Trend and prevalence of overweight and obesity among the military population – a systematic review Authors:

Prevalence of overweight and obesity are escalating globally among the general population. However, there are limited evidence on the trends and prevalence of overweight /obesity in the military setting. Increased rates of injuries, low work productivity, incurred higher healthcare costs and prematurely discharge from service are consequences of overweight/obesity among the military. Therefore, we aimed to systematically describe the trends and prevalence of overweight and obesity in the military population, by regions and military service branches. Databases including PubMed, Scopus, Web of Science and Google Scholar were used. Inclusion criteria were military population (inclusive of all service branches) with BMI reported as the overweight/obesity indicator. Population related to military but not exclusively military personnel such as the retirees, the veterans and their dependents were excluded. From the 27 included studies, 13 were published between year 2010 to 2014 and half were conducted in the United States. Overall, studies showed increasing trend in the prevalence of overweight (30% to 50%) and obesity (2% to 30%); only one study showed a decreasing trend of 0.9% and 0.6% for the prevalence of overweight and obesity respectively. However, the rates of increment differed between countries, where Asian countries demonstrated lower overweight prevalence compared to the United States and the European countries. In conclusion, the military population is not protected from overweight and obesity. Interventions should be implemented to prevent overweight / obesity among the military personnel.


Introduction
Prevalence of overweight and obesity is increasing in the general population. Almost all the countries across the world show a rise in both overweight and obesity prevalence, albeit at different rates of increment. However, these studies understandably did not include sample from exclusive groups or organization such as the military. The high prevalence of overweight and obesity in the general population, especially among adolescent and young adult has affected the military recruitments (1). These were evidenced among the Polish conscripts where their prevalence of overweight has risen from 10.5% in 2000 to 15.5% in 2010 (2). The prevalence of obesity also showed an increase from 2.5% to 3.8% over the same period. Similar trends were observed among the applicants the US military whereby the prevalence of overweight and obesity increased from 22.8% to 27.15 and from 2.8% to 6.8% respectively from 1993 to 2006 (3). Recruits with high BMI were more likely to sustained injuries during military training compared to their normal weight comrades, thus incurred higher healthcare costs (4,5). They were also more likely to be prematurely discharged from the military due to their inability to perform their tasks as a consequences of overweight and obesity (6,7).
Unlike voluminous publications on overweight and obesity among the general population, studies in the military setting are relatively lacking. The military population are synonyms with strict entrance screening, strenuous basic training and highly physically demanding job. Therefore, they are assumed to be immune from obesity. However, several studies had shown otherwise, with comparable prevalence to the general population. To the best of our knowledge, there is only one systematic review on obesity in military population (8), which focused on the factors and treatment of obesity. Thus, this review aimed to collectively and systematically review the trend and prevalence of overweight and obesity in the military population.

Inclusion/exclusion criteria
Studies were included in this systematic review if the study setting was in military population and reported outcomes measuring the prevalence of overweight and/or obesity. Only studies published after the year 2000 and in English language are eligible for this review. In addition, the measurement of overweight and obesity must be BMI as its proxy. Any studies that used other measurements of adiposity such as BF% or WC and using other classification such as Asian classification were excluded. In this review, military population is inclusive of all the three main service branches; Army, Navy, and Air Forces. Studies that measure the prevalence in a population related to military but not exclusively military personnel such as the retirees, the veterans and their dependents were also excluded.  (13). The QAT contained 9 items (Table 1).

Selection strategy and procedures
The first five items assessed the general quality of the selected studies, while the remaining items were designed specifically to determine the trend and prevalence of overweight and obesity in the military population. A total score of 0 -33% is considered weak, while 34 -66% is moderate and 67 -100% is high quality studies based on the modified QAT criteria (12). This review did not proceed to meta-analysis in view of different time where the studies were conducted and limited number of studies between different military branches.

General description of studies
A total 303 articles were retrieved from Scopus, Web of Science, PubMed and Google Scholar.
After study selection, only 27 articles were eligible to be included in the review (Figure 1). Quality assessment score was given to the selected studies based on the modified QAT ( Table 2).

Study setting and sample size
About half of the studies (n = 13) were conducted in the United States (Table 4). One third were carried out in the United Kingdom (UK) and European countries including two studies in Belgium (20,35) and one study each in Germany (30), Finland (22), and Greece (32). Only three studies were from the Asian countries ie: South Korea (24), Thailand (36), and Malaysia (14). Two studies were conducted in the Middle Eastern countries including from Iran (27) and the Kingdom of Saudi Arabia (26). The Army being the biggest military branch in most nations was the most researched group with 13 studies. Another nine studies were carried out in the overall Armed Forces, which included the Army, Navy, Marines and the Air Forces. There were four studies conducted in the Navy population (14,19,37,38), and only one study among the Air Forces personnel (25,31).
The 27 selected studies were conducted between 1992 and 2017. The total sample involved was more than 5.7 million military personnel. Study with the biggest sample size was conducted between 2009 and 2012 totalling up to more than 3.6 million Active Duty military personnel in the US (39).
Three more studies with a big sample size of more than 300,000 to more than 700,000 participants were also from the US (17,19,25). Around 70% or 19 studies had a sample size ranging from 2,000 to 7,000 participants. Only four studies had a sample size of less than 1,000 participants (14,(30)(31)(32).   (18). Majority of these studies (89%) reported an overall prevalence above 40%. Only three of the latest publications reported an overall overweight prevalence of less than 35% (17,18,25). All four studies that provided the overweight prevalence for males and females showed that overweight prevalence among males were higher (50% to 60%) compared to females (20% to 40%) (21, 23,33,39).
The overall prevalence of obesity among the US personnel ranged from 18.8% (31) to 4.2% (25).
Majority of these studies (77%) reported an overall obesity prevalence of more than 10%. Meanwhile, among the US male personnel, the prevalence of obesity ranged from 9.8% (23) to 20.4% (39). These figures were higher than the US female personnel whose obesity prevalence were between 3.8% (23) to 10 (14), and the Royal Thai Army in 2005 (36); the overall overweight prevalence ranged from 27% to 32%. Meanwhile, the overweight prevalence for Asian males and females ranged from 30% to 40% and 10% to 15% respectively. The prevalence for overall, male and female obesity were all less than 5% except for the study in the Royal Malaysian Navy, which recorded 7.2% for male obesity (14).
The prevalence of overweight for overall, male and female were comparable between the US, Europeans and Middle Eastern countries, although there were no data available for female prevalence from the Middle Eastern countries. On the contrary, the overweight prevalence among the Asian countries was lower for all categories (Table 4).
Similar patterns were observed for the prevalence of obesity except the Middle Eastern countries had higher overall prevalence of obesity compared to the US and European countries. However, data from the Middle Eastern country was reported from a single study (26) only. The prevalence of obesity among the Asian countries was much lower and did not exceed 5% except for one study among the Royal Malaysian Navy that recorded male prevalence of 7.2% (14). respectively (39). Meanwhile, the Korean Army recorded the lowest overall and male obesity prevalence at 2.1% (24). Although, these were recorded in 2000, and the trend was increasing since then, the Korean Army overall and male obesity prevalence did not exceed 4.0%. The obesity prevalence among the female Army personnel was all less than 10%, except for the Czech Army that recorded 14.6% in 2000 (16). This has declined since then and remained below 10% since 2004. The Korean female Army obesity prevalence was the lowest (1.45%) (24).
A total of eight studies combined all the main service branches of the Armed Forces including Army, Navy, Air Force (15,25,26,29,32) and some studies included the Marine (33,34,40) as well.
The overall overweight prevalence among the Armed Forces ranged from 33% (25) to 54% (33). Both were recorded in the US Armed forces between 2008 and 2015, and in 1998 respectively. While the range for the female overweight was between 25% and 30%, the male prevalence showed larger variation. The lowest male overweight prevalence (26.6%) was recorded in the Greek Army in 1998 (32), and the highest (58.6%) was recorded in the US Armed Forces in 1998 (33). More recent study among the US Armed Forces persistently demonstrated that the male obesity prevalence was more than 50% (21).
In general, the overall obesity prevalence among the Armed Forces was below 15%, except for the Saudi Arabia Armed Forces (29%) (26). The lowest overall obesity prevalence was 4.2%, which was recorded in the US Armed Forces between 2008 and 2015 (25). The male obesity prevalence was between 10% and 15%, except for the Greek Armed Forces (4.8%) (32). The highest male obesity prevalence was 25%, which was recorded in the UK Armed Forces (29 There were four studies conducted among the Navy personnel, with three from the US (19,37,38) and one from Malaysia, among the Royal Malaysian Navy (14). The overall overweight and obesity prevalence among the US Navy were between 40% and 50%, and between 10% and 15% respectively. The Royal Malaysian Navy recorded a lower overweight and obesity prevalence with 30% and 7% respectively. Lennon et al. (2015) was the only study that provided the obesity prevalence for male and female Navy personnel with 15.4% and 4.6% respectively (19).
There was only one study involving the Air Force personnel, from the US (31). Compared to the other service branches, the Air Force overweight and obesity prevalence was on the higher side with 54.5% and 18.8% respectively. However, this was only based on a single study. Overall, the estimated prevalence for overweight and obesity were comparable between different service branches (Table   5), except the Air Force.

Discussion
This systematic review demonstrated that there is an increasing trend in terms of overweight and obesity among the military population. The rates of overweight were higher than the general population while the opposite was observed for the prevalence of obesity. There were variations in the prevalence of overweight and obesity among the military between and within countries, even within the same service branches. This review may be the first to systematically assess the trend and prevalence of overweight /obesity among the military population.
From a total of 27 included studies, approximately 90% of them were published in the last 10 years.
Most of the studies were conducted in the Western countries with only three studies from the Asian countries. The prevalence of overweight and obesity in the Asian countries were around 30% and 2% to 5% respectively. These were considered relatively low compared to the Western countries with prevalence harbouring around 40% to 50% for overweight and 10% to 20% for obesity. However, the increment rates of overweight and obesity prevalence were much faster in Asian countries. This was partly due to the increased in the obesogenic environment, which was influenced by the development in the Asian countries. Furthermore, the standard operating procedures and enforcement on obesity differed between countries, including different cut-off used in the administrative regulation of personnel BMI. The lack of studies among the Asian and Middle Eastern countries may have limited these comparisons.
Contrary to the country and regions comparison, the prevalence of overweight and obesity between the service branches did not differ much. The lower prevalence found in the Asian's Army and Navy may not be representative as majority of the studies were from the US and the European countries.
Thus, the prevalence of overweight and obesity especially among the Army and the Armed Forces reflected more on the prevalence of the US and the European countries. Only the Army and the Armed Forces have acceptable number of studies and data to allow generalisation of the results. More studies among the Navy and Air Force personnel are needed to enable more meaningful comparisons to be made.
Compared to their respective general population, the military population has a higher prevalence of overweight, but lower prevalence of obesity. The military population also showed a higher increment in the prevalence of overweight. The increment in the prevalence of obesity was comparable between the military and general population. The higher prevalence of overweight among the military personnel may be due to the nature of their physically demanding jobs that predisposed them to develop bigger muscle mass. Overweight personnel may have an advantage in terms of muscular strength, which is very much required for physical jobs such as heavy lifting and load carrying. Meanwhile, there were two possibilities of lower prevalence of obesity among the military personnel. They could have either shred off their fat through routine physical training or those who exceeded the BMI cut-off point were terminated from the service. Thus, it is unlikely to have obese personnel in service.
The key limitation to this systematic review was that the prevalence of overweight and obesity from different studies was measured at different time points. Comparison between countries and military branches could not be conducted at the same time point. However, the available results provided evidence on the military population is experiencing the problem of overweight and obesity and there is an increasing trend observed. Despite these limitations, this review was able to systematically demonstrate the trend and prevalence of overweight and obesity in military population between different countries and regions. These findings may be useful for the policy makers to plan for intervention programs to prevent the consequences of overweight /obesity among the military population such as increased rates of injuries, low work productivity, incurred higher healthcare costs and prematurely discharge from service. .

Conclusion:
This systematic review has shown that the military population is not protected from the problems of overweight and obesity despite their physically active work culture. The prevalence is increasing in