Sex differences in dietary intake in British Army recruits

Abstract

Background:
British Army Phase One training exposes men and women to challenging distances of 13.5 km·d- 1 vs. 11.8 km·d- 1 and energy expenditures of ~ 4000 kcal·d- 1 and ~ 3000 kcal·d- 1, respectively. As such, it is essential that adequate nutrition is provided to support training demands. However, to date, there is a paucity of data on habitual dietary intake of British Army recruits. The aims of this study were to: (i) compare habitual dietary intake in British Army recruits undergoing Phase One training to Military Dietary Reference Values (MDRVs), and (ii) establish if there was a relative sex difference in dietary intake between men and women.

Method:
Researcher led weighed food records and food diaries were used to assess dietary intake in twenty-eight women (age 21.4 ± 3.0 yrs., height: 163.7 ± 5.0 cm, body mass 65.0 ± 6.7 kg), and seventeen men (age 20.4 ± 2.3 yrs., height: 178.0 ± 7.9 cm, body mass 74.6 ± 8.1 kg) at the Army Training Centre, Pirbright for 8-days in week ten of training. Macro and micronutrient content were estimated using dietary analysis software (Nutritics, Dublin) and assessed via an independent sample t-test to establish if there was a sex difference in daily energy, macro or micronutrient intakes.

Results:
Estimated daily energy intake was less than the MDRV for both men and women, with men consuming a greater amount of energy compared with women (2846 ± 573 vs. 2207 ± 585 kcal·day- 1, p < 0.001). Both sexes under consumed carbohydrate (CHO) when data was expressed relative to body mass with men consuming a greater amount than women (4.8 ± 1.3 vs. 3.8 ± 1.4 g·kg- 1·day- 1, p = 0.025, ES = 0.74). Both sexes also failed to meet MDRVs for protein intake with men consuming more than women (1.5 ± 0.3 vs. 1.3 ± 0.3 g·kg- 1·day- 1, p > 0.030, ES = 0.67). There were no differences in dietary fat intake between men and women (1.5 ± 0.2 vs. 1.5 ± 0.5 g·kg- 1·day- 1, p = 0.483, ES = 0.00).

Conclusions:
Daily EI in men and women in Phase One training does not meet MDRVs. Interventions to increase macronutrient intakes should be considered along with research investigating the potential benefits for increasing different macronutrient intakes on training adaptations.

Full text

R E S E A R C H A R T I C L E Open Access
Sex differences in dietary intake in British
Army recruits undergoing phase one
training
Shaun Chapman
1,2*
, Justin Roberts
2
, Lee Smith
2
, Alex Rawcliffe
1
and Rachel Izard
1
Abstract
Background: British Army Phase One training exposes men and women to challenging distances of 13.5 km·d
−1
vs.
11.8 km·d
−1
and energy expenditures of ~ 4000 kcal·d
−1
and ~ 3000 kcal·d
−1
, respectively. As such, it is essential that
adequate nutrition is provided to support training demands. However, to date, there is a paucity of data on
habitual dietary intake of British Army recruits. The aims of this study were to: (i) compare habitual dietary intake in
British Army recruits undergoing Phase One training to Military Dietary Reference Values (MDRVs), and (ii) establish if
there was a relative sex difference in dietary intake between men and women.
Method: Researcher led weighed food records and food diaries were used to assess dietary intake in twenty-eight
women (age 21.4 ± 3.0 yrs., height: 163.7 ± 5.0 cm, body mass 65.0 ± 6.7 kg), and seventeen men (age 20.4 ± 2.3 yrs.,
height: 178.0 ± 7.9 cm, body mass 74.6 ± 8.1 kg) at the Army Training Centre, Pirbright for 8-days in week ten of
training. Macro and micronutrient content were estimated using dietary analysis software (Nutritics, Dublin) and
assessed via an independent sample t-test to establish if there was a sex difference in daily energy, macro or
micronutrient intakes.
Results: Estimated daily energy intake was less than the MDRV for both men and women, with men consuming a
greater amount of energy compared with women (2846 ± 573 vs. 2207 ± 585 kcal·day
−1
,p< 0.001). Both sexes under
consumed carbohydrate (CHO) when data was expressed relative to body mass with men consuming a greater
amount than women (4.8 ± 1.3 vs. 3.8 ± 1.4 g·kg
−1
·day
−1
,p= 0.025, ES = 0.74). Both sexes also failed to meet MDRVs for
protein intake with men consuming more than women (1.5± 0.3 vs. 1.3 ± 0.3 g·kg
−1
·day
−1
,p> 0.030, ES = 0.67). There
were no differences in dietary fat intake between men and women (1.5 ± 0.2 vs. 1.5 ± 0.5 g·kg
−1
·day
−1
,p=0.483,
ES = 0.00).
Conclusions: Daily EI in men and women in Phase One training does not meet MDRVs. Interventions to increase
macronutrient intakes should be considered along with research investigating the potential benefits for increasing
different macronutrient intakes on training adaptations.
Keywords: Dietary intake, Military, Sex differences, Exercise training
© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
* Correspondence: shaun.chapman101@mod.gov.uk
1
HQ Army Recruiting and Initial Training Command, UK Ministry of Defence,
Upavon, UK
2
Cambridge Centre for Sport and Exercise Sciences, School of Psychology
and Sport Science, Anglia Ruskin University, East Road, Cambridge CB1 1PT,
England
Chapman et al. Journal of the International Society of Sports Nutrition
(2019) 16:59
https://doi.org/10.1186/s12970-019-0327-2

Introduction
British Army standard entry Phase One training is a 14-
week training syllabus that includes physical training, field
exercises and training on a variety of military-specific skills
including load carriage, marching, military drill and
weapon and equipment handling [1]. It is characterised by
high rates of injury and medical discharge (MD) [1–3]. In
Phase One training the overall rate of injury is 0.07 people
injured per 100 person-days and that the overall MD rate
is 0.02 people injured per 100 person-days [2]. Recruits are
exposed to high daily training loads and energy expendi-
tures (EE) which, without adequate nutrient provision, may
contribute to a reduction in mood state [4] compromised
physical performance, increased musculoskeletal injury
(MSKi) risk [5,6] and medical discharge (MD). Estimated
daily EE and training distance covered in Phase One train-
ing in men has been reported to be ~ 4000 kcal and 13.5 ±
6.6 km and in women was ~ 3000 kcal and 11.8 ± 4.9 km
for men and women, respectively [1]. Women are at
greater risk of MSKi during British Army Phase One train-
ing and this is supported by evidence that demonstrates
women to be 2–3 times at greater risk of injury [2]. The in-
creased risk is not due to sex differences per se but likely
due to lower aerobic fitness levels in women, resulting in
higher internal load [1,2,7]. Therefore, women may re-
quire additional dietary support, such as energy and/or
protein intake, to facilitate skeletal muscle repair and sup-
port the higher training load compared to men [1]. To
date, however, there is no suggestion that separate protein
intakes should be recommended for men and women. To
maintain muscle mass, strength and performance during
periods of substantial metabolic demands and concomitant
negative energy balance it is recommended a protein intake
of at least 1.5 g·kg
−1
·d
−1
is consumed [8].
In response to a similar training load women have been
shown to have greater fatigue resistance and maintenance
of muscle function to men [9]. Following a loaded march
during British Army training, men had a greater loss in
maximal voluntary contractions (MVC) of the knee exten-
sors than women (12 ± 9% vs. 9 ± 13%, p= 0.03). The au-
thors suggested that this may have been due to woman
possessing a greater proportion of type 1 muscle fibres in
the knee extensor muscles. Nevertheless, the MVC and
vertical jump height of men following load carriage was
still higher than the pre-exercise values for the women
and therefore, muscle performance rather than fatigability
per se, may contribute to the sex difference in injury inci-
dence [2,9]. The higher baseline values in the men per-
haps allows for greater degradation [9]. Therefore, the
lower baseline values in the women may indicate a re-
quirement for nutritional interventions to enhance skeletal
muscle recovery. Women may also require other dietary
interventions to support training, particularly as recent
evidence has shown women to under consume various
micronutrients such as iron and calcium, during military
training by 77 and 75%, respectively [10].
Dietary intake should match energy expenditure to
maintain health and performance and evidence to support
this has been extensively reviewed [11–13]. Specifically, an
inadequate energy intake (EI) is harmful to performance
[4], bone health [5,14,15], immune function [16], cogni-
tion [17], mood [4] and MSKi risk [5]. It has therefore
been recommended to consume 3100–4100 kcal·d
−1
,spe-
cific to Phase one training [18]. Moreover, a negative en-
ergy balance of > 500 kcal·d
−1
is detrimental to health in
the longer term. It has been shown that an energy deficit
of this magnitude suppresses the hormone milieu, reduces
thyroid function and reduces exercise performance by
9.8% [19]. Reduced thyroid function is of particular con-
cern in military populations due to the suppression on
bone formation markers and subsequent risk of a stress
fracture [20]. In a crossover study, endurance trained run-
ners undergoing an intense 11-day training programme
whilst habitually consuming a diet lower in CHO (5.4
g·kg
−1
·d
−1
) experienced a greater deterioration in global
mood scores, than when consuming a diet with a higher
CHO content (8.5 g·kg
−1
·d
−1
)[4]. In military populations
it is generally found that soldiers fail to meet recom-
mended energy and nutrient intakes [10,21–27]. McA-
dam et al. (2018) found that recruits undergoing Basic
Training in the United States (U.S.) experienced a 595±
896 kcal·d
−1
deficit and 70% of recruits consumed less
than the lower limit (6 g·kg
−1
·d
−1
) for recommended
carbohydrate intake (CHO). Given the large standard de-
viation for energy intake (896 kcal·d
−1
)somerecruits
would have been in a larger energy deficit across the train-
ing phase. It is possible that this deficit was underesti-
mated due to the use of an accelerometer to quantify EE.
Energy expenditure was estimated via an Actigraph
wGT3X monitor using the Sasaki equation which has
been shown to have a mean bias of −0.23 compared to in-
direct calorimetry [28]. It is also possible that EI was also
underestimated due to an acute food diary collection
period being used for analysis [29]. In the United King-
dom (UK), the Scientific Advisory Committee on Nutri-
tion (SACN) have developed Military Dietary Reference
Values (MDRVs) for British Army recruits [18], but no
study has yet quantified dietary intake to establish if these
are habitually met.
The aim of this study was therefore to quantify energy,
macro and micronutrient intake of British Army recruits
to determine if these were adequate compared to MDRVs
and Recommended Daily Allowances (RDA). A secondary
aim was to compare dietary intake between sexes to estab-
lish if future dietary interventions during training needed
to be sex specific. Based on other studies in military popu-
lations, we hypothesized that men and women would not
meet MDRVs for energy intake and that women would be
Chapman et al. Journal of the International Society of Sports Nutrition (2019) 16:59 Page 2 of 9

at greater risk of nutrient deficiency compared to men
due to a lower energy intake. The findings of this investi-
gation will provide novel data into the nutritional intake
of British Army recruits in Phase One training. This data
may be used to inform future interventions aimed at im-
proving nutrient intake in this population during British
Army training.
Materials/ methods
Ethical approval
This study was approved by the U.K. Ministry of Defence
Research Ethics Committee (MODREC). For inclusion, re-
cruits at the Army Training Centre Pirbright (ATC(P)),
Surrey, UK in week ten of training, were invited to take
part. Interested participants received verbal explanation of
the study from the research team and provided written in-
formed consent. Twenty-eight women (mean ± SD: age
21.4 ± 3.0 yrs., height: 163.7 ± 5.0 cm, body mass 65.0 ± 6.7
kg, body mass index: 24.2 ± 2.6 kg·m
2
) and seventeen men
(mean ± SD: age 20.4 ± 2.3 yrs., height: 178.0 ± 7.9 cm,
body mass 74.6 ± 8.1 kg, body mass index: 22.5 ± 1.7
kg·m
2
) volunteered for this study, which was conducted in
accordance with the declaration of Helsinki.
Study design
This was an observational cross-sectional study over an
8-day period. Sample size was based on a priori power
analysis using G*power (v3.1.9.2, Dusseldorf) based on
previously collected energy intake data in the literature
[26]. It was determined that 24 participants (12 men and
12 women) were required to replicate the highest signifi-
cant effect size of 1.05 for a between-sex difference in
energy intake using α= 0.05, β= 0.80. Participant demo-
graphics were collected on day one and diet analysis was
collected on each day (days 1 to 8).
Physical characteristics
Height (cm) and body mass (kg) were recorded with re-
cruits wearing Army uniform except for boots using a
seca 213 mobile stadiometer and pre-calibrated seca flat
scales (Hamburg, Germany).
Diet logs
Dietary intake was recorded using researcher-led food
weighing at breakfast, lunch and dinner in the training
centre dining facility. On arrival, participants chose their
food and each portion was weighed using pre-calibrated
food scales (Salter, 1066 BKDR15, Kent, UK). After each
meal, participants were instructed to leave food discards
so that these could also be weighed and subtracted from
the original weight; to give the actual food portion con-
sumed for that meal [30]. To capture dietary intake be-
tween meals and off-camp, participants completed food
diaries following guided instructions and estimated the
portion size using practical measures (1 cup, 2 handfuls,
1 palm size etc.) [29] and kept any snack or ration dis-
cards in discard bags to cross examine against food diar-
ies. Participants were briefed on how to accurately
complete a food diary and these were then checked by a
member of the research team each day to clarify any un-
clear information.
Nutritics analysis
Food records were entered into nutritional analysis soft-
ware (Nutritics, Dublin, Ireland) for the generation of
mean daily energy, macronutrient and micronutrient in-
takes using the UK Scientific Advisory Committee on
Nutrition (SACN) database. The recipes of foods which
did not already exist in the database (i.e. ration pack
foods) were manually entered using the recipe or nutri-
tional content information provided by the caterer. All
data was inputted by the same researcher to reduce data
processing variability [31].
Data presentation and statistical analysis
Physical characteristics and mean nutrient intakes were
compared between sexes using an independent samples
t-test. Prior to this, dietary intake data was tested for
normality using a Shapiro-Wilks test (IBM SPSS v24).
Where data showed a significant deviation from a nor-
mal distribution, a non-parametric equivalent (Mann
Whitney U test) was used. Cohen’s d effects (small = 0.2,
medium = 0.5, large = 0.8) were calculated for differences
in nutrient intakes between men and women. Following
an appropriate Bonferroni adjustment, an alpha level of
p< 0.001 was set.
Results
Physical characteristics
There was a statistically significant difference between
sexes in stature (t [22]= 6.521, p= < 0.001) and body
mass (t [32]= 3.920, p= < 0.001) but not age (Z = −
1.126, p= .260) or BMI (t [32]= −1.224, p= 0.228).
Energy intake
There was a statistically significant difference between
sexes with men consuming more than women (t [32]=
3.508, p= 0.001, ES = 1.10). Both men and women con-
sumed less than the MDRVs, with men consuming 69%
and women consuming 72% of the recommended energy
intake (Table 2). When data was expressed as relative to
body there was no differences in energy intake between
sexes (t [32]=1.396, p= 0.170, ES = 0.46) (Table 2).
Macronutrient intake
Compared to the MDRVs, men and women under con-
sumed CHO and protein with men consuming a greater
absolute total daily amount of CHO than women (Z = -
Chapman et al. Journal of the International Society of Sports Nutrition (2019) 16:59 Page 3 of 9

3.708, p< 0.001, ES = 1.27). Men also consumed a greater
total daily amount of protein than women (Z = -3.708, p <
0.001, ES = 1.28). Total fat intake was not different between
sexes t [32]=1.113, p= 0.272, ES = 0.37) but under con-
sumed by men. Men consumed a greater amount of fibre
than women (t [32]=2.422, p= 0.020, ES = 1.16) (Table 1).
When data was expressed relative to body mass there was
no difference between sexes for CHO (t [32]=2.333, p=
0.025, ES = 0.74), protein (t [32]=2.241, p=0.030, ES=
0.67), fat (t [32]= −0.708, p= 0.483, ES = 0.00) or fibre in-
take (t [32]=0.840, p= 0.406, ES = 0.00) (Table 2).
Micronutrient intake
When compared to men, women consumed less calcium
(t [32]= 3.645, p= 0.001, ES = 1.06),iron (t [32]=4.262, p<
0.001, 1.18), sodium (t [32]=2.700, p= 0.010, ES = 0.77),
vitamin B
6
(Z = -3.123,p= 0.002, ES = 0.91), vitamin B
12
(Z = -3.477,p= 0.001, ES = 1.11), potassium (Z = -2.537,
p= 0.011, ES =0.86), niacin (Z = -4.062, p<0.001,ES=
1.42), iodine (Z = -2.733, p= 0.006, ES = 0.91), thiamine
(Z = -2.355, p= 0.010), riboflavin (Z = -3.576, p<0.001,
ES = 0.97), phosphorus (Z = -2.976, p= 0.003, ES = 0.97)
and folate (Z = -3.391, p= 0.001, ES = 1.17). Men and
women consumed less than the RDA for copper, magne-
sium and vitamin D with women consuming significantly
less magnesium (Z = -2.464, p= 0.014, ES = 0.84) and vita-
min D (Z = -2.257, p= 0.024, ES = 1.00) but not copper (t
[32]=1.035, p= 0.306, ES = 0.47). Women consumed an
inadequate amount of vitamin A when compared to the
RDA and this was significantly less than men (Z = -2.562,
p= 0.010, ES = 0.84). Both men and women consumed ad-
equate amounts of vitamin C when compared to the RDA
with no differences between sexes (Z = -1.049, p=0.294,
ES = 0.45). When micronutrient data was expressed rela-
tive to body mass there was no difference for iron (t [32]=
2.468, p= 0.18, ES = 0.75), calcium (t [32]=2.28, p=0.027,
ES = 0.71), magnesium (t [32]=1.513, p= 0.138, ES = 0.46),
vitamin A (t [32]=1.808, p= 0.078, ES = 0.58), vitamin C (t
Table 1 Absolute nutrient intake for participants compared to MDRVs and RDA
Nutrient All Men MDRV Women MDRV
Energy (kcal·day
−1
) 2439 ± 653 2846 ± 573* 4100.0 2207 ± 585* 3100.0
CHO (g·day
−1
) 283 ± 98 352 ± 92* 513–615 243 ± 79* 388–465
PRO (g·day
−1
) 94 ± 27 114 ± 29 123–154 83 ± 18 93–116
Fat (g·day
−1
) 103 ± 25 109 ± 21 128–159 100 ± 27 96–121
Fibre (g·day
−1
) 20±6 23±5 30 18±1 30
Calcium (mg·d
−1
) 837.0 ± 383.0 1078.0 ± 418.0* 700.0 699.0 ± 287.0* 700.0
Copper (mg·d
−1
) 0.9 ± 0.3 1.0 ± 0.0 1.2 0.9 ± 0.3 1.2
Folate (μg·d
−1
) 173.0 ± 84.0 231.0 ±95.0* 200.0 140.0 ± 55.0* 200.0
Iodine (μ·d
−1
) 99.0 ± 64.0 135.0 ± 79.0 140.0 77.0 ± 44.0 140.0
Iron (mg·d
−1
) 8.7 ± 3.0 10.0 ± 3.0* 8.7 7.0 ± 2.0* 14.8
Magnesium (mg·d
−1
) 198.0 ± 77.0 239.0 ± 94.0 300.0 174.0 ± 55.0 270.0
Niacin (mg·d
−1
) 14.8 ± 6.3 19.9 ± 7.3* 16.5 12.0 ± 3.0* 13.2
Phosphorus (mg·d
−1
) 997.0 ± 382.0 1227.0 ± 461.0 550.0 865.0 ± 254.0 550.0
Potassium (mg·d
−1
) 2386.0 ± 877.0 2859.0 ± 1051.0 3500.0 2115.0 ± 634.0 3500.0
Riboflavin (mg·d
−1
) 1.1 ± 0.7 1.6 ± 0.8* 1.3 0.8 ± 0.4* 1.1
Selenium (μg·d
−1
) 39.0 ± 21.0 57.0 ± 25.0 75.0 29.0 ± 11.0 60.0
Sodium (g·d
−1
) 2.7 ± 0.7 3.0. ± 0.6 2.4 2.5 ± 0.7 2.4
Thiamin (mg·d
−1
) 1.3 ± 0.5 1.5 ± 0.5 1.0 1.1 ± 0.3 0.8
Vitamin A (μg·d
−1
) 634.0 ± 410.0 840.0 ± 388.0 700.0 516.0 ± 380.0 600.0
Vitamin B
12
(μg·d
−1
) 4.3 ± 2.6 6.0 ± 3.2* 1.5 3.3 ± 1.3* 1.5
Vitamin B
6
(mg·d
−1
) 1.5 ± 0.9 2.0 ± 1.2 1.4 1.2 ± 0.3 1.2
Vitamin C (mg·d
−1
) 55.0 ± 38.0 67.0 ± 49.0 40.0 49.0 ± 29.0 40.0
Vitamin D (μg·d
−1
) 2.0 ± 1.0 2.0 ±1.0 10.0 1.0 ± 1.0 10.0
Zinc (mg·d
−1
) 7.1 ± 2.5 8.0 ± 3.0 9.5 6.0 ± 1.0 7.0
Energy, macronutrient and micronutrient intake of all participants and with data grouped according sex to establish differences in intakes. Intakes for each sex
were then compared to recommendations. The recommended MDRV for CHO, protein and fat towards total energy intake is 50-60%, 12-15% and 28-35%,
respectively. These values were used to calculate the absolute amount of CHO, protein and fat needed to achieve the required energy intake in men (4100
kcal·d
-1
) and women (3100 kcal·day
-1
). EI Energy intake , MDRV Military Dietary Reference Value , CHO Carbohydrate , grams·body mass
-1
·day
-1
(g·kg
-1
·d
-1
),
milligrams·day
-1
(mg·d
-1
) and micrograms·day
-1
(μg·d
-1
). *indicates a statistically significant differecnce between sexes
Chapman et al. Journal of the International Society of Sports Nutrition (2019) 16:59 Page 4 of 9

[32]=0.289, p= 483, ES = 0.21), vitamin B
12
(t [42] = 3.043,
p= 0.004, ES = 0.95), phosphorus (t [32]=1.913, p=0.063,
ES = 0.58), potassium (t [32]=1.584, p= 0.121, ES = 0.48),
selenium (t [19.791] = 3.351, p= 0.003, ES = 1.11), sodium
(t [32]=0.733, p= 0.468, ES = 0.00), zinc (t [32]=0.2130,
p= 0.039, ES = 0.57), iodine (t [32]=2.228, p=0.031, ES=
0.67), niacin (t [20.989] = 3.249, p= 0.004, ES = 1.10), fol-
ate (t [32]=2.756, p= 0.009, ES = 0.70), vitamin D (Z = −
1.786, 0.074, ES = 0.00), vitamin B
6
(Z = -1.837, p=0.066,
ES = 0.63), copper (Z = -0.266, p= 0.790, ES = -0.45),
thiamine (Z = -1.102, p= 0.271, ES = 0.00) or riboflavin (Z
=−2.807, p= 0.005, ES = 0.57) (Table 2).
Discussion
The aim of this study was to quantify daily energy, macro
and micronutrient intake of British Army recruits in Phase
One training and to compare intakes between men and
women. Our primary finding was that men and women
under consumed daily energy intake by ~ 1200 and ~ 800
kcal·d
−1
, respectively when compared to MDRVs. The
MDRVs are based on measurements of daily energy ex-
penditures via the doubly labelled water method in a simi-
lar cohort within this population whilst undertaking the
same programme in British Army Phase One training
[18]. The reported underconsumption of daily energy in-
take in this population observed in this study is typical of
military populations and values estimated here are similar
to other research [21,23,25–27]. The observed under
consumption of total calories in this study, meant that re-
cruits did not meet MDRV and RDAs for specific macro
and micronutrients. Furthermore, due to a lower daily en-
ergy intake of women compared to men, and higher RDA
for some micronutrients (i.e. iron), women are at greater
risk of inadequate intakes when compared to guidelines
and need to increase habitual iron intake by ~ 53% to
meet the RDA of 14.8 mg·d
−1
(Table 1).
Energyintakeofmenandwomeninthisstudywasinad-
equate when compared to MDRVs (Table 1)andthismay
increase the incidence of reduced energy availability [33]
which, in turn, may in increase the risk of injury [5,14].
Table 2 Relative daily nutrient intakes for participants compared to MDRVs/RDA and Sport Nutrition guidelines
Nutrient All Men MDRV Women MDRV
Energy (kcal·kg
−1
·d
−1
) 35.7 ± 9.5 38.3 ± 7.3 55.0 34.2 ± 10.3 48.0
CHO (kcal·kg
−1
·d
−1
) 4.1 ± 1.4 4.8 ± 1.3 6.0–8.0 3.8 ± 1.4 6.0–7.0
PRO (kcal·kg
−1
·d
−1
) 1.4 ± 0.4 1.5 ± 0.3 1.6–2.0 1.3 ± 0.3 1.4–1.8
Fat (kcal·kg
−1
·d
−1
) 1.5 ± 0.4 1.5 ± 0.2 1.7–2.1 1.5 ± 0.5 1.5–1.9
Fibre (kcal·kg
−1
·d
−1
) 0.3 ± 0.1 0.3 ± 0.1 0.4 0.3 ± 0.1 0.5
Calcium (mg·kg
−1
·d
−1
) 12.17 ± 5.18 14.43 ± 5.21 9.38 10.88 ± 4.78 10.80
Copper (mg· kg
−1
·d
−1
) 0.01 ± 0.01 0.01 ± 0.01 0.02 0.02 ± 0.01 0.02
Folate (μg· kg
−1
·d
−1
) 2.50 ± 1.12 3.08 ± 1.19 2.68 2.18 ± 0.95 3.08
Iodine (μg· kg
−1
·d
−1
) 1.44 ± 0.91 1.83 ± 1.06 1.88 1.22 ± 0.74 2.15
Iron (mg· kg
−1
·d
−1
) 0.12 ± 0.04 0.15 ± 0.04 0.12 0.12 ± 0.04 0.23
Magnesium (mg·kg
−1
·d
−1
) 2.90 ± 1.07 3.22 ± 1.21 4.02 2.72 ± 0.96 4.15
Niacin (mg· kg
−1
·d
−1
) 0.41 ± 0.15 0.51 ± 0.17 0.22 0.36 ± 0.09 0.20
Phosphorus (mg·kg
−1
·d
−1
) 14.54 ± 5.18 16.46 ± 5.89 7.37 13.45 ± 4.48 8.46
Potassium (mg· kg
−1
·d
−1
) 34.74 ± 11.86 38.42 ± 13.70 46.91 32.63 ± 10.35 53.85
Riboflavin (mg· kg
−1
·d
−1
) 0.02 ± 0.01 0.02 ± 0.01 0.02 0.01 ± 0.01 0.02
Selenium (μg· kg
−1
·d
−1
) 0.57 ± 0.29 0.77 ± 0.35 1.00 0.46 ± 0.18 0.92
Sodium (g· kg
−1
·d
−1
) 0.04 ± 0.01 0.04 ± 0.01 0.03 0.04 ± 0.01 0.04
Thiamin (mg· kg
−1
·d
−1
) 0.02 ± 0.01 0.02 ± 0.01 0.01 0.02 ± 0.01 0.01
Vitamin A (μg· kg
−1
·d
−1
) 9.25 ± 5.94 11.34 ± 5.12 9.38 8.05 ± 6.13 9.23
Vitamin B
12
(μg·kg
−1
·d
−1
) 0.06 ± 0.04 0.08 ± 0.04 0.02 0.05 ± 0.02 0.02
Vitamin B
6
(mg· kg
−1
·d
−1
) 0.02 ± 0.01 0.03 ± 0.02 0.02 0.02 ± 0.01 0.02
Vitamin C (mg·kg
−1
·d
−1
) 0.81 ± 0.54 0.89 ± 0.62 0.54 0.77 ± 0.49 0.62
Vitamin D (μg· kg
−1
·d
−1
) 0.03 ± 0.02 0.03 ± 0.02 0.13 0.03 ± 0.02 0.15
Zinc (mg· kg
−1
·d
−1
) 0.10 ± 0.03 0.12 ± 0.04 0.13 0.10 ± 0.03 0.11
Daily nutrient intakes of all participants with data separated for sex to establish relative differences. Data was compared to recommendations. Military dietary
reference values (MDRVs) were used for energy, macro and micronutrient intake recommendations. Recommended relative intakes were calculated by dividing
the recommended absolute intake by the average body mass for each sex. Data presented as mean ± standard deviations. No statistically significant differences
between sexes were observed.
Chapman et al. Journal of the International Society of Sports Nutrition (2019) 16:59 Page 5 of 9

Reduced chronic energy availability may lead to impaired
physiological functions such as metabolic rate, protein syn-
thesis, bone health, menstrual function and cardiovascular
health [33]. Musculoskeletal injury risk (MSKi) may be in-
creased during periods of reduced energy availability with
concomitant reductions in skeletal muscle mass are ob-
served due to reduced protein turnover [34,35]Further-
more, skeletal muscle response to the training stimulus
maybe downregulated during periods of reduced energy
availability. For example, a daily energy surplus of ~ 358–
478 kcal·d
−1
is recommended to maximise muscle hyper-
trophy with resistance training [36]. Energy restriction has
been shown to downregulate mTOR signalling activity and
this is likely due to the inhibited protein translation and
subsequently lower phosphorylation of protein kinase B
(AKt), the mammalian target of rapamycin (mTOR), ribo-
somal protein S6 kinase (P70S6K) and ribosomal protein
S6 (rps6) [37]. An energy deficit of ~ 40% upregulates
mRNA of the skeletal muscle ubiquitin proteasome system
(UPS) which regulates skeletal muscle proteolysis [38]. Our
data demonstrates men and women consumed adequate
energy to prevent an estimated deficit vs. the MDRVs of
≤40% and consumed ~ 31% and ~ 29% less than the
MDRVs, respectively, which may still be considered as a
considerable energy deficit. In relation to bone health, re-
duced energy availability reduces calcium absorption,
bone turnover and bone mineral density [5], and thus,
increases stress fracture risk [39] with women appear-
ing to be more affected than men [40]. Furthermore, a
reduced energy availability will increase the risk of in-
adequate supply of macro and micronutrients, which
will likely impair physical performance and increase the
risk of injury further [6].
Men and women both consumed less than the mini-
mum recommended intake for CHO compared to
MDRVs (Table 1-2). These results are similar to intakes
of U.S. Army personnel, which found ~ 70% of personnel
consumed less than 6 g·kg
−1
·d
−1
carbohydrate [27].
Given that participants undergoing Phase One training
have energy expenditures between ~ 3000 to ~ 4000
kcal·d
−1
[1] which is comparable to athletes in team
sports [41] it may be appropriate to aim for similar
CHO intakes per day (5–7 g·kg
−1
·d
−1
)[42]. As such,
British Army recruits may not be maintaining muscle
glycogen stores to support training. Lower intakes of
CHO during intensified training periods have been
shown to reduce exercise performance and mood state
in athletes [4] and contribute to immunosuppression
[32]. Sub-optimal intakes of CHO during hard training
periods in athletes, increases concentrations of cortisol
whilst attenuating the secretion of immunoglobin-A
(SlgA), and thus, increases the risk of contracting an
upper respiratory tract infection [32,43]. Taken to-
gether, CHO intakes below recommended intakes whilst
undergoing military training may result in missed train-
ing days and possibly failure to complete training due to
increased illness and injury risk. Future research should
assess the effects of additional CHO intake on training
outcomes, illness and injury incidence. Furthermore, re-
search investigating the impact of nutrient timing in this
population is also warranted given the influence this
may have on recovery, tissue repair, muscle protein syn-
thesis and psychological mood [44]. It has been shown
that British Army officer cadets may under consume
suboptimal levels of CHO and protein between meal-
times [45] but data in the recruit population is currently
lacking.
Protein intakes in men and women were less than the
MDRVs but were in-line with sport nutrition guidelines
(1.2–2.0 g·kg
−1
·d
−1
)[12] although women did have a
lower relative intake than men (Table 2). To date, how-
ever, specific protein intakes are not recommended for
British Army recruits. Intakes in the range of 1.2–2.0
g·kg
−1
·d
−1
are recommended in athletes to support
metabolic adaptation, repair, remodelling, and for pro-
tein turnover [12]. Despite both sexes meeting this range
in this study, it should be noted that intakes were at the
lower end of this, and that true protein requirements
may be at the upper limit of this range to meet training
demands (1.5–2.0 g·kg
−1
·d
−1
). In fact, evidence now sug-
gests endurance athletes require more than the original
recommended intake of 1.2–1.4 g·kg
−1
·d
−1
and instead
should consume 1.6–1.8 g·kg
−1
·d
−1
on intense training
days [46]. Given the arduous nature of military training
and that military type exercise (i.e. load carriage) stimu-
lates muscle protein synthesis more than endurance type
exercise (i.e. running) [47], military personnel may re-
quire a daily protein intake of ≥1.5 g·kg
−1
[8]. Further-
more, intakes of > 2.0 g·kg
−1
during energy restriction
may be needed to maximise the loss of fat-mass whilst
also maintaining lean-tissue mass [13]. A protein intake
higher than that observed in the current study has been
shown to have physiological and performance benefits
[48–50]. A protein intake of 3.0 g·kg·
−1
d
−1
resulted in a
30% possibility that the decrement in time trial perform-
ance pre-and-post the intervention was attenuated vs. a
moderate protein intake (1.5 g·kg
−1
·d
−1
)[49]. U.S. Marines
who were supplemented daily with protein (12 g protein,
9.6 g CHO, 3.6 g fat) for 54-days had 14% fewer visits to the
medical centre compared to the placebo group (0 g protein,
9.6 g CHO, 3.6 g fat) and 40% less visits to the medical
centre compared to the control group [48]. More recently,
U.S. Army soldiers participating in Initial Entry Training
who supplemented daily with whey protein (77 g, 580 kcal)
had a greater reduction of fat-mass (−4.5 kg, Cohen’sd=−
0.67 vs. -2.7 kg, Cohen’sd=−0.40) compared to a group
who supplemented daily with CHO (127 g, 580 kcal). The
total daily protein intake was 2.8 g·kg
−1
·d
−1
in the protein
Chapman et al. Journal of the International Society of Sports Nutrition (2019) 16:59 Page 6 of 9

group, which is far greater than both men and women in
the current study (Table 2)[50]. An increased protein in-
take > 1.5 g·kg
−1
·d
−1
may also have psychological benefits.
Endurance trained cyclists undergoing three weeks of high-
intensity training had a 97% chance that a higher protein
intake (3 g·kg
−1
·d
−1
) attenuated increased symptoms of
stress compared to a moderate protein intake (1.5 g·kg
−1
·d
−
1
) when participants were weight stable and when CHO in-
take was matched between conditions (6 g·kg
−1
·d
−1
)[49].
This provides the rationale that protein intake should
be considered in relation to other functions other
than muscle protein synthesis and that a daily protein
intake > 1.5 g·kg
−1
may provide psychological benefits
to individuals undergoing intense training (i.e. military
training). Given the apparent benefits on increasing
dietary protein to > 2.0 g·kg
−1
·d
−1
in periods of ardu-
ous training, it should be investigated if an additional
protein intake to that of habitual intakes in British
Army recruits in Phase One training influences train-
ing adaptions and training outcomes.
The total micronutrient intake data for the cohort
showed that there was an inadequate intake of magne-
sium, vitamin D, potassium, selenium, copper, iodine
and folate (Table 1-2). Similarly, data collected in men
and women during Basic Combat Training in the U.S.
Army showed an inadequate intake of vitamin D, mag-
nesium and potassium with women under consuming
calcium and iron [10]. Given the reported intake of
calcium (699 ± 287 mg·d
−1
) and iron (7 ± 2 mg·d
−1
)in
women in this study, the risk of an inadequate intake of
these micronutrients in this population is highlighted.
Previously, it has been observed that training increase
bone mineral content (BMC) and bone mineral density
(BMD) of the arms, legs and pelvis in men and women
undergoing the same training course at ATC(P). Con-
versely, it was observed training reduced BMC for the
trunk and ribs and BMD for the ribs in both men and
women (unpublished observations). These changes in
BMD and BMC may be explained by habitual calcium
intakes (837 ± 383 mg·d
−1
) with some consuming less
than the RDA as shown by the reported standard devi-
ation. Furthermore, it has previously been reported that
only 9% of men and 36% of women entering Phase one
training are vitamin D sufficient [51]. Given the inad-
equate intake of vitamin D and calcium, it should be in-
vestigated if increasing the intake of these micronutrients
benefits training outcomes. For instance, female U.S. Navy
recruits undergoing basic training who supplemented
daily with 2000mg calcium and 800IU vitamin D had a
21% reduction in stress fracture incidence compared to a
control group [52]. It is unknown, however, if the reduc-
tion was due to an increased calcium or vitamin D intake.
The low habitual intake of iron in women compared to
the RDA (Table 1-2) is comparable to that of their U.S.
Army counterparts [10]. British Army training appears to
have a deleterious effect on iron status with ferritin and
haemoglobin decreasing significantly pre and post Phase
One training in men and women. Ferritin has been shown
to reduce from 105.1 to 78.7 μg·L
−1
in men and from 52.7
to 47.7 μg·L
−1
in women. Haemoglobin has been shown
to reduce from 149.7 to 147.1 g·dL
−1
in men and from
139.2 to 132.1 g·dL
−1
in women in 14 weeks of training.
These changes in iron status contributed to a 6.9 and 2.3%
development of anaemia in women and men, respectively
[53]. As such, research investigating iron requirements
and the potential benefits of iron supplementation in
British Army recruits undergoing Phase One training may
be warranted. It is possible that recruits may require 70%
more than the RDA [12]. For example, similar to athletes,
British Army recruits who engage in regular exercise in-
crease hepcidin levels which then inhibits iron absorption
and contributes to a decrease in iron status [54]. There-
fore an intervention may be to increase dietary iron intake
particularly during periods not in close proximity to exer-
cise to promote iron absorption and thus iron status [12].
Conclusion
EnergyintakeinmenandwomeninBritishArmyPhase
One training is inadequate when compared to MDRVs.
When considered to MDRVs, men and women both under
consume CHO and protein and therefore interventions to
combat this should be considered. Given this and the po-
tential benefits of increasing protein intakes above 1.5
g·kg
−1
·d
−1
in military populations, future research investi-
gating this should be explored. Furthermore, research aim-
ing to better understand habitual protein requirements
may be warranted. Given the low vitamin D intakes in both
sexes and low iron and calcium intakes in women, research
investigating the effects of micronutrient supplementation
on training outcomes is needed. Finally, research which in-
vestigates changes in habitual dietary intake during Phase
Onetrainingshouldbeconsideredaswellasdataonthe
timing of daily energy and macronutrients intakes due to
the potential effects on training adaptations and the impli-
cations of nutritional based interventions.
Abbreviations
Akt: Protein kinase B; ATC(P): Army training centre pirbright; BMC: Bone
mineral content; BMD: Bone mineral density; CHO: Carbohydrate; EE: Energy
expenditure; EI: Energy intake; Kcal: Kilocalorie; LBM: Lean body mass;
MD: Medical discharge; MDRV: Military dietary reference values;
MODREC: Ministry of defence research ethics committee; MRNA: Messenger
RNA; MSKi: Musculoskeletal injury risk; mTOR: Mammalian target of
rapamycin; P70S6K: Ribosomal protein S6 kinase; RDA: Recommended daily
allowance; rps6: Ribosomal protein S6; SACN: Scientific advisory committee
on nutrition; SD: Standard deviation; SIgA: Secretory immunoglobulin A;
U.K.: United Kingdom; U.S.: United States
Acknowledgements
The authors would like to acknowledge Miss Louise Corfield, Miss Bethan
Moriarty, Mr. Luke Davies and Mr. Alfie Gordon for their assistance with
Chapman et al. Journal of the International Society of Sports Nutrition (2019) 16:59 Page 7 of 9

participant recruitment and data collection. As well as the training staff and
recruits who volunteered to take part.
Authors’contributions
SC and RI designed the study. SC and AR recruited participants and
conducted data collection. SC and AR undertook analysis of all data. SC, JR
and LS interpreted the data. SC wrote the paper. All authors reviewed and
approved the final manuscript.
Funding
This study was funding by the Army Recruiting and Initial Training
Command, U.K. Ministry of Defence.
Availability of data and materials
Datasets used and/or analysed during the study are available from the
corresponding author in reasonable request.
Ethics approval and consent to participate
This study was conducted in accordance with the declaration of Helsinki and
was approved by the United Kingdom Ministry of Defence Ethics Committee
(843/MODREC/18). Written informed consent was provided by all individual
participants in this study.
Consent for publication
Not applicable
Competing interests
There are no competing interests from the authors.
Received: 30 August 2019 Accepted: 26 November 2019
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