BMI changes among U.S. Navy and Marine Corps active-duty service members during the COVID-19 pandemic, 2019–2021

Abstract

Background

The COVID-19 pandemic disrupted the daily life and routines of Americans across the United States (U.S.), including those of our active-duty service members (ADSMs). Limited movement orders enacted during this time to promote social distancing prohibited access to fitness and dining facilities for ADSMs. This study aims to expand on previous work identifying changes in body mass index (BMI) among U.S. Army service members by identifying changes in body mass index (BMI) among active-duty service members from both the Navy and Marine Corps during the same time period.

Methods

We conducted a retrospective cohort study of active-duty service members from the Navy and Marine Corps using data from the Military Health System Data Repository. BMI was calculated and categorized according to CDC guidelines both before (February 2019 - January 2020) and during the pandemic (September 2020 - June 2021). Women who were pregnant or delivered during and one year prior to the study periods were excluded. Statistical analyses included paired t-tests evaluating mean BMI, percent change, and the Stuart-Maxwell test for marginal homogeneity.

Results

We identified 98,330 active-duty Sailors and 55,298 active-duty Marines for inclusion in this study. During the pandemic period the percentage of Sailors with Underweight decreased by 11%, Healthy weight decreased by 11.1%, Overweight increased by 2.1%, and the percentage of Sailors with Obesity increased by 16.5%. During this same time period, Marines with Underweight decreased by 1%, Healthy weight decreased by 16%, Overweight increased by 3.0%, and Marines with Obesity increased by 51%. The largest increases in service members with overweight and obesity observed among both cohorts were among female service members, service members under age 20, and service members with a Junior Enlisted rank.

Conclusions

Significant increases in obesity were observed amongst active-duty United States Navy and Marine Corps service members during DoD pandemic mitigation efforts. Increased rates of obesity likely effected fitness and force readiness. Future interventions should be targeted at younger, Junior-Enlisted Marines and Sailors to promote healthy lifestyles and provide education on nutrition, appropriate exercise, sleep hygiene, and stress management.

Background

The COVID-19 pandemic disrupted the daily life and routines of Americans across the United States (U.S.), including those serving on active-duty in the Armed Forces. During the pandemic the Department of Defense (DoD), alongside other federal and state agencies, enacted public health protection measures that limited movement and promoted social distancing, prohibiting access to dining and fitness facilities for active-duty service members (ADSMs) [1, 2]. Literature has begun to demonstrate the substantial impact that these measures have had on physical and mental health [3,4,5,6]. Both popular media and academic literature have noted the impact that the increase in sedentary activities brought about by the COVID-19 pandemic lockdown and social distancing measures has had on rates of obesity and overweight among both the general public and U.S. service members [7,8,9,10,11]. Obesity is associated with increased risk for several serious and costly health conditions, including diabetes, arthritis, cardiovascular disease, and metabolic syndrome [12]. Among the military population, rates of obesity have climbed from 10.4% in 2012 to 21.6% in 2022 [13].

Increases in service members with overweight and obesity decreases the fitness and force readiness of the U.S. military. Overweight and obesity have been shown to increase risk of injury, stroke, and musculoskeletal injuries among ADSMs by up to 47% and had 49% higher health care utilization than their peers who meet height and weight standards [14, 15]. Higher BMI has also been associated with increased odds of endocrine and metabolic disorders, nervous system diseases, circulatory system diseases, musculoskeletal diseases, and mental or behavioral disorders among ADSMs [16]. Conditions related to overweight and obesity also result in lost duty days. It is estimated that overweight and obesity account for 658,000 lost duty days annually [17]. In addition to the $103 million spent each year due to this loss in manpower, the DoD spends an estimated $1.5 billion annually on obesity-related health care costs and on replacing personnel deemed unfit for service due to obesity [17]. Replacing personnel is also a challenge, as increasing rates of obesity in the U.S. make recruitment efforts difficult – according to the Centers for Disease Control and Prevention (CDC) only two in five young adults aged 17–24 are eligible to serve in the military based on their weight and physical fitness levels [13, 17]. This has, in part, led to declines in recruitment and inability to meet recruitment goals in recent years [18]. The monetary and personnel costs associated with overweight and obesity present a significant threat to military readiness.

Understanding the impact that the COVID-19 pandemic has had on the body mass index (BMI) of ADSMs is important in preparation for future public health crises. Wuerdeman et al. [7]. identified changes in body mass index among U.S. Army service members during the COVID-19 pandemic; this study seeks to expand on that work by identifying changes in BMI among active-duty service members from both the Navy and Marine Corps during the same time period [7]. This will allow comparison of the impact of pandemic lockdown and social distancing measures between service branches to help understand the impact of these measures on the health of U.S. military service members.

Methods

The methods for this study have been previously described in Wuerdeman et al. [7]. We have adapted these methods for the Navy and Marine Corps populations, allowing for direct comparison of results between these service branches. We identified one cohort of active-duty Navy and one cohort of Marine Corps service members ages 17 and older with a reported BMI in both the pre-pandemic time period and pandemic time period using the Military Health System Data Repository (MDR). The MDR is a central repository of administrative and healthcare data for all Military Health System (MHS) beneficiaries who receive care at military treatment facilities or at civilian fee-for-service facilities [19]. The pre-pandemic time period was defined as one year before COVID-19 mitigation efforts were enacted by the DoD (February 2019 to January 2020). The pandemic time period was defined as September 2020 to June of 2021 for this study. We excluded personnel in the reserves (both active and inactive) due to inconsistent access to care within the MHS and female Sailors and Marines who had been pregnant during the year prior or who became pregnant at any time during the study period [7]. Pregnant women were identified using International Classification of Disease, tenth revision, diagnosis codes (ICD-10 CM): Z33, Z34, Z3A, Z36-Z39, O00-O9A [7, 20].

We calculated BMI utilizing both the height and weight data for both pre-pandemic and pandemic and the imperial formula and expressed as kg/m2. We then categorized BMI using the CDC classification system of Underweight (BMI < 18.5), Healthy weight BMI (18.5–24.9), Overweight (BMI 25.0–29.9) and Obese (BMI ≥ 30.0). We then used an interquartile method to identify and remove BMI values that were higher or lower than three standard deviations from the mean to account for any implausible BMI calculations. If a Sailor or Marine had multiple BMI measurements in each observed period (pre-/ pandemic), the most recent measurements were preferentially used to provide the most accurate and timely measurement of BMI during the DoD COVID-19 mitigation efforts. We calculated BMI measurements only from in-person encounters at military treatment facilities due to the availability of necessary height and weight data. Active-duty service members are required to receive their care at military treatment facilities, but virtual care appointments would not capture this data accurately. Patient demographics, such as gender, age, race, and rank were identified at the time of their most recent BMI measurement during the pre-pandemic period and used in analysis [7].

Our performed study analyses included descriptive statistics on patient cohort demographics from both Sailors and Marines and stratified by the two observation periods; BMI trends by gender, age groups (5-year increments from < 20 to 50+), race as reported in the MDR (American Indian or Alaskan Native, Asian or Pacific Islander, Black, White, other), and rank category (Junior Enlisted (United States Navy (USN) & United States Marine Corps (USMC): E1-E4), Senior Enlisted (USN & USMC: E5-E9), Junior Officer (USN: O1-O4, USMC: O1-O3), Senior Officer (USN: O5 and above, USMC: O4 and above), Warrant Officer (USN & USMC: W1-W5), other); and percent change in Overweight and Obesity BMI categories from pre-pandemic to post-pandemic. Percent change was calculated using the following formula: ((pandemic #-prepandemic #) ÷ prepandemic #) ×100. Additionally, we performed the Stuart-Maxwell test of marginal homogeneity to identify statistically significant differences in BMI category distributions over the study period. The Stuart-Maxwell test was chosen based on the paired design of the study, in which each subject’s BMI status was assessed at two different time points (pre-pandemic and during the pandemic). Statistical significance was determined as a p-value < 0.05. All statistical analyses were performed using SAS, version 9.4 (SAS Institute Inc., Cary, NC). This research was reviewed and found exempt by the Uniformed Services University Institutional Review Board [7].

Results

Cohort demographics

We identified 98,330 active-duty Sailors and 55,298 active-duty Marines for inclusion in this study (Fig. 1). Male service members comprised the majority of each cohort, making up 76.6% of the identified Sailors and 89.7% of the identified Marines (Table 1). The majority of each cohort was comprised of Sailors and Marines ages 20–24 years (25.4% and 44.4%, respectively) and ages 25–29 years (22.7% and 16.5%, respectively), identifying as White (61.0% and 80.8%, respectively). The most frequent rank among the Sailor population in our cohort was Senior Enlisted (45.5%), while among the Marine population the most frequent rank was Junior Enlisted rank (56.2%). These cohorts are demographically representative of the Navy and Marine Corps active-duty populations [21].

Table 1 Demographic distributions of the Navy and Marine Corps Cohorts

Fig. 1

A CONSORT diagram illustrating application of the inclusion and exclusion criteria to the starting population to determine the final study population. Abbreviations: BMI = body mass index, USN = US Navy, USMC = US Marine Corps, ADSM = active-duty service member

Navy

During the pre-pandemic period, we observed 0.5% of the cohort with Underweight, 27.6% with Healthy weight, 46.9% with Overweight, and 25.0% with Obese BMIs. During the pandemic period the percentage of Sailors with Overweight decreased to 45.9%, a percent change of -2.1%, and the percentage of Sailors with Obesity increased to 29.1%, a percent change of 16.5%. The Underweight and Healthy weight categories both decreased percent change of 11% and 11.1% respectively (Supplemental Table S1). Notable changes were seen across BMI categories from the pre-pandemic to pandemic period, including a 50.1% of Underweight Sailors moved to Healthy weight, 24.5% of Healthy weight to Overweight, and 16.7% of Overweight to Obese. In the Obese category there were 23.4% who decreased BMI to the Overweight category (Table 2). A Stuart-Maxwell test for homogeneity was significant p < 0.0001 for all categories.

Fig. 2

Sankey diagram of BMI changes in the U.S. navy cohort during the COVID-19 pandemic

Table 2 Comparison of Navy Cohort BMI category prior to and during COVID-19 Pandemic*

Figure 2 illustrates changes in BMI category from the pre-pandemic BMI to the pandemic BMI among the Navy cohort. This diagram illustrates the movement between BMI categories during the two time periods, with the bands on the left indicating the pre-pandemic BMI category of cohort members by color and the bands on the right indicating the pandemic BMI category of cohort members.

Percent change analysis by pre-pandemic cohort demographics was completed for Overweight and Obese categories (Supplemental Table S2). Among female Sailors in the cohort there was a 32% increase in the Obesity during the pandemic period compared to 13% increase among males. Notable changes in Obesity were also observed among those under 20 years old (< 20 age group) and among those with a Junior Enlisted rank. An 88% and 36% increase, respectively, was observed in Sailors during the pandemic period.

Marine corps

During the pre-pandemic period, we observed 0.3% of the cohort with Underweight, 37.4% with Healthy weight, 53.9% with Overweight, and 8.4% with Obese BMIs. During the pandemic period the proportion of Marines with Overweight increased to 55.8%, representing a percentage increase of 3%, and the proportion with Obesity increased to 12.6%, a percentage increase of 51.0%. Percentage decreases were also observed in the Underweight and Healthy weight categories during the pandemic period, with a 1% and 16% decrease, respectively (Supplemental Table S3). Notable changes from pre-pandemic to pandemic BMI were observed within each BMI category, including a 63.6% movement from Underweight to Healthy weight, 26.4% of Healthy weight to Overweight, and 11.2% of Overweight to Obese (data not shown). In the Obese category there were 23.4% who decreased BMI to the Overweight category (data not shown). The Stuart-Maxwell test for homogeneity indicated significant changes in distributions across all BMI categories.

Fig. 3

Sankey diagram of BMI changes in the U.S. marine Corps cohort dcuring the COVID-19 pandemic

Figure 3 illustrates changes in BMI category from the pre-pandemic BMI to the pandemic BMI among the Marine Corps cohort. This diagram illustrates the movement between BMI categories during the two time periods, with the bands on the left indicating the pre-pandemic BMI category of cohort members by color and the bands on the right indicating the pandemic BMI category of cohort members.

Demographic analysis was completed for Overweight and Obese categories in each of the subgroups (Supplemental Table S4). Among female Marines in the cohort there was a 111% increase in the Obese category compared to a 49% increase among males. Among the < 20 age group there was a 231% increase in Marines with Obesity and among the Junior Enlisted rank there was an 87% increase in Marines with Obesity, both being the highest percentage increases in their respective categories.

Discussion

The current study indicated that during the pandemic period, the proportion of Sailors with Underweight, Healthy weight, and Overweight decreased, while the proportion of Sailors with Obese increased 16.5% compared to pre-pandemic levels. The proportion of Marines with Underweight and Healthy weight decreased while the proportion of Marines with Overweight and Obese increased 3.5% and 50.8%, respectively, compared to pre-pandemic levels. The increase in Sailors with Obesity within the Navy cohort (16.5%) was substantially lower than the Marine Corps cohort (51%) and the Army cohort from Wuerdeman et al. (27%) [7]. All of these increases in active-duty service members with obesity are significantly higher than that of the U.S. adult population (3%) [9]. Our demographic subgroup findings were consistent with findings among the Army cohort population in Wuerdeman et al., indicating that among both Sailors and Marines, women and those in Junior Enlisted ranks experienced the greatest rates of increases in obesity [7]. Our findings differed from a study by Legg et al. that examined Periodic Health Assessment data, which found that while the prevalence of vigorous exercise decreased following the onset of the pandemic, there was no abrupt change in obesity, finding only a 0.33% absolute increase in mean monthly obesity prevalence [22]. However, in concurrence with our analysis, they also found that those in Junior Enlisted ranks were among the highest increases [22].

A noteworthy finding from our analysis was that the cohort of female Marines experienced a 111% increase in obesity. This is surprising because the Department of Defense Health of the Force 2021 report indicated that the Marine Corps had the lowest prevalence of obesity across all Service branches at 11% overall, with prevalence of obesity higher among male service members compared to female service members [23]. A technical report by Potter et al. indicated that the Marine Corps as a whole had low average body fat averages when compared with both civilians and with the other Services, with an average of 30% body fat for women [24]. Body fat standards for female Marines were updated as of January 2023, increasing by 1% to more closely align with male standards when accounting for biological differences [25]. Research on rates of obesity among female Marines in the post-pandemic period is needed.

Increases in obesity among military service members, and among the general population who may be eligible for service, remain a threat to force readiness [17]. Service branches experiencing difficulties in their recruiting efforts are increasing their BMI cutoffs or waiving the body fat assessment for promising recruits who fail to meet the current standards [26, 27]. These initiatives will likely lead to increases in health services utilization and DoD healthcare expenditures. Findings from Shiozawa et al. indicate that overweight and obese service members have higher rates of health services utilization, which they suggest may be due to service members with obesity performing less military training and having a greater number of health issues [28]. Thus, while these initiatives may bolster recruitment numbers, they may further detract from the overall readiness of the force.

There has been concern about the validity of using BMI to assess the threat of overweight and obesity on the military population, with concern that BMI may overrepresent obesity rates due to higher levels of musculature among service members [13, 29]. However, the literature does not support this notion, indicating instead that BMI is more likely to underreport overweight and obesity among service members [13, 29]. A study by Grier et al. found that although Army Soldiers with overweight and obesity had additional lean body mass, this was accompanied by a disproportionate increase in additional body fat [30]. Another study by Gaiser et al. found that the standard cutoffs for obesity significantly underestimated excess body fat among both active duty and retired U.S. Navy Sailors [31]. The impact of this misconception may lead to delays in medical evaluation and treatment. Clutter et al. found that of service members that meet prediabetes screening criteria by BMI, only a fraction are actually being screened [32]. Given this, the rates of Sailors and Marines with obesity and overweight in our analysis may actually underestimate the true extent of the problem rather than overestimate it [13, 29].

Our analysis indicates concerning trends in rates of overweight and obesity among the Navy and Marine Corps populations. An analysis of BMI trends among the Air Force population is needed to make comparisons between all Services. Future study is also needed examining the post-pandemic period to assess whether discontinuation of public health protection measures has resulted in decreases in overweight and obesity among the active-duty service member population. Additionally, interventions promoting healthy lifestyles and providing education on nutrition, appropriate exercise, sleep hygiene, and stress management should be targeted at younger, Junior-Enlisted Sailors and Marines are needed.

This study has some limitations. This study is a descriptive study of BMI changes among the U.S. Navy and Marine Corps populations and thus cannot be used to establish a causal relationship between the pandemic and increases in BMI among Sailors and Marines. However, this analysis is still an important addition to the literature as it helps to highlight the issue of obesity among active-duty service members and offers comparisons for trends among Army Soldiers already in the literature. It is important to note that this study is based solely on BMI and does not include other metrics such as waist circumference, skinfold measurements, or body fat percentages, which can be misleading for overly muscular individuals. Additionally, data from the MDR may not be a comprehensive representation of medical history that may indicate medical causes for weight gain, other than pregnancy, which was accounted for in this study. The MDR also will only capture data from those receiving medical care, and will not capture those who do not seek care, however, active-duty service members are required to receive a annual physical so this would not have a significant impact on our results.

Conclusions

Significant increases in obesity were observed amongst active-duty United States Navy and Marine Corps service members during DoD pandemic mitigation efforts. Increased rates of obesity are likely to result in decreased fitness and force readiness. Future interventions should be targeted at younger, Junior-Enlisted Marines and Sailors to promote healthy lifestyles and provide education on nutrition, appropriate exercise, sleep hygiene, and stress management.