Presentation of obesity may range from asymptomatic to presentation complicated by multiple comorbidities, including cancer, CAD, diabetes, hypertension, gout, obstructive sleep apnoea, and osteoarthritis.
The definitive test for the diagnosis of obesity remains the BMI (obesity is defined as a BMI ≥30 kg/m^2).
Central or abdominal obesity has a stronger association with obesity-related comorbidity than peripheral (i.e., subcutaneous) obesity, so waist circumference may be a better indicator of the risk for obesity-related comorbidity than BMI.
The mainstay of non-surgical treatment of obesity is diet and exercise, with psychological therapy as a recommended adjunct for all patients. The risk of complications is low, but the overall efficacy and durability of this combination is poor.
Drug therapy may be considered as an adjunct to diet and exercise (never as monotherapy) for patients with a BMI ≥30 kg/m^2. Pharmacotherapy has modest short-term efficacy but a high attrition rate and a lack of long-term efficacy.
Surgical treatment is an option for patients with BMI ≥40 kg/m^2, or ≥35 kg/m^2 with significant comorbidities. In general, weight-reductive surgery works through manipulation of the stomach or small bowel, or a hybrid of both. Potential complications are numerous.
Obesity can be defined as a chronic adverse condition due to an excess amount of body fat. While there are many methods to determine the relative amount of body fat, the most widely used method to determine obesity is the BMI, defined as weight divided by height squared ([weight in kg]/[height in m]^2).   
Chicago Institute of Minimally Invasive Surgery
Minimally Invasive Surgery Fellowship Program
St. Francis Hospital
Clinical Professor of Surgery
University of Illinois
CTF declares that he has no competing interests.
Associate Director, General Surgery Residency Program
Rush Medical College
Associate Professor of Surgery
Department of General Surgery
Rush University Medical Center
MBL declares that he has no competing interests.
Dr Constantine T. Frantzides and Dr Minh B. Luu would like to gratefully acknowledge Dr Scott N. Welle and Dr Mark A. Carlson, previous contributors to this topic. SNW declares that he has no competing interests. MAC declares that he is the author of the Daily Diet Score, a freely available online weight loss method.
Consultant in Metabolic Medicine
Imperial College London
Charing Cross Hospital
CLR declares that he has no competing interests.
Professor of Medicine
Chair for Obesity Research & Management
University of Alberta
Royal Alexandra Hospital
AMS declares that he has no competing interests.
Chair in Surgery
Division of Gastrointestinal and Endocrine Surgery
University of Texas
Southwestern Medical Center
EHL declares that he has no competing interests.
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