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The Acute Effects of Swimming on Appetite, Food Intake, and Plasma Acylated Ghrelin

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Swimming may stimulate appetite and food intake but empirical data are lacking. This study examined appetite, food intake, and plasma acylated ghrelin responses to swimming. Fourteen healthy males completed a swimming trial and a control trial in a random order. Sixty min after breakfast participants swam for 60 min and then rested for six hours. Participants rested throughout the control trial. During trials appetite was measured at 30 min intervals and acylated ghrelin was assessed periodically (0, 1, 2, 3, 4, 6, and 7.5 h. N = 10). Appetite was suppressed during exercise before increasing in the hours after. Acylated ghrelin was suppressed during exercise. Swimming did not alter energy or macronutrient intake assessed at buffet meals (total trial energy intake: control 9161 kJ, swimming 9749 kJ). These findings suggest that swimming stimulates appetite but indicate that acylated ghrelin and food intake are resistant to change in the hours afterwards.
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Hindawi Publishing Corporation
Journal of Obesity
Volume 2011, Article ID 351628, 8pages
doi:10.1155/2011/351628
Research Article
The Acute Effects of Swimming on Appetite, Food Intake, and
Plasma Acylated Ghrelin
James A. King, Lucy K. Wasse, and David J. Stensel
School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire LE11 3TU, UK
Correspondence should be addressed to David J. Stensel, d.j.stensel@lboro.ac.uk
Received 30 April 2010; Revised 8 July 2010; Accepted 9 September 2010
Academic Editor: Eric Doucet
Copyright © 2011 James A. King et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Swimming may stimulate appetite and food intake but empirical data are lacking. This study examined appetite, food intake,
and plasma acylated ghrelin responses to swimming. Fourteen healthy males completed a swimming trial and a control trial in a
random order. Sixty min after breakfast participants swam for 60min and then rested for six hours. Participants rested throughout
the control trial. During trials appetite was measured at 30 min intervals and acylated ghrelin was assessed periodically (0, 1, 2, 3, 4,
6, and 7.5 h. N=10). Appetite was suppressed during exercise before increasing in the hours after. Acylated ghrelin was suppressed
during exercise. Swimming did not alter energy or macronutrient intake assessed at buet meals (total trial energy intake: control
9161 kJ, swimming 9749 kJ). These findings suggest that swimming stimulates appetite but indicate that acylated ghrelin and food
intake are resistant to change in the hours afterwards.
1. Introduction
Regular physical activity is important for the maintenance
of body weight and its composition within a healthy range
[1,2]. All forms of physical activity can contribute to success-
ful energy balance by increasing daily energy expenditure.
Swimming is an attractive mode of physical activity due to
the reduced musculoskeletal and thermoregulatory stresses
(i.e., elevation in body temperature) imposed in comparison
with other land-based activities such as running and cycling.
Swimming may therefore oer an appealing form of physical
activity for individuals seeking to prevent weight gain and/or
to maintain a reduced body weight after successful weight
loss.
Despite the attractiveness of swimming as a mode of
physical activity, the ability of swimming to favourably
influence body weight and body composition remains
contentious. In obese individuals research has shown that
swimming may not induce body weight and fat loss [3,4]
whereas walking and cycling interventions of similar inten-
sity and duration do [3]. Considering the heightened energy
output elicited by all forms of exertion the most logical
explanation for these findings is that swimming stimulates
a compensatory increase in energy intake [5]. This notion is
consistent with anecdotal reports of swimming stimulating
appetite. Specifically, it has been stated that individuals often
feel like “eating a horse” after an acute bout of swimming [6].
This suggestion is consistent with empirical research which
has described elevations in energy intake after cycling-based
exercise performed on a modified ergometer in cold water
[5,7]. Despite these findings, there remains a paucity of data
about the precise eects of swimming on appetite and food
intake.
The mechanisms by which exercise influences appetite
have recently begun to receive significant interest with
specific attention being given to peptides implicated in the
neuroendocrine regulation of feeding [8,9]. Ghrelin is an
acylated peptide secreted primarily from the stomach and
remains unique as the only circulating gut peptide that stim-
ulates appetite [10]. Defined roles of ghrelin in both short-
and long-term feeding regulation have been uncovered [11],
and more recently investigators have sought to determine
how exercise influences circulating levels of ghrelin [1214].
These studies suggest that intense exercise induces a transient
suppression in circulating acylated ghrelin concentrations.
Concomitant suppressions in hunger have been reported by
2Journal of Obesity
Broom and colleagues [12,14] raising the possibility that
acylated ghrelin may be important in determining changes
in appetite resulting from exercise.
The primary aim of this investigation was to examine
the influence of an acute bout of swimming on appetite and
energy intake in an eort to determine whether a stimulatory
increase in these variables may explain data suggesting a
relative inecacy of swimming for the purposes of weight
control. A subsidiary aim of this investigation was to explore
the potential role of acylated ghrelin as a mediator of appetite
and food intake, during and after exercise.
2. Methods
2.1. Participants. Following university ethical advisory com-
mittee approval 14 healthy male volunteers (age 22.0 ±
0.5 y, BMI 23.2 ±0.6 kg·m2, body fat 17.2 ±1.2%, mean
±SEM) gave their written informed consent to participate.
Participants were nonsmokers, had no known history of
cardiovascular/metabolic disease, were not dieting, did not
have any atypical dietary habits (assessed by the three-
factor eating questionnaire), were not taking medication,
and were not obese (BMI 29.9kg·m2)orhypertensive
(resting blood pressure <140/90 mmHg). Participants were
habitually active but were not trained athletes, with most
individuals typically participating in games activities such as
soccer, hockey, and rugby on a regular basis at a recreational
level. The nature of the study demanded that participants
were competent at swimming; however, it was ensured that
individuals taking part in swimming at a competitive level
were not recruited for the study.
2.2. Procedure. Prior to main trials participants visited the
laboratory to undergo screening and preliminary testing. On
arrival at the laboratory participants were provided with an
information sheet detailing the demands of the study. The
information sheet stated that the aims of the study were to
examine the eects of swimming on appetite, energy intake,
and acylated ghrelin but did not provide any indication of
the hypothesised direction of responses. After confirming
that participants understood the study demands written
informed consent was obtained. Thereafter, questionnaires
were completed to assess health status, physical activity
habits, and food preferences. Height was determined to
the nearest 0.1 cm using a stadiometer (Seca 214, Seca
Ltd, Germany), and body weight was measured to the
nearest 0.1 kg using a digital scale (Seca 770, Seca Ltd,
Germany). Body density was estimated via subcutaneous
fat measurements [15] made using skinfold callipers (Baty
International, West Sussex, UK), and body fat percentage was
then ascertained [16].
Participants were then taken to the university swim-
ming pool to confirm swimming competence and to be
familiarised with procedures in anticipation of main trials.
For this, participants were asked to complete a 60min
intermittent swimming set which was to be performed
during the exercise trial. In this familiarisation session
participants were accustomed to wearing heart rate monitors
in the pool and taking recordings periodically. They were also
familiarised with the ratings of perceived exertion scale [17].
After an interval of at least one week participants then
completed two eight-hour trials (swimming and control) in
a randomized-crossover fashion. Each trial was separated
by at least one week. On the morning of main trials
participants arrived at the laboratory having fasted overnight
and not eaten breakfast. Main trials commenced at 09:00
with the consumption of a standard breakfast snack. This was
consumed within 5 min. On the exercise trial participants
rested within the laboratory for the first 40 min, after which
they were escorted to the university swimming pool via
motorised transport, in time for commencing swimming at
the beginning of the second trial hour. At this time, partici-
pants began a 60 min intermittent swimming set. The set was
composed of six 10 min blocks. In each block participants
swam continuously for seven min using their preferred stroke
and then rested for three min. The speed of swimming was
ultimately determined by the participant although they were
instructed to swim at a moderate intensity, defined as a rating
of perceived exertion between 12 and 14. During exercise
the distance completed was recorded. Heart rate was also
assessed using short range telemetry. Upon completion of
each swimming block participants rested on the pool side
with their legs immersed in the water. Ratings of perceived
exertion were then assessed. After completing the swimming
protocol participants were escorted back to the research
laboratory where they rested for a further six hours. Identical
procedures were completed in the control trial except that
no exercise was performed. Instead, during the equivalent
time period resting metabolic rate was assessed via indirect
calorimetry in order to permit the calculation of net energy
expenditure (gross energy expenditure minus resting energy
expenditure) during exercise.
2.3. Physical Activity and Dietary Standardization. Partic-
ipants completed a weighed food record of all items
consumed within the 24 h preceding their first main trial.
Alcohol and caeine were not permitted during this period.
This feeding pattern was replicated prior to the second main
trial. Participants refrained from strenuous physical activity
during this time.
2.4. Appetite and Environmental Conditions. At baseline, 0.5-
hour, 1-hour, and 30 min intervals thereafter appetite per-
ceptions (hunger, satisfaction, fullness, and prospective food
consumption) were assessed using 100 mm visual analogue
scales [18]. Environmental temperature and humidity were
also measured at these times using a handheld hygrometer
(Omega RH85, Manchester, UK). The temperature of the
swimming pool was monitored using a glass thermometer
(Fisher Scientific, UK).
2.5. Breakfast and Ad Libitum Buet Meals. During each
main trial all food was consumed within the research
laboratory and was quantified by the investigators. Main
trials commenced with breakfast consumption (09:00).
The breakfast provided was standardised to body weight
Journal of Obesity 3
and consisted of a commercial cereal bar (Kellogg’s Nutri-
grain). Participants received 1.06 g per kilogram of body
weight measured on the first trial visit. Identical amounts
were consumed across trials. For a 70kg individual this
provided 1092 kJ of energy, 6 g of fat, 4 g of protein, and 48 g
of carbohydrate.
At 3 h (12:00) and 7.5 h (16:30) into trials participants
were given access to a buet meal for a period of 30 min
from which they could consume food ad libitum.Thebuet
meal provided diversity in protein, fat, and carbohydrate
content in order to facilitate the detection of macronutrient
preferences (Table 3 ). Food was presented in excess of
expected consumption. Participants were told to eat until
satisfied and that additional food was available if desired.
Participants consumed meals in isolation so that social influ-
ence did not constrain food selection. Food consumption
was ascertained by examining the weighted dierence in
each food item remaining compared with the weight of that
initially presented. The energy and macronutrient content
of the items consumed was ascertained using manufacturer
values.
2.6. Acylated Ghrelin. To explore the eects of swimming on
circulating concentrations of acylated ghrelin, blood samples
were collected from 10 of the 14 participants at baseline,
1 h (pre-exercise), 2 h (post-exercise), 3 h, 4 h, 6 h, and 7.5 h.
(We did not measure acylated ghrelin in four participants for
logistical reasons, i.e., the room we used for blood sampling
at the swimming pool was not always available). In both
the swimming and control trials baseline samples and the
equivalent pre- and postexercise blood samples were taken
via venepuncture of an antecubital vein. Thereafter, the
remaining samples were collected via a cannula (Venflon,
Becton Dickinson, Helsinborg, Sweden) positioned in an
antecubital vein. Details of sample preparation, collection,
and analysis have been described in depth previously [12,
14]. The within batch coecient of variation for the acylated
ghrelin ELISA assay was 6.4%.
2.7. Energy Expenditure Estimation. Energy expenditure dur-
ing swimming was estimated using equations based on mul-
tiples of resting metabolism (METs) [19]. Specifically, energy
expenditure was estimated by multiplying each participant’s
estimated resting energy expenditure (kJ·min1) in the
control trial by an appropriate MET value for the stroke used
during each seven- minute block of swimming: general breast
stroke (10 METs), general backstroke (7METs), slow crawl
(0.95 m·s1—8.0 METs), and fast crawl (>0.95 m·s1
11 METs).
2.8. Statistical Analysis. All data was analyzed using the
Statistical Package for the Social Sciences (SPSS) software
version 16.0 for Windows (SPSS Inc, Chicago, IL, US.). Area
under the concentration versus time curve calculations were
performed using the trapezoidal method. Student’s t-tests
for correlated data were used to assess dierences between
fasting and area under the curve values for appetite percep-
tions, acylated ghrelin, temperature, and humidity between
the control and swimming trials. Repeated measures, two-
factor ANOVA was used to examine dierences between
the swimming and control trials over time for appetite
perceptions, energy and macronutrient intake, and acylated
ghrelin. The Pearson product moment correlation coe-
cient was used to examine relationships between variables.
Correction of acylated ghrelin values for changes in plasma
volume did not alter the statistical significance of findings
therefore for simplicity the unadjusted values are presented.
Statistical significance was accepted at the 5% level. Results
are presented as mean ±SEM. A power calculation indicated
that 13 participants were needed to provide sucient power
(80%) to detect a 50% compensation in energy intake with
alpha set at 5%.
3. Results
3.1. Exercise Responses and Resting Oxygen Consumption.
During the 42 min of swimming (6 ×7 min intervals) the
mean distance completed was 1875 ±156 m. The mean
swimming speed performed was 0.74 ±0.1 m·s1, and this
elicited an estimated net energy expenditure (exercise minus
resting) of 1921 ±83 kJ. The corresponding mean heart rate
and rating of perceived exertion values during the sessions
were 155 ±5beats·min1and 14 ±0. To complete the
swimming session four participants swam breaststroke for
all of the intervals whilst three participants used only front
crawl and two participants used only backstroke. Three par-
ticipants used a combination of front crawl and breast stroke
whilst two participants alternated between breaststroke and
backstroke. Participants’ mean oxygen consumption at rest
during the second hour of the control trial (i.e., the time
when they were swimming during the exercise trial) was 0.32
±0.01 L·min1(6.5 ±0.3 kJ·min1).
3.2. Baseline Parameters. No between-trial dierences
existed at baseline for any of the ratings of appetite assessed
or in plasma concentrations of acylated ghrelin (student’s
t-test, P>.05 for each).
3.3. Appetite, Energy and Macronutrient Intake. Perceived
ratings of hunger and prospective food consumption were
suppressed during and immediately after swimming before
increasing above values exhibited during the control trial
in the hours after exercise (two-factor ANOVA, trial ×
time interaction; P<.05 for each). Conversely, perceived
ratings of fullness and satisfaction were increased transiently
during swimming before decreasing below control values
in the hours thereafter (two-factor ANOVA, trial ×time
interaction; P<.05 for each) (Figure 1). Analysis of the
appetite area under the curve (AUC) data confirmed these
results. After the morning meal the hunger AUC (3.5–8 h)
was significantly higher in the swimming trial as compared
with control (swimming 178 ±20, control 152 ±19;
student’s t-test, P=.028) whilst fullness tended to be
reduced (swimming 227 ±21, control 243 ±17; student’s
t-test, P=.052). Moreover, from baseline to consumption
of the morning buet meal the fullness AUC (0–3h) was
4Journal of Obesity
Tab le 1: Energy intake (kJ) in the control and swimming trials (n=
14). There were no significant dierences between the swimming
and control trials (P>.05).
Control Swimming
Morning meal 5517 ±434 5856 ±403
(3–3.5 h)
Afternoon meal 3644 ±459 3893 ±577
(7.5–8 h)
Total trial 9161 ±719 9749 ±809
Tab le 2: Macronutrient intake in the control and swimming trials.
Values are gram and (%) (n=14). There were no significant
dierences between the swimming and control trials (P>.05).
Control trial Fat Carbohydrate Protein
Morning meal
(3–3.5 h) 54 ±5 (34.1) 156 ±11
(49.1) 59 ±9 (16.8)
Afternoon meal
(7.5–8 h) 33 ±5 (33.8) 107 ±15
(49.9) 38 ±8 (16.3)
To t a l Tr i a l 8 7 ±8 (34.9) 263 ±21
(49.1) 97 ±9 (16.0)
Swimming trial Fat Carbohydrate Protein
Morning meal
(3–3.5 h) 55 ±5 (34.0) 164 ±12
(49.3) 60 ±8 (16.7)
Afternoon meal
(7.5–8 h) 35 ±5 (33.1) 117 ±20
(50.2) 38 ±7 (16.7)
To t a l Tr i a l 9 0 ±9 (34.2) 281 ±26
(49.4) 98 ±9 (16.4)
significantly higher in the swimming trial as compared with
control (swimming 74 ±12, control 54 ±8; student’s
t-test, P=.025) whilst prospective food consumption was
suppressed (swimming 221 ±12, control 231 ±11; P=
.049).
Energy intake was significantly higher at the morning
buet meals compared with the afternoon meals (two-
factor ANOVA, main eect of time; P=.003); however,
there were no between-trial dierences in energy intake
at either feeding opportunity (two-factor ANOVA, trial
and interaction main eects; P>.05 for each). Relative
energy intake (energy intake—net energy cost of exercise)
was therefore significantly lower on the swimming trial as
compared with control (swimming 7828 ±774 kJ, control
9163 ±720). Tab l e 1 presents the energy intake data for the
control and swimming trials.
Two-factor ANOVA showed no trial or interaction (trial
×time) main eects for macronutrient intake (absolute
amount or percentage intake) indicating that no significant
dierences existed between trials for the intake of fat,
carbohydrate or protein (Table 2 ).
3.4. Acylated Ghrelin. Data for ten participants showed that
plasma concentrations of acylated ghrelin were suppressed
during swimming and after consumption of the morning
buet meal (two-factor ANOVA, main eect of trial; P=
Tab le 3: Items presented at buet meals.
Coco-pops—Cereal
Cornflakes—Cereal
Rice Krispies—Cereal
Frosties—Cereal
Milk
Cereal Bar
White Bread
Brown Bread
Tuna
Cheese
Ham
Butter
Mayonnaise
Salted Crisps
Apple
Orange
Banana
Chocolate rolls
Chocolate muns
Plain muns
Cookies
Chocolate bar (Mars fun size)
.038). On closer inspection of the data one participant was
a clear outlier exhibiting fasting values on both trials which
were approximately nine times (26 standard deviations)
higher than the mean fasting values of the other nine partici-
pants (949 pg·mL1for the outlier versus 108 ±10 pg·mL1
for the mean (±SEM) of the other nine participants). Upon
removal of this outlier the suppression of acylated ghrelin at
the end of the swimming bout and after the first meal on each
trial is displayed with greater clarity (two-factor ANOVA,
trial ×time interaction; P<.001) (Figure 2). Examination of
the acylated ghrelin AUC (outlier excluded, n=9) confirmed
suppressed concentrations of acylated ghrelin prior to the
first buet meal (0–3 h) on the swimming trial (swimming
473 ±232, control 505 ±217 pg·mL1·3 h) (student’s t-test,
P<.001).
To examine the relationship between acylated ghrelin and
energy intake, at both the morning and afternoon buet
meals correlations were performed between acylated ghrelin
values immediately prior to each meal and subsequent
energy intake. Moreover, correlations were also performed
using the acylated ghrelin AUC leading up to the morning
(0–3 h AUC) and afternoon (3–8 h AUC) buet meals. In
all instances no significant relationships were found between
acylated ghrelin and energy intake.
3.5. Body Mass, Fluid Intake, and Environmental Conditions.
There were no significant dierences between the control and
swimming trials (all P>.05) in body weight (control 76.7 ±
2.1, swimming 76.5 ±2.2 kg), water intake (control 1402 ±
219, swimming 1302 ±226 mL) laboratory atmospheric
Journal of Obesity 5
Hunger (0-100)
0
20
40
60
80
100
0
20
40
60
80
100
0
20
40
60
80
100
0
20
40
60
80
100
012345678
PFC (0-100) Satisfaction (0-100)
Time (hours)
012345678
Time (hours)
Fullness (0-100)
(a)
(b)
(c)
(d)
Figure 1: Ratings of hunger (a), fullness (b), satisfaction (c), and prospective food consumption (d) in the swimming () and control ()
trials. Values are mean ±SEM (n=14). Black rectangle indicates breakfast snack, hatched rectangle indicates swimming, and diagonal
rectangles indicate buet meals. Two-factor ANOVA revealed a trial ×time interaction eect for each (P<.05).
temperature (control 21.6 ±0.3, swimming 21.4 ±0.3C),
and relative humidity (control 37.8 ±4.1, swimming 37.8 ±
4.1%). The atmospheric temperature and relative humidity
at the swimming pool were 26.4 ±0.8C and 50.9 ±1.7%,
respectively. The temperature of the swimming pool water
was 28.1 ±0.1C.
4. Discussion
The main findings arising from this investigation are three-
fold. Firstly, moderate intensity swimming exhibited a bipha-
sic influence on appetite with an inhibition existent during
exercise and a later stimulation in the hours thereafter.
Secondly, swimming did not influence ad libitum energy
or macronutrient intake. Finally, our exploratory analyses
showed that swimming transiently suppressed circulating
concentrations of the orexigenic peptide, acylated ghrelin;
however, no eects were apparent after exercise. This out-
come indicates that acylated ghrelin does not mediate the
reported stimulation of appetite after swimming.
The suppression of appetite (decreased hunger and
prospective food consumption/elevated satisfaction and full-
ness) observed during swimming is a novel finding yet is
consistent with previous research showing a transient inhibi-
tion of appetite resulting from land-based exercise modalities
such as running and cycling [20,21]. This phenomenon has
been termed exercise-induced anorexia [22] and has been
consistently observed during land-based activities performed
at moderate intensities or higher (>60% VO2max). Broom
et al. [12] reported suppressed hunger and plasma acylated
ghrelin during treadmill running and suggested a potential
role of acylated ghrelin in determining suppressed appetite
during exercise. The findings from the present study con-
firm that acylated ghrelin and appetite are concomitantly
suppressed during swimming; however, the absence of any
significant correlations between acylated ghrelin and any of
the appetite markers assessed, during exercise or immediately
after, suggests that there may not be a strong association
between these variables. Given the diversity of the role
of ghrelin in human physiology [23] it is possible that
6Journal of Obesity
012345678
Time (hours)
0
20
40
60
80
100
120
140
Acylated ghrelin (pg·mL1)
Figure 2: Plasma concentrations of acylated ghrelin in the swim-
ming () and control () trials. Values are mean ±SEM (n=
9). Black rectangle indicates breakfast snack, hatched rectangle
indicates swimming, diagonal rectangles indicate buet meals. Two-
factor ANOVA revealed a significant trial ×time interaction eect
(P<.001).
the transient suppression of circulating acylated ghrelin
observed during exercise is entirely unrelated to appetite
regulation. At present though, the physiological relevance of
thisresponseisnotknown.
In the hours after consumption of the morning buet
meal, ratings of hunger and prospective food consumption
were higher in the swimming trial than the control trial
whilst ratings of fullness were reduced. These findings
indicate that swimming stimulated a delayed increase in
appetite. This response is contrary to research which has
examined appetite responses to land-based activities which
have typically shown no acute compensation in appetite
after performing exercise, even when significant amounts
of energy are expended [2022,24]. The mechanism
responsible for these discrepant findings is not immediately
clear. It has been suggested that changes in body temperature
may be important [5,6]; however, this is unlikely in the
present study as appetite was not stimulated until more than
two hours after swimming. By this time core temperature
would almost certainly have normalised. White et al. [5]
speculate that the cooling and then subsequent reheating
of the body may be associated with the release of “certain
hormones” which stimulate the appetite. In the present study
we measured circulating concentrations of acylated ghrelin, a
peptide responsible for stimulating appetite and food intake
[25,26]. The present findings suggest that acylated ghrelin
is not responsible for the augmented appetite response after
swimming as circulating concentrations were not dierent
from control after the morning buet meal. It remains
possible that compensatory changes in fasting or meal-
related acylated ghrelin profiles may occur over a longer
duration; however, further work is needed to examine this. It
must also be considered that appetite is regulated on an acute
basis by many circulating peptides in addition to acylated
ghrelin, including peptide YY, pancreatic polypeptide, and
glucagon-like peptide-1 [10]. It is therefore feasible that
changes in these peptides may have influenced the acylated
ghrelin and appetite responses observed.
Research indicates that swimming may be less eective
than land-based activities for inducing weight loss or
reductions in body fat [3,4]. Consistent with this, it has
been observed that levels of adiposity are typically higher in
swimmers than equal calibre runners [27,28]. It has been
suggested that an unparalleled stimulation of appetite and
energy intake after swimming may explain these findings [6].
Despite the changes in appetite observed, the present inves-
tigation did not find any significant dierences in energy
or macronutrient intake between the swimming and control
trials, either during the morning or afternoon meals. These
findings are dicult to reconcile. It is known that food intake
is influenced by a host of physiological, environmental,
psychological, and social factors, some of which are learned
over time and are resistant to change [29]. In this study it
seems that the factors influencing appetite were insucient
to overcome other competing forces governing food intake.
Nonetheless, as a consequence of the lack of change in energy
intake, participants therefore failed to compensate for the
energy expended during exercise and relative energy intake
(energy intake—net energy cost of exercise) was subse-
quently lower on the swimming trial as compared with con-
trol (swimming 7828 ±774 kJ, control 9163 ±720 kJ; stu-
dent’s t-test, P=.008). This outcome contradicts the sugges-
tion that energy intake is augmented by swimming and there-
fore does not support the notion that swimming is an inef-
fective exercise modality for successful body weight control.
When comparing the present findings to previous data
water temperature emerges as an important variable influ-
encing food intake responses to exercise performed in water.
White et al. [5] examined energy intake responses in healthy
participants who performed cycling exercise while immersed
in either cold water (20C) or neutral water (33C) and
compared these responses to control responses (i.e., while
resting in a dry environment). Energy intake was significantly
higher after exercise in cold water (3653kJ) as compared
with the neutral water (2544 kJ) and the resting trials
(2586 kJ). These results indicate that exercise in cold water
stimulates energy intake. In similar fashion, Dressendorfer
[7] submitted six trained males to 30 min of modified
cycling in cold water (22C), warm water (34C), cycling
on land, and a resting control trial. Participants consumed
significantly more energy in the cold water trial than all
other trials at a buet meal provided immediately after
exercise. Furthermore, energy intake in the warm water trial
was significantly less than all other trials. Collectively, these
findings suggest that water temperature and possibly sub-
sequent core body temperature are important determinants
of feeding responses after exercise in water. Despite these
established findings, no study has previously examined the
specific eects of swimming (rather than modified cycling)
on appetite and food intake. Our findings appear to support
the notion that exercise only in cold water stimulates food
intake because in the present study the water temperature
was moderate (28–28.5C) and no change in energy intake
was observed. The idea that exercise only in cold water
Journal of Obesity 7
stimulates food intake is also supported by the finding
that metabolic rate (and hence energy expenditure) is not
increased by immersion in water at a temperature of 32C
(not that dissimilar from the temperature of the water in
the present study) whereas metabolic rate is increased by
immersionincoldwater(either14
Cor20
C) [30]and
by cold air, possibly due to activation of brown adipose
tissue [31]. It might be anticipated that immersion in
water will only increase appetite and food intake if the
water temperature lowers core temperature, eliciting an
increase in metabolic rate either by shivering or nonshivering
thermogenesis although this is speculation. Unfortunately
core temperature was not assessed in the present study,
therefore the exact relationship between this variable and
energy intake cannot be explored. Further work is needed to
examine this issue.
This investigation has some notable limitations. Firstly,
an immersed, resting control trial was not included therefore
making it dicult to determine whether the reported
increase in appetite was due to immersion in water or
the physical work completed. Despite this, the majority
of previous investigations which have examined appetite
responses to exercise have not observed increases in appetite
afterwards [9], thus we believe that our findings still oer
novel, interesting data. Secondly, although we have examined
energy/macronutrient intake responses over an extended
period, it remains possible that changes may occur over
a longer duration of time, for example, on the day after
exercise. An even longer period of observation would be
necessary in future studies to test this hypothesis. Thirdly,
this study did not directly compare the eects of swimming
with those of other modes of exercise and this limits the
extent to which conclusions can be drawn in this regard.
Finally, participants were young, healthy males and we
do not know if these findings would generalise to other
populations such as females, the elderly or overweight and
obese individuals. Additional work is required to examine
these issues, particularly in overweight individuals as it is
within this population that findings hold the most clinical
importance.
In conclusion, this investigation has shown that an acute
bout of moderate intensity swimming suppresses appetite
during exercise before leading to an increase later on in
the day. Despite this, energy intake and macronutrient
selection appear resistant to change over the duration of time
examined. Circulating concentrations of acylated ghrelin
were suppressed during swimming and this may possibly
have contributed to the reduction in appetite observed.
Nonetheless, acylated ghrelin does not appear to mediate
the reported increase in appetite in the hours after exercise.
These findings provide novel information regarding the
influence of swimming on the acute regulation of energy
homeostasis.
Acknowledgments
The authors would like to thank all of the participants for
dedicating their time to take part in this study. They would
like to thank Mr. James Carson and Mr. Michael Sawrey
for their assistance with participant recruitment and data
collection. They would also like to thank Miss Karen Shilton
for organising access to the university swimming pool.
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