Page 98 - JSOM Spring 2023

An Ongoing Series

Association of Body Mass Index with Injuries

A Systematic Review and Meta-Analyses Comparing Healthy Weight
Military Service Members with Underweight, Overweight, and Obese

Joseph J. Knapik, ScD *; Sally Hoedebecke, MS, RD 2
1

ABSTRACT
Obesity is a worldwide health problem that has reached pan- Several national and international organizations, including the
demic proportions. In the military, obesity and overweight are National Heart, Lung, and Blood Institute (NHLBI), the Cen-
associated with health problems, attrition from military service, ters for Disease Control and Prevention (CDC), and the WHO
and reduced job performance. National and international or- have recommended body mass index (BMI) as a population
ganizations suggest body mass index (BMI) as a population screening tool for evaluating overweight and obesity. 1,15,16 BMI
screening tool to define overweight and obesity. BMI is calcu- is calculated as weight in kg divided by the square of height
lated as weight/height (kg/m ). Four categories of adult BMI are in meters (i.e., weight/height expressed in units of kg/m ).
2
2
2
2
underweight (<18.5 kg/m ), healthy weight (18.5–24.9 kg/m ), The NHLBI and CDC define four categories of adult BMI:
2
2
overweight (25.0–29.9 kg/m ), and obese (≥30.0 kg/m ). This <18.5-kg/m , underweight; 18.5–24.9-kg/m , healthy weight;
2
2
2
2
article reports on a systematic review and meta-analysis exam- 25.0–29.9-kg/m , overweight; and ≥30.0-kg/m , obese. 15,16
2
2
ining the association between BMI and injury risk among mil-
itary service members (SMs). Studies were selected for review Despite recommendations by the NHLBI, CDC, and WHO,
if they involved military personnel, were prospective or retro- BMI has been criticized as an index of overweight and obesity
spective observational studies, and contained original quanti- among adults because body weight includes both lean body
tative data on injury risk at all four BMI levels. Nine studies mass (bone and muscle tissue) and fat mass. The assumption
met the review criteria. Pooled data from these investigations that BMI reflects adiposity assumes that lean body mass is
indicated that underweight, overweight, and obese individuals similar at any given height so that higher BMI (at a particular
were at 1.17 (95% confidence interval [95%CI]=1.07–1.28), height) reflects higher body fat. 17,18 However, the proportion of
1.03 (95%CI=1.01–1.06), and 1.15 (95%CI=1.11–1.20) times the body that is lean body mass varied by at least 20% from
higher risk of injury than healthy weight individuals, respec- the group mean in one study of normal men and women. 19
tively. Compared with healthy weight SMs, military personnel
with both low and high BMI are at higher injury risk. A recent systematic review and meta-analysis of 19 studies
20
indicated that the ability of BMI to identify obesity had a
Keywords: Body Mass Index; Injury; Underweight; Over- specificity (ability to correctly identify people without obe-
weight; Obese; Meta-Analysis; Systematic Review sity) of >95%, but only about 50% sensitivity (ability to cor-
rectly identify individuals with obesity). The high specificity
indicates that individuals with lower BMI are likely to have
less excess body fat (i.e., fewer false positives); however, only
Introduction
about 50% of individuals with excess body fat will have a
The World Health Organization (WHO) defines obesity as higher BMI (i.e., many false negatives). The ability of BMI to
“abnormal or excessive fat accumulation that may impair identify obesity among military populations may be higher, at
1
health.” Obesity has been recognized as a major worldwide least among men. A study involving male infantry soldiers
21
1–3
public health problem. The reason for this concern is the found the correlation between body fat determined by dual
association of obesity with a wide range of health problems, X-ray absorptiometry (DXA) and BMI was 0.86, with a spec-
most notably Type 2 diabetes, cardiovascular disease, cer- ificity of 100% and a sensitivity of 77%. In another study
5–8
4–6
22
tain cancers, 6,9,10 and mental health disorders. 11–14 involving active duty (74%) and retired (26%) male Navy
*Correspondence to joseph.j.knapik.vol@health.mil
1 MAJ (Ret) Joseph J. Knapik served over 50 years with the US Military as a wheel vehicle mechanic, medic, Medical Service Corps officer, Depart-
ment of Defense civilian, and contractor. He is currently a research physiologist at the US Army Research Institute of Environmental Medicine
and an adjunct professor at Uniformed Services University (Bethesda MD) and Bond University (Robina, Australia). COL (Ret) Sally Hoede-
2
becke MS, RD, served 30 years as a dietitian in the US Army. She had a variety of assignments, including deployment during Desert Storm. She
completed a Fellowship in Health Care Policy at George Washington University and has specialized in nutrition, fitness, and policy.
96