Introduction
Diet and nutrition have long been established as a crucial component to military readiness and performance(Reference Ramsey, Hostetler and Andrews1–Reference Pļaviņa and Ģēģere3). Adequate dietary nutrients are vital to maintain optimal health, protect against both physical and mental illness, and promote resilience and recovery(Reference Karl, Margolis, Fallowfield, Child, Martin and McClung4). The nutritional requirements of defence members vary according to their work environment (i.e. hot desert environments, tropical humid environments and cold arctic climates) and the physical requirements specific to their role (i.e. carrying provisions and gear, lifting supplies and equipment, digging, climbing, and marching)(Reference Collins, Baker, Coyle, Rollo and Burrows5,Reference Jaenen6) . As a result, military dietary reference intakes (MDRI) have been developed by some defence forces to guide nutritional requirements for defence members(Reference Baker-Fulco, Bathalon, Bovill and Lieberman7). The MDRI have been adapted from the recommended daily allowances, published by the Institute of Medicine in the USA(8). The most recent MDRI were updated in 2017 and are based on physically active military men and non-lactating, non-pregnant women, aged 17–50 years(Reference Regulation9). While the MDRI for some nutrients are the same as the general population, some specific nutrients, such as Na, are required in higher quantities.
The Committee on Diet and Health of the Food and Nutrition Board recommends that Na intake should not exceed 2400 mg/d(Reference Baker-Fulco, Bathalon, Bovill and Lieberman7). However, the Committee on Military Nutrition Research highlights that this intake is too low for military purposes due to the potential risk of Na depletion experienced under certain conditions, predominantly in hot environments without adequate periods of adaptation(Reference Palmer10). For most nutrients, the MDRI are set at the highest sex-specific reference value or recommended daily allowance, with the exception of Ca, P and Fe for males and Ca, P and Mg for females(Reference Baker-Fulco, Bathalon, Bovill and Lieberman7). Recommendations for energy (kcal) intake are divided into different levels of activity (light, moderate, heavy and exceptional)(Reference Baker-Fulco, Bathalon, Bovill and Lieberman7).
Historically, military nutrition research has focussed on optimising field/combat ration pack composition(Reference Karl, Margolis, Fallowfield, Child, Martin and McClung4), particularly in regard to energy intake and macronutrient balance(Reference Probert and Bui11–Reference Lenferna De La Motte, Schofield, Kilding and Zinn13). Previous research has also investigated the taste, texture and palatability of field/combat rations, with a focus on improving consumption compliance among defence members deployed or on exercise(Reference Huang, Gan and Law14,Reference Bui and Coad15) . Other studies investigate the success of healthy eating initiatives and programmes in garrison delivered at military dining facilities(Reference Belanger and Kwon16–Reference Kullen, Mitchell, O’Connor, Gifford and Beck18). More recently, research has begun to focus on the usual dietary patterns, food habits and nutritional intake of defence members during non-deployment free-living(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19–Reference Ramsey, Hostetler and Andrews21). However, to date, no comprehensive international systematic literature review has evaluated the overall dietary intake, composition and quality, or nutritional status of military personnel.
This review aimed to explore the diets of military populations internationally and assess whether their diets meet national nutritional guidelines and country-specific MDRI. The review aimed to determine which components of defence members diets require attention and highlight priority areas for policy makers, governments and defence organisations. Evaluating dietary intake is crucial in order to help influence dietary education materials and target future nutritional interventions.
Methods
Data source and search strategies
A protocol was developed according to the Preferred Reporting Items For Systematic Reviews And Meta-Analysis Protocols (PRISMA-P) 2020 statement(Reference Page22) (Supplementary file 1). The review was registered with the International Prospective Register of Systematic Reviews, PROSPERO (registration ID: CRD42023402198).
The primary outcome was to synthesise the dietary intake, composition and diet quality of military populations and compare intakes relative to dietary reference values such as the MDRI for individual nutrients. Additional outcomes included identifying which dietary components require improvements, by assessing the frequency of food consumption (e.g. number of serves of vegetables consumed per day) and identifying nutrient excesses or deficiencies compared to the MDRI values.
A literature search was conducted in the following databases: CINAHL, Scopus (Elsevier), Pubmed and AMED. A combination of Medical Subject Headings (MeSH) and free terms were used with Boolean operators integrated for advanced searches. The search used a combination of two search strings: the first one using terms for diet and nutrition, the second one using terms for military personnel and veterans. The following search is an example for the search used in PubMed, with the terms were adapted for each database:
(Diet [MeSH] OR Diet, Food, and Nutrition [MeSH] OR Diet Quality OR Diet Intake OR Nutrition Assessment [MeSh] OR Nutrient Intake OR Nutritional Status OR Nutrition) AND (Military Personnel [MeSH] OR Military Health [MeSH] OR Military [Title/Abstract] OR Army [Title/Abstract] OR Airforce [Title/Abstract] OR Navy [Title/Abstract] OR Veterans [MeSH]).
Screening of grey literature such as government reports/websites and clinical practice guidelines was also performed, along with hand searching the reference list of the included articles. Studies identified through database searching were exported and stored in EndNote X9(23). Articles were then imported into Covidence(24) where they were screened by title and abstract first, and later assessed as full text by J.B. and E.B. Covidence is a web-based collaboration software platform that streamlines the production of systematic and other literature reviews(24). The initial database search was performed by J.B. and final articles reviewed by E.B.
Inclusion and exclusion criteria
Original research published up to 21 February 2023, which assessed usual dietary intake, quality or composition (from either free living or in garrison), or nutritional status in current/active serving military populations were included in the review. Current serving military populations refers to all full time or part time military personnel, including national guard and reservists. All research designs were deemed eligible, including observational research designs (cross-sectional, cohort, case-control) and qualitative research designs (focus groups, interviews, etc). Experimental research designs (randomised control trials (RCT) and quasi-experimental studies) were included only when data on dietary intake or nutrition status was reported at baseline or for the control group.
Articles were excluded from the review if they constituted literature reviews, duplicate studies, conference proceedings, commentaries, abstracts, short communications and letters to the editor or reported findings from animal model research, in vivo and in vitro research. Research examining the nutritional quality or effects of combat rations or field rations on military personnel were also excluded, as reviews on this topic have already been conducted. Instead, this review focuses on dietary intake from either free living or in garrison.
Quality appraisal
Each paper was critically appraised for methodological consistency using risk of bias (ROB) critical appraisal tools. The Joanna Briggs Institute (JBI) checklists(Reference Tufanaru, Munn, Aromataris, Campbell and Hopp25) for cross-sectional studies and quasi-experimental studies were used and the Critical Appraisal Skills Programme (CASP) checklist for cohort studies and RCT were also used. The JBI critical appraisal tools have been developed by the JBI and collaborators and approved by the JBI scientific committee following extensive peer review(Reference Tufanaru, Munn, Aromataris, Campbell and Hopp25). The checklists ask questions which result in answers of yes/no or unclear. The checklist for cross-sectional studies includes eight questions which evaluate inclusion and exclusion criteria, study setting, measurement reliability, confounding factors and statistical analysis. A score of zero to three was considered a high ROB, a score of four to five was considered a medium ROB and a score of six to eight was considered a low ROB. The checklist for quasi-experimental studies includes nine questions which assess clarity of “cause” and “effect” variables, comparisons/control group similarity, measurement reliability, follow-up and statistical analysis. A score of one to three was considered a high risk of bias, a score of four to six was considered a medium risk of bias and a score of seven to nine was considered a low risk of bias.
The CASP checklist for cohort studies has twelve questions which evaluate measurement accuracy, confounders and follow-up. A score of zero to four was considered a high ROB, a score of five to eight was considered a medium ROB and a score of nine to twelve was considered a low ROB. The CASP checklist for RCT has eleven questions which evaluate randomisation, blinding, methodology and results. A score of zero to four was considered a high ROB, a score of five to eight was considered a medium ROB and a score of nine to eleven was considered a low ROB. ROBwas assessed by J.B. and reviewed by E.B. and disagreements were resolved through discussion. Table 1 displays the results from the critical appraisal.
Table 1. Risk of bias results
Key: Y, yes; N, no; UC, unclear/cannot tell; N/A, not applicable
Joanna Briggs Institute checklist for cross sectional studies:
1. Were the criteria for inclusion in the sample clearly defined?
2. Were the study subjects and the setting described in detail?
3. Was the exposure measured in a valid and reliable way?
4. Were objective, standard criteria used for measurement of the condition?
5. Were confounding factors identified?
6. Were strategies to deal with confounding factors stated?
7. Were the outcomes measured in a valid and reliable way?
8. Was appropriate statistical analysis used?
CASP checklist for cohort studies:
1. Did the study address a clearly focused issue?
2. Was the cohort recruited in an acceptable way?
3. Was the exposure accurately measured to minimise bias?
4. Was the outcome accurately measured to minimise bias?
5. (a) Have the authors identified all important confounding factors?
(b) Have they taken account of the confounding factors in the design and/or analysis?
6. (a) Was the follow up of subjects complete enough?
(b) Was the follow up of subjects long enough?
7. What are the results of this study? Have they been reported accurately?
8. How precise are the results?
9. Do you believe the results?
10. Can the results be applied to the local population?
11. Do the results of this study fit with other available evidence?
12. Are there implications of this study for practice?
CASP checklist for RCT:
1. Did the study address a clearly focused research question?
2. Was the assignment of participants to interventions randomised?
3. Were all participants who entered the study accounted for at its conclusion?
4. Were the participants “blind” to intervention they were given? Were the investigators “blind” to the intervention they were giving to participants? Were the people assessing/analysing outcome/s “blinded”?
5. Were the study groups similar at the start of the randomised controlled trial?
6. Apart from the experimental intervention, did each study group receive the same level of care (that is, were they treated equally)?
7. Were the effects of intervention reported comprehensively?
8. Was the precision of the estimate of the intervention or treatment effect reported?
9. Do the benefits of the experimental intervention outweigh the harms and costs?
10. Can the results be applied to your local population/in your context?
11. Would the experimental intervention provide greater value to the people in your care than any of the existing interventions?
Joanna Briggs Institute checklist for quasi-experimental studies:
1. Is it clear in the study what is the “cause” and what is the “effect” (i.e. there is no confusion about which variable comes first)?
2. Were the participants included in any comparisons similar?
3. Were the participants included in any comparisons receiving similar treatment/care, other than the exposure or intervention of interest?
4. Was there a control group?
5. Were there multiple measurements of the outcome both pre and post the intervention/exposure?
6. Was follow up complete and if not, were differences between groups in terms of their follow up adequately described and analyzed?
7. Were the outcomes of participants included in any comparisons measured in the same way?
8. Were outcomes measured in a reliable way?
9. Was appropriate statistical analysis used?
Data extraction
Predetermined data extraction was registered with PROSPERO prior to commencing the review. The Cochrane Data Extraction Template for Included Studies was used to extract key information from each of the final included studies(Reference Thomas, Higgins, Chandler, Cumpston, Li, Page and Welch26). The template is designed to capture all relevant information about the included studies and their results(Reference Thomas, Higgins, Chandler, Cumpston, Li, Page and Welch26). It comprises of seven sections including: (1) General review information (title, authors, year of publication, funding sources); (2) Methods of the study (study design, number of participants, location, setting); (3) Risk of bias assessment (results from the JBI and CASP ROB assessments); (4) Study characteristics – participants (age, sex, inclusion/exclusion criteria for the study, comorbidities, military branch e.g., Army, Navy or Air Force); (5) Study characteristics – interventions and comparisons; (6) Study characteristics – outcomes; (7) Data and results (diet data, including diet quality score (DQS) if available). The extracted data from the final articles is summarised in Table 2.
Table 2. Data summary table
Key: AI, adequate intake; AA, arachidonic acid; AHEI, Alternative Healthy Eating Index; ARFS, Australian Recommended Food Score; bw, body weight; CHO, carbohydrate; DF, dining facility; DFE, dietary folate equivalents; DHQ, Diet History Questionnaire; DQES, Dietary Questionnaire for Epidemiology Studies; DRI, Dietary Reference Intake; F, Female; HDI, Healthy Diet Indicator*; HEI, Healthy Eating Index**; HES-5, Healthy Eating Score***; M, male; MDRI, military dietary reference intake; NR, not reported; RCT, randomised control trial; Se, Selenium; Ω-3, omega 3
*HDI scores: 6–7 = good diet, 4–5 = fair diet, requires improvement, and 0–3 = a poor diet
**HEI scores: >80 = good diet, scores 51–80 = fair diet, requires improvement, and scores <51 = a poor diet
***HES-5 scores: ≥20 = good diet, 13–19 = fair diet, ≤12 = poor diet
All energy measurements converted from kcal to kjs and Vitamin D IU converted to μg
Results
Identification of studies
The article selection process is outlined in Figure 1. The initial search identified 7567 papers. After the removal of 1304 duplicates, articles were screened by title and abstract. A total of 352 articles were then screened by full text. Initially, 157 studies met the full inclusion criteria; however, a large number of these were over 30 years old. In order to present a contemporary overview of the current dietary intake of military personnel, the inclusion criteria were further refined to only include articles published within the last 10 years and to exclude veteran populations. We recommend that an additional review be conducted to examine veteran dietary intake separately, as the dietary and energy needs of active serving military and veterans varies considerably. These additional refinements resulted in 36 articles which met the full inclusion criteria and are presented in this review.
Fig. 1. PRISMA 2020 flow diagram for new systematic reviews which included searches of databases, registers and other sources. From: Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ 2021;372:n71. doi:10.1136/bmj.n71. For more information, visit: http://www.prisma-statement.org/.
Critical appraisal results
Table 1 displays the ROB score for each included article. For the cross-sectional studies (n 21), the majority had a low ROB (n 10)(Reference Ramsey, Hostetler and Andrews21,Reference Smith27–Reference Salehi, Ghosn, Rahbarinejad and Azadbakht35) or a medium ROB (n 9)(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Purvis, Lentino, Jackson, Murphy and Deuster36–Reference Edwards43) , with only two studies(Reference Mullie, Deliens and Clarys44,Reference De Bry, Mullie, D’Hondt and Clarys45) displaying a possible high ROB. The main issues observed included the sample inclusion criteria not being clearly defined, confounding factors not being adequately identified and a lack of reported strategies to deal with confounding factors. None of the cohort studies (n 10) had a high ROB, four had a medium ROB(Reference Carlson, Smith and McCarthy46–Reference Peoples49) and six had a low ROB(Reference Lutz20,Reference Farina50–Reference Chapman54) . The main issues observed in the cohort studies was the lack of reported techniques to correct, control or adjust for confounding factors, in addition to a lack of precision when reporting the results (e.g. lack of confidence intervals). For the two RCT, one had a medium ROB(Reference Frank and McCarthy55) and one had a low ROB(Reference Gaffney-Stomberg56). For the quasi-experimental studies (n 3), one study had a medium ROB(Reference Barringer57) and two had a low ROB(Reference Bukhari17,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) . The risk of bias analysis revealed an overall low risk of bias among the included articles in this review suggesting a high level of confidence in the reported results.
Study characteristics
Several different study designs were included in this review. The majority were cross-sectional studies (n 21) or cohort studies (n 10), with only a few using RCT (n 2) or quasi-experimental (n 3) designs. The number of participants in each study ranged from 12 participants to 27 034 participants. A total of 69 351 participants were included in this review. Fourteen studies included only male participants and one did not report participant sex(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19). The vast majority of studies were conducted in the USA; n 20)(Reference Bukhari17,Reference Lutz20,Reference Ramsey, Hostetler and Andrews21,Reference Smith27,Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30,Reference Nakayama, Lutz, Hruby, Karl, McClung and Gaffney-Stomberg31,Reference Daniels and Hanson33,Reference Purvis, Lentino, Jackson, Murphy and Deuster36,Reference Beals38,Reference Hruby, Lieberman and Smith39,Reference Rittenhouse, Scott and Deuster42,Reference Carlson, Smith and McCarthy46,Reference Farina50–Reference Lutz, Nakayama, Karl, McClung and Gaffney-Stomberg53,Reference Frank and McCarthy55–Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) , with the remaining studies conducted in Iran (n 5)(Reference Rahmani, Milajerdi and Dorosty-Motlagh29,Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Parastouei, Sepandi and Eskandari34,Reference Salehi, Ghosn, Rahbarinejad and Azadbakht35,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37) , England (n 3)(Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Edwards43,Reference Chapman54) , Australia (n 2)(Reference Kullen, Farrugia, Prvan and O’Connor28,Reference Peoples49) , Belgium (n 2)(Reference Mullie, Deliens and Clarys44,Reference De Bry, Mullie, D’Hondt and Clarys45) , Finland (n 1)(Reference Nykänen, Pihlainen, Santtila, Vasankari, Fogelholm and Kyröläinen47), Poland (n 1)(Reference Anyżewska41), Greece (n 1)(Reference Doupis48) and Canada (n 1)(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19). The majority of studies were conducted in Army members (n 27), three were conducted in all services (Army, Navy and Air Force)(Reference Smith27,Reference Nakayama, Lutz, Hruby, Karl, McClung and Gaffney-Stomberg31,Reference Hruby, Lieberman and Smith39) , two were conducted in the Navy/Marines(Reference Doupis48,Reference Sepowitz, Armstrong and Pasiakos51) and two did not report which service members were included(Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Parastouei, Sepandi and Eskandari34) .
Diet measurement
The majority of studies used standard FFQ (n 23), with the most common being block FFQ (n 11) which are designed based on the block dietary data systems and include a standardised format and item list designed to capture a wide range of commonly consumed foods(Reference Wakimoto and Block59). Three studies asked general questions about food consumption as part of larger surveys(Reference Smith27,Reference Hruby, Lieberman and Smith39,Reference Mullie, Deliens and Clarys44) . One study used digital photographs to assess food intake(Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) and three assessed food weight and plate waste(Reference Edwards43,Reference Chapman54,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) . Seven studies used food diaries or food logs to assess food intake(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Edwards43,Reference De Bry, Mullie, D’Hondt and Clarys45,Reference Nykänen, Pihlainen, Santtila, Vasankari, Fogelholm and Kyröläinen47,Reference McAdam52,Reference Chapman54) , and two used blood tests to assess nutrient status(Reference Peoples49,Reference Barringer57) . A range of different nutrients were assessed across the included articles. The majority of studies (n 23) assessed energy (kJ) and macronutrients (protein, carbohydrates and fats). Many also assessed fibre, essential fatty acids and a number of micronutrients (vitamins and minerals). The most common micronutrients assessed included vitamin A, C, D and K, folate, Na, Ca, Mg, K, Se, Fe and Zn. Some studies also assessed caffeine, water and added sugar consumption.
Diet quality scores
Eight of the included studies calculated a diet quality score from the food FFQ results(Reference Lutz20,Reference Kullen, Farrugia, Prvan and O’Connor28,Reference Rahmani, Milajerdi and Dorosty-Motlagh29,Reference Parastouei, Sepandi and Eskandari34,Reference Purvis, Lentino, Jackson, Murphy and Deuster36,Reference Rittenhouse, Scott and Deuster42,Reference Farina50,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) . The most commonly used scores were the Healthy Diet Indicator(Reference Parastouei, Sepandi and Eskandari34), Healthy Eating Index(Reference Lutz20,Reference Rittenhouse, Scott and Deuster42,Reference Farina50,Reference Sepowitz, Armstrong and Pasiakos51,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) and Healthy Eating Score(Reference Purvis, Lentino, Jackson, Murphy and Deuster36). The Australian Recommended Food Score was used for one study(Reference Kullen, Farrugia, Prvan and O’Connor28). For each of these diet quality scores, the overall diet quality is rated as: (1) poor diet quality; (2) fair diet quality – requires improvement; (3) good diet quality. In all eight studies which calculated a diet quality score, the results indicated poor to fair diet quality which indicates improvement is necessary(Reference Lutz20,Reference Kullen, Farrugia, Prvan and O’Connor28,Reference Parastouei, Sepandi and Eskandari34,Reference Purvis, Lentino, Jackson, Murphy and Deuster36,Reference Rittenhouse, Scott and Deuster42,Reference Farina50,Reference Sepowitz, Armstrong and Pasiakos51,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) .
Energy and macronutrients
Twenty-three of the studies assessed daily energy intake (kJ). Twenty of these studies found that defence members did not meet energy requirements according to their country’s MDRI(Reference Bukhari17,Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Ramsey, Hostetler and Andrews21,Reference Rahmani, Milajerdi and Dorosty-Motlagh29–Reference Salehi, Ghosn, Rahbarinejad and Azadbakht35,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Edwards43,Reference De Bry, Mullie, D’Hondt and Clarys45,Reference Nykänen, Pihlainen, Santtila, Vasankari, Fogelholm and Kyröläinen47,Reference Sepowitz, Armstrong and Pasiakos51,Reference McAdam52,Reference Chapman54–Reference Gaffney-Stomberg56) , while only three studies reported adequate intake(Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Carlson, Smith and McCarthy46,Reference Peoples49) . The majority of studies which assessed carbohydrate intake reported adequate intake (n 12)(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30,Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Salehi, Ghosn, Rahbarinejad and Azadbakht35,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Carlson, Smith and McCarthy46,Reference Nykänen, Pihlainen, Santtila, Vasankari, Fogelholm and Kyröläinen47,Reference Peoples49,Reference McAdam52,Reference Chapman54–Reference Gaffney-Stomberg56) and only three reported inadequate intakes(Reference Edwards43,Reference De Bry, Mullie, D’Hondt and Clarys45,Reference Sepowitz, Armstrong and Pasiakos51) . All 19 studies that assessed protein intake reported an adequate intake which exceeded the country’s recommendations(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Ramsey, Hostetler and Andrews21,Reference Rahmani, Milajerdi and Dorosty-Motlagh29–Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Salehi, Ghosn, Rahbarinejad and Azadbakht35,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Edwards43,Reference De Bry, Mullie, D’Hondt and Clarys45–Reference Nykänen, Pihlainen, Santtila, Vasankari, Fogelholm and Kyröläinen47,Reference Sepowitz, Armstrong and Pasiakos51,Reference McAdam52,Reference Chapman54–Reference Gaffney-Stomberg56) . Fat intake was assessed by 21 studies, with only two reporting inadequate intake(Reference Rahmani, Milajerdi and Dorosty-Motlagh29,Reference McAdam52) . Nineteen reported an intake which exceeded recommendations(Reference Bukhari17,Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Ramsey, Hostetler and Andrews21,Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30–Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Salehi, Ghosn, Rahbarinejad and Azadbakht35,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Edwards43,Reference De Bry, Mullie, D’Hondt and Clarys45–Reference Nykänen, Pihlainen, Santtila, Vasankari, Fogelholm and Kyröläinen47,Reference Peoples49,Reference Sepowitz, Armstrong and Pasiakos51,Reference Chapman54–Reference Gaffney-Stomberg56) . Six studies assessed essential fatty acids with all reporting suboptimal intake(Reference Bukhari17,Reference Rittenhouse, Scott and Deuster42,Reference Peoples49–Reference Sepowitz, Armstrong and Pasiakos51,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) . Two studies also assessed trans-fat, with both indicating a high consumption which exceeded recommendations(Reference Bukhari17,Reference Peoples49) . Eight studies assessed fibre, with six reporting inadequate intake(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Ramsey, Hostetler and Andrews21,Reference Daniels and Hanson33,Reference Parastouei, Sepandi and Eskandari34,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Nykänen, Pihlainen, Santtila, Vasankari, Fogelholm and Kyröläinen47) and only two reporting adequate intake(Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Salehi, Ghosn, Rahbarinejad and Azadbakht35) .
Vitamins
A variety of different vitamins were assessed including; A, B1, B2, B3, B5, B12, K C, D, E and folate. Inadequate intake of vitamin A was reported in four studies(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) , with only two reporting adequate intake(Reference Ramsey, Hostetler and Andrews21,Reference Daniels and Hanson33) . Inadequate intake of vitamin C was reported in two studies(Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) , while five studies indicated adequate intake(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Ramsey, Hostetler and Andrews21,Reference Daniels and Hanson33,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Frank and McCarthy55) . Inadequate intake of vitamin D was indicated in three studies(Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Carlson, Smith and McCarthy46,Reference Barringer57) , while adequate intake was indicated in five studies(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Frank and McCarthy55,Reference Gaffney-Stomberg56) . Inadequate intake of vitamin E was reported in three studies(Reference Ramsey, Hostetler and Andrews21,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Beals38) , with only one reporting adequate intake(Reference Daniels and Hanson33). Inadequate intake of vitamin K was reported in two studies(Reference Beals38,Reference Carlson, Smith and McCarthy46) , while four reported adequate intake(Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Carlson, Smith and McCarthy46,Reference Frank and McCarthy55) . Six studies assessed folate, with three reporting inadequate intake(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) and three reporting adequate intake(Reference Ramsey, Hostetler and Andrews21,Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30,Reference Daniels and Hanson33) . Most studies indicated adequate B vitamins, excluding one study which reported inadequate B3(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19).
Minerals
A variety of minerals were assessed among the studies, including Na, Mg, Fe, Zn, Ca, K, I, Se and P. Suboptimal intake of Na was reported in six studies(Reference Ramsey, Hostetler and Andrews21,Reference Parastouei, Sepandi and Eskandari34,Reference Rittenhouse, Scott and Deuster42,Reference Farina50,Reference Sepowitz, Armstrong and Pasiakos51,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) and inadequate intake of Mg was reported in three studies(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) . Two studies found that iron intake among female defence members was inadequate(Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) , while four reported adequate intake(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Ramsey, Hostetler and Andrews21,Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Daniels and Hanson33) . Inadequate intake of Zn was reported in four studies(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) and only one reported adequate intake(Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37). Inadequate intake of Ca was reported in four studies(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Gaffney-Stomberg56) , while adequate intake was reported in seven studies(Reference Ramsey, Hostetler and Andrews21,Reference Nakayama, Lutz, Hruby, Karl, McClung and Gaffney-Stomberg31–Reference Daniels and Hanson33,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Carlson, Smith and McCarthy46,Reference Frank and McCarthy55) . Inadequate intake of potassium was reported in four studies(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Nakayama, Lutz, Hruby, Karl, McClung and Gaffney-Stomberg31,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) , while adequate intake was reported in five studies(Reference Ramsey, Hostetler and Andrews21,Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Carlson, Smith and McCarthy46,Reference Frank and McCarthy55) . Both studies which assessed iodine intake reported inadequate intake(Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40) . Inadequate intake of selenium was reported in one study(Reference Chapman, Roberts, Smith, Rawcliffe and Izard40), while adequate intake was reported in three studies(Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Taleghani, Sotoudeh, Amini, Araghi, Mohammadi and Yeganeh37,Reference Beals38) . All seven studies which assessed P intake reported adequate intake(Reference Ahmed, Mandic, Lou, Goodman, Jacobs and L’Abbé19,Reference Lutz, Gaffney-Stomberg, Karl, Hughes, Guerriere and McClung30,Reference Ghodsi, Rostami, Parastouei, Taghdir, Esfahani and Nobakht32,Reference Beals38,Reference Chapman, Roberts, Smith, Rawcliffe and Izard40,Reference Carlson, Smith and McCarthy46,Reference Frank and McCarthy55) .
Food groups
Several studies assessed daily serves of food groups such as fruits, vegetables, wholegrains, seafood/plant protein, meat, dairy, fats, added sugars and fast food. All thirteen studies which assessed food group portions reported inadequate intakes of fruits, vegetables, seafood, plant proteins, nuts and wholegrains(Reference Smith27–Reference Rahmani, Milajerdi and Dorosty-Motlagh29,Reference Nakayama, Lutz, Hruby, Karl, McClung and Gaffney-Stomberg31,Reference Purvis, Lentino, Jackson, Murphy and Deuster36,Reference Hruby, Lieberman and Smith39,Reference Anyżewska41,Reference Rittenhouse, Scott and Deuster42,Reference Mullie, Deliens and Clarys44,Reference Doupis48,Reference Farina50,Reference Sepowitz, Armstrong and Pasiakos51,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) . A further five studies assessed added sugars with all reporting higher than recommended intake(Reference Hruby, Lieberman and Smith39,Reference Anyżewska41,Reference Rittenhouse, Scott and Deuster42,Reference Doupis48,Reference Cole, Bukhari, Champagne, McGraw, Hatch and Montain58) . Of the two studies that assessed processed meat intake, both reported intake that exceeded recommendations(Reference Parastouei, Sepandi and Eskandari34,Reference Anyżewska41) .
Discussion
This is the first systematic literature review to assess the dietary intake and nutritional status of defence members worldwide. The overall quality of the evidence was high with a low risk of bias. The evidence presented in this review demonstrates that overall, defence members have a low diet quality, and one that may not be conducive to the nutritional requirements for the rigours of active duty. In particular, defence members display low intakes of fruits, vegetables, wholegrains, seafood, plant protein and nuts. The low intake of these food groups may explain the inadequate intake of several vital nutrients, particularly fibre, essential fatty acids, vitamin A, vitamin E, folate, Mg, Zn and iodine.
The low intake of nutrients identified in this review is concerning considering their importance in ensuring military readiness, optimal performance, recovery after training, and physical exertion, and prevention of injury(Reference Ramsey, Hostetler and Andrews1–Reference Pļaviņa and Ģēģere3). For example, essential fatty acids such as PUFA, can reduce exercise-induced muscle damage(Reference Kyriakidou, Wood, Ferrier, Dolci and Elliott60). Exercise-induced muscle damage leads to transient muscle inflammation, loss of strength, reduced range of motion, delayed onset muscle soreness and impaired recovery, causing reduced exercise performance(Reference Harty, Cottet, Malloy and Kerksick61). Increased intake of PUFA have shown to reduce the effects of exercise-induced muscle damage via its anti-inflammatory action(Reference Kyriakidou, Wood, Ferrier, Dolci and Elliott60). Mg is another crucial nutrient important for optimal physical performance and recovery(Reference Hunt, Sukumar and Volpe62). It is involved in protein synthesis, bone metabolism, electrolyte balance and neuromuscular functions(Reference Hunt, Sukumar and Volpe62). Mg has also been shown to increased physical endurance and reduce muscle cramps(Reference Hunt, Sukumar and Volpe62). Therefore, ensuring adequate intake among defence members should be considered a priority.
Recently, mounting evidence has highlighted the important role of diet and nutrition for mental health(Reference Bayes, Schloss and Sibbritt63,Reference Marx64) . Given the unique challenges and stress that accompany military life(Reference Dell65) and the increased risk of mental health conditions among defence members(Reference Fikretoglu66), nutrition which supports mental wellbeing should be a priority. This review has shown that defence members consume inadequate quantities of several key nutrients important for mental health including folate, vitamin A, Mg, Zn and PUFA which have been reported to play an important role in the pathophysiology of depression(Reference LaChance and Ramsey67). More research is needed to thoroughly explore the effect of dietary intake and nutritional quality on mental health outcomes in defence members.
This review has found substantial evidence that the diet quality and nutrition intake of defence members is suboptimal. Particular areas found for improvement included intake of fibre, essential fatty acids, vitamin A, vitamin E, folate, Mg, Zn and I. This has important implications for policymakers and governments who wish to implement frameworks, policies and strategies to improve the nutrition and health of defence members and optimise military performance. These results can be used to help identify priority areas which demand urgent attention. Supplementation, as well as dietary modification, may be supported where nutritional deficiencies remain consistent or are unable to be modified by diet alone due to resource or logistical constraints.
This review found high consumption of added sugars, trans fats and processed meat among defence members. Consumption of these foods has been linked to a number of diseases, including obesity(Reference Mozaffarian68), cardiovascular disease(Reference Nestel and Mori69) and diabetes(Reference Mozaffarian70). As diet is considered a significant modifiable risk factor for each of these conditions, it is important that defence members are provided with healthy food options which reduce chronic disease risk. Resource and logistical constraints affecting diet during deployment or on exercise are expected, but this review highlights that the diets of military members remain poor even without these constraints. It is therefore important that the military food environment is conducive in supporting healthy diets. Unfortunately, studies have shown that the military food environment and options available to defence members on-base do not support healthy eating(Reference Carins and Rundle-Thiele71). On-base grocery stores and food vendors are often dominated by fast-food outlets, convenience/processed foods and snack foods high in added sugar, Na and fat(Reference Quadri72,73) . This issue requires the urgent attention of policymakers in order to facilitate change to the military food environment, and support healthy eating among defence members.
While the overall quality of the included articles was high, this review has limitations that need to be acknowledged. The initial search resulted in a large number of diverse studies. However, a significant number of these were over 30 years old. Therefore, to provide a contemporary synthesis of the current diet intake of defence members, the inclusion criteria were further refined to only include articles published within the last 10 years and to exclude veteran populations. While this refinement of the inclusion and exclusion criteria allowed for a more focused review, it may have resulted in an incomplete or biased representation of results.
An additional review examining the diet quality of veterans is required, as the dietary and energy needs of active serving military and veterans varies considerably. Given the long-term and often inter-generational impact of nutritional status, studies of the long-term impact of military service on dietary behaviours of military and veteran populations may also be warranted. Additionally, although the findings suggesting requirements to improve diet quality was observed across all study settings in this review, over half of all included studies were from the USA and data were completely absent for most other countries. Broader international attention is required for this important issue. This review provides a narrative synthesis of the results which comes with a risk of interpretation bias from the authors. Only published trials available on the preselected databases were available to be reviewed, which may have skewed the findings.
Conclusion
This review has critically appraised existing evidence related to the diet quality and nutritional intake of defence members. The overall quality of the included articles was high with a low risk of bias. In all eight studies which calculated a diet quality score, the results showed poor to fair diet quality which requires improvement. In particular, defence members displayed low intakes of fruits, vegetables, wholegrains, seafood, plant protein and nuts and high intakes of added sugars, trans fat and processed meat. The review also found suboptimal intake of nutrients, particularly fibre, essential fatty acids, vitamin A, vitamin E, folate, Mg, Zn and iodine. The suboptimal intake of these vital nutrients may lead to reduced performance, increased risk of chronic diseases and mental health disorders. More research is needed that explores the long-term consequences of poor diet quality in defence members. These results require the attention of policymakers to ensure that military education and food environment is supportive of healthy eating.
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/S0954422424000143.
Statement of authors’ contributions to manuscript
J.B., R.L. and J.W. contributed to the design of the research question, development of the search terms, and contributed to the review protocol. J.B. conducted the initial database search with the final articles reviewed by E.B. J.B. and E.B. conducted the ROB analysis. J.B. extracted and analysed the data. J.B. drafted the manuscript with reviews and edits by E.B., R.L. and J.W. J.B. has primary responsibility for the final content. All authors have read and approved the final manuscript.
Financial support
This research did not receive any funding.
Competing interests
The authors have no conflicts of interest to declare.
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