Changes in gut hormones and leptin in military personnel during

operational deployment in Afghanistan

Neil Hill1,2, Joanne Fallowfield3, Simon Delves3, Christian Ardley1, Michael Stacey1,2, Mohammad

Ghatei2, Stephen Bloom2, Gary Frost2, Stephen Brett2, Duncan Wilson1, Kevin Murphy2

1. Royal Centre for Defence Medicine, Birmingham, UK

2. Imperial College London, London, UK

3. Institute of Naval Medicine, Alverstoke, Hampshire, UK

Running Head: Gut hormones in deployed military personnel

Corresponding author and person to who reprints should be addressed: Dr Neil Hill

Email: n.hill@imperial.ac.uk

Address: Section of Investigative Medicine, 6th Floor, Commonwealth Building, Imperial College

London, Du Cane Road, London, W12 0NN

Telephone: +44 7989501465

Fax: +44 208 383 8320

Word count: 3451

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What is already known about this subject?  

Loss of appetite and body mass in military personnel on operational deployment or exercise is a

widely recognized but poorly understood phenomenon.

 

Appetite regulation is determined by a complex neuroendocrine system that signals between the

gastrointestinal tract, adipose tissue and specific brain regions.

 

Identifying the mechanisms of weight loss in deployed military personnel may suggest new targets for

obesity treatments.

 

What does this study add? 

 

Changes in ghrelin and leptin during deployment suggest they were more likely to have been caused

by the observed body mass loss, rather than driving it.

 

Sustained energy deficit with a small associated body and fat mass loss in a lean population results in

a significant reduction in circulating leptin levels.

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Abstract

Objective

Understanding the mechanisms that drive weight loss in a lean population may elucidate systems that

regulate normal energy homeostasis. This prospective study of British military volunteers investigated

the effects of a six month deployment to Afghanistan on energy balance and circulating

concentrations of specific appetite regulating hormones.

Design & Methods

Measurements were obtained twice in the UK (during the pre-deployment period) and once in

Afghanistan, at mid-deployment. Body mass, body composition, food intake and appetite regulatory

hormones (leptin, active and total ghrelin, PYY, PP, GLP-1) were measured.

Results

Repeated measures analysis of 105 volunteers showed body mass decreased by 4.9 ±3.7% (p<0.0001)

during the first half of the deployment. Leptin concentrations were significantly correlated with

percentage body fat at each time point. The reduction in percentage body fat between Pre-deployment

and Mid-deployment was 8.6%, with a corresponding 48% decrease in mean circulating leptin. Pre-

deployment leptin, total and active ghrelin levels correlated with subsequent change in body mass,

however no changes were observed in the anorectic gut hormones GLP-1, PP or PYY.

Conclusions

These data suggest that changes in appetite regulating hormones in front-line military personnel occur

in response to, but do not drive, reductions body mass.

Keywords: Body Weight, Dietary Intake, Energy Balance, Appetite Regulation, Leptin

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Introduction

Recent media reports have highlighted apparently significant body mass loss observed in United

Kingdom Armed Forces personnel serving in Afghanistan [1,2]. Loss of appetite in military personnel

on operational deployment or exercise is a widely recognised phenomenon, and loss of body mass is

also common [3]. The physiological processes that drive this loss of appetite and body mass remain

unclear. Supplying adequate amounts of food is vital for sustaining military performance, but even

with sufficient food availability, military personnel still lose body mass [3,4]. Environmental

temperature can influence energy requirements [5,6], and evidence suggests that a hot environment

suppresses appetite [7,8]. However, military deployments in temperate climates are also associated

with body mass loss [9]. Understanding appetite regulation in deployed military personnel may

inform feeding provision in order to support the preservation of body mass and physical fitness, and

may also elucidate the mechanisms regulating normal energy homeostasis.

Appetite regulation is determined by multiple factors. Acute and chronic energy requirements are

regulated by a complex neuroendocrine system that signals between the gastrointestinal tract, adipose

tissue and the appetite regulating regions of the brain, in particular the hypothalamus and the brain

stem (10). Social and environmental influences are integrated with psychological factors, which

include emotional responses and learned behaviours, to influence food intake (11).

Leptin is released by white adipose tissue in proportion to fat mass, and communicates information on

stored energy reserves to the central nervous system. Food intake does not greatly affect leptin levels

in the fed state. However, short-term (72-hour) dietary restriction leads to a disproportionately large

reduction in circulating leptin relative to body mass loss in lean and obese subjects, These reduced

leptin concentrations can be restored to control levels by a single meal [12-14]. Leptin also has

immune and neuroendocrine functions [12], and leptin deficiency is likely responsible for the

compromised immune function and suppressed reproductive and thyroid axes observed in starvation

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[12,13,15]. However, it is unclear how leptin changes in response to more moderate reductions in

energy intake over a prolonged period of time.

In response to food intake, the gut hormones peptide tyrosine tyrosine (PYY) and glucagon-like

peptide-1 (GLP-1) are released from the small bowel and colon, and pancreatic polypeptide (PP) is

released from the pancreas. These three hormones reduce food intake through local actions and via

central mechanisms [16-18], and GLP-1 also enhances glucose-mediated insulin release [19]. In

contrast, the gastric hormone ghrelin is released from the stomach in anticipation of food and

increases food intake [20,21].

Military personnel deployed on the front line provide a rare opportunity to study the hormonal effects

and possible causes of body mass loss in a relatively young and fit population exposed to particular

environmental stressors and dietary limitations. Thus, the current study investigated the effect of a

military deployment to Afghanistan on energy balance, and whether the resulting changes in energy

intake and changes in body composition were associated with alterations in circulating concentrations

of specific appetite regulating hormones.

Materials & Methods

Study Design

This was a within subject, repeated measures study. Volunteers’ anthropometric (body mass, body

height and body composition) measures were taken and dietary intake and physical capability were

assessed on two occasions in the UK Pre-Deployment (January and March 2010), and Mid-

Deployment in Camp Bastion before 14 days of mid-tour leave (Rest & Recuperation, R&R) (June –

Aug 2010). Mean (±SD) time Pre- to Mid-Deployment was 121 (±18) days (Range: 90–153 days).

Volunteer body mass was stable during the three-month pre-deployment period, but significantly

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decreased during the first half of the deployment [4]. As such, gut hormone and leptin concentrations

were measured at the first three time-points in January, March and Mid-Deployment (referred to as

Baseline, Pre-Deployment and Mid-Deployment). The outcome measures for this part of the study

were changes in body mass, body composition and gut hormone levels over time.

This study was conducted according to the guidelines laid down in the Declaration of Helsinki and all

procedures involving human volunteers were approved by the Ministry of Defence Research Ethics

Committee (090/GEN/09). Written informed consent was obtained from all volunteers. This work

comprised part of the British Surgeon General’s Armed Forces Feeding Project (SGAFFP) [4].

Research Participants

A unit of approximately 750 Royal Marines was approached to take part. The study sample was

limited to those in camp during Pre-Deployment measurements. However, it was confirmed following

recruitment that the study sample was representative of the deploying unit in terms of age, military

experience and rank structure. All participants were at least 18 years old at deployment, operationally

fit and medically healthy. A cohort of 249 volunteers was recruited (139 Marines; 90 Non-

Commissioned Officers; 10 Officers; 10 Other).

Measurements

Anthropometric assessment

Pre-Deployment anthropometric measures were undertaken in the UK, Mid-Deployment measures

were undertaken at Camp Bastion, Afghanistan. Thus, volunteers were measured within seven days of

leaving the frontline. Body mass (Seca scales, Hamburg, Germany; accuracy 0.1 kg), height (Invicta

stadiometer, Leicester, England; accuracy 0.1 cm), body composition as assessed by skin-fold

thickness measured with Harpenden callipers (Bodycare, UK) at four sites by the same trained

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observers at each time-point, as described in the Anthropometric Standardisation Reference Manual

[22]. Body Mass Index (BMI) was calculated from body mass (kg) and height (m). Percent body fat

was estimated using the method of Durnin and Womersley [23].

Measurement of appetite regulatory hormones

Blood samples were collected in a 6 ml EDTA tube between 06.00 am and 09.00 am, following an

overnight fast, at Baseline, Pre- and Mid-Deployment. The sample was centrifuged immediately at

1600 g for 15 minutes. A 500 μl aliquot of plasma was separated and added to 25 μl 1M HCl to

facilitate the measurement of active ghrelin [24]. All samples were frozen and stored at -80°C prior to

analysis.

Total ghrelin, PP, PYY and GLP-1 were measured by radioimmunoassay as previously described

[16,24-26]. All samples were measured in one assay to avoid inter-assay variation. The calculated

intra-assay coefficient of variation for PYY was 6.0% and the specific activity of the label was 54

Bq/fmol. The intra-assay coefficient of variation for ghrelin was 12.2% and the specific activity of the

label was 48 Bq/fmol. The intra-assay variation for PP was 7.3% and the specific activity of the label

was 54 Bq/fmol. The intra-assay coefficient of variation for GLP-1 was 8.7% and the specific activity

of the label was 8 Bq/fmol.

Multiplex assays (Millipore, Billerica, MA, USA) were performed in duplicate for active ghrelin,

leptin and insulin according to the manufacturer’s instructions. The intra-assay precision (percent

coefficient of variation, %CV) for each hormone was reported as <11%. The inter-assay precision

(%CV) for each assay was reported as <19%.

.

Nutritional assessment

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Dietary intake of volunteers was recorded over representative 4-day periods Pre- and Mid-

Deployment using a customized food diary developed from the Ministry of Defence Food Record

Card [27]. Dietary intake data were analysed using an analysis package (WinDiets, Aberdeen,

Scotland, UK).

Statistical Analysis

Data were checked for normality using the Shapiro-Wilk test. Measurements more than two standard

deviations from the mean for each gut hormone at each time-point were not included in the final

analyses to account for extreme outliers. Unpaired T test or Mann-Whitney test were used to compare

changes in gut hormone levels relative to changes in body mass. Repeated measures analysis of

variance (ANOVA) was performed for multiple time-point analysis of matched data with post hoc

Bonferonni correction for parametric data, and the Friedman test with Dunn’s post hoc analysis for

non-parametric data. For unpaired data, one-way ANOVA was used with post hoc Bonferonni

correction for parametric data, and the Kruskal-Wallis test with Dunn’s post hoc analysis for non-

parametric data. The strengths of linear relations were determined using Spearman (for parametric

data) or Pearson’s (for non-parametric data) rank correlation. Nested multivariate regression analysis

of those variables with significant correlations with body mass was also performed.

Statistical analyses were performed with the GraphPad Prism (version 5.00 for Windows, GraphPad

Software, San Diego, California, USA) and Stata computer packages (StataCorp. 2013. Stata

Statistical Software: Release 13. College Station, TX: StataCorp LP). Statistical significance was set

at the 5% level.

Results

Demographics

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In January 2010, 201 male servicemen were recruited to take part in the SGAFFP. Further

measurements were undertaken in March 2010, when 212 servicemen were measured, 48 of whom

were new to the study, resulting in a total cohort of 249 volunteers in the study. Mid-deployment, 153

volunteers were measured. Body mass and body composition were measured at each of the three time-

points in 105 volunteers; due to operational constraints not all volunteers could attend at each time-

point. The average age of the men on the first day of baseline measurements was 28 years (range 19-

54).

Environment

The peak daytime temperatures in Camp Bastion during the summer months of 2010 ranged between

35-45C. The majority of personnel were based in a Forward Operating Base with no access to air-

conditioning and were involved with daily patrols, varying in duration from a couple of hours to most

of the day (>10 h) depending on the Commander's objectives. Soldiers on patrol in Afghanistan carry

between 30-54 Kg (which includes body armour, weapons and backpack), and may have been

required to sprint short distances, climb compound walls and fire weapons. On non-patrolling days

activities included sentry and Quick Reaction Force duty, patrol briefs, personal administration (e.g.

cleaning kit), physical training, or recreational activities (e.g. reading or watching DVDs). The Royal

Marines were fed the Multi-Climate Ration (MCR) during the deployment which is designed to feed

one person for 24 hours and includes a minimum of 550 g of carbohydrate (55% intake), 100-120 g of

protein (10-12%) and about 133 g of fat (30%), and if all of the components are consumed, provides a

minimum of 4000 kcal of energy, or the 10-man operational ration pack (which theoretically equates

to 4 684 kcal per person per day). The MCR was supplemented with fresh rations, when these were

available through re-supply. Energy intake data for this cohort has previously been reported [4].

Body mass and body composition

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Body mass and anthropometric measurements were assessed across the three time-points (Baseline,

Pre-deployment and Mid-deployment) in 105 matched volunteers (Figure 1.A-C). Body fat increased

significantly by 0.52 0.85 Kg (p<0.05) from Baseline to Pre-deployment, though body mass and

BMI did not change. Body mass, BMI and body fat at Mid-deployment had decreased relative to Pre-

deployment measurements (p<0.0001 for all). Change in body mass ranged from -11.4 Kg to +2.7 Kg

(-13.4% to +3.4%). The change in body mass represent an estimated energy deficit of approximately

143 kcal/day between the Pre-deployment and Mid-deployment time-points [4]. To ensure the paired

results reflected the wider data set, unpaired results from the three time-points were also analysed, and

were found to show similar patterns. Anthropometric data for this cohort has previously been reported

[4].

Appetite-regulating hormones

Leptin (assessed in 51 volunteers) increased between Baseline and Pre-deployment (2.15 0.20

ng/ml vs. 2.76 0.20 ng/ml, p<0.01) but decreased between Pre-deployment and Mid-deployment

(2.76 0.20 ng/ml vs. 1.44 0.12 ng/ml, p<0.0001) (Figure 1.D). Relative to Baseline, mean leptin

levels significantly increased by 28.4% at Pre-deployment, coinciding with a significant 2.9%

increase in mean body fat percentage. The percentage reduction in mean body fat between Pre-

deployment and Mid-deployment was 8.6%, with a corresponding 47.9% decrease in mean circulating

leptin (both P<0.05).

Total ghrelin, active ghrelin, PYY, and PP concentrations were not different across the three time-

points in the paired dataset (Figures 1.E-H). GLP-1 concentrations significantly increased by 10.3

26.2 pmol/l between Baseline and Pre-deployment but were not significantly different between Pre-

deployment and Mid-deployment (Figure 1.I).

Unpaired data were also analysed (Table 1); these showed a similar pattern of changes. Active ghrelin

concentrations increased significantly (p<0.05) between Pre- and Mid-deployment, to a level slightly

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higher than at Baseline. Similarly, PP concentrations increased incrementally across the three time-

points, with Mid-deployment levels being significantly higher than at Baseline (p<0.05).

Relationship between body composition, energy intake and gut hormone and leptin levels

Body fat strongly correlated with leptin at Baseline r=0.59; at Pre-deployment r=0.58; and at Mid-

deployment r=0.51 (all p<0.0001) (Figure 2). None of the other hormones measured were correlated

with anthropometric measurement at any of the three time-points. As expected, total ghrelin and

active ghrelin were correlated (all p<0.0001) at Baseline (r=0.47, n=120), Pre-deployment (r=0.55,

n=132) and Mid-deployment (r=0.37, n=91). There were no consistent correlations between other gut

hormones at any of the three time-points. Pre-deployment leptin (r= 0.51, p<0.0001) and total and

active ghrelin (r= 0.21, p=0.03 and r=0.25, p=0.01 respectively) correlated with subsequent change in

body mass (occurring between Pre-deployment and Pre-R&R).

Although energy intake was significantly lower at Mid-deployment compared to Pre-deployment

levels (2841 116 vs. 2620 102 kcal, n=60, p<0.05), there were no associations between changes

in gut hormone concentrations (between Pre-deployment and Mid-deployment) and change in energy

consumption over the same period, nor between gut hormone or leptin levels and energy intake at any

single time point.

The body mass loss observed varied widely between individuals. Loss of body mass can affect some

facets of military performance [28]. The data was therefore partitioned to identify the 10% of the

cohort with the greatest body mass loss and the 10% with the lowest body mass loss, and analysed to

establish if body composition or the levels of gut hormones or leptin at Pre-deployment could predict

subsequent loss of body mass. Nested multivariate regression analysis was performed with respect to

those variables with significant correlations with body mass. Stepwise analysis revealed that Pre-

deployment body mass and leptin were able to account for nearly one third of the change in body

mass that occurred between Pre-deployment and Mid-deployment (R2= 0.33, p=0.002). The addition

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of active ghrelin did not statistically improve the predictive value of the model. In accord with these

data, the differences in leptin, and total and active ghrelin levels between the 10% cohorts losing the

most and the least body mass were significant (Table 2). At Pre-deployment, the 10% of volunteers

who went on to lose the most body mass had significantly lower active ghrelin levels, higher leptin

levels, and greater body mass and body fat than the 10% who subsequently lost the least body mass.

Discussion

The results of this study indicate that changes in leptin and ghrelin concentrations observed in front

line military personnel occur in response to, rather than actively driving, measured changes in body

mass and fat mass. Our novel data suggests that those personnel who lost the most body mass were

those with higher body mass and body fat at the Pre-deployment time-point, and that this body mass

loss was associated with significant changes in total and active ghrelin levels. Moreover, relatively

small changes in fat mass had a significant influence on circulating leptin concentrations in this fit,

lean male population.

The mean change in body mass seen in deployed Royal Marines, though significant, was modest

(~3.5-4.2 Kg). Body mass loss up to approximately 6% has been reported to not adversely affect

operational capability of military personnel [28]. Approximately one third of the cohort in the current

study lost more body mass than this, but given that those who lost the greatest amount of body fat

tended to have a higher percentage body fat before deployment, it seems likely that most of the loss

represented fat mass rather than lean mass. Though it is possible that alterations in fluid balance may

have caused some of the change in body mass, this seems unlikely; volunteers had free access to

water at all points, and although acute fluctuations in water balance due to the effects of patrolling in

hot conditions may have occurred, the Marines’ weights were not measured until they had flown back

to Camp Bastion from their FOB, by which time they would have had ample time to rehydrate.

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The leptin results reported here are in accord with previous studies demonstrating that body mass loss

and short-term starvation in lean populations can result in a large change in plasma leptin with a

relatively small reduction in body (or fat) mass [12-14]. The leptin levels measured in this healthy

military cohort likely reflect changes in fat mass rather than acute nutritional status; the small but

significant gain in body fat between Baseline and Pre-deployment was associated with increased

leptin levels. Furthermore, the Royal Marines who lost most body mass (and body fat) during the first

half of their operational tour also had the greatest reduction in circulating leptin. Reduced circulating

leptin is known to induce neuro-humoral and metabolic adaptations to manage the consequences of

body mass loss, and it is interesting to speculate whether energy expenditure was affected by the large

proportional drop in leptin which corresponded with the modest body mass loss observed. The lower

correlation of leptin and body fat at Mid-deployment may reflect the reduced food intake observed at

this time-point.

Ghrelin levels are lower in obese than in normal weight (defined by BMI) humans [29]. The decrease

in circulating ghrelin levels observed at Mid-deployment suggests that this relationship also holds for

smaller differences in body mass in a lean population. However, such a putative effect appears easily

masked by the variation in ghrelin levels, as there were no marked associations between total or active

ghrelin with body mass or fat mass. Data from the current study did show that ghrelin levels were

elevated in those volunteers who lost the greatest amount of body mass as a result of military

deployment, suggesting a greater physiological drive towards energy consumption exists in those with

greater loss of body mass.

PP increased when body mass was reduced at Mid-deployment. Alterations to autonomic tone may

have influenced PP levels in our study. The vagus nerve controls both elements of the biphasic release

of PP in response to food ingestion; cholinergic vagal activity is the most potent stimulus for release

of PP [30], though the late postprandial release of PP is only partially inhibited by vagotomy,

suggesting that non-cholinergic mechanisms also contribute [17]. Fasting serum levels of PP to

increase two- to three-fold from baseline in Norwegian military cadets undertaking endurance

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physical exercise, with sleep deprivation and energy restriction over a period of 4-5 days [31,32]. It is

interesting to speculate that the raised PP levels Mid-deployment may reflect the physical or

psychological stress of front line deployment, and may in part drive the reduced body mass observed

at Mid-deployment. However, there were no significant correlations between PP and body mass or fat

mass, suggesting that other factors were likely involved.

The reasons for the inadequate energy intake in the study population are unknown. Many of the

servicemen reported that they were ‘just not hungry’, suggesting that their appetite was suppressed. It

is interesting that the reduction in leptin and the increase in ghrelin in those losing the most weight (as

would be predicted) does not lead to a reactive hyperphagia, suggesting that there is an unidentified

factor that is able to suppress food intake. It remains possible that changes in food-induced release of

the gut hormones may have contributed, but it was logistically difficult to investigate this possibility

in the field. Alternatively, non-hormonal systems may have been involved. It is also possible that

psychological stress, mediated through alterations in appetite regulatory hormones, contributes to loss

of body mass commonly observed on military deployments. In rodents, restraint stress increased

leptin and decreased ghrelin levels, which could be accounted for by activation of the sympathetic

‘fight-or-flight’ response [33]. However, in other studies, ghrelin has been found to be upregulated in

models of stress [34,35]. With the available data, it was not possible to untangle the effects of

alterations in body mass and those of chronic stress on hormone levels in our cohort. The definition of

what constitutes stress and duration of insult varies considerably between rodent studies and the

presumed and unquantified stress encountered within this population of deployed Royal Marines.

Further investigations measuring ACTH/cortisol levels, or other surrogate biomarkers of stress such

as catecholamines might perhaps allow better elucidation of the influence of stress during

deployment.

In summary, servicemen on operational deployment in Afghanistan lost a modest but statistically

significant amount of body mass during the first half of their deployment due, at least partly, to

inadequate energy intake despite an adequate food supply. Gut hormones, notably ghrelin and leptin,

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were altered during the course of a deployment. However, the pattern of these changes suggest they

were more likely to represent a response to the loss of body mass, rather than being responsible for it.

Further study is required to investigate the factors responsible for the loss of body mass in deployed

servicemen lose body mass in spite of the increased hormonal drive to restore energy homeostasis.

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Acknowledgements

The Funder (Ministry of Defence) was not involved in the study design, data collection or analysis

and reviewed the manuscript for security issues only.

The Section of Investigative Medicine is funded by grants from the MRC, BBSRC, NIHR, an

Integrative Mammalian Biology (IMB) Capacity Building Award, an FP7- HEALTH- 2009- 241592

EuroCHIP grant and is supported by the NIHR Imperial Biomedical Research Centre Funding

Scheme. 

© British Crown Copyright 2014 /MOD. Published with the permission of the Controller of Her

Britannic Majesty’s Stationery Office.

Conflicts of interest

The authors have no conflicts of interest.

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34. Kristensson E, Sundqvist M, Hakanson R & Lindstrom E. High gastrin cell activity and low

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35. Asakawa A, Inui A, Kaga T, Yuzuriha H, Nagata T, Fujimiya M, et al. A role of ghrelin in

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147.

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Tables

Leptin (ng/ml)

p<0.0001

Total ghrelin

(pmol/)

p=0.43

Active ghrelin (pmol/l)

p=0.05

GLP-1 (pmol/l)

p=0.17

PP (pmol/l)

p=0.01

PYY (pmol/l)

p=0.44

Mean (SEM) n Mean (SEM) n Mean (SEM) n Mean (SEM) n Mean (SEM) nMean

(SEM)n

Baseline 2.05 (0.12) 124 434.3 (15.2) 135 31.9 (1.7) 126 58.3 (2.7) 121 165.7 (8.1) 128 27.1 (1.0) 113

Pre-

deployment

2.37 (0.12) 141 408.6 (14.4) 156 28.4 (1.3) 138 64.8 (2.7) 139 180.7 (7.6) 136 27.0 (1.0) 131

Pre-R&R 1.48 *** (0.09) 98 434.1 (17.7) 99 32.9 * (1.6) 97 58.7 (2.6) 93 205.8+ (11.7) 96 29.1 (1.4) 79

Table 1. Unpaired plasma levels of gut hormones and adipokines in Royal Marines at three time-points in the SGAFFP. Mean (SEM) values are

shown. P values refer to results of one-way ANOVA with Bonferroni post-hoc analysis. + p<0.05 vs. Baseline; * p<0.05 vs. Pre-deployment; *** p<0.0001 vs.

Pre-deployment

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Greatest weight loss

(top 10%)

Least weight

loss

(bottom 10%)

Mean

(SEM)n

Mean

(SEM)n

Δ Body mass (Kg) -9.7 (0.3) 13 1.5 (0.2) 13

Δ Leptin (ng/ml)

p<0.0001

-3.4 (0.5) 11 0.15 (0.2) 7

Δ Total ghrelin (pmol/l)

p=0.03

62.4 (28.7) 12 -69.3 (50.5) 12

Δ Active ghrelin

(pmol/l)

p=0.008

36.2 (13.0) 11 -42.2 (14.8) 9

Table 2. Difference in body mass, ghrelin & leptin in Royal Marines in the decile (10%) who lost

the greatest and least body mass between Pre-deployment and Mid-deployment. Mean (SEM)

values are shown. P values are for unpaired T-tests between greatest and least weight loss.

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Figure Legends

Figure 1. Paired measurements of body mass, body composition and plasma levels of gut

hormones and leptin in Royal Marines at three time-points: Baseline (Base), Pre-deployment

(Pre-), and Mid-deployment (Mid-). Mean (SEM) values are shown for (A) Body mass, (B) body

mass index, (C) body fat, (D) leptin (E) total ghrelin, (F) active ghrelin, (G) peptide YY, (H)

pancreatic polypeptide, and (I) glucagon-like peptide-1. Numbers in columns refer to numbers of

volunteers sampled. P values refer to results of repeated measures one-way ANOVA with Bonferroni

post-hoc analysis. * p<0.05; *** p<0.0001

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Figure 2. Correlation between leptin and body fat in Royal Marines before and during deployment. The relationship between leptin and body fat was

analysed at (A) Baseline (n=122), (B) Pre-deployment (n=137) and (C) Mid-deployment (n=98) time-points during the study. All correlations were

statistically significant (p<0.0001.)

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