Abstract

The main objectives were to analyse the validity and accuracy of Body Mass Index (BMI) and Waist Circumference (WC) to evaluate obesity by excess of body fat in older adults and to identify more adequate cut-off points for this age group. The recommended cut-off points for BMI (25, 27 or 30 kg/m²) and WC (≥ 102 cm for men and ≥ 88 cm for women or ≥ 90cm for men and ≥ 80 cm for women) were compared to the total body densitometry. BF was defined by a value higher than the 90th percentile. Out of the 132 participants, 61% were women and aged between 60 and 91 years. The recommended cut-off points of BMI ≥ 25kg/m² and BMI ≥ 27 kg/m² showed similar performances. BMI ≥ 30 kg/m² showed high specificity but low sensitivity to identify BF in men and better performance in women. Conventional WC cut-off points showed low sensitivity and specificity. Based on our analyses, new cut-off points for BMI (25 kg/m² for men and 26.6 kg/m² for women) and WC (98.8 cm for men and 77.8cm for women) were proposed. The new cut-off points showed sensitivity and specificity values > 74% and accuracy > 76%. The areas under the curve (ROC) were > 0.86. The new BMI and WC cut-off points proposed in the present study for the diagnosis of obesity in older adults showed the best levels of sensitivity and specificity for this age group.

Keywords
Sensitivity and Specificity; Obesity; Body composition; Ageing

Introduction

Obesity remains one of the main public health challenges reaching pandemic levels¹1 Swinburn BA, Sacks G, Hall KD, McPherson K, Finegood DT, Moodie ML, Gortmaker SL. The global obesity pandemic: shaped by global drivers and local environments. Lancet 2011; 378(9793):804-814. and is associated to clinical complications and various chronic conditions²2 Agborsangaya CB, Ngwakongnwi E, Lahtinen M, Cooke T, Johnson JA. Multimorbidity prevalence in the general population: the role of obesity in chronic disease clustering. BMC Public Health 2013; 13:1161.. Despite being extensively investigated, there is still a lack of consensus on the most appropriate method for its diagnosis among older adults. The Body Mass Index (BMI) and waist circumference (WC) are the most widely used methods to identify global and central obesity respectively. Therefore, there is a clear need for studies to evaluate their capacity to predict capacity in order to obtain a consensus on their diagnostic cut-off points for the different population age groups. Evidence from the general adult population showed that BMI has high specificity level but low sensitivity³3 Okorodudu DO, Jumean MF, Montori VM, Romero-Corral A, Somers VK, Erwin PJ, Lopez-Jimenez F. Diagnostic performance of body mass index to identify obesity as defined by body adiposity: A systematic review and meta-analysis. Int J Obes 2010; 34(5):791-799. to identify adiposity⁴4 Hou XG, Wang C, Ma ZQ, Yang WF, Wang JX, Li CQ, Wang YL, Liu SM, Hu XP, Zhang XP, Jiang M, Wang WQ, Ning G, Zheng HZ, Ma AX, Sun Y, Song J, Lin P, Liang K, Liu FQ, Li WJ, Xiao J, Gong L, Wang MJ, Liu JD, Yan F, Yang JP, Wang LS, Tian M, Zhao RX, Jiang L, Chen L. Optimal waist circumference cut-off values for identifying metabolic risk factors in middle-aged and elderly subjects in Shandong Province of China. Biomed Env Sci 2014; 27(5):353-359..

The applicability and accuracy of using the same diagnostic cut-off points for both adults and older adults are inappropriate and not accepted widely⁴4 Hou XG, Wang C, Ma ZQ, Yang WF, Wang JX, Li CQ, Wang YL, Liu SM, Hu XP, Zhang XP, Jiang M, Wang WQ, Ning G, Zheng HZ, Ma AX, Sun Y, Song J, Lin P, Liang K, Liu FQ, Li WJ, Xiao J, Gong L, Wang MJ, Liu JD, Yan F, Yang JP, Wang LS, Tian M, Zhao RX, Jiang L, Chen L. Optimal waist circumference cut-off values for identifying metabolic risk factors in middle-aged and elderly subjects in Shandong Province of China. Biomed Env Sci 2014; 27(5):353-359. due to the aging related body composition changes such as body fat redistribution and muscle mass and bone density reductions. There are only few studies that investigated the predicted capability of BMI for cardiovascular risk⁵5 Martins MV, Queiroz Ribeiro A, Martinho KO, Silva Franco F, Souza JD, Morais KBD, Gonçalves Leite IC, Araújo Tinôco AL. Anthropometric indicators of obesity as predictors of cardiovascular risk in the elderly. Nutr Hosp 2015; 31(6):2583-2589. and body fat diagnosis⁶6 Vasconcelos FAG, Cordeiro BA, Rech CR, Petroski EL. Sensitivity and specificity of the body mass index for the diagnosis of overweight/obesity in elderly. Cad Saude Publica 2010; 26(8):1519-1527. in older adults. In addition, they did not propose a cut-off for this age group⁴4 Hou XG, Wang C, Ma ZQ, Yang WF, Wang JX, Li CQ, Wang YL, Liu SM, Hu XP, Zhang XP, Jiang M, Wang WQ, Ning G, Zheng HZ, Ma AX, Sun Y, Song J, Lin P, Liang K, Liu FQ, Li WJ, Xiao J, Gong L, Wang MJ, Liu JD, Yan F, Yang JP, Wang LS, Tian M, Zhao RX, Jiang L, Chen L. Optimal waist circumference cut-off values for identifying metabolic risk factors in middle-aged and elderly subjects in Shandong Province of China. Biomed Env Sci 2014; 27(5):353-359.. Therefore, because of population ageing is a major challenge it becomes important to establish more accurate cut-off points to predict body fat in older adults in the public health arena as well as in clinical settings. This way, there would be improvements in nutritional diagnosis and the planning of interventions.

Regarding the WC, the cut-off points to predict metabolic risk showed gender differences in different populations⁴4 Hou XG, Wang C, Ma ZQ, Yang WF, Wang JX, Li CQ, Wang YL, Liu SM, Hu XP, Zhang XP, Jiang M, Wang WQ, Ning G, Zheng HZ, Ma AX, Sun Y, Song J, Lin P, Liang K, Liu FQ, Li WJ, Xiao J, Gong L, Wang MJ, Liu JD, Yan F, Yang JP, Wang LS, Tian M, Zhao RX, Jiang L, Chen L. Optimal waist circumference cut-off values for identifying metabolic risk factors in middle-aged and elderly subjects in Shandong Province of China. Biomed Env Sci 2014; 27(5):353-359.^,77 Gharipour M, Sadeghi M, Dianatkhah M, Bidmeshgi S, Ahmadi A, Tahri M, Sarrafzadegan N. The cut-off values of anthropometric indices for identifying subjects at risk for metabolic syndrome in iranian elderly men. J Obes 2014; 2014:907149.. A recent meta-analysis demonstrated an increased mortality risk in older adults with increased WC even between different BMI categories, suggesting the need to re-evaluate the WC values in older adults⁸8 de Hollander EL, Bemelmans WJ, Boshuizen HC, Friedrich N, Wallaschofski H, Guallar-Castillón P, Walter S, Zillikens MC, Rosengren A, Lissner L, Bassett JK, Giles GG, Orsini N, Heim N, Visser M, de Groot LC; WC elderly collaborators. The association between waist circumference and risk of mortality considering body mass index in 65- to 74-year-olds: A meta-analysis of 29 cohorts involving more than 58 000 elderly persons. Int J Epidemiol 2012; 41(3):805-817..Therefore, based on the available evidence, the present study aimed at analysing the validity and accuracy of both BMI and WC in predicting excess body fat and identifying more accurate and appropriate cut-off points for older Brazilian adults.

Methods

The present study is a subsample of the cohort “Situação de Saúde e Indicadores Antropométricos para Avaliação do Estado Nutricional de Idosos Usuários do Sistema Único de Saúde de Goiânia” or “Projeto Idosos Goiânia” that started in 2008 with a probabilistic sample of 418 community-dwelling older adults aged 60 and older residing in the city of Goiania, Goias. The Projeto Idosos Goiânia only included those individuals aged 60 or older who attended at least an outpatient consultation twelve months before the baseline data collection date. This inclusion criteria allowed the researchers to establish whether the participants were users of the Brazilian Unified Health Service (SUS). A more detailed description of the cohort study can be found elsewhere⁹9 Pagotto V, Nakatani AYK, Silveira EA. Fatores associados à autoavaliação de saúde ruim em idosos usuários do Sistema Único de Saúde. Cad Saude Publica 2011; 27(8):1593-1602.

10 Pagotto V, Silveira EA. Methods, Diagnostic Criteria, Cutoff Points, and Prevalence of Sarcopenia among Older People. Sci World J 2014; 2014:231312.^-1111 Silva RRV, Silveira MF, Pena GG, Martins TCR, Pinheiro UB, Monteiro Júnior RS, Santos SHS, Paula AMB, Rodrigues Neto JF, Guimarães ALS. Genetic variation in the promoter region of the TNF rs1800629 gene is not associated with adiposity index, but AA genotype is more likely to have low cellular membrane integrity. Meta Gene 2017; 13:85-91..

The sample size calculation was estimated based on two-sided test of significance α= 0.05, ß = 0.05, power of 95% and an expected correlation coefficient of 0.35, resulting in a sample of at least 100 individuals¹²12 Browner W, Newman T, Cummings S, Huley S. Designing Clinical Research: an epidemiologic approach. Philadelphia: LWW; 2001.. In order to have a balanced proportion of men and women as well as different BMI categories,132 individuals were randomly selected. For the random selection only those individuals who fulfilled the criteria for the Dual Energy X-Ray Absorptiometry - DEXA (Total Body Densitometry) were eligible i.e. weight < 100kg (equipment maximum capacity), not having a pacemaker and provided an informed consent. The participants were initially contacted by telephone and informed about this stage of the study. The selected participants were informed about all interview procedures and fasting before the health examination i.e. DEXA. At the examination date, the participants were driven to the clinic and the assessments were carried out by trained and well qualified technicians leading to more reliable and accurate estimates.

The following measurements were performed: weight, height, body mass index (BMI), waist circumference (WC) and body fat percentage (%BF). Weigh was recorded to the nearest 0.1 kgusing a portable electronic digital scale (Tanita^Ò) and height was measured using a measuring tapeto the nearest 0.1 cm¹³13 Gordon C, Chumlea WRT. Stature, recumbent length, and weight. In: Anthropometric Standardization Reference Manual. Champaign: Human Kinetics Books; 1988. p. 3-8.. BMI was subsequently derived using the standard formula: weight divided by height squared (kg/m²) and categorized into: 1) overweight = BMI ≥ 25 kg/m² and obesity = BMI ≥ 30 Kg/m²; according to theWorld Health Organization¹⁴14 World Heatlh Organization (WHO). Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: WHO; 1995. [World Health Organization technical report series 854], 2)excess weight = BMI > 27 kg/m², classification used by the Nutrition Screening Initiative¹⁵15 Nutrition Screening Iniciative (NSI). Nutrition interventions manual for professionals caring for older Americans. Washington: NSI; 1992., and also recommended by other authors¹⁶16 Silveira EA, Kac G, Barbosa LS. Prevalência e fatores associados à obesidade em idosos residentes em Pelotas, Rio Grande do Sul, Brasil: classificação da obesidade segundo dois pontos de corte do índice de massa corporal. Cad Saude Publica 2009; 25(7):1569-1577..

During the health examination, two measurements of waist circumference were taken at the midpoint between the lower rib and the iliac crest using measuring tape with a 0.1cm level of precision¹⁷17 Lohman TG, Roche AF, Martorell R. Anthropometric Standardization Reference Manual. Champaign: Human Kinetics Books; 1988.. The identification of the anatomic points for the anthropometric measurements were done using standard procedures¹⁷17 Lohman TG, Roche AF, Martorell R. Anthropometric Standardization Reference Manual. Champaign: Human Kinetics Books; 1988.. Next, WC was categorised according to the following cut-off points: 1) ≥ 94 cm for menand ≥ 80 cm for women, recommended by the World Health Organization¹⁴14 World Heatlh Organization (WHO). Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: WHO; 1995. [World Health Organization technical report series 854]; 2)≥ 102 for men and ≥ 88 cmfor women recommended by the National Institutes of Health and the National Cholesterol Education Program¹⁸18 Baik I. Optimal Cutoff Points of Waist Circumference for the Criteria of Abdominal Obesity. Circ J 2009; 73(11):2068-2075.

19 Rotterdam ESHRE/ASRM-Sponsored PCOS consensus workshop group. Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome (PCOS). Hum Reprod 2004; 19(1):41-47.^-2020 National Institutes of Health (NIH). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults-The Evidence Report. Obesity research. Bethesda: NIH; 1988.; 3) higher than 90 cm and 80 cm for men and women respectively, proposed by the International Diabetes Federation²¹21 International Diabetes Federation (IDF). The IDF consensus worldwide definition of the metabolic syndrome. Brussels: IDF; 2005..

Body fat was measured in a specialised image clinic using the DEXA (Lunar^Ò, DPX-MD PLUS, program 7.52.002 DPX-L). During the examination, the participants were wearing a light apron and no metals such as jewellery. The excess body fat was defined using the 90^th percentile of the sample stratified by gender and age group²²22 Kyle UG, Genton L, Slosman DO, Pichard C. Fat-free and fat mass percentiles in 5225 healthy subjects aged 15 to 98 years. Nutrition 2001; 17(7-8):534-541., following the criteria previously published²³23 Habicht J-P. Estandarizacion de métodos epidemiológicos cuantitativos sobre el terreno. Bolletin de la Oficina Sanitaria Panamericana 1974; 76(5):374-384..

All statistical analyses were performed using the STATA, SE version 12.0. The normality of variables was tested using the Shapiro-Wilk test. The Pearson Chi-squared test was used to test differences in proportions by gender with a 5% significance level.

A Receiver Operating Characteristic (ROC) was performed to analyse the variations in sensitivity and specificity values of different WC cut-off points in relation to the gold standard measure. Next, WC cut-off values were calculated with their corresponding confidence intervals for sensitivity, specificity and accuracy taking into account a minimum sensitivity and specificity of 60% and total area under the ROC curve greater than 0.70.

The project was approved by the Ethics Committee of the Federal University of Goias. All participants were informed about the research objectives and provided a signed informed consent form.

Results

The sample was comprised of 132 older adults aged between 60 and 91 years. Overall, there were more participants from the age group 60-69 (52.3%) and women (60.6%). The average BMI values were 25.7 ± 4.0 kg/m² for men and 27.4 ± 5.7 kg/m² for women. WC average values were 95.7 ±11,5 cm and 93.7 ±14,5 cm for men and women, respectively. The average body fat percentage was 30.2 ± 8,6% in men and 42.8 ± 9,0% in women. These variables were normally distributed according to the Shapiro-Wilk test. Women had higher total and central obesity according to the WHO and NCEP criteria as well as percentage of body fat (Table 1).

Table 2 shows the performance of the different cut-off points to predict excess body fat. BMI ≥ 25 kg/m² and ≥ 27 kg/m² showed similar prediction performance in both men and women. The cut-off point of ≥ 30 kg/m² showed high specificity but low specificity sensitivity i.e. 25% in men, with a better prediction of elevated body fat percentage in women. The predict capability for WC was similar for all the different cut-off points assessed. However, the specificity was higher for men i.e. 91.7% and higher sensitivity for women (84.4%) when considering the highest cut-off points.

Regarding the proposed cut-off points by the present study based on the ROC curve, the BMI and WC values with the best sensitivity, specificity and accuracy values were 25 kg/m² and 98.8 cm for men, 26.6 kg/m² and 90.5 cm for women (Table 3).

Lastly, the area under the curve (Figures 1 and 2) showed that the capacity to detect correctly the presence or absence of excess body fat was 88% for both BMI and WC in men and 89% (BMI) and 86% (WC) in women. All the 95% confident intervals’ lower limits were above 0.78.

Discussion

The present study proposes new cut-off points for BMI and waist circumference (WC)to diagnosis obesity in older adults. Our main findings showed that the most accurate cut-off points to evaluate excess body fat in older adults were BMI≥ 25 kg/m² and WC ≥ 98,8 cm in men; and BMI ≥ 26,6 kg/m² and WC ≥ 90,5 cm in women. These cut-off points showed higher levels of accuracy i.e. between 76.2 and 84.3% to identify excess body fat/obesity in older men and women. Our findings represent an important contribution to research on anthropometry, ageing and morbidity since there is large controversy on the predict capacity of BMI and WC in older adults³3 Okorodudu DO, Jumean MF, Montori VM, Romero-Corral A, Somers VK, Erwin PJ, Lopez-Jimenez F. Diagnostic performance of body mass index to identify obesity as defined by body adiposity: A systematic review and meta-analysis. Int J Obes 2010; 34(5):791-799.^,44 Hou XG, Wang C, Ma ZQ, Yang WF, Wang JX, Li CQ, Wang YL, Liu SM, Hu XP, Zhang XP, Jiang M, Wang WQ, Ning G, Zheng HZ, Ma AX, Sun Y, Song J, Lin P, Liang K, Liu FQ, Li WJ, Xiao J, Gong L, Wang MJ, Liu JD, Yan F, Yang JP, Wang LS, Tian M, Zhao RX, Jiang L, Chen L. Optimal waist circumference cut-off values for identifying metabolic risk factors in middle-aged and elderly subjects in Shandong Province of China. Biomed Env Sci 2014; 27(5):353-359.. The adoption of the same cut-off point for obesity across different age groups from different populations is highly criticised because of considerable physiologic age-related changes in body composition. Therefore, the present study brings new evidence to shade some light on the current controversy.

The performance analysis of the existing cut-off points for WC carried out in the present study revelled a level of accuracy lower than 74% as well as lower values for specificity and sensitivity⁴4 Hou XG, Wang C, Ma ZQ, Yang WF, Wang JX, Li CQ, Wang YL, Liu SM, Hu XP, Zhang XP, Jiang M, Wang WQ, Ning G, Zheng HZ, Ma AX, Sun Y, Song J, Lin P, Liang K, Liu FQ, Li WJ, Xiao J, Gong L, Wang MJ, Liu JD, Yan F, Yang JP, Wang LS, Tian M, Zhao RX, Jiang L, Chen L. Optimal waist circumference cut-off values for identifying metabolic risk factors in middle-aged and elderly subjects in Shandong Province of China. Biomed Env Sci 2014; 27(5):353-359.. The BMI ≥ 30kg/m² also showed a poorer performance, sensitivity of 25% in men and 53% in women. These findings corroborate evidence from Australia, North America, China and from a meta-analysis including twenty five studies with 31,968 individuals³3 Okorodudu DO, Jumean MF, Montori VM, Romero-Corral A, Somers VK, Erwin PJ, Lopez-Jimenez F. Diagnostic performance of body mass index to identify obesity as defined by body adiposity: A systematic review and meta-analysis. Int J Obes 2010; 34(5):791-799.^,66 Vasconcelos FAG, Cordeiro BA, Rech CR, Petroski EL. Sensitivity and specificity of the body mass index for the diagnosis of overweight/obesity in elderly. Cad Saude Publica 2010; 26(8):1519-1527.^,2424 Romero-Corral A, Somers V, Sierra-Johnson J, Thomas RJ, Collazo-Clavell ML, Korinek J, Allison TG, Batsis JA, Sert-Kuniyoshi FH, Lopez-Jimenez F. Accuracy of Body Mass Index to Diagnose Obesity In the US Adult Population. Int J Obes 2010; 32(6):959-966.. Despite all the controversy surrounding the use of a BMI ≥ 30kg/m² as the cut-off point for obesity in older adults, some international institutions still recommend its use for such purpose¹⁴14 World Heatlh Organization (WHO). Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: WHO; 1995. [World Health Organization technical report series 854].

High BMI cut-off points, such as 30 kg/m², are not appropriate to identify older obese adults due to their low sensitivity. Our findings together with the ones from another study²⁵25 Barbosa MH, Bolina AF, Luiz RB, Oliveira KF, Virtuoso Júnior JS, Rodrigues RA, Silva LC, Cunha DF, De Mattia AL, Barichello E. Body mass index as discriminator of the lean mass deficit and excess body fat in institutionalized elderly people. Geriatr Nurs 2015; 36(3):202-206., showed that BMI values of 27 kg/m² and 25 kg/m² have higher sensitivity and are more accurate. This could be attributed to increases in body fat and reductions in muscle and bone masses that occur during ageing. These changes are more pronounced in women²⁵25 Barbosa MH, Bolina AF, Luiz RB, Oliveira KF, Virtuoso Júnior JS, Rodrigues RA, Silva LC, Cunha DF, De Mattia AL, Barichello E. Body mass index as discriminator of the lean mass deficit and excess body fat in institutionalized elderly people. Geriatr Nurs 2015; 36(3):202-206.. Therefore, BMI and WC cut-off points should consider such differences. On the other hand, the performance analysis of lower BMI values (25 kg/m² and 27 kg/m²) showed better balance between sensitivity and specificity as well as better accuracy.

Central obesity has been recommended as one of the best anthropometric predictors for visceral adiposity and metabolic syndrome risk¹⁴14 World Heatlh Organization (WHO). Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. Geneva: WHO; 1995. [World Health Organization technical report series 854]^,2626 Zhu S, Wang Z, Heshka S, Heo M, Faith MS, Heymsfield SB. Waist circumference and obesity-associated risk factors among whites in the third National Health and Nutrition Examination. Am J Clin Nutr 2002; 76(4):743-749.. Its association to mortality and risk factors is stronger compared BMI⁸8 de Hollander EL, Bemelmans WJ, Boshuizen HC, Friedrich N, Wallaschofski H, Guallar-Castillón P, Walter S, Zillikens MC, Rosengren A, Lissner L, Bassett JK, Giles GG, Orsini N, Heim N, Visser M, de Groot LC; WC elderly collaborators. The association between waist circumference and risk of mortality considering body mass index in 65- to 74-year-olds: A meta-analysis of 29 cohorts involving more than 58 000 elderly persons. Int J Epidemiol 2012; 41(3):805-817.^,2626 Zhu S, Wang Z, Heshka S, Heo M, Faith MS, Heymsfield SB. Waist circumference and obesity-associated risk factors among whites in the third National Health and Nutrition Examination. Am J Clin Nutr 2002; 76(4):743-749.. However, due to age related variations in body composition, research on WC performance in older adults are needed since this age group is associated with more negative health outcomes⁷7 Gharipour M, Sadeghi M, Dianatkhah M, Bidmeshgi S, Ahmadi A, Tahri M, Sarrafzadegan N. The cut-off values of anthropometric indices for identifying subjects at risk for metabolic syndrome in iranian elderly men. J Obes 2014; 2014:907149.^,88 de Hollander EL, Bemelmans WJ, Boshuizen HC, Friedrich N, Wallaschofski H, Guallar-Castillón P, Walter S, Zillikens MC, Rosengren A, Lissner L, Bassett JK, Giles GG, Orsini N, Heim N, Visser M, de Groot LC; WC elderly collaborators. The association between waist circumference and risk of mortality considering body mass index in 65- to 74-year-olds: A meta-analysis of 29 cohorts involving more than 58 000 elderly persons. Int J Epidemiol 2012; 41(3):805-817.^,2727 Fauziana R, Jeyagurunathan A, Abdin E, Vaingankar J, Sagayadevan V, Shafie S, Sambasivam R, Chong SA, Subramaniam M. Body mass index, waist-hip ratio and risk of chronic medical condition in the elderly population: Results from the Well-being of the Singapore Elderly (WiSE) Study. BMC Geriatr 2016; 16:125.. Thus, it is important to establish specific cut-off points for excess body fat later in life⁸8 de Hollander EL, Bemelmans WJ, Boshuizen HC, Friedrich N, Wallaschofski H, Guallar-Castillón P, Walter S, Zillikens MC, Rosengren A, Lissner L, Bassett JK, Giles GG, Orsini N, Heim N, Visser M, de Groot LC; WC elderly collaborators. The association between waist circumference and risk of mortality considering body mass index in 65- to 74-year-olds: A meta-analysis of 29 cohorts involving more than 58 000 elderly persons. Int J Epidemiol 2012; 41(3):805-817.^,2828 Chen Y-M, Ho SC, Lam SSH, Chan SSG. Validity of body mass index and waist circumference in the classification of obesity as compared to percent body fat in Chinese middle-aged women. Int J Obes 2006; 30(6):918-925..

The WC cut-off points analysed in the present study showed that ≥ 90 cm for men and ≥ 80 cm for women (IDF)²⁹29 Alberti KG, Eckel RH, Grundy SM, Zimmet PZ, Cleeman JI, Donato KA, Fruchart JC, James WP, Loria CM, Smith SC Jr; International Diabetes Federation Task Force on Epidemiology and Prevention; Hational Heart, Lung, and Blood Institute; American Heart Association; World Heart Federation; International Atherosclerosis Society; International Association for the Study of Obesity. Harmonizing the metabolic syndrome: A joint interim statement of the international diabetes federation task force on epidemiology and prevention; National heart, lung, and blood institute; American heart association; World heart federation; International atherosclerosis society; And international association for the study of obesity. Circulation 2009; 120(16):1640-1645. and WC ≥ 102 cm for men and ≥ 88 cm for women (NCEP) were more accurate. On the other hand, the WHO cut-off points of ≥ 94 cm for men and ≥ 80 cm for women showed low specificity in both men and women and, consequently, a higher percentage of false-positive cases. Therefore, even the IDF cut-offs mentioned above i.e. 90 cm for men and 80 cm for women should not be used for women²⁹29 Alberti KG, Eckel RH, Grundy SM, Zimmet PZ, Cleeman JI, Donato KA, Fruchart JC, James WP, Loria CM, Smith SC Jr; International Diabetes Federation Task Force on Epidemiology and Prevention; Hational Heart, Lung, and Blood Institute; American Heart Association; World Heart Federation; International Atherosclerosis Society; International Association for the Study of Obesity. Harmonizing the metabolic syndrome: A joint interim statement of the international diabetes federation task force on epidemiology and prevention; National heart, lung, and blood institute; American heart association; World heart federation; International atherosclerosis society; And international association for the study of obesity. Circulation 2009; 120(16):1640-1645.. Furthermore, a study with 3,435 Tunisian adults found that the best cut-off form men was 85 cm and 79 cm for women, since these values had high specificity and sensitivity³⁰30 Bouguerra R, Alberti H, Smida H, Salem LB, Rayana CB, El Atti J, Achour A, Gaigi S, Slama CB, Zouari B, Alberti KG. Waist circumference cut-off points for identification of abdominal obesity among the tunisian adult population. Diabetes Obes Metab 2006; 9(6):859-868..

Studies with Asian³¹31 Aye M, Sazali M. Waist circumference and BMI cut-off points to predict risk factors for metabolic syndrome among outpatients in a district hospital. Singapore Med J 2012; 53(8):545-550., Korean and Chinese⁴4 Hou XG, Wang C, Ma ZQ, Yang WF, Wang JX, Li CQ, Wang YL, Liu SM, Hu XP, Zhang XP, Jiang M, Wang WQ, Ning G, Zheng HZ, Ma AX, Sun Y, Song J, Lin P, Liang K, Liu FQ, Li WJ, Xiao J, Gong L, Wang MJ, Liu JD, Yan F, Yang JP, Wang LS, Tian M, Zhao RX, Jiang L, Chen L. Optimal waist circumference cut-off values for identifying metabolic risk factors in middle-aged and elderly subjects in Shandong Province of China. Biomed Env Sci 2014; 27(5):353-359.^,1818 Baik I. Optimal Cutoff Points of Waist Circumference for the Criteria of Abdominal Obesity. Circ J 2009; 73(11):2068-2075. populations found different cut-off points, highlighting the importance of our findings suggesting cut-off points specific for older Brazilian adults.

Brazilian studies that evaluated both anthropometric parameters i.e. WC and BMI in older adults and their capacity to predict obesity⁵5 Martins MV, Queiroz Ribeiro A, Martinho KO, Silva Franco F, Souza JD, Morais KBD, Gonçalves Leite IC, Araújo Tinôco AL. Anthropometric indicators of obesity as predictors of cardiovascular risk in the elderly. Nutr Hosp 2015; 31(6):2583-2589.^,66 Vasconcelos FAG, Cordeiro BA, Rech CR, Petroski EL. Sensitivity and specificity of the body mass index for the diagnosis of overweight/obesity in elderly. Cad Saude Publica 2010; 26(8):1519-1527.^,2525 Barbosa MH, Bolina AF, Luiz RB, Oliveira KF, Virtuoso Júnior JS, Rodrigues RA, Silva LC, Cunha DF, De Mattia AL, Barichello E. Body mass index as discriminator of the lean mass deficit and excess body fat in institutionalized elderly people. Geriatr Nurs 2015; 36(3):202-206. and cardiovascular risk⁵5 Martins MV, Queiroz Ribeiro A, Martinho KO, Silva Franco F, Souza JD, Morais KBD, Gonçalves Leite IC, Araújo Tinôco AL. Anthropometric indicators of obesity as predictors of cardiovascular risk in the elderly. Nutr Hosp 2015; 31(6):2583-2589. found a great variation of recommended cut-off points for BMI and WC with different sensitivity and specificity values⁵5 Martins MV, Queiroz Ribeiro A, Martinho KO, Silva Franco F, Souza JD, Morais KBD, Gonçalves Leite IC, Araújo Tinôco AL. Anthropometric indicators of obesity as predictors of cardiovascular risk in the elderly. Nutr Hosp 2015; 31(6):2583-2589.. The cut-off points proposed in the present study are similar to the ones suggested by Barbosa et al.²⁵25 Barbosa MH, Bolina AF, Luiz RB, Oliveira KF, Virtuoso Júnior JS, Rodrigues RA, Silva LC, Cunha DF, De Mattia AL, Barichello E. Body mass index as discriminator of the lean mass deficit and excess body fat in institutionalized elderly people. Geriatr Nurs 2015; 36(3):202-206. having, overall, better sensitivity, specificity and accuracy. Differences found between international studies as well as between different regions within the same country, could be explained by the differences in outcomes used, analytical approach, presentation of the findings and heterogeneity of each population.

Our proposed cut-off points could potentially be used in older Brazilian adults from different regions within Brazil and also in other South American countries. This last point is particularly important since the cut-off points currently recommended in this region have been based on populations from Europe and North America²¹21 International Diabetes Federation (IDF). The IDF consensus worldwide definition of the metabolic syndrome. Brussels: IDF; 2005.^,2929 Alberti KG, Eckel RH, Grundy SM, Zimmet PZ, Cleeman JI, Donato KA, Fruchart JC, James WP, Loria CM, Smith SC Jr; International Diabetes Federation Task Force on Epidemiology and Prevention; Hational Heart, Lung, and Blood Institute; American Heart Association; World Heart Federation; International Atherosclerosis Society; International Association for the Study of Obesity. Harmonizing the metabolic syndrome: A joint interim statement of the international diabetes federation task force on epidemiology and prevention; National heart, lung, and blood institute; American heart association; World heart federation; International atherosclerosis society; And international association for the study of obesity. Circulation 2009; 120(16):1640-1645.. The current cut-off points for BMI used to diagnose obesity have high specificity but a sensitivity value lower than 50%. Our findings reinforce the ones from international studies that criticise the existing cut-offs since they ignore the body fat gain related to ageing.

Therefore, our results seek to help the process of establishing more sensitive and specific WC cut-off points leading to improvements in the diagnosis of obesity in older Brazilian adults by using simple anthropometric measures. This way, they would also contribute to the development of strategies for prevention and treatment of obesity associated morbidities.

One of the potential limitations of the present study could be its small sample size. However, because it was designed to test the accuracy and validation of anthropometric measures the number of participants investigated was sufficient according to the power calculation performed a priori. It is worth mentioning that the gold standard used i.e. total body densitometry is a high precision technique to diagnose body composition. This fact increases the validity of the comparisons of the anthropometric measures used and our findings.

Based on our findings, the cut-off points of 25kg/m² and 98.8cm for men and 26.6 kg/m² and 90.5cm for women are recommended to evaluate excess body fat/obesity specifically in older adults. The use of more accurate BMI and WC cut-offs in the health services as well as in the family health strategy program could potentially enhance the diagnosis of obesity in older adults. The importance of establishing accurate cut-off points is the fact that their operational simplicity and good accuracy are great advantages for health settings. Furthermore, they allow getting a better understanding of obesity in specific population groups in epidemiological research.

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