- Email: [email protected]
Weight Gain of Service Members After Basic Military Training
RESEARCH BRIEF
Weight Gain of Service Members After Basic Military Training Bryant J. Webber, MD, MPH,1 Stefani A. Ruiz, MHS,1,2 Gerald W. Talcott, PhD,3 Melissa A. Little, PhD, MPH,3 Deborah F. Tate, PhD4
Introduction: Despite weight and fitness requirements, the prevalence of overweight and obesity in the U.S. military approaches that in the general population. The purpose of this study is to assess trends in anthropometric measurements shortly after military enlistment.
Methods: This longitudinal study evaluated the change in objectively measured body weight and waist circumference in the population of U.S. Air Force members who enlisted in 2012−2013 and graduated from Basic Military Training (n=49,466). Individuals were followed for 4 years or until they left the military, for a mean follow-up of 1,218 (SD=261) days. Data were collected in 2018 and analyzed in 2019.
Results: Among Basic Military Training graduates with available and plausible baseline data (n=46,706), weight increased incrementally by a mean of 1.5−1.8 kg per year and waist circumference by 0.3−1.1 cm per year. Over the 4-year period, total mean weight gain was 6.6 (SD=7.7) kg and waist circumference increase was 3.1 (SD=6.4) cm. Male graduates gained 7.0 (SD=7.7) kg and female graduates gained 4.7 (SD=7.5) kg. Of those who stayed in the military for 4 years, 37.3% transitioned to a higher BMI category (i.e., from normal to overweight/obese or from overweight to obese), whereas 3.9% transitioned to a lower category.
Conclusions: Future research is needed to understand determinants of unhealthy weight gain and the association between weight gain and physical fitness among young adults embarking on a military career.
Am J Prev Med 2020;58(1):117−121. Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine.
INTRODUCTION
N
early two thirds of active duty U.S. service members are overweight or obese per BMI,1 approaching the prevalence in the general U.S. population.2 Obesity in the military is associated with musculoskeletal injuries,3 cardiovascular disease,4 mental health problems,4 and absenteeism and presenteeism.5 Body composition of military members is assessed during periodic fitness assessments. In the U.S. Air Force, 20% of the fitness score is based on waist circumference. A measurement exceeding 100 cm (male members) or 91 cm (female members) results in assessment failure, unless the member excels at the muscular components and 1.5-mile run and has a BMI <25 kg/m2 or body fat percentage ≤18% (male members) or ≤26% (female members). Fitness failures may impair career
opportunities, and 4 failures within a 24-month period compel administrative action.6 Between 1995 and 2008, overweight and obesity increased across all age and rank categories of the armed forces, including the youngest and most junior enlisted.7 Weight gain during early adulthood, which has been From the 1Public Health and Preventive Medicine Department, U.S. Air Force School of Aerospace Medicine, Wright-Patterson AFB, Ohio; 2Solutions Through Innovative Technologies, Inc., Fairborn, Ohio; 3Center for Addiction and Prevention Research, University of Virginia, Charlottesville, Virginia; and 4Department of Health Behavior, Gillings School of Global Public Health, University of North Carolina−Chapel Hill, Chapel Hill, North Carolina Address correspondence to: Bryant J. Webber, MD, MPH, 2510 Fifth Street, Bldg 840, Rm W318, Wright-Patterson AFB OH 45433. E-mail: [email protected]. 0749-3797/$36.00 https://doi.org/10.1016/j.amepre.2019.08.022
Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine.
Am J Prev Med 2020;58(1):117−121
117
118
Webber et al / Am J Prev Med 2020;58(1):117−121
described in the civilian population8 and linked to chronic disease risk during middle adulthood,9 has not been analyzed in the military. Moreover, most military studies have been cross-sectional and have not included other anthropometric measures. The purpose of this study is to evaluate weight and waist circumference changes over the first 4 years of military service, which may inform interventions that promote healthy weight management and reduce military discharge.
METHODS This longitudinal study assessed the population of U.S. Air Force enlistees between January 2012 and December 2013 who graduated from Basic Military Training. This study was approved by the Air Force Research Laboratory IRB. Height, weight, and waist circumference data were obtained from recorded measurements during the last week of training and served as baseline measures. Subsequent measures were recorded in a standardized manner at fitness assessments over the next 4 years.6 The last assessment during each year was used, with the first year restricted to 6−12 months following graduation to allow time for body composition change. Sex, age, self-reported race and ethnicity, marital status, career field, and highest education level achieved were obtained from personnel records and defined at baseline. Population change in BMI and waist circumference was defined as the mean difference between baseline and each time point. National Heart, Lung, and Blood Institute categories were used to classify individuals at each time point according to their BMI as underweight (<18.5), normal (18.5−24.9), overweight (25.0−29.9), and obese (≥30.0), and according to their waist circumference as either normal (male individuals ≤102 cm and female individuals ≤88 cm) or elevated (male individuals >102 cm and female individuals >88 cm).10 These nearly correspond to the cut offs used by the U.S. Air Force for fitness assessment failure. To account for data entry errors, implausible data points were excluded in a two-step fashion. First, for all baseline and subsequent measures, published methodology3,11 was used to exclude implausible height (<137 or ≥213 cm), weight (<36 or ≥204 kg), and BMI (<10 or ≥50) values. Second, for percentage change between baseline and subsequent measures, Grubbs’ test was used to identify and exclude extreme outliers (4,779 data points), defined as values beyond the outer fences (Q3+3*IQR). Some members (n=8,491) separated from the military during the follow-up period, explaining why the population size diminished over time. Data were collected in 2018 and analyzed in 2019. Descriptive statistics were performed in Base SAS, version 9.4.
RESULTS Of U.S. Air Force service members who enlisted in 2012 and 2013 and had anthropometric measurements available from Basic Military Training graduation (n=47,054), 348 were excluded owing to implausible baseline measurements. Most of the included members were male (81.7%) and aged 18−29 years (97.1%). Male members had a
mean BMI of 24.0 (SD=2.3) and waist circumference of 79.8 (SD=5.1) cm, and female members had a mean BMI of 23.6 (SD=2.4) and waist circumference of 71.6 (SD=5.6) cm. Members gained a mean of 1.5−1.8 kg annually after graduating from Basic Military Training. The mean weight gain over the 4-year period was 6.6 (SD=7.7) kg. Male members gained 7.0 (SD=7.7) kg and female members gained 4.7 (SD=7.5) kg. Mean 4-year weight gain exceeded 7.0 kg for both black, non-Hispanic and Hispanic members; for married members; and for those in the support career field (Table 1). Waist circumference increased incrementally by 0.3−1.2 cm annually, with a mean increase of 3.1 (SD=6.4) cm over the 4-year period. Waist circumference trends (Table 2) largely mirrored body weight trends across demographic, occupational, and educational variables. Among service members who completed their 4-year enlistment period, 56.4% maintained the BMI category they held at graduation. A total of 9,877 (25.3%) members transitioned from normal to overweight, 3,546 (9.1%) from overweight to obese, and 1,123 (2.9%) from normal to obese. Conversely, 1,340 (3.4%) members transitioned from overweight to normal, 129 (0.3%) from obese to overweight, and 76 (0.2%) from obese to normal. Seventy (0.2%) male and 72 (0.8%) female members transitioned from a normal to an elevated waist circumference category, whereas just 3 (0.006%) members transitioned from elevated to normal.
DISCUSSION Enlisted U.S. Air Force personnel gained a mean of 6.6 kg during a 4-year period after Basic Military Training. Their 1.5−1.8 kg mean annual weight gain was substantially higher than the 0.6 kg self-reported annual weight gain in a demographically and occupationally diverse sample of U.S. service members (n=30,708).12 Weight gain during young adulthood, which has been well documented in the civilian population,8 appears to affect the same demographic within the U.S. Air Force, despite the presence of fitness and anthropometric requirements. Although many individuals transitioned to higher BMI categories (n=14,546), only 142 moved to a greater waist circumference category, which partially may be due to outcome dichotomization as either normal or elevated. The observed trend of increasing BMI and waist circumference, irrespective of categorical shifts in either metric, suggests that abdominal adipose deposition is contributing to weight gain. This is concerning because abdominal adipose tissue (both visceral and subcutaneous) is correlated with a number of metabolic risk www.ajpmonline.org
Webber et al / Am J Prev Med 2020;58(1):117−121
119
Table 1. Baseline Weight and Weight Gain (in kg) After Basic Military Training Graduation After graduation Variable Total population Sex Male Female Age, years 18−24 25−29 30−39 Race/ethnicity White, non-Hispanic Black, non-Hispanic Hispanic Other Marital status Single Married Other Career field Operations Logistics Support Medical Acquisition Other Educational attainment High school/GED Some college College degree and aboveb Unknown
a
Baseline
180−365 days
366−730 days
731−1,095 days
1,095−1,460 days
n=46,706 72.6 (10.0)
n=26,625 1.7 (5.0)
n=41,841 3.3 (6.2)
n=40,880 5.1 (7.1)
n=38,509 6.6 (7.7)
n=38,178 74.8 (9.0) n=8,528 62.6 (7.7)
n=21,665 1.8 (5.1) n=4,960 1.2 (4.4)
n=34,520 3.5 (6.3) n=7,321 2.2 (5.7)
n=34,008 5.5 (7.1) n=6,872 3.5 (6.9)
n=32,321 7.0 (7.7) n=6,188 4.7 (7.5)
n=32,767 72.0 (9.8) n=12,592 73.8 (10.4) n=1,347 74.8 (10.2)
n=23,876 1.6 (5.0) n=2,742 2.4 (4.9) n=6 0.7 (3.6)
n=35,605 3.2 (6.3) n=6,176 3.8 (5.8) n=60 3.7 (7.6)
n=31,625 5.2 (7.3) n=8,658 4.9 (6.5) n=597 5.3 (6.5)
n=25,865 6.8 (7.9) n=11,370 6.3 (7.3) n=1,274 6.4 (6.8)
n=32,997 73.1 (9.8) n=7,053 72.5 (10.4) n=984 70.4 (10.2) n=5,672 70.0 (10.2)
n=19,193 1.7 (5.1) n=4,172 1.7 (5.0) n=202 2.2 (4.7) n=3,058 1.6 (4.8)
n=29,994 3.3 (6.3) n=6,407 3.4 (6.3) n=544 3.7 (5.9) n=4,896 3.2 (6.0)
n=29,257 5.1 (7.1) n=6,023 5.5 (7.3) n=741 5.7 (7.0) n=4,859 4.9 (6.9)
n=27,307 6.5 (7.7) n=5,612 7.1 (7.9) n=877 7.4 (7.5) n=4,794 6.4 (7.4)
n=27,188 72.3 (9.8) n=17,835 73.1 (10.3) n=1,683 70.1 (10.5)
n=21,238 1.5 (4.9) n=5,282 2.4 (5.4) n=105 0.9 (4.5)
n=29,926 3.1 (6.1) n=11,497 3.9 (6.6) n=418 2.6 (5.9)
n=25,607 4.9 (7.0) n=14,354 5.6 (7.4) n=919 4.3 (6.7)
n=21,734 6.3 (7.5) n=15,287 7.1 (7.9) n=1,488 5.3 (7.3)
n=8,549 72.4 (10.2) n=17,694 73.4 (9.5) n=15,375 72.8 (10.1) n=3,977 68.6 (10.4) n=702 71.2 (10.6) n=400 72.7 (10.6)
n=4,741 1.8 (4.9) n=9,887 1.6 (5.2) n=8,840 1.8 (5.0) n=2,311 1.4 (4.6) n=371 2.0 (5.4) n=458 1.7 (5.0)
n=7,611 3.3 (6.1) n=15,952 3.2 (6.3) n=13,780 3.6 (6.3) n=3,459 2.7 (5.9) n=612 3.5 (6.6) n=410 3.6 (6.2)
n=7,550 5.0 (6.8) n=15,681 5.1 (7.3) n=13,408 5.4 (7.1) n=3,330 4.2 (6.9) n=596 5.1 (7.3) n=309 5.8 (8.0)
n=7,163 6.3 (7.4) n=14,913 6.7 (7.8) n=12,556 7.0 (7.7) n=3,066 5.6 (7.4) n=545 6.4 (7.4) n=259 6.4 (8.4)
n=35,401 72.4 (9.9) n=7,713 73.1 (10.3) n=3,254 72.9 (10.6) n=338 72.9 (9.7)
n=20,217 1.6 (5.0) n=1,857 2.1 (4.8) n=4,356 1.9 (4.9) n=195 1.1 (5.2)
n=31,724 3.3 (6.3) n=2,922 3.2 (5.7) n=6,898 3.4 (5.9) n=297 2.7 (6.3)
n=30,817 5.3 (7.3) n=2,904 4.3 (6.3) n=6,858 4.9 (6.8) n=301 4.9 (7.2)
n=29,041 6.8 (7.9) n=2,750 5.5 (6.8) n=6,446 6.2 (7.3) n=272 6.3 (7.5)
Note: All values are shown in mean (SD). a The first year was restricted to months 6−12 to allow time for weight change. b Includes Associate’s, Bachelor’s, and advanced degrees.
January 2020
Webber et al / Am J Prev Med 2020;58(1):117−121
120
Table 2. Baseline Waist Circumference and Waist Circumference Increase (in cm) After Basic Military Training Graduation After graduation a
Variable
Baseline
180−365 days
366−730 days
731−1,095 days
1,095−1,460 days
Total population
n=46,694 77.8 (5.9)
n=25,969 0.3 (5.5)
n=40,120 1.2 (5.8)
n=39,465 2.3 (6.2)
n=36,553 3.1 (6.4)
n=38,166 79.2 (5.1) n=8,528 71.7 (5.5)
n=21,110 0.2 (5.4) n=4,859 0.9 (5.7)
n=33,023 1.2 (5.8) n=7,097 1.2 (5.9)
n=32,773 2.4 (6.1) n=6,692 1.8 (6.4)
n=30,639 3.3 (6.4) n=5,914 2.4 (6.7)
n=32,757 77.4 (5.8) n=12,589 78.6 (5.9) n=1,348 79.4 (6.0)
n=23,275 0.2 (5.5) n=2,687 1.4 (5.2) n=6 1.7 (2.7)
n=34,125 1.0 (5.9) n=5,935 2.0 (5.5) n=60 2.7 (5.2)
n=30,508 2.2 (6.3) n=8,381 2.6 (5.8) n=576 2.9 (5.6)
n=24,559 3.0 (6.6) n=10,778 3.2 (6.1) n=1,216 3.5 (5.6)
n=32,990 78.6 (5.8) n=7,052 75.6 (5.6) n=983 77.4 (6.0) n=5,669 76.4 (6.1)
n=18,726 0.3 (5.5) n=4,058 0.4 (5.3) n=197 0.4 (5.5) n=2,988 0.4 (5.6)
n=28,718 1.1 (5.8) n=6,152 1.3 (5.8) n=523 1.4 (5.5) n=4,727 1.3 (5.7)
n=28,236 2.2 (6.2) n=5,828 2.5 (6.3) n=721 2.7 (6.3) n=4,680 2.3 (6.1)
n=25,897 3.0 (6.4) n=5,315 3.5 (6.6) n=844 3.7 (6.4) n=4,497 3.2 (6.5)
n=27,181 77.7 (5.8) n=17,830 78.2 (6.0) n=1,683 76.4 (6.6)
n=20,699 0.1 (5.4) n=5,165 1.1 (5.7) n=105 0.1 (5.2)
n=28,712 0.9 (5.7) n=11,008 1.9 (6.0) n=400 1.0 (5.9)
n=24,701 2.0 (6.1) n=13,886 2.8 (6.3) n=878 2.1 (6.0)
n=20,591 2.8 (6.4) n=14,555 3.6 (6.5) n=1,407 2.3 (6.3)
n=8,547 77.6 (6.0) n=17,692 78.4 (5.6) n=15,368 78.0 (5.9) n=3,977 75.4 (6.4) n=701 76.9 (6.3) n=400 77.4 (6.2)
n=4,696 0.9 (5.4) n=9,583 0.0 (5.5) n=8,549 0.3 (5.4) n=2,299 0.4 (5.5) n=369 1.0 (5.5) n=456 1.2 (5.9)
n=7,427 1.5 (5.7) n=15,148 0.9 (5.9) n=13,095 1.3 (5.8) n=3,430 1.0 (5.8) n=606 1.8 (5.8) n=397 1.9 (5.7)
n=7,380 2.3 (6.0) n=15,037 2.2 (6.3) n=12,869 2.3 (6.1) n=3,294 2.0 (6.3) n=584 2.5 (6.0) n=295 2.8 (6.6)
n=6,854 3.0 (6.3) n=14,093 3.1 (6.5) n=11,850 3.2 (6.5) n=2,991 2.8 (6.5) n=511 3.4 (6.1) n=248 3.2 (6.7)
n=35,391 77.7 (5.8) n=7,711 78.2 (6.1) n=3,254 77.8 (6.3) n=338 78.2 (6.0)
n=19,708 0.2 (5.5) n=1,817 1.2 (5.3) n=4,256 0.7 (5.4) n=188 0.2 (5.7)
n=30,400 1.1 (5.9) n=2,805 1.5 (5.4) n=6,633 1.4 (5.7) n=282 0.6 (5.9)
n=29,706 2.3 (6.2) n=2,817 2.2 (5.7) n=6,655 2.3 (6.0) n=287 2.2 (6.2)
n=27,546 3.2 (6.5) n=2,616 2.9 (5.8) n=6,127 2.9 (6.2) n=264 3.0 (6.4)
Sex Male Female Age, years 18−24 25−29 30−39 Race/ethnicity White, non-Hispanic Black, non-Hispanic Hispanic Other Marital status Single Married Other Career field Operations Logistics Support Medical Acquisition Other Educational attainment High school/GED Some college College degree and aboveb Unknown
Note: All values are shown in mean (SD). a The first year was restricted to months 6−12 to allow time for waist circumference change. b Includes Associate’s, Bachelor’s, and advanced degrees.
www.ajpmonline.org
Webber et al / Am J Prev Med 2020;58(1):117−121
factors, including hypertension and impaired fasting glucose,13 and waist circumference in the upper range of normal is associated with greater mortality, even among those who are not obese according to BMI.14 Military weight studies have been limited by reliance on self-reported data, the use of serial cross-sectional samples to evaluate trends, and potential misclassification of adiposity based on BMI.4,7 By utilizing objective weight data from fitness assessments, following the same cohort longitudinally, and demonstrating concomitant increases in waist circumference, this study avoids these shortcomings and substantiates concerns regarding unhealthy body weight trends in the armed forces.
Limitations The study has several limitations. First, although measurements were obtained in a standardized approach,6 scale calibration could not be certified. Second, manual entry of measurements into the Air Force fitness database may have introduced errors. Third, this study was conducted on a cohort of enlisted Air Force personnel, most of whom were young and male, limiting its generalizability to other populations. Finally, aerobic and anaerobic fitness metrics were not obtained; the association between body composition change and physical performance should be assessed in future studies.
CONCLUSIONS This study highlights the need for ongoing research and interventions that promote healthy weight maintenance among young adults embarking on a military career.
ACKNOWLEDGMENTS The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Air Force, Department of Defense, or U.S. Government. No financial disclosures were reported by the authors of this paper. Author contributions: Conception and design (BJW, GWT, MAL, DFT), acquisition of data (SAR), analysis and interpretation of data (BJW, SAR, GWT, MAL, DFT), drafting manuscript (BJW, SAR), critical revision of manuscript (GAW, MAL, DFT), final approval of manuscript (BJW, SAR, GWT, MAL, DFT).
January 2020
121
REFERENCES 1. Meadows SO, Engel CC, Collins RL, et al. 2015 Health related behaviors survey: summary findings and policy implications. Santa Monica, CA: RAND Corporation; 2018. www.rand.org/pubs/research_briefs/ RB9955.html. Accessed September 5, 2019. 2. CDC. Table 53. Selected health conditions and risk factors, by age: United States, selected years 1988−1994 through 2015−2016. www. cdc.gov/nchs/data/hus/2017/053.pdf. Accessed September 5, 2019. 3. Hruby A, Bulathsinhala L, McKinnon CJ, et al. BMI and lower extremity injury in U.S. Army soldiers, 2001−2011. Am J Prev Med. 2016;50(6):e163–e171. https://doi.org/10.1016/j.amepre.2015.10.015. 4. Rush T, LeardMann CA, Crum-Cianflone NF. Obesity and associated adverse health outcomes among US military members and veterans: findings from the Millennium Cohort Study. Obesity (Silver Spring). 2016;24(7):1582–1589. https://doi.org/10.1002/oby.21513. 5. Dall TM, Zhang Y, Chen YJ, et al. Cost associated with being overweight and with obesity, high alcohol consumption, and tobacco use within the military health system’s TRICARE prime-enrolled population. Am J Health Promot. 2007;22(2):120–139. https://doi.org/ 10.4278/0890-1171-22.2.120. 6. U.S. Department of the Air Force. Fitness Program. Air Force instruction 36−2905. https://static.e-publishing.af.mil/production/1/af_a1/ publication/afi36-2905/afi36-2905.pdf. Published 2013. Accessed September 5, 2019. 7. Reyes-Guzman CM, Bray RM, Forman-Hoffman VL, Williams J. Overweight and obesity trends among active duty military personnel: a 13-year perspective. Am J Prev Med. 2015;48(2):145–153. https:// doi.org/10.1016/j.amepre.2014.08.033. 8. Dutton GR, Kim Y, Jacobs DR Jr, et al. 25-year weight gain in a racially balanced sample of U.S. adults: the CARDIA study. Obesity (Silver Spring). 2016;24(9):1962–1968. https://doi.org/10.1002/oby.21573. 9. Zheng Y, Manson JE, Yuan C, et al. Associations of weight gain from early to middle adulthood with major health outcomes later in life. JAMA. 2017;318(3):255–269. https://doi.org/10.1001/jama.2017.7092. 10. NIH, National Heart, Lung, and Blood Institute. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults: the evidence report. Bethesda, MD: HHS; 1998. www.ncbi. nlm.nih.gov/books/NBK2003/. Accessed September 5, 2019. 11. Hruby A, Hill OT, Bulathsinhala L, et al. Trends in overweight and obesity in soldiers entering the US Army, 1989‒2012. Obesity (Silver Spring). 2015;23(3):662–670. https://doi.org/10.1002/oby.20978. 12. Littman AJ, Jacobson IG, Boyko EJ, Powell TM, Smith TC, Millennium Cohort Study Team. Weight change following US military service. Int J Obes (Lond). 2013;37(2):244–253. https://doi.org/10.1038/ ijo.2012.46. 13. Fox CS, Massaro JM, Hoffmann U, et al. Abdominal visceral and subcutaneous adipose tissue compartments: association with metabolic risk factors in the Framingham Heart Study. Circulation. 2007;116 (1):39–48. https://doi.org/10.1161/CIRCULATIONAHA.106.675355. 14. Cho GJ, Yoo HJ, Hwang SY, et al. Differential relationship between waist circumference and mortality according to age, sex, and body mass index in Korean with age of 30‒90 years; a nationwide health insurance database study. BMC Med. 2018;16(1):131. https://doi.org/ 10.1186/s12916-018-1114-7.
Weight Gain of Service Members After Basic Military Training Bryant J. Webber, MD, MPH,1 Stefani A. Ruiz, MHS,1,2 Gerald W. Talcott, PhD,3 Melissa A. Little, PhD, MPH,3 Deborah F. Tate, PhD4
Introduction: Despite weight and fitness requirements, the prevalence of overweight and obesity in the U.S. military approaches that in the general population. The purpose of this study is to assess trends in anthropometric measurements shortly after military enlistment.
Methods: This longitudinal study evaluated the change in objectively measured body weight and waist circumference in the population of U.S. Air Force members who enlisted in 2012−2013 and graduated from Basic Military Training (n=49,466). Individuals were followed for 4 years or until they left the military, for a mean follow-up of 1,218 (SD=261) days. Data were collected in 2018 and analyzed in 2019.
Results: Among Basic Military Training graduates with available and plausible baseline data (n=46,706), weight increased incrementally by a mean of 1.5−1.8 kg per year and waist circumference by 0.3−1.1 cm per year. Over the 4-year period, total mean weight gain was 6.6 (SD=7.7) kg and waist circumference increase was 3.1 (SD=6.4) cm. Male graduates gained 7.0 (SD=7.7) kg and female graduates gained 4.7 (SD=7.5) kg. Of those who stayed in the military for 4 years, 37.3% transitioned to a higher BMI category (i.e., from normal to overweight/obese or from overweight to obese), whereas 3.9% transitioned to a lower category.
Conclusions: Future research is needed to understand determinants of unhealthy weight gain and the association between weight gain and physical fitness among young adults embarking on a military career.
Am J Prev Med 2020;58(1):117−121. Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine.
INTRODUCTION
N
early two thirds of active duty U.S. service members are overweight or obese per BMI,1 approaching the prevalence in the general U.S. population.2 Obesity in the military is associated with musculoskeletal injuries,3 cardiovascular disease,4 mental health problems,4 and absenteeism and presenteeism.5 Body composition of military members is assessed during periodic fitness assessments. In the U.S. Air Force, 20% of the fitness score is based on waist circumference. A measurement exceeding 100 cm (male members) or 91 cm (female members) results in assessment failure, unless the member excels at the muscular components and 1.5-mile run and has a BMI <25 kg/m2 or body fat percentage ≤18% (male members) or ≤26% (female members). Fitness failures may impair career
opportunities, and 4 failures within a 24-month period compel administrative action.6 Between 1995 and 2008, overweight and obesity increased across all age and rank categories of the armed forces, including the youngest and most junior enlisted.7 Weight gain during early adulthood, which has been From the 1Public Health and Preventive Medicine Department, U.S. Air Force School of Aerospace Medicine, Wright-Patterson AFB, Ohio; 2Solutions Through Innovative Technologies, Inc., Fairborn, Ohio; 3Center for Addiction and Prevention Research, University of Virginia, Charlottesville, Virginia; and 4Department of Health Behavior, Gillings School of Global Public Health, University of North Carolina−Chapel Hill, Chapel Hill, North Carolina Address correspondence to: Bryant J. Webber, MD, MPH, 2510 Fifth Street, Bldg 840, Rm W318, Wright-Patterson AFB OH 45433. E-mail: [email protected]. 0749-3797/$36.00 https://doi.org/10.1016/j.amepre.2019.08.022
Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine.
Am J Prev Med 2020;58(1):117−121
117
118
Webber et al / Am J Prev Med 2020;58(1):117−121
described in the civilian population8 and linked to chronic disease risk during middle adulthood,9 has not been analyzed in the military. Moreover, most military studies have been cross-sectional and have not included other anthropometric measures. The purpose of this study is to evaluate weight and waist circumference changes over the first 4 years of military service, which may inform interventions that promote healthy weight management and reduce military discharge.
METHODS This longitudinal study assessed the population of U.S. Air Force enlistees between January 2012 and December 2013 who graduated from Basic Military Training. This study was approved by the Air Force Research Laboratory IRB. Height, weight, and waist circumference data were obtained from recorded measurements during the last week of training and served as baseline measures. Subsequent measures were recorded in a standardized manner at fitness assessments over the next 4 years.6 The last assessment during each year was used, with the first year restricted to 6−12 months following graduation to allow time for body composition change. Sex, age, self-reported race and ethnicity, marital status, career field, and highest education level achieved were obtained from personnel records and defined at baseline. Population change in BMI and waist circumference was defined as the mean difference between baseline and each time point. National Heart, Lung, and Blood Institute categories were used to classify individuals at each time point according to their BMI as underweight (<18.5), normal (18.5−24.9), overweight (25.0−29.9), and obese (≥30.0), and according to their waist circumference as either normal (male individuals ≤102 cm and female individuals ≤88 cm) or elevated (male individuals >102 cm and female individuals >88 cm).10 These nearly correspond to the cut offs used by the U.S. Air Force for fitness assessment failure. To account for data entry errors, implausible data points were excluded in a two-step fashion. First, for all baseline and subsequent measures, published methodology3,11 was used to exclude implausible height (<137 or ≥213 cm), weight (<36 or ≥204 kg), and BMI (<10 or ≥50) values. Second, for percentage change between baseline and subsequent measures, Grubbs’ test was used to identify and exclude extreme outliers (4,779 data points), defined as values beyond the outer fences (
RESULTS Of U.S. Air Force service members who enlisted in 2012 and 2013 and had anthropometric measurements available from Basic Military Training graduation (n=47,054), 348 were excluded owing to implausible baseline measurements. Most of the included members were male (81.7%) and aged 18−29 years (97.1%). Male members had a
mean BMI of 24.0 (SD=2.3) and waist circumference of 79.8 (SD=5.1) cm, and female members had a mean BMI of 23.6 (SD=2.4) and waist circumference of 71.6 (SD=5.6) cm. Members gained a mean of 1.5−1.8 kg annually after graduating from Basic Military Training. The mean weight gain over the 4-year period was 6.6 (SD=7.7) kg. Male members gained 7.0 (SD=7.7) kg and female members gained 4.7 (SD=7.5) kg. Mean 4-year weight gain exceeded 7.0 kg for both black, non-Hispanic and Hispanic members; for married members; and for those in the support career field (Table 1). Waist circumference increased incrementally by 0.3−1.2 cm annually, with a mean increase of 3.1 (SD=6.4) cm over the 4-year period. Waist circumference trends (Table 2) largely mirrored body weight trends across demographic, occupational, and educational variables. Among service members who completed their 4-year enlistment period, 56.4% maintained the BMI category they held at graduation. A total of 9,877 (25.3%) members transitioned from normal to overweight, 3,546 (9.1%) from overweight to obese, and 1,123 (2.9%) from normal to obese. Conversely, 1,340 (3.4%) members transitioned from overweight to normal, 129 (0.3%) from obese to overweight, and 76 (0.2%) from obese to normal. Seventy (0.2%) male and 72 (0.8%) female members transitioned from a normal to an elevated waist circumference category, whereas just 3 (0.006%) members transitioned from elevated to normal.
DISCUSSION Enlisted U.S. Air Force personnel gained a mean of 6.6 kg during a 4-year period after Basic Military Training. Their 1.5−1.8 kg mean annual weight gain was substantially higher than the 0.6 kg self-reported annual weight gain in a demographically and occupationally diverse sample of U.S. service members (n=30,708).12 Weight gain during young adulthood, which has been well documented in the civilian population,8 appears to affect the same demographic within the U.S. Air Force, despite the presence of fitness and anthropometric requirements. Although many individuals transitioned to higher BMI categories (n=14,546), only 142 moved to a greater waist circumference category, which partially may be due to outcome dichotomization as either normal or elevated. The observed trend of increasing BMI and waist circumference, irrespective of categorical shifts in either metric, suggests that abdominal adipose deposition is contributing to weight gain. This is concerning because abdominal adipose tissue (both visceral and subcutaneous) is correlated with a number of metabolic risk www.ajpmonline.org
Webber et al / Am J Prev Med 2020;58(1):117−121
119
Table 1. Baseline Weight and Weight Gain (in kg) After Basic Military Training Graduation After graduation Variable Total population Sex Male Female Age, years 18−24 25−29 30−39 Race/ethnicity White, non-Hispanic Black, non-Hispanic Hispanic Other Marital status Single Married Other Career field Operations Logistics Support Medical Acquisition Other Educational attainment High school/GED Some college College degree and aboveb Unknown
a
Baseline
180−365 days
366−730 days
731−1,095 days
1,095−1,460 days
n=46,706 72.6 (10.0)
n=26,625 1.7 (5.0)
n=41,841 3.3 (6.2)
n=40,880 5.1 (7.1)
n=38,509 6.6 (7.7)
n=38,178 74.8 (9.0) n=8,528 62.6 (7.7)
n=21,665 1.8 (5.1) n=4,960 1.2 (4.4)
n=34,520 3.5 (6.3) n=7,321 2.2 (5.7)
n=34,008 5.5 (7.1) n=6,872 3.5 (6.9)
n=32,321 7.0 (7.7) n=6,188 4.7 (7.5)
n=32,767 72.0 (9.8) n=12,592 73.8 (10.4) n=1,347 74.8 (10.2)
n=23,876 1.6 (5.0) n=2,742 2.4 (4.9) n=6 0.7 (3.6)
n=35,605 3.2 (6.3) n=6,176 3.8 (5.8) n=60 3.7 (7.6)
n=31,625 5.2 (7.3) n=8,658 4.9 (6.5) n=597 5.3 (6.5)
n=25,865 6.8 (7.9) n=11,370 6.3 (7.3) n=1,274 6.4 (6.8)
n=32,997 73.1 (9.8) n=7,053 72.5 (10.4) n=984 70.4 (10.2) n=5,672 70.0 (10.2)
n=19,193 1.7 (5.1) n=4,172 1.7 (5.0) n=202 2.2 (4.7) n=3,058 1.6 (4.8)
n=29,994 3.3 (6.3) n=6,407 3.4 (6.3) n=544 3.7 (5.9) n=4,896 3.2 (6.0)
n=29,257 5.1 (7.1) n=6,023 5.5 (7.3) n=741 5.7 (7.0) n=4,859 4.9 (6.9)
n=27,307 6.5 (7.7) n=5,612 7.1 (7.9) n=877 7.4 (7.5) n=4,794 6.4 (7.4)
n=27,188 72.3 (9.8) n=17,835 73.1 (10.3) n=1,683 70.1 (10.5)
n=21,238 1.5 (4.9) n=5,282 2.4 (5.4) n=105 0.9 (4.5)
n=29,926 3.1 (6.1) n=11,497 3.9 (6.6) n=418 2.6 (5.9)
n=25,607 4.9 (7.0) n=14,354 5.6 (7.4) n=919 4.3 (6.7)
n=21,734 6.3 (7.5) n=15,287 7.1 (7.9) n=1,488 5.3 (7.3)
n=8,549 72.4 (10.2) n=17,694 73.4 (9.5) n=15,375 72.8 (10.1) n=3,977 68.6 (10.4) n=702 71.2 (10.6) n=400 72.7 (10.6)
n=4,741 1.8 (4.9) n=9,887 1.6 (5.2) n=8,840 1.8 (5.0) n=2,311 1.4 (4.6) n=371 2.0 (5.4) n=458 1.7 (5.0)
n=7,611 3.3 (6.1) n=15,952 3.2 (6.3) n=13,780 3.6 (6.3) n=3,459 2.7 (5.9) n=612 3.5 (6.6) n=410 3.6 (6.2)
n=7,550 5.0 (6.8) n=15,681 5.1 (7.3) n=13,408 5.4 (7.1) n=3,330 4.2 (6.9) n=596 5.1 (7.3) n=309 5.8 (8.0)
n=7,163 6.3 (7.4) n=14,913 6.7 (7.8) n=12,556 7.0 (7.7) n=3,066 5.6 (7.4) n=545 6.4 (7.4) n=259 6.4 (8.4)
n=35,401 72.4 (9.9) n=7,713 73.1 (10.3) n=3,254 72.9 (10.6) n=338 72.9 (9.7)
n=20,217 1.6 (5.0) n=1,857 2.1 (4.8) n=4,356 1.9 (4.9) n=195 1.1 (5.2)
n=31,724 3.3 (6.3) n=2,922 3.2 (5.7) n=6,898 3.4 (5.9) n=297 2.7 (6.3)
n=30,817 5.3 (7.3) n=2,904 4.3 (6.3) n=6,858 4.9 (6.8) n=301 4.9 (7.2)
n=29,041 6.8 (7.9) n=2,750 5.5 (6.8) n=6,446 6.2 (7.3) n=272 6.3 (7.5)
Note: All values are shown in mean (SD). a The first year was restricted to months 6−12 to allow time for weight change. b Includes Associate’s, Bachelor’s, and advanced degrees.
January 2020
Webber et al / Am J Prev Med 2020;58(1):117−121
120
Table 2. Baseline Waist Circumference and Waist Circumference Increase (in cm) After Basic Military Training Graduation After graduation a
Variable
Baseline
180−365 days
366−730 days
731−1,095 days
1,095−1,460 days
Total population
n=46,694 77.8 (5.9)
n=25,969 0.3 (5.5)
n=40,120 1.2 (5.8)
n=39,465 2.3 (6.2)
n=36,553 3.1 (6.4)
n=38,166 79.2 (5.1) n=8,528 71.7 (5.5)
n=21,110 0.2 (5.4) n=4,859 0.9 (5.7)
n=33,023 1.2 (5.8) n=7,097 1.2 (5.9)
n=32,773 2.4 (6.1) n=6,692 1.8 (6.4)
n=30,639 3.3 (6.4) n=5,914 2.4 (6.7)
n=32,757 77.4 (5.8) n=12,589 78.6 (5.9) n=1,348 79.4 (6.0)
n=23,275 0.2 (5.5) n=2,687 1.4 (5.2) n=6 1.7 (2.7)
n=34,125 1.0 (5.9) n=5,935 2.0 (5.5) n=60 2.7 (5.2)
n=30,508 2.2 (6.3) n=8,381 2.6 (5.8) n=576 2.9 (5.6)
n=24,559 3.0 (6.6) n=10,778 3.2 (6.1) n=1,216 3.5 (5.6)
n=32,990 78.6 (5.8) n=7,052 75.6 (5.6) n=983 77.4 (6.0) n=5,669 76.4 (6.1)
n=18,726 0.3 (5.5) n=4,058 0.4 (5.3) n=197 0.4 (5.5) n=2,988 0.4 (5.6)
n=28,718 1.1 (5.8) n=6,152 1.3 (5.8) n=523 1.4 (5.5) n=4,727 1.3 (5.7)
n=28,236 2.2 (6.2) n=5,828 2.5 (6.3) n=721 2.7 (6.3) n=4,680 2.3 (6.1)
n=25,897 3.0 (6.4) n=5,315 3.5 (6.6) n=844 3.7 (6.4) n=4,497 3.2 (6.5)
n=27,181 77.7 (5.8) n=17,830 78.2 (6.0) n=1,683 76.4 (6.6)
n=20,699 0.1 (5.4) n=5,165 1.1 (5.7) n=105 0.1 (5.2)
n=28,712 0.9 (5.7) n=11,008 1.9 (6.0) n=400 1.0 (5.9)
n=24,701 2.0 (6.1) n=13,886 2.8 (6.3) n=878 2.1 (6.0)
n=20,591 2.8 (6.4) n=14,555 3.6 (6.5) n=1,407 2.3 (6.3)
n=8,547 77.6 (6.0) n=17,692 78.4 (5.6) n=15,368 78.0 (5.9) n=3,977 75.4 (6.4) n=701 76.9 (6.3) n=400 77.4 (6.2)
n=4,696 0.9 (5.4) n=9,583 0.0 (5.5) n=8,549 0.3 (5.4) n=2,299 0.4 (5.5) n=369 1.0 (5.5) n=456 1.2 (5.9)
n=7,427 1.5 (5.7) n=15,148 0.9 (5.9) n=13,095 1.3 (5.8) n=3,430 1.0 (5.8) n=606 1.8 (5.8) n=397 1.9 (5.7)
n=7,380 2.3 (6.0) n=15,037 2.2 (6.3) n=12,869 2.3 (6.1) n=3,294 2.0 (6.3) n=584 2.5 (6.0) n=295 2.8 (6.6)
n=6,854 3.0 (6.3) n=14,093 3.1 (6.5) n=11,850 3.2 (6.5) n=2,991 2.8 (6.5) n=511 3.4 (6.1) n=248 3.2 (6.7)
n=35,391 77.7 (5.8) n=7,711 78.2 (6.1) n=3,254 77.8 (6.3) n=338 78.2 (6.0)
n=19,708 0.2 (5.5) n=1,817 1.2 (5.3) n=4,256 0.7 (5.4) n=188 0.2 (5.7)
n=30,400 1.1 (5.9) n=2,805 1.5 (5.4) n=6,633 1.4 (5.7) n=282 0.6 (5.9)
n=29,706 2.3 (6.2) n=2,817 2.2 (5.7) n=6,655 2.3 (6.0) n=287 2.2 (6.2)
n=27,546 3.2 (6.5) n=2,616 2.9 (5.8) n=6,127 2.9 (6.2) n=264 3.0 (6.4)
Sex Male Female Age, years 18−24 25−29 30−39 Race/ethnicity White, non-Hispanic Black, non-Hispanic Hispanic Other Marital status Single Married Other Career field Operations Logistics Support Medical Acquisition Other Educational attainment High school/GED Some college College degree and aboveb Unknown
Note: All values are shown in mean (SD). a The first year was restricted to months 6−12 to allow time for waist circumference change. b Includes Associate’s, Bachelor’s, and advanced degrees.
www.ajpmonline.org
Webber et al / Am J Prev Med 2020;58(1):117−121
factors, including hypertension and impaired fasting glucose,13 and waist circumference in the upper range of normal is associated with greater mortality, even among those who are not obese according to BMI.14 Military weight studies have been limited by reliance on self-reported data, the use of serial cross-sectional samples to evaluate trends, and potential misclassification of adiposity based on BMI.4,7 By utilizing objective weight data from fitness assessments, following the same cohort longitudinally, and demonstrating concomitant increases in waist circumference, this study avoids these shortcomings and substantiates concerns regarding unhealthy body weight trends in the armed forces.
Limitations The study has several limitations. First, although measurements were obtained in a standardized approach,6 scale calibration could not be certified. Second, manual entry of measurements into the Air Force fitness database may have introduced errors. Third, this study was conducted on a cohort of enlisted Air Force personnel, most of whom were young and male, limiting its generalizability to other populations. Finally, aerobic and anaerobic fitness metrics were not obtained; the association between body composition change and physical performance should be assessed in future studies.
CONCLUSIONS This study highlights the need for ongoing research and interventions that promote healthy weight maintenance among young adults embarking on a military career.
ACKNOWLEDGMENTS The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Air Force, Department of Defense, or U.S. Government. No financial disclosures were reported by the authors of this paper. Author contributions: Conception and design (BJW, GWT, MAL, DFT), acquisition of data (SAR), analysis and interpretation of data (BJW, SAR, GWT, MAL, DFT), drafting manuscript (BJW, SAR), critical revision of manuscript (GAW, MAL, DFT), final approval of manuscript (BJW, SAR, GWT, MAL, DFT).
January 2020
121
REFERENCES 1. Meadows SO, Engel CC, Collins RL, et al. 2015 Health related behaviors survey: summary findings and policy implications. Santa Monica, CA: RAND Corporation; 2018. www.rand.org/pubs/research_briefs/ RB9955.html. Accessed September 5, 2019. 2. CDC. Table 53. Selected health conditions and risk factors, by age: United States, selected years 1988−1994 through 2015−2016. www. cdc.gov/nchs/data/hus/2017/053.pdf. Accessed September 5, 2019. 3. Hruby A, Bulathsinhala L, McKinnon CJ, et al. BMI and lower extremity injury in U.S. Army soldiers, 2001−2011. Am J Prev Med. 2016;50(6):e163–e171. https://doi.org/10.1016/j.amepre.2015.10.015. 4. Rush T, LeardMann CA, Crum-Cianflone NF. Obesity and associated adverse health outcomes among US military members and veterans: findings from the Millennium Cohort Study. Obesity (Silver Spring). 2016;24(7):1582–1589. https://doi.org/10.1002/oby.21513. 5. Dall TM, Zhang Y, Chen YJ, et al. Cost associated with being overweight and with obesity, high alcohol consumption, and tobacco use within the military health system’s TRICARE prime-enrolled population. Am J Health Promot. 2007;22(2):120–139. https://doi.org/ 10.4278/0890-1171-22.2.120. 6. U.S. Department of the Air Force. Fitness Program. Air Force instruction 36−2905. https://static.e-publishing.af.mil/production/1/af_a1/ publication/afi36-2905/afi36-2905.pdf. Published 2013. Accessed September 5, 2019. 7. Reyes-Guzman CM, Bray RM, Forman-Hoffman VL, Williams J. Overweight and obesity trends among active duty military personnel: a 13-year perspective. Am J Prev Med. 2015;48(2):145–153. https:// doi.org/10.1016/j.amepre.2014.08.033. 8. Dutton GR, Kim Y, Jacobs DR Jr, et al. 25-year weight gain in a racially balanced sample of U.S. adults: the CARDIA study. Obesity (Silver Spring). 2016;24(9):1962–1968. https://doi.org/10.1002/oby.21573. 9. Zheng Y, Manson JE, Yuan C, et al. Associations of weight gain from early to middle adulthood with major health outcomes later in life. JAMA. 2017;318(3):255–269. https://doi.org/10.1001/jama.2017.7092. 10. NIH, National Heart, Lung, and Blood Institute. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults: the evidence report. Bethesda, MD: HHS; 1998. www.ncbi. nlm.nih.gov/books/NBK2003/. Accessed September 5, 2019. 11. Hruby A, Hill OT, Bulathsinhala L, et al. Trends in overweight and obesity in soldiers entering the US Army, 1989‒2012. Obesity (Silver Spring). 2015;23(3):662–670. https://doi.org/10.1002/oby.20978. 12. Littman AJ, Jacobson IG, Boyko EJ, Powell TM, Smith TC, Millennium Cohort Study Team. Weight change following US military service. Int J Obes (Lond). 2013;37(2):244–253. https://doi.org/10.1038/ ijo.2012.46. 13. Fox CS, Massaro JM, Hoffmann U, et al. Abdominal visceral and subcutaneous adipose tissue compartments: association with metabolic risk factors in the Framingham Heart Study. Circulation. 2007;116 (1):39–48. https://doi.org/10.1161/CIRCULATIONAHA.106.675355. 14. Cho GJ, Yoo HJ, Hwang SY, et al. Differential relationship between waist circumference and mortality according to age, sex, and body mass index in Korean with age of 30‒90 years; a nationwide health insurance database study. BMC Med. 2018;16(1):131. https://doi.org/ 10.1186/s12916-018-1114-7.