric measures as risk factors for diabetes.Diabetes Care2019 42 (1):126–133. 2019. doi: 10.2337/dc18-1413 Epub 2018 Oct 23. 