The Effect of Water Loading on Acute Weight Loss Following Fluid Restriction in Combat Sports Athletes

Abstract

Novel methods of acute weight loss practiced by combat sport athletes include 'water loading'; the consumption of large fluid volumes for several days prior to restriction. We examined claims this technique increases total body water losses, while also assessing the risk of hyponatremia. Male athletes were separated into control (CON, n=10) and water loading (WL, n=11) groups and fed a standardised energy-matched diet for 6 days. Day 1-3 fluid intake was 40 mL. kg-1 and 100 mL. kg-1 for CON and WL, respectively with both groups consuming 15 mL. kg-1 on Day 4 and following the same rehydration protocol on Days 5-6. We tracked body mass (BM), urine sodium, specific gravity (USG) and volume, training-related sweat losses and blood concentrations of renal hormones and urea and electrolytes (U+Es) throughout. Physical performance was assessed pre-and post-intervention. Following fluid restriction, there were substantial differences between groups in the ratio of fluid input/output (39%, p < 0.01, ES=1.2) and BM loss (0.6%BM, p=0.02, ES=0.82). Changes in USG, U+Es and renal hormones occurred over time (p < 0.05), with an interaction of time and intervention on blood sodium, potassium, chloride, urea, creatinine, USG and vasopressin (p < 0.05). Measurements of U+E remained within reference ranges and no differences in physical performance were detected over time or between groups. Water loading appears to be a safe and effective method of acute BM loss under the conditions of this study. Vasopressin regulated changes in aquaporin channels may potentially partially explain the mechanism of increased body water loss with water loading.

Full text

Title: The Effect of Water Loading on Acute Weight Loss Following Fluid Restriction in Combat Sports
Athletes
Submission Type: Original research
Authors: Reid Reale1,2, Gary Slater2, Gregory R Cox1,2, Ian C Dunican3, Louise M Burke1,4,
1 Australian Institute of Sport, Canberra, Australian Capital Territory, Australia
2 University of Sunshine Coast, Sippy Downs, Queensland, Australia
3 University of Western Australia, Perth, Australia
4 Australian Catholic University, Melbourne, Victoria, Australia
Address for correspondence:
Reid Reale
Australian Institute of Sport
Telephone: +1 941 900 5930
E-mail: reid.reale@gmail.com
Running Head: Water loading in combat sports
Key words: Weight cutting, rapid weight loss, weigh-in
Abstract Word Count: 246 words.
Text-Only Word Count: 2999
Number of Figures and Tables: 6 figures.

Abstract
Novel methods of acute weight loss practiced by combat sport athletes include ‘water loading’; the
consumption of large fluid volumes for several days prior to restriction. We examined claims this
technique increases total body water losses, while also assessing the risk of hyponatremia. Male
athletes were separated into control (CON, n=10) and water loading (WL, n=11) groups and fed a
standardised energy-matched diet for 6 days. Day 1-3 fluid intake was 40 mL.kg-1 and 100 mL.kg-1 for
CON and WL, respectively with both groups consuming 15 mL.kg-1on Day 4 and following the same
rehydration protocol on Days 5-6. We tracked body mass (BM), urine sodium, specific gravity (USG)
and volume, training-related sweat losses and blood concentrations of renal hormones and urea and
electrolytes (U+Es) throughout. Physical performance was assessed pre-and post-intervention.
Following fluid restriction, there were substantial differences between groups in the ratio of fluid
input/output (39%, p < 0.01, ES=1.2) and BM loss (0.6%BM, p=0.02, ES=0.82). Changes in USG, U+Es
and renal hormones occurred over time (p < 0.05), with an interaction of time and intervention on
blood sodium, potassium, chloride, urea, creatinine, USG and vasopressin (p < 0.05). Measurements
of U+E remained within reference ranges and no differences in physical performance were detected
over time or between groups. Water loading appears to be a safe and effective method of acute BM
loss under the conditions of this study. Vasopressin regulated changes in aquaporin channels may
potentially partially explain the mechanism of increased body water loss with water loading.

Introduction
Combat sport athletes commonly manipulate body mass (BM) prior to competition, attempting to gain
real or perceived advantages by competing in weight divisions lighter than their day-to-day BM
(Franchini, Brito et al. 2012). Aside from chronic fat mass reductions, athletes acutely reduce BM pre-
weigh-in. Common and effective methods include active and passive sweating, diuretics, fluid and
sodium restriction (reducing body water) and reduction of gut contents via laxative use, fasting,
reducing food volume and reduced carbohydrate and/or fibre intake (Franchini, Brito et al. 2012,
Reale, Slater et al. 2016).
‘Water loading’ is a recent addition to these methods; purportedly decreasing BM via increased urine
production (Reale, Slater et al. 2016). This technique involves consuming large fluid volumes (i.e. 7-
10+ L/d) for several days followed by fluid restriction; allegedly manipulating renal hormones and
urine output, thus increasing fluid losses relative to fluid restriction following ad-libitum fluid intake
(Reale, Slater et al. 2016). Anecdotes exist among body builders and power lifters as well as in combat
sports. Two recent investigations have confirmed the use of water loading in UK combat sport athletes
(Crighton, Close et al. 2015, Matthews and Nicholas 2016) and data from this group indicates >40% of
Australian Olympic combat sport athletes have used this method at some stage (Reale et al. 2017).
However, these athletes commonly manipulate sodium and other nutrients alongside fluid intake
while ‘making weight’, thus confounding the ability of anecdotal ‘evidence’ to provide insights into its
efficacy. Given the prevalence of use, the lack of scientific investigation and the potential risk of
hyponatremia associated with consuming large volumes of fluid, further research is warranted.
Accordingly, the aim of this study was to examine water loading in a controlled setting, investigating
the efficacy, safety and potential underlying mechanisms.

Methods
Overview
This study was conducted at the Australian Institute of Sport as a parallel intervention. Subjects were
separated into a control (CON) or intervention group (water loading (WL)). The Human Research Ethics
Committee of the University of the Sunshine Coast approved the study. Subjects provided written
informed consent prior to participation. The project took place over eight days: two ‘pre’ testing days
prior to intervention (Day -1 and 0), six intervention days (Day 1-6) and post’ testing (Day 6). See Figure
1 for study overview. Figure 2 summarises timelines and details of key data collection points.
Figure 1. Study outline: DXA- dual energy x-ray absorptiometry, WL – water loading group, CON –
control group

Figure 2. Laboratory data collection and Physical testing undertaken on days -1 and 0 (pre-
intervention) and day 6 (post-intervention): USG – urine specific gravity, Na – sodium, K – potassium,
Cl – chloride, U – urea, Cr – creatinine, IMTP – isometric mid thig pull, IBP – isometric bench press,
CMJ – counter movement jump, RSA – repeated sprint ability
Subjects
Subjects were 22 male grapplers (jiu-jitsu, judo and wrestling athletes) with at least 4 years
competition experience, currently training ≥8 hours per week. One subject withdrew from the study
prior to completion for reasons unrelated to the intervention, thus 21 were included in the final
analysis. Subjects were stratified into blocks, matching for BM and then simple randomisation was
used to place subject into CON (n = 10; 77.2±8.7kg, 178.9±5.7cm, 15.1±4.2% body fat, 24.9±4.0years)
and WL groups (n = 11; 77.8±8.0kg, 176.2±6.4cm, 15.5±2.9% body fat, 28.3±3.5years). All subjects
reported having lost weight in order to make weight in the past with the four indicating previous water
loading experience allocated evenly between the WL and CON groups.
Body composition assessment
On Day -1, body composition was assessed by a trained technician, using dual energy x-ray
absorptiometry (iDEXA GE Healthcare, Madison, WI) according to the standardised protocol
developed at the Australian Institute of Sport (Nana, Slater et al. 2016).

Physical performance testing
Physical performance measures included maximal isometric strength, lower body power and repeated
sprint ability (RSA) tests (Figure 2). Subjects performed familiarisation sessions on Day -1, with pre-
intervention testing undertaken on Day 0 and replicated on Day 6. Testing occurred at the same time
daily, following morning blood collection and a standardised breakfast. It was conducted by the same
scientists in a noise sensitive laboratory. Instructions to give maximal effort were provided prior to,
but not during testing.
Testing consisted of a standardised warm-up followed by 3 maximal efforts of; countermovement
jump (CMJ), isometric mid-thigh pull and isometric bench press conducted on a force plate. Testing
was completed according to the methodology used by Halperin et al (Halperin, Williams et al. 2016).
Subjects then performed the RSA test after a cycle ergometer warm-up (Wattbike Ltd, Nottingham,
UK). Handlebar/saddle position were self-selected and replicated between trials.
Diets
Standardised diets during the intervention provided an energy content of 125 kJ·kg FFM-1 to meet
resting requirements, plus additional energy accounting for exercise induced thermogenesis
(estimated based on BM and training duration (Montoye 2000)). This represents a mild energy
restriction of ˜14-18 kJ·kg FFM-1, maintaining moderate energy availability (Loucks 2004): protein:
2.2-2.5g·kg FFM-1, carbohydrate: 5-6g·kg BM-1 and fat: 1-2 g·kg BM-1. Sodium prescription was
~300mg·Mj-1 and fibre 10-13 g, representing a reduced residue diet recommended to athletes “making
weight” as a means to reduce the weight of gut content/ overall BM. Main meals were consumed in
the presence of researchers and subjects verified all snacks were consumed as prescribed. No
differences existed in dietary intake between the groups.

Fluid prescription
During Days 1-3 of the intervention, fluid intake (tap water) was clamped at 100 mL·kg-1 BM for WL
and 40 mL·kg-1 BM for CON. On Day 4, both groups restricted intake to 15 ml·kg-1 BM. No fluid was
consumed on Day 5 until after the morning laboratory data collection. Both groups followed the same
re-hydration protocol after this point; fluid intake of 30 mL·kg-1 BM + 150% of the BM loss incurred
during the fluid restriction period (morning of Day 4 until post Day 5 data collection). Daily fluid targets
were divided into an hourly volume to be consumed during waking hours.
Training
The training schedule aimed to replicate combat sport athletes’ competition preparation, consisting
of two training sessions daily during Days 1-3, one session on Day 4 and no training on Day 5. All
subject completing the same training sessions throughout the study.
Laboratory data collection
The standardised protocol for laboratory data collection (Figure 2) involved morning testing following
an overnight fast (no food or fluid) at 7 am (Day -1 to Day 6) and evening testing at 6 pm (Day 1-5). No
food was consumed for ῀3 h and no fluid for ῀1 h prior to the 6pm testing. Each time point involved
the collection of urine, venous and capillary blood, BM measurements, blood pressure, heart rate, and
completion of a gastro intestinal (GI) symptoms questionnaire.

Body mass
BM measurements were conducted after bladder voiding using the BWB800S digital BM scales (Tanita,
Tokyo, Japan). In addition to laboratory data collection time points, naked BM was measured before
and after training sessions and used alongside urine output and fluid intake to estimate sweat losses
(i.e. sweat loss = BM change + fluid intake – urine output).
Urine collection and analysis
Waking urine samples were analysed for specific gravity (USG) using the UG-1 digital refractometer
(ATAGO, Tokyo, Japan). Twenty-four-hour urine collection was undertaken Days 1-6 in 2 collection
periods daily. Sodium concentration was determined using the B-722 Laqua twin (Horiba, Kyoto,
Japan).
Blood collection and hormone analysis
Phlebotomists collected venous blood (3 x EDTA tubes, 1 x serum separated tube (SST), totalling 26.5
ml per collection point) following ~30 min supine rest for renal hormones measurement (vasopressin,
renin and aldosterone). Samples were mixed and allowed to clot (when appropriate) before being
centrifuged and frozen at -80o until analysis. Vasopressin concentrations were determination using
the Buhlmann Vasopressin double-antibody radioimmunoassay method (Buhlmann Laboratories,
Schönenbuch, Switzerland) based on the method of Glick and Kagan (Glick and Kagan 1979). Inter-
assay CV and intra-assay CV for vasopressin determination are between 1.8–3.5% and 5.6–9.5%
respectively.2.3-9.5% 6.8-13.0%. Aldosterone and renin concentrations were determined by a
LIAISON Analyzer (DiaSorin Inc, Via Crescentino, Italy), using a competitive assay (sheep monoclonal
antibody) and a sandwich chemiluminescence immunoassay (specific mouse monoclonal antibody)

respectively (Derkx, De Bruin et al. 1996, Cartledge and Lawson 2000). Inter-assay and intra-assay
coefficients of variability (CV) for renin determination are between 2.1–2.4% and 6.8–7.3%,
respectively. Inter-assay CV and intra-assay CV for aldosterone determination are between 1.8–3.5%
and 5.6–9.5% respectively.
Fingertip capillary blood (95uL) was then collected to analyse concentrations of sodium, potassium,
chloride, urea and creatinine using the i-STAT Point of Care device and chem8+ cartridges (Abbott
Laboratories, Abbott Pak, IL, USA). Inter-assay CV and intra-assay CV for all blood chemistry measures
are ≤3.5% except for urea which at low concentration (1.7 mmol/L) is ≤11.2%.
Heart rate and blood pressure
Following blood collection, resting blood pressure and heart rate measurements were taken using the
HEM-7325 automatic blood pressure monitor (Omron Healthcare, Kyoto, Japan).
Gastrointestinal symptoms
Three questions relating to GI symptoms associated with fluid intake from a validated questionnaire
(Bovenschen, Janssen et al. 2006) were administered. Subjects rated nausea, bloating, and loss of
appetite using a 1-7 Likert scale.
Data analysis
Conventional statistical analysis was used to calculate mean ± SD for each variable. Where
appropriate, results were analysed and reported as absolute and/or delta scores. D'Agostino-Pearson
and Levene’s tests were used to assess normality and homogeneity respectively, where data were not

distributed normally, square root transformations were performed in order to achieve normality.
Repeated measures two-way-ANOVAs with Bonferroni post-hoc tests were used to compare between
groups and across time using the PRISM v 6.0 statistical analysis package (GraphPad Software, San
Diego, California, USA). When data were transformed to achieve normality, statistical analyses were
completed on the transformed data, with back transformed data being displayed in tables and figures
for ease of visualisation. Significance was set at p<0.05. Additionally, 95% confidence intervals (CI95%)
and Cohen d effect sizes (ES) were reported when appropriate. Magnitudes of ES were classified as
trivial (0–0.19), small (0.20–0.49), medium (0.50–0.79) and large (≥0.80) (Cohen 1992).

Results
Body mass
BM changes are displayed in Figure 3. Time had a significant effect on cumulative and day-to-day BM
changes and an interaction between time and fluid intake existed. Within both groups, a significant
cumulative change in BM change across each successive day existed, with the exception of Day 3 to
Day 4 (P < 0.05). Rehydration returned BM at Day 6 to levels equivalent to Days 3 and 4.

Figure 3. Changes in body mass across the 6-day intervention. Cumulative body mass (BM) change
between groups, expressed as percentage of BM ±SD normalised to day 1 (A). Day to day BM change,
expressed as percentage of BM ±SD (B). Main effect of time on cumulative BM change and day to
day BM change (p<0.0001). Interaction between treatment and time on cumulative BM change
(p=0.027) and day to day BM change (p=0.02). Within both groups; significant differences were
found for cumulative BM change between successive days except for Day 3 to Day 4. Rehydration
returned BM at Day 6 to levels equivalent to Day 3/4

Fluid balance and urine analysis
Fluid balance and urine analyses are displayed in Figure 4. There was a main effect of time for all
measures, a main effect of fluid intake on USG, and an interaction between fluid intake and time for
USG and fluid output.

Figure 4. Urine and fluid balance analysis. Daily fluid output (urine + sweat), expressed as
percentage of fluid intake ±SD (A). Daily waking urine specific gravity ±SD (B). Daily absolute sweat
losses ±SD (C). Daily urine sodium output, expressed as percentage of sodium intake ±SD (D). Daily
absolute urine output ±SD (E). 2 way ANOVAs revealed a main effect of time on; fluid output
(p<0.0001), urine specific gravity (p<0.0001), sweat losses (p<0.0001), sodium output (p = 0.035),
and urine output (p<0.0001), a main effect of fluid intake on urine specific gravity (p<0.029) and
urine output (p<0.0001), and an interaction between time and fluid intake on; fluid output
(p<0.0001), urine specific gravity (p = 0.006) and urine output (p<0.0001).

Renal hormone changes are displayed in Figure 5. Main effects of time were found for all measures,
and an interaction was found between treatment and time for fold changes and absolute values in
vasopressin.

Figure 5. Changes in renal hormones across the 6-day intervention: aldosterone (A), renin (B),
aldosterone/renin ratio (C) and vasopressin (D), expressed as fold change from baseline (mean ±SD).
Main effect of time on aldosterone (p<0.0001), renin (p=0.0187), renin/aldosterone ratio (p<0.0001)
and vasopressin (p<0.0001). Interaction between treatment and time on vasopressin.

Blood chemistry
Blood chemistry is displayed in Figure 6. Main effects were found for time with all measures, and an
interaction was found between treatment and time for sodium, chloride and urea. Indices remained
within critical values; none deviated significantly from typical clinical reference ranges for greater than
one time point.

Figure 6. Blood chemistry across the 6-day intervention. Sodium (A), Potassium (B), Chloride (C),
urea (D), and creatinine (E), expressed as mean ±SD. Main effect of time on sodium (p <0.0001),
potassium (p<0.0001), chloride (p<0.0001), urea (p<0.0001) and creatinine (p<0.0001). Main effect
of treatment on urea (p=0.0137). Interaction between treatment and time on sodium (p=0.0096),
chloride (p=0.0137) and urea (p=0.0043).

Gastro intestinal symptoms
A main effect of time for ‘nausea’ (p=0.023) and ‘bloating’ (p=0.0005) was revealed, with nausea
peaking (mean 1.2±0.1) during fluid restriction and bloating peaking (mean 1.4±0.2) prior to dietary
standardisation. ‘Loss of appetite’ was not affected by fluid intake or time.
Heart rate and blood pressure
A main effect of time for ‘heart rate’ (p<0.0001) was revealed; with the lowest values occurring on
Day 0 and 6 (AM) and Day 5 (PM). No differences existed between groups. Blood pressure was not
affected by fluid intake or time.
Physical testing
No differences between groups for physical performance tests existed. A main effect of time
(p=0.0354) for total work completed during the RSA test and for peak displacement in the CMJ test
(p<0.0001) was found. Subjects completed more total work during the RSA on Day 6 compared to Day
0 (pooled means; Day 0: 7542.8±371.5W vs Day 6: 7790.5±301.1W). Peak displacement was higher in
the Day 6 CMJ post-test than the Day 0 pre-test (pooled means; pre-test 45.4±1.3cm vs post-test
47.6±0.8cm).

Discussion
This is the first investigation of the effectiveness and safety of ‘water loading’ as a means of
manipulating BM in the context of weight category sports. The key findings were water loading was
effective in increasing fluid and BM loss accompanying fluid restriction; this may potentially be
mediated in part via the interventions effects on vasopressin. Water loading, as practiced in the
current investigation (i.e. 100mL/kg dispersed evenly throughout the day), appears to be safe since
there was no evidence of problematic blood chemistry changes or impairment of physical
performance following rehydration.
These results support anecdotal outcomes described by athletes. We found the intake of large
volumes (100 mL.kg.d-1 or ~ 7-8L/d) of water for 3 days prior to one day of fluid restriction (15 mL.kg.d-
1) was associated with increased urine production, both during the days of high fluid consumption and
fluid restriction. Specifically, diuresis continued during fluid restriction, leading to greater fluid losses
relative to intake on the day as well as the losses recorded for a control group who had consumed 40
mL.kg.d-1 (~ 3L/d) prior to this day. This was effective in achieving greater BM loss following the 5 d
intervention in the WL group than the CON group. The combination of 5 days of a potentially mild
energy deficit and reduced residue diet, including 1 day of fluid restriction, achieved total mean BM
losses of 3.2 and 2.4% for WL and CON groups, respectively.
This acute BM loss was achieved in a scenario simulating the preparation for weigh-in and competition
in combat sports, but without resorting to more extreme practices of severe energy restriction and
active dehydration commonly observed (Franchini, Brito et al. 2012). However, before advocating
water loading, investigation of safety concerns is necessary. It is well documented that excessive fluid
intake is causative in hyponatremia (Adrogué and Madias 2000) with substantial lowering of blood
sodium leading to negative outcomes, including death (Garigan and Ristedt 1999, Adrogué and
Madias 2000). In the present investigation, however, no clinical meaningful blood chemistry changes

occurred with water loading, with perturbations following expected changes due to differences in fluid
intake.
The present water loading protocol appeared to not increase hyponatremia risk; indeed cases in which
fluid intake in healthy individuals has resulted in death, generally involved substantially greater intakes
over much shorter time frames (e.g. >10 litres in 6 hours) (Garigan and Ristedt 1999, Adrogué and
Madias 2000). Dilutional hyponatremia results when fluid ingestion rate exceeds excretion capacity
(Adrogué and Madias 2000). Thus, in this intervention, it appears dispersing intake across the day,
allowed renal adjustments to compensate. The hormone analysis provides some insight into a
plausible mechanism providing blood chemistry maintenance and the water loading effect on fluid
output. Although no main effect of fluid intake on vasopressin was evident, there was trend for lower
vasopressin in the WL group and a significant interaction was present; that is mean vasopressin was
decreased during the water loading phase in WL (and lower than in CON), before ‘rebounding’ to
concentrations higher than baseline and higher than seen in the CON group following fluid restriction.
Blood sodium decreased in the WL group during the water loading phase, but normalised in line with
the CON group after water loading.
As vasopressin is under osmoregulation (Robertson, Shelton et al. 1976), blood sodium decreases in
WL may explain the vasopressin suppression observed. Furthermore, vasopressin binds to
vasopressin-2 receptors (V2R) found within the collecting ducts of the kidneys. This initiates a
metabolic cascade increasing the permeability of the collecting ducts, and thus water reabsorption,
via the insertion of aquaporin channels (Verbalis 2003), notably; aquaporin-2 (AQP2) channels.
Conversely, in the absence of vasopressin, AQP2 channels (thus water reabsorption) are reduced
(Verbalis 2003), assisting acute fluid regulation (Kwon et al. 2013). This mechanism has been directly
observed in rodent models, with 24 hours of water loading associated with a reduction in
intramembrane AQP2 channels and water permeability in the kidney collecting ducts (Lankford, Chou
et al. 1991, Knepper 1997). Additionally, infusion of vasopressin has been shown to increase AQP2

channels mRNA expression (Knepper 1997). In rats unable to manufacture endogenous vasopressin,
vasopressin infusion may take 3-5 days to ‘return’ mRNA expression of AQP2 channels to ‘normal’
levels (Kishore, Terris et al. 1996). Whilst the present data cannot confirm this hypothesis, this
mechanism possibly explains persistent fluid losses evident following fluid restriction in WL.
Body mass losses prior to fluid restriction
Significant BM losses (~1-2%BM) occurred in both groups following days 1 and 2, before plateauing
until fluid restriction. It is possible the mild energy deficit allowed a loss of fat mass and/or glycogen.
However, the energy deficit required for this degree of fat loss is substantial and a major restriction
of carbohydrate would be needed to create such glycogen depletion. Therefore, reduced gut content
resulting from decreased fibre intake is the most plausible cause of the initial BM loss, especially
considering the time frame. Low fibre/residue diets have been used by combat sport athletes and
recommended by sports nutrition professionals (Reale, Slater et al. 2016) as a way to incur BM loss
without the disadvantages associated with severe dehydration and energy restriction. Different foods
possess different faecal bulking properties (Monro 2000), with those high in fibre drawing water into
the intestinal space, increasing stool bulk. Reducing dietary fibre reduces undigested plant matter,
equating to reduced gut contents and a lower overall BM. There is a linear relationship between fibre
intake and bowel content (Wu, Rayner et al. 2011), with the adoption of a low fibre diet for even two
days helping empty the bowel (Wu, Rayner et al. 2011) and seven days being as effective as pre-
surgery bowel preparation formulas (Lijoi, Ferrero et al. 2009). Indeed, surgery preparation formulae
have been shown to achieve BM reductions of 1.6% (Holte, Nielsen et al. 2004), in line with the ~1.5%
BM loss in our study following 48 hours of lowered fibre intake. Considerable variability in whole gut
transit times exists (~10-96 hours) (Lee, Erdogan et al. 2014), but in the absence of investigations of
low fibre diets in the context of weight making for weight category sports, the present findings could
be valuable in identifying the timeframe required to achieve significant BM loss using this technique.

The lack of a control group on a “normal” (higher fibre) intake is a limitation of our study, however,
the measurement of fluid balance in our groups eliminates hypohydration as a confounding variable.
The use of low residue diets in weight-making warrants further investigation.
Limitations
The major limitation of this study is the lack of a standardised ‘lead-in’ period prior to the
commencement of the controlled diets. Achieving stable BM and increasing confidence in the
prescription of appropriate energy and carbohydrate intakes would have allowed greater certainty in
interpreting the source of BM losses in days 1-2 of our intervention. However, the standardisation
which did take place prior to fluid restriction, combined with the careful observations of daily fluid
input/output allows strong conclusions about the effect of water loading on fluid balance to be drawn.
Additionally, since we only assessed blood sodium at specific time points, we cannot rule out the
possibility that values were lower (and thus possibly indicated preliminary signs of hyponatremia) at
other times points throughout the day.
Conclusions
Three days of dispersed consumption of large volumes of water (100 mL.kg.d-1), prior to one day of
fluid restriction, appears to be a safe and effective method of acutely reducing BM via a reduction in
body water secondary to increased fluid losses. We suggest increased fluid consumption creates a
small but potentially physiologically significant reduction in blood sodium concentration, which
suppresses vasopressin release and downregulates the appearance of AQP2 channels in the collecting
ducts in the kidneys. When this is employed immediately prior to fluid restriction, there is a
continuation of increased fluid loss leading to greater losses relative to fluid restriction alone.

Novelty statement
This study is the first to investigate the acute weight loss method; ‘water loading’. Under the
conditions utilised in the present study, water loading was an effective and safe (no sign of
hyponatremia) procedure to increase fluid losses during fluid restriction.
Practical application
Water loading represents another ‘tool in the tool belt’ which could be used alongside more traditional
methods of acute weight loss. Nutrition professionals working with weight category sport athletes
now have an evidence base from which to draw upon when educating athletes on the use of this
method.

Acknowledgments, authorships, declarations of funding sources and conflicts of interest
The authors would like to acknowledge the support and cooperation of the nutrition, physiology and
combat centre departments at the Australian Institute of Sport as well as the individual athletes who
participated as subjects.
Special mentions go to Israel Halperin and Steven Hughes (Australian Institute of Sport) for their help
conducting the fitness testing and to Anthony Meade (Royal Adelaide Hospital) for his help
interpreting the blood chemistry.
The study was designed by Reid Reale (RR), Gary Slater (GS), Louise Burke (LB), Ian Dunican (ID) and
Gregory Cox (GC); data were collected by RR, ID, LB and analysed by RR and LB; data interpretation
and manuscript preparation were undertaken by RR, GS, GC and LB. All authors approved the final
version of the paper.
This study received funding form the Australian Institute of Sport, High Performance Sports Research
Fund.
All the authors declare that they have no conflict of interest derived from the outcomes of this study.

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