Dietary Assessment Methods in Military and Veteran Populations: A Scoping Review

Optimal dietary intake is important for the health and physical performance of military personnel. For military veterans, the complex nature of transition into civilian life and sub-optimal dietary intake is a leading contributor to the increased burden of disease. A scoping review was undertaken to determine what is known about the assessment and reporting of dietary intakes within both military and veteran populations. In addition, this review determines if studies reporting on the dietary intake of military personnel or veterans include comparisons with dietary guidelines. Six databases were searched to identify papers published from the database inception to April 2019. Observational and intervention studies were searched to identify if they assessed and reported whole dietary intake data, reported data exclusively for a military or veteran population, and included only healthy populations. A total of 89 studies were included. The majority of studies used one dietary assessment method (n = 76, 85%) with fewer using multiple methods (n = 13, 15%). The most frequent methodology used was food frequency questionnaires (FFQ) (n = 40, 45%) followed by 24-hour recalls (n = 8, 9%) and food records (n = 8, 9%). The main dietary outcomes reported were macronutrients: carbohydrate, protein, fat, and alcohol (n = 66, 74%) with total energy intake reported in n = 59 (66%). Fifty four (61%) studies reported a comparison with country-specific dietary guidelines and 14 (16%) reported a comparison with the country-specific military guidelines. In conclusion, dietary intake in military settings is most commonly assessed via FFQs and 24-hour recalls. Dietary intake reporting is mainly focused around intakes of energy and macronutrients. Most studies compare against dietary guidelines, however, comparison to specific military dietary guidelines is minimal.


Introduction
Optimal dietary intake is a crucial component of a military environment due to the high physical and mental demands placed on personnel [1][2][3][4]. Research to date has shown that the health, fitness and performance of military personnel is highly reliant on their nutritional status during training, and, therefore, their readiness to be deployed can be negatively affected by suboptimal nutrient intakes [2][3][4][5]. This is particularly relevant to service members in combat roles when on base preparing/training for field deployment [6]. To support their training, a focus on a healthy and optimal diet is essential for

Search Strategy and Study Selection
The search strategy and databases were selected in consultation with a research librarian and six databases were searched-CINHAL, Cochrane, EMBASE, Medline, Proquest (Military Database), and Scopus. The search strategy consisted of associated terms in term groups; diet and military (Table 1) and included English language studies published from database inception until April 2019. The reference lists of key papers were also searched. The review included all study designs, excluding narrative reviews, case report/series, commentaries, editorials, Letters to the Editor, theses and conference proceedings.
Studies were included if they assessed and reported whole dietary intake data such as food groups, macronutrients and/or micronutrients, reported data exclusively for populations of military personnel or military veterans and included only healthy populations, meaning those personnel without specific disease states (e.g., sickle-cell anaemia, eosonphillic eosophogitis). Studies that included individuals with those conditions were excluded from the review. Studies that reported on dietary intake from supplements Tables S1 and S2 as a primary outcome, or only a single aspect of diet, such as only energy intake or vitamin D intake, were also excluded. The decision to exclude these studies was made due to interest in dietary assessment methods of whole diet, and therefore studies not reporting on multi-nutrient intake were excluded.

Study Selection
After removal of duplicates (Figure 1), two researchers (RC, TB) conducted title and abstract screening. Regular discussions were had between researchers to ensure consistency was being applied to the screening. Conflicts between searchers were removed by a third party (MR) was consulted and any discrepancies were resolved. A full-text review (n = 329) was then completed by two researchers (RC, DC, BB), with any conflicts reviewed by a third researcher (TB).

Data Charting
Data were extracted and charted using a data extraction table designed in consultation with all authors. This was initially piloted with 5% of studies to ensure all information was being collected consistently. The extraction table was modified after piloting to include both the main outcomes of the study and the reported outcomes specific to nutrition as it was noted that the main outcomes and nutrition outcomes were often separate. Two researchers conducted the data extraction (RC, DC) which was then checked by a third researcher (BB) for consistency. Study description and outcomes can be viewed in Table 2. For the purpose of this review studies were classified by dietary assessment method (e.g., food frequency questionnaire (FFQ), 24-hour recall, food records). Studies were defined as multi-method if they included more than one form of dietary assessment method, such as a FFQ with food records, and were classified as validated, if the tool utilised in the study was a standardised measure i.e., diet history or direct observation, or referenced a method validation paper. Methods employed were first checked for validation within a general population, followed by validation within military populations. Studies were classified on the number of dietary intake outcomes reported (i.e., energy, fat, protein etc.) and were categorised into one of three groups: less than five outcomes, five to 10 outcomes, or greater than 10 outcomes.

Search Results
The search strategy identified 11,567 citations ( Figure 1). After removal of duplicates, 9920 citations were screened. Following title and abstract review, 311 studies underwent full text screening, of which 233 studies were excluded (Figure 1). The main reasons for study exclusions were; study design (n = 106, 44%) e.g., if the study did not include quantitative dietary intake measures, or study outcomes (n = 52, 21%) e.g., if the study reported energy expenditure outcomes as opposed to dietary energy or nutrient intake outcomes

Search Results
The search strategy identified 11,567 citations ( Figure 1). After removal of duplicates, 9920 citations were screened. Following title and abstract review, 311 studies underwent full text screening, of which 233 studies were excluded (Figure 1). The main reasons for study exclusions were; study design (n = 106, 44%) e.g., if the study did not include quantitative dietary intake measures, or study outcomes (n = 52, 21%) e.g., if the study reported energy expenditure outcomes as opposed to dietary energy or nutrient intake outcomes

Twenty Four-Hour Recalls
The studies that used 24-hour recall (n = 8, 9%) [30,34,41,77,81,[93][94][95] varied in the number of times administered. Four studies administered a 24-hour recall once throughout the study [30,77,81,95], one study administered two 24-hour recalls at two time points [36], one study the method was administered twice in the main group and two to three times in a subset of participants [94], another had all participants undertake a 24-hour recall three times with a subset undertaking a further three recalls [93]. One study administered four 24-hour recalls [41]. The use of a multiple-pass dietary recall (MPR) approach, within the administration of 24-hour recall, was only reported in one study [77].

Discussion
The aim of this scoping review was to provide a broad overview of the dietary assessment methods used to assess the whole dietary intakes of military personnel and military veterans with fresh food access in a broad range of settings. The review identified 89 studies, of which 71 were conducted with active military personnel, with many published since 2010 indicating increased recognition of nutrition in the maintenance of health and military performance of personnel [109]. Most of the studies were based in the USA and were carried out in garrison settings and conducted less often in free-living military groups. Macronutrients were the most reported dietary outcome and the majority of studies reported a comparison with dietary counties. Despite the amount of research dedicated to developing military specific dietary guidelines, most studies did not compare against military specific guidelines.
Across all studies, FFQs were the most commonly used dietary intake method. FFQs have been shown to be a useful tool in the study of non-military populations, however, most FFQs have been designed for use in the general population, or for specific disease states [110]. Moreover, while most studies used validated tools, only two were reported to be validated in military populations. It is important to carry out such studies given the food lists within dietary assessment tools, such as FFQs, should be population-specific where possible. In 2009, Mullie et al. [71] developed a semi quantitative FFQ with 150 food items specific for military men, which was reported to reliably determine the dietary intake of military men. However, this tool was validated specifically within administrative military personnel and may not be valid in more intensive military settings [71]. Of the included studies, biomarkers used for validation purposes as objective measures of dietary intake were used in four studies; doubly-labelled water [37] and metabolites including alpha-carotene and beta-carotene [53,64,93]. This highlights the need for further research to validate self-reported dietary intake using objective measures rather than validating against other self-reported measures which have the same reporting bias. There was no apparent relationship between diet assessment method and study design.
Research has shown that between four to eight administrations of MPR, 24-hour recalls are required to minimise error in dietary intake data, with the inclusion of weekends or days off, to cover the change in intake [111][112][113]. Three of the studies included used the automated self-assessment 24-hour recall method at only one time point which is a limited reflection of usual dietary intake [111,113]. Wherever practicable, dietary research within military and military veteran populations should consider using the 24-hour MPR method over non-consecutive days to obtain data more likely to be reflective of habitual intake [114,115]. Recent research suggests combining methods of dietary intake collection is best to reduce the limitations of individual methodologies [113].
In this current review, total energy intake and macronutrients, including alcohol, were the most common dietary outcomes reported, with other aspects of dietary intake reported less often including diet quality. More specifically, alcohol consumption was the most commonly reported outcome component and was most often assessed through FFQs. This is an important area of research, given alcohol misuse is suspected to be attributed to increased stress exposure in military service, in particular those with post-traumatic stress disorder (PTSD) [116].
Results of this review show that army personnel (soldiers) is by far the most studied military population when it comes to the assessment of dietary intake. This could be contributed to army branches being the largest military branches in countries such as the USA where the majority of studies arise from, in addition to, Britain and Australia [117][118][119]. Armies are diverse and generally include groups of occupations from those directly involved in warfighting such as infantry, artillery, cavalry, and special forces, to those supporting front-line warfighters, such as Combat Engineers [14,120]. One of the most frequently studied sub-groups of the Army were those undertaking basic training or cadet training, which may be due to new recruits being placed in very physically demanding situations with increased nutrition requirements. The USA contributes the majority of research into the area of dietary intake amongst its military branches with 62% of studies originating from this country. This may be reflective of larger military groups, or higher access to military research funding.
When compared to veteran populations, the numbers of all actively serving personnel are much less by comparison [119]. For example, in the USA veteran numbers are reported at 20 million compared to around 400,000 currently serving in the US army [117]. In this current review, less than 25% of all studies included participants from this large veteran population indicating a large research gap for assessing and improving the diets of those in military veteran groups. The veteran population have differing nutritional needs and requirements post-discharge including transition to the civilian community, different accommodation environments, a more sedentary lifestyle in addition to high rates of mental illness, disability, and health conditions in general, thus it has been shown that the USA veteran population has an increased burden of disease when compared to non-veteran populations [121]. Given sup-optimal dietary intake is a leading contributor to disease, it is likely to contribute to a higher prevalence of ill health, or overweight and obesity rates of veterans, making this a research priority area [117,122]. A number of studies have demonstrated that military populations are experiencing a trend towards being increasingly obese, which mirrors the pattern among the general population [123]. A cross-sectional study undertaken by Breland et al. (2017) found the prevalence of obesity amongst veteran population in the USA was 41% (44% females, 41% males). Similarly, in a USA cohort study of the military, obesity among service members was 20%, and significantly higher among veterans (32%). A 2011 Australian Senate Estimates Brief titled "Obesity in Defence" stated that approximately 15% of Australian Defence Force personnel had a BMI in the obese range.
The current review also found a marked increase in studies investigating females only from 2000 onwards, which is important as 16% of the currently enlisted USA Military are female, an increase of 13% since voluntary military service commenced in the USA [124]. Studies regarding the dietary intake of female military members are notably less in numbers than those with a focus on male members, however, this has been increasing steadily post-2000. It has previously been reported by Goldzweig et al. (2006), that since 2000 there has been an increase in female military recruits who now make up 20% of total new recruits. This increase also coincides with the decision in 2013 by countries, including the USA and Australia, to open frontline combat roles to women [125,126]. The increased numbers of female military personnel has been recognised by the US Department of Veterans Affairs, and may explain the reason for the increase in focus on the specific dietary and health needs of female military recruits [127]. Another reason may be the unique nutrition requirements of females in the military. Many women in the US do not meet the Recommended Dietary Allowances of important nutrients such as calcium and iron, and in a military setting with increased physical training, these inadequate intakes could lead to long-term negative health outcomes [59].
This scoping review has several strengths including a comprehensive systematic search and review protocol, including a detailed data extraction process. Moreover, military experts were consulted at all stages in the development of this review to provide input to ensure data and reporting were accurate and relevant. Limitations include that only studies in English were included which may have limited the extent of military dietary data access. As such, non-English studies from countries such as China and Russia, which have large military spends and large military services, were not included. The current review reflects only those databases searched and may not reflect unpublished or other military specific journals not commonly available to researchers. Grey literature was also not searched, further limiting full access to published dietary intake data.
In conclusion, dietary intake in military settings is most commonly assessed via the FFQ and 24-hour recall methodologies, however not all tools used were specifically validated for military populations. Dietary intake reporting was mainly focused around overall individual energy intake, and the intake of macronutrients including carbohydrates, proteins, fats, and alcohol. Comparison to dietary guidelines was used in the majority of studies, however the comparison to specific military dietary guidelines is minimal.