Dietary reference intake for military operations: a scoping review

Search for literature on DRI for military operations using PubMed

The search yielded eight references, seven of which were excluded as they did not target the military. The accepted reference (Collins et al., 2020) was a scoping review of dietary assessment methods in military personnel and veterans. A keen study of this scoping review by Collins et al. (2020) revealed survey reports of dietary intake standards for the military in the USA (Baker-Fulco et al., 2001; Department of Defense, 2001; Department of Defense, 2017) and Australia (Forbes-Ewan & DSTO, 2009). Moreover, the Nordic countries (Denmark, Finland, Ireland, Norway, and Sweden) utilize the DRI (NATO, 2010) developed by NATO. Meanwhile, another report (Valk & Pasman, 2005) described dietary intake in the Dutch military.

Collins et al.’s (2020) scoping review selected 89 research reports from 16 countries (USA, Belgium, Finland, UK, Norway, Italy, Greece, France, Israel, Iran, Malaysia, Japan, Australia, Cameroon, South Africa, and Brazil). In addition, since only research reports written in English were accepted, only four countries in Asia (Israel, Iran, Malaysia, and Japan) were represented.

Search for information on DRI for military operations (survey reports, materials, etc.) using the Google browser

A Google search was conducted targeting 37 countries and one institution, including the countries identified in Collins et al. (2020) review, as well as countries in East Asia and Southeast Asia. As a result, survey reports and related materials on eight DRI for military operations for eight militaries (USA, Australia, NATO, Netherlands, UK, China, South Korea, and Singapore) were found (Chan, 2016; Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; Guo et al., 2016; MND, 2017; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b; Valk & Pasman, 2005).

Organizing the contents of research reports and documents that describe DRI for military operations

After carefully reading the contents of the research reports that were finally selected, the Dutch (Valk & Pasman, 2005) survey report had “Content describing protocol limitations and protocol details for testing the effects of dietary interventions in military settings”. Three countries, Singapore (Chan, 2016), China (Guo et al., 2016), and South Korea (MND, 2017), were not included in the review due to insufficient description of the basis for their formulation and were instead used as reference materials. Finally, we scrutinized the DRI for the military operations of three countries and one organization: Australia, UK, USA, and NATO (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). We referred to the unrevised DRI (Baker-Fulco et al., 2001; Casey, 2008; Department of Defense, 2001; Forbes-Ewan, Materials Research Laboratory & Defence Science and Technology Organisation (DSTO), 1993; Forbes-Ewan, DSTO-Scottsdale & CBRN Defence Centre Platform Sciences Laboratory, 2002; SACN, 2020; IOM, 1994), the DRI for the civilian public (Department of Health, 1991; IOM, 1997; NHMRC, 2017; Scientific Advisory Committee on Nutrition, 2011; Scientific Advisory Committee on Nutrition, 2015; Scientific Advisory Committee on Nutrition, 2016a; Subcommittee on the Tenth Edition of the RDAs, 1989), and materials citing these. Based on this, we summarized four published DRIs for military operations, outlined the basics of their formulation, and organized the standards for energy and nutrients that had been formulated.

Established energy and nutrients in the four published DRIs for military operations

All four published DRIs for military operation formulations were based on the referenced DRIs for civilians; however, standards were set by adding the amount necessary for members who have a high level of physical activity and are responsible for military activities in special environments (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). The basis for determining the required intake in high-intensity physical activity and special environments was (1) research reports, survey reports, etc., describing research findings (Askew, 1995; IOM, 1996; Rodriguez, Di Marco & Langley, 2009; Tarnopolsky et al., 2005; Tomczak et al., 2016) and (2) data on the physical characteristics of the military members, their basal metabolic rates, physical activity, etc. (Baker-Fulco et al., 2001; Department of Defense, 2001; Forbes-Ewan et al., 1995; Paquette, Gordon & Bradtmiller, 2009). Table 3 presents the comparison of DRIs for military operations.

Energy and nutrient indicators are important (King, Vorster & Tome, 2007) and are formulated and displayed in various ways (Tables 2 and S1). Therefore, we organized the data based on the type of indicator (Table 3). Australia, the UK, and the USA have set new standards for their military based on indicators of DRI for civilians (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; Scientific Advisory Committee on Nutrition, 2016b). Moreover, NATO used the NIV by King, Vorster & Tome (2007), which differs from the NRV (NHMRC, 2017) index (NATO, 2010).

PAL category definitions and estimated energy requirement calculations vary among nations/organizations by age, sex, reference body size, and activity level (Tables S2 and S3). Specific energy and nutrient DRIs for civilian and military populations by nation/organization are depicted in Supplementary Tables S4–S18. These supplementary tables were used to develop the consolidated framework needed to illustrate differences in DRIs between civilian and military populations, as provided in Table 3 and PAL categories in Table 4.

PAL categories and energy requirements

Energy requirements were common to all four published DRIs for military operations (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b), with PALs and corresponding energy requirements that reflected the high physical activity of military personnel and differed from those in the DRI for civilians (Department of Health, 1991; IOM, 1997; NHMRC, 2017; Scientific Advisory Committee on Nutrition, 2011; Scientific Advisory Committee on Nutrition, 2015; Scientific Advisory Committee on Nutrition, 2016a; Subcommittee on the Tenth Edition of the RDAs, 1989) (Table 3). The PAL categories and energy requirements in DRIs for civilians and military are presented in Table S2, while the reference body size and estimated formula in DRIs for military operations is shown in Table S3.

The range of PAL categories for civilians is 1.20–2.20 (Department of Health, 1991; IOM, 1997; NHMRC, 2017; Scientific Advisory Committee on Nutrition, 2011), whereas the DRI for military operations ranges from similar PAL categories (low physical activity (1.50), general population (1.63), etc.) to categories reflecting higher levels of physical activity associated with engaging in military activities (1.50–3.20 in the case of Australia) (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). A meta-analysis by Murphy et al. (2018) showed that insufficient energy intake in military personnel reduces lower extremity performance during military operations. Moreover, energy deficiency among military personnel is associated with heart disease risk (Hilgenberg et al., 2016). In contrast, overweight and obesity among military personnel is also a concern (Herzman-Harari et al., 2013). This suggests that adequate intake of the required amount of energy is very important for military personnel. Therefore, for military personnel, proper intake of the necessary amount of energy is important.

Moreover, the range of energy consumption varies depending on the job type of military personnel (Forbes-Ewan et al., 1990; Forbes-Ewan & Waters, 1991; Forbes-Ewan & DTSO, 2009; Tharion et al., 2005), and the range is wider than that of civilians. Tharion et al. (2005) found that the energy expenditures measured in 424 military members across all four military services, in a variety of occupations, climates, and environments (field vs. garrison) ranged from 13.0–29.8 MJ (3,109–7,131 kcal)/day for male military members and 9.8–23.4 MJ (2,332–5,597 kcal)/day for female military members. The category of “Believed to approach the limit of human endurance” (PAL 3.20) in Australia was based on the energy consumption of 28 MJ (6,692 kcal)/day for members selected for Special Air Service Regiments. Furthermore, since these military members are actively moving their bodies for about 20 h a day, they have a special system in which they only get about four hours of sleep (Erdman et al., 2006).

In the DRI for military operations, not only the amount of physical activity but also the environment was considered, and target categories were established, and energy and nutrients were formulated accordingly (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). In NATO’s DRI (NATO, 2010), the environmental cut-off values in the review by Askew (1995) (hot environment: >30 °C or >86° F; cold environment: <0 °C or <32° F; high-altitude environment: >3,050 m or >10,000 ft elevation) was used, and three extreme environmental categories were established.

Previous studies have reported that the amount of energy and nutrients required differ depending on the extreme environment (Tassone & Baker, 2017). A report by Tharion et al. (2005) showed that energy consumption did not tend to be affected by hot environments, but it tended to increase in cold and high-altitude environments. Meanwhile, a prospective cohort study by Gan et al. (2022) evaluated changes in energy and physical performance during ranger training (62 days) in a hot and humid environment in 17 male army personnel. The total daily energy expenditure (TDEE) estimated by the double-labeled water method was 4,756 kcal/day, while the average energy intake was 3,882 kcal/day, indicating an energy deficit of 874 kcal/day (18%). In addition, body weight decreased by 4.6 (2.6) kg, or 6.7 (3.8%), over 62 days, with some members losing up to 10.1 kg (14.9%), which also showed a decline in performance evaluation. Ahmed et al. (2019) evaluated dietary intake under four conditions: (1) exercise (as standardized infantry activities) in the heat (30 °C), (2) exercise in the cold (−10 °C), (3) exercise in temperate thermoneutral (21 °C) air temperatures and (4) a resting (sedentary) trial (21 °C). As in other previous studies (Johnson et al., 2018), the results indicated that even with a significant increase in energy expenditure and exposure to severe stress due to temperature, the energy intake from the diet of the military remained the same as at rest, leading to an energy deficit, which is problematic. Therefore, it is very important to consider not only physical activity but also extreme environmental conditions.

Although there are various methods for formulating the energy consumption and basal metabolic rate, the same estimation formula as the DRI for civilians (Henry, 2005; IOM, 1997; Schofield, 1985) was used as a reference. These estimation formulas used reference body size that reflected the physical characteristics of the military members. (Table S3) (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b) Australia, the UK, and the USA used the physical characteristics of their own military members as reference body size, while NATO used the reference body size of American male members (Baker-Fulco et al., 2001; Department of Defense, 2001). As mentioned above, previous research has identified the lack of energy among military personnel as an important issue (Barringer et al., 2018; Murphy et al., 2018; O’Leary, Wardle & Greeves, 2020; Vyas & Cialdella-Kam, 2020). This also suggests that the accumulation of data on the physical characteristics and basal metabolic rate of military personnel, which is common to all four published DRIs, is an issue for the future. Hence, the future challenge for all four published DRIs for military operations were to accumulate data on military personnel’s physical characteristics and basal metabolic rates (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). The UK uses the same equation to estimate energy requirements for both civilian and military populations (Henry, 2005); although the aim is to derive an equation specific for military DRI once sufficient data are available (Scientific Advisory Committee on Nutrition, 2016b; SACN, 2020).

Protein

The required amount of protein was formulated by reflecting the military’s PAL in all four published DRIs for military operations (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b), which differed from the DRI for civilians (Table S4) (Department of Health, 1991; IOM, 1997; NHMRC, 2017). Table S4 shows “Protein in Dietary Reference Intakes (DRI) for civilians and military (/day)”. Australia, the USA, and NATO listed the intake weight (g or g/kg) (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010), while the UK only listed the percentage (%) of macronutrient energy distribution (Scientific Advisory Committee on Nutrition, 2016b). These are developed with PAL and military environments in mind; the RDA for protein for civilians is 45–65 g/day (Department of Health, 1991; IOM, 1997; NHMRC, 2017), whereas for military values 1.2 to 4.8 times higher than RDA for civilians were established (55–307 g/day) (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). These reasons include the need to increase intake according to the PAL category (Chapman et al., 2020; Chapman et al., 2021; Tarnopolsky et al., 2005) and, at the same time, from the perspective of preventing increased urinary calcium excretion and kidney disease due to excessive protein intake (Fouque, Laville & Boissel, 2006). In reports on athletes and sports enthusiasts, it has been argued that protein intake should be a balance between “effectiveness for high performance” and “safety to avoid the risk of kidney damage” (Marinaro, Alexander & de Waal, 2021).

Macronutrient energy distribution

For the macronutrient energy distribution, the four published DRIs for military operations (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b) had different energy ratios (%) than those for civilians (Department of Health, 1991; IOM, 1997; NHMRC, 2017; Scientific Advisory Committee on Nutrition, 2011; Scientific Advisory Committee on Nutrition, 2015) (Tables S4, S5, S6, S7 and S8). The USA and NATO recommended a balance with a high proportion of carbohydrates in high-altitude environments (Department of Defense, 2017; NATO, 2010).

Fats differed from DRI for civilians (Department of Health, 1991; IOM, 1997; NHMRC, 2017) in all four published DRIs for military operations (Table S5) (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). In Australia and the UK, DRI for civilians were used as a reference, but as the number of PALs increased, the ratio decreased for each category (Forbes-Ewan & DSTO, 2009; Scientific Advisory Committee on Nutrition, 2016b). In the USA, energy consumption was set at less than 30%; therefore, it was within the range of DRI for civilians (Acceptable Macronutrient Distribution Range; AMDR) (Department of Defense, 2017). NATO reflected the same energy ratio as DRI for civilians (NRV) (NATO, 2010).

Carbohydrate intake is important when considering optimal performance at varying levels of physical activity and within extreme environments, such as heat, cold, and high–altitude. Therefore, Australia, the UK, and the USA have set higher standards depending on PAL and environmental extremes (IOM, 1996; Rodriguez, Di Marco & Langley, 2009; Tarnopolsky et al., 2005). Accordingly, the DRI for military operations (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; Scientific Advisory Committee on Nutrition, 2016b) in these three countries was 1.0–5.2 times higher than the DRI for civilians (Table S7) (Department of Health, 1991; IOM, 1997; NHMRC, 2017; Scientific Advisory Committee on Nutrition, 2015). In NATO, the need to increase carbohydrate standards was considered in personnel with high physical activity (Tarnopolsky et al., 2005), but no changes were made to the energy ratio of carbohydrates in DRI for military operations, as an increase in the PAL category would inevitably increase carbohydrate intake without an increase in the energy ratio of carbohydrates (NATO, 2010). Therefore, NATO’s DRI (NIV) was set at approximately 1–1.7 times the NRV (NHMRC, 2017) of the DRI for civilians, lower than the standards for the other three countries (NATO, 2010).

The macronutrient energy distribution in Australia and the UK was formulated based on the DRI for civilians (Department of Health, 1991; NHMRC, 2017; Scientific Advisory Committee on Nutrition, 2015), such that as the PAL category increased, the proportion of energy from protein decreased while that from carbohydrates increased, and fat changes were minimal (Department of Defense, 2017; Scientific Advisory Committee on Nutrition, 2016b). Additionally, to prevent acute mountain sickness (Askew, 2004; IOM, 1996), Australia and NATO have established a category with a high carbohydrate ratio in high-altitude environments (Forbes-Ewan & DSTO, 2009; NATO, 2010). Hence, the energy ratio from each macronutrient should consider the PAL for optimal energy balance, with the following specific recommendations. (1) Set the intake protein weight based on the above matters; (2) The upper limit for lipids should be the energy ratio for civilians; (3) carbohydrate intake should be set to increase as PAL increases, and should be high in high-altitude environments (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b).

Dietary fiber

For dietary fiber, the same DRI was used for civilians (Department of Health, 1991; IOM, 1997; NHMRC, 2017; Scientific Advisory Committee on Nutrition, 2015) and was reflected in DRI for military operations in Australia, the UK, and NATO (Table S9) (Forbes-Ewan & DSTO, 2009; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). The USA also stated in a survey report (Department of Defense, 2017) that the DRI for civilians (IOM, 1997) was to be reflected; however, a keen analysis of the survey revealed a different adequate intake (AI) (DRI: male 30 g/day, female 21–25 g/day (IOM, 1997); MDRI: male 34 g/day, female 28 g/day (Department of Defense, 2017)). Presumably, the total carbohydrate intake has increased; thus, the recommended amount of dietary fiber has also been added.

Vitamin B₁, vitamin B₂, niacin, and vitamin B₆

For vitamin B₁, excluding Australia, the DRI for civilians (Department of Health, 1991; IOM, 1997; NHMRC, 2017) is also reflected in the DRI for military operations (Table S10) (Department of Defense, 2017; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). Australia (Forbes-Ewan & DSTO, 2009) recommends an increase in vitamin B₁ of 0.1 mg per unit of energy (MJ) rather than following the DRI for civilians (NHMRC, 2017).

For vitamin B₂, the DRI for civilians (Department of Health, 1991; IOM, 1997) was reflected in the UK and USA (Table S11) (Department of Defense, 2017; Scientific Advisory Committee on Nutrition, 2016b). Although the DRIs in Australia and NATO were based on the recommended dietary intake (RDI) for civilians (NHMRC, 2017), they were developed for each PAL category and extreme environment for military activities (Forbes-Ewan & DSTO, 2009; NATO, 2010). Australia recommended to increase vitamin B₂ by 0.15 mg per energy (MJ) (Forbes-Ewan & DSTO, 2009). In NATO (NATO, 2010), 2.5 mg/day was formulated for combat or special forces operations and in extreme environments, which is 1.9 times the NRV of the DRI for civilians (NHMRC, 2017).

The DRI for niacin for civilians (Department of Health, 1991; IOM, 1997; NHMRC, 2017) was reflected in the DRI for military operations, except in Australia (Table S12) (Department of Defense, 2017; NATO, 2010; Scientific Advisory Committee on Nutrition, 2016b). Australia recommended to increase niacin by 1.6 mg per energy (MJ) (Forbes-Ewan & DSTO, 2009).

Vitamin B₆ was formulated in Australia and NATO for each PAL category and extreme environment for military activities, although it was based on the RDI of the DRI for civilians (NHMRC, 2017) (Table S13) (Forbes-Ewan & DSTO, 2009; NATO, 2010). Australia formulated the per PAL category as 0.02 mg per g of protein (Forbes-Ewan & DSTO, 2009). In combat or special forces operations and extreme environments in NATO, (NATO, 2010) 2.6 mg/day was recommended, double the DRI for civilians (NHMRC, 2017).

Vitamin B₁, vitamin B₂, niacin, and vitamin B6 were added to the recommended amounts in Australia and NATO due to the increased energy and protein intake.

Sodium, iron, zinc, copper

Due to a lack of scientific evidence, most micronutrients reflect the same DRIs as for civilians; however, sodium has been formulated at more than twice the DRI for civilians in Australia, the USA, and NATO (Table S14) (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010). Many previous studies have reported that sodium intake affects the risk of high blood pressure and coronary heart disease (Xue et al., 2020). Therefore, in the DRI for civilians, indicators such as the upper level of intake (UL), tolerable upper intake level (UL), and lower reference nutrient intake (LRNI) have been established to set upper limits (IOM, 1997; NHMRC, 2017). However, the DRI for military operations (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010) has considered that engaging in military activities leads to increased sweating and sodium loss in sweat (IOM, 1996; Tomczak et al., 2016). The NRV of the DRIs for Australia and NATO civilians are AI 460–920 mg/day and UL 2,300 mg/day (NHMRC, 2017). The DRI for Australia military operations was increased from 920–23,00 mg/day to 920–3,200 mg/day for increasing PAL categories, with <4,600 mg/day recommended for personnel not accustomed to hot environments (Forbes-Ewan & DSTO, 2009). NATO recommended a DRI of 920 mg/day and supplementation of 1,200–4,800 mg, depending on perspiration rate, for personnel engaged in military activities during practice or operations and in extreme environments (NATO, 2010). In the USA, the UL in the DRI for civilians (2005) (IOM, 1997) was reflected in the MDRI (<2,300 mg/day) (Department of Defense, 2017). Thus, the three DRIs for military operations had formulated values that were more than twice as high, but were within the range of DRIs for civilians as the scientific evidence was still lacking and did not consider the physique and physical activity level of the military personnel (Department of Defense, 2017; Forbes-Ewan & DSTO, 2009; NATO, 2010).

Although there are limited studies on sodium requirements for military personnel, there have been reports on athletes (Baker et al., 2016; Barnes et al., 2019; Rollo et al., 2021). Barnes et al. (2019) evaluated sweat production and sodium loss in 1,303 athletes from various sports from 2000 to 2017 and reported significant differences among events in whole-body sweating rate. Individual differences were observed; however, American football, endurance sports (runners, cyclists, and triathletes), basketball, and soccer had the greatest sweat loss, respectively, and baseball players having the least. Therefore, as more research reports are accumulated, it is expected that details of the recommended amount of sodium for athletes and military personnel will be established.

For iron, zinc, and copper, the DRI of NATO alone was based on the DRI for civilians (NHMRC, 2017), while the DRI for nutrients was established based on military activities and extreme environments (Tables S15–S17) (NATO, 2010). NATO’s DRI was 1–1.83 times greater than the DRI for civilians for iron, 1–1.43 times greater for zinc, and 1–1.06 times greater for copper. For NATO, the recommended zinc (+7%), iron (+75%), and copper (+6%) intakes were higher for combat than during normal operations (NATO, 2010). They reported that sweating associated with increased physical activity would sufficiently increase sweat losses of zinc, iron, copper, and sodium to merit a compensatory increase in daily intake during combat operations.