Bariatric treatments for adult obesity - Institute of Health Economics

This report addresses obesity in adults only (≥ 18 years, both genders) and the condition is referredto here as adult obesity.Definition, classification, and description of adult obesityObesity is defined as an accumulation of excess body fat (adipose tissue) that may impair one’shealth and may result in reduced quality of life (QoL) and increased morbidity and prematuremortality (www.who.int/mediacentre/factsheets/fs311/en/index.html, accessed 23 July2010). 1,2,5,6,11,13,14,16-27 A variety of methods have been proposed to measure body fat accurately orreliably, among which the most complex include densitometry, bioelectrical impedance analysis, dualenergy x-ray, and computed tomography or magnetic resonance imaging scanning. 1,2,10,13,19,28However, these methods require expensive equipment and highly trained professionals and their useis not feasible in current practice.A common alternative is to define obesity as excess body weight rather than excess body fat(www.who.int/mediacentre/factsheets/fs311/en/index.html, accessed 23 July 2010). 1,2,5-7,11,13,14,16-27International and Canadian guidelines for body weight classification in adults define obesity for bothgenders and all age groups in relation to body mass index (BMI), which is calculated as weight(expressed in kilograms) divided by height (expressed in meters squared, or kg/m 2 ). Within thisframework, the term obesity applies when the BMI is equal to or greater than (>) 30 kg/m 2 .As BMI is highly correlated with reference measures of body fat, it is widely used to indicatedifferent levels of health risks associated with obesity and to predict future health status in men andwomen (www.who.int/mediacentre/factsheets/fs311/en/index.html, accessed 23 July 2010). 1,2,6,9-14,16,17,19-22,24,27,29-31Because BMI varies greatly among adults, obesity has been divided into three classes(class I or mild obesity; class II or moderate obesity; and class III or severe/extreme/morbidobesity), with successive values representing escalating health risk levels. According to the Canadianguidelines for body weight classification in adults, which are in line with those of the WHO, adultsin class I (BMI between 30.0 kg/m 2 and 34.9 kg/m 2 ) have a high risk of developing healthproblems. 22 For those in class II (BMI between 35.0 kg/m 2 and 39.9 kg/m 2 ), the risk is very high.And for those in class III (BMI of 40 kg/m 2 or more), the risk is extremely high.Assessing body weight using BMI cut-off points is simple and convenient; but it has a number oflimitations because it does not take into consideration body composition. 1,2,5,6,9-13,16,17,19,22,24,25,27,30,32BMI does not measure body fat or the distribution of body fat directly and does not distinguish fatfrom fat-free mass such as muscle and bone. While it provides a useful surrogate for total adiposity,BMI is influenced by, and needs adjustment for, gender, age, and ethnicity/race. Because of bodycomposition differences, women generally have a higher percentage of body fat than do men andolder individuals tend to have a higher percentage of body fat than do younger adults with the sameBMI. Furthermore, BMI classifications are based on the body types of those ofCaucasian/European descent, which are different than Asian and Aboriginal body types. 1,22,30 ForAsian and Aboriginal populations, more research is needed to determine whether current BMIclassifications apply. 1,22For these reasons, although BMI is a good measure of adult obesity at the population level, it maynot be an accurate predictor for obesity-related health risks for certain groups because it does notcorrespond to the same degree of fatness in different adults. 1,2,5,6,11,16,17,19,22,24,25,30,32 Therefore, BMIbasedobesity classification may underestimate or overestimate the effect of excess body weight andfat on health risks for some diseases in specific groups such as:Bariatric treatments for adult obesity – March 2012 4