Examination of the obese patient

According to the NHLBI guidelines [5], assessment of risk status due to overweight or obesity is based on the patient's body mass index (BMI), waist circumference and the overall risk status. BMI is calculated as weight (kg)/height (m)2, or as weight (pounds)/height (inches)2 x 703. A BMI table is more conveniently used for simple reference (see Table 9.1). Classifying obesity by BMI units replaces previous weight-height terminology such as percent ideal or desirable body weight. These previous terms were often difficult to interpret and difficult for patients to understand. BMI is recommended since it provides an estimate of body fat, is related to risk of disease and has been established as an independent risk factor for premature mortality [6]. A desirable or healthy BMI is 18.5 to 24.9kg/m2, overweight is 25 to 29.9kg/m2, and obesity is >30kg/m2. Obesity is further sub-defined into class I (30.0-34.9kg/m2), class II (35.0-39.9kg/m2) and class III (>40kg/m2) (Table 9.2). Lower BMI cut-offs for overweight

Body Mass Index Table

BMI

19

20

Normal 21 22

23

24

25

Overweight 26 27 28

29

30

31

Obese 32

33

34

35

36

37

38

39

40

41

42

Extreme Obesity 43 44 45 46

47

48

49

50

51

52

53

54

Height (inches) 58

91

96

100

105

110

115

119

124

129

134

138

143

148

153

158

Body Weight (pounds) 162 167 172 177 181

186

191

196

201

205

210

215

220

224

229

234

239

244

248

253

258

59

94

99

104

109

114

119

124

128

133

138

143

148

153

158

163

168

173

178

183

188

193

198

203

208

212

217

222

227

232

237

242

247

252

257

262

267

60

97

102

107

112

118

123

123

133

138

143

148

153

158

163

168

174

179

184

189

194

199

204

209

215

220

225

230

235

240

245

250

255

261

266

271

276

61

100

106

111

116

122

127

132

137

143

148

153

158

164

169

174

180

185

190

195

201

206

211

217

222

227

232

238

243

248

254

259

264

269

275

280

285

62

104

109

115

120

126

131

136

142

147

153

158

164

169

175

180

186

191

196

202

207

213

218

224

229

235

240

246

251

256

262

267

273

278

284

289

295

63

107

113

118

124

130

135

141

146

152

158

163

169

175

180

186

191

197

203

208

214

220

225

231

237

242

248

254

259

265

270

278

282

287

293

299

304

64

110

116

122

128

134

140

145

151

157

163

169

174

180

186

192

197

204

209

215

221

227

232

238

244

250

256

262

267

273

279

285

291

296

302

308

314

65

114

120

126

132

138

144

150

156

162

168

174

180

186

192

198

204

210

216

222

228

234

240

246

252

258

264

270

276

282

288

294

300

306

312

318

324

66

118

124

130

136

142

148

155

161

167

173

179

186

192

198

204

210

216

223

229

235

241

247

253

260

266

272

278

284

291

297

303

309

315

322

328

334

67

121

127

134

140

146

153

159

166

172

178

185

191

198

204

211

217

223

230

236

242

249

255

261

268

274

280

287

293

299

306

312

319

325

331

338

344

68

125

131

138

144

151

158

164

171

177

184

190

197

203

210

216

223

230

236

243

249

256

262

269

276

282

289

295

302

308

315

322

328

335

341

348

354

69

128

135

142

149

155

162

169

176

182

189

196

203

209

216

223

230

236

243

250

257

263

270

277

284

291

297

304

311

318

324

331

338

345

351

358

365

70

132

139

146

153

160

167

174

181

188

195

202

209

216

222

229

236

243

250

257

264

271

278

285

292

299

306

313

320

327

334

341

348

355

362

369

376

71

136

143

150

157

165

172

179

186

193

200

208

215

222

229

236

243

250

257

265

272

279

286

293

301

308

315

322

329

338

343

351

358

365

372

379

386

72

140

147

154

162

169

177

184

191

199

206

213

221

228

235

242

250

258

265

272

279

287

294

302

309

316

324

331

338

346

353

361

368

375

383

390

397

73

144

151

159

166

174

182

189

197

204

212

219

227

235

242

250

257

265

272

280

288

295

302

310

318

325

333

340

348

355

363

371

378

386

393

401

408

74

148

155

163

171

179

186

194

202

210

218

225

233

241

249

256

264

272

280

287

295

303

311

319

326

334

342

350

358

365

373

381

389

396

404

412

420

75

152

160

168

176

184

192

200

208

216

224

232

240

248

256

264

272

279

287

295

303

311

319

327

335

343

351

359

367

375

383

391

399

407

415

423

431

76

156

164

172

180

189

197

205

213

221

230

238

246

254

263

271

279

287

295

304

312

320

328

336

344

353

361

369

377

385

394

402

410

418

426

435

443

Source: Adapted from Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report.

Table 9.2

Classification of Weight Status and Risk of Disease

[If a patient is 18 circumference to blood pressure or years or older, use the body mass index (BMI) and waist estimate weight status and relative risk for diabetes, high heart disease]

Risk of disease (relative to having a healthy weight and waist size)

Underweight Healthy weight Overweight Obesity class I Obesity class II Obesity class III (extreme obesity)

BMI below 18.5 BMI 18.5-24.9 BMI 25.0-29.9 BMI 30.0-34.9 BMI 35.0-39.9 BMI 40 or more

Waist circumference:* 35" or less (women) 40" or less (men)

Increased High

Very high Extremely high

Waist circumference:* More than 35" (women) More than 40" (men)

High

Very high Very high Extremely high

* Measure waist circumference at the level of the iliac crest. An increased waist circumference may indicate increased disease risk even at a normal weight. Source (adapted from): National Institutes of Health, National Heart, Lung, and Blood Institute. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. U.S. Department of Health and Human Services, Public Health Service; 1998 [5]

and obesity for the Asian-Pacific region have been proposed. After obtaining the patient's measured height and weight, the BMI and Classification Tables should be used to categorize overweight and obesity and to document this information in the medical record.

Although BMI is the accepted methodology to categorize obesity, it does not distinguish the composition of fat versus lean tissue. An older adult with a normal BMI may be obese due to having an unusually low lean body mass, while a body builder may have an elevated BMI due to having increased muscularity, but may not actually be obese. Skinfold anthropometry and bioelectrical impedance analysis (BIA), two bedside tests, can be routinely recommended for office use in evaluating an obese patient's lean body mass and body fat mass.

An increased waist circumference is independently associated with impaired health and increased cardiovascular risk compared to those with normal waist circumferences [7, 8]. Abdominal fat is clinically defined as a waist circumference >102 cm (>40 inches) in men and >88 cm (>35 inches) in women. According to the Practical Guide, "to measure waist circumference, locate the upper hip bone and the top of the right iliac crest. Place a measuring tape in a horizontal plane around the abdomen at the level of the iliac crest. Before reading the tape measure, ensure that the tape is snug, but does not compress the skin, and is parallel to the floor. The measurement is made at the end of a normal expiration." Any person with a BMI <35 and a waist circumferences exceeding these limits should be urged more strongly to pursue weight reduction as their increased waist circumference increases disease risk for each BMI class (see Table 9.2).

Determination of fitness level is another factor in assessing risk associated with BMI. Longitudinal studies from The Cooper Institute in Dallas, Texas, have shown that cardiorespiratory fitness (as measured by a maximal treadmill exercise test) is an important predictor of all-cause mortality independent of BMI and body composition. The authors observed that fit obese men had a lower risk of all-cause and CVD mortality than did unfit, lean men [9]. Similar results have been demonstrated among women [10].

The exact contribution of genetics or biology to obesity is a topic currently under debate, the main question being how large of a role do biology, psychology and the environment actually play? James O. Hill, M.D., states that, "Despite obesity having strong genetic determinants, the genetic composition of the population does not change rapidly. Therefore, the large increase in obesity must reflect major changes in non-genetic factors." In the upcoming decade, research into potential hormones related to obesity may uncover further aspects to this discussion [11].

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