Acute effect of environmental temperature during exercise on
subsequent energy intake in active men
1–3Allison L Shorten, Karen E Wallman, and Kym J Guelfi ABSTRACT
Background:The performance of exercise while immersed in cold water has been shown to influence energy intake in the subsequent meal. However, the effect of ambient temperature during land-based exercise is not known.
Objectives: Our aims were to investigate the effect of exercise performed in the heat on energy intake in the subsequent meal and to determine concentrations of circulating appetite-related hormones. Design:In a randomized, counterbalanced design, 11 active male participants completed 3 experimental trials in a fasted state: exer-cise in the heat (36°C), exercise in a neutral temperature (25°C), and a resting control (25°C). The exercise trials consisted of treadmill running for 40 min at 70%V_O2peak. After each trial, participants were presented with a buffet-type breakfast of precisely known quantity and nutrient composition, which they could consume ad libitum.
Results: Energy intake was greater after exercise in the neutral temperature compared with the control (P= 0.021) but was similar between exercise in the heat and the control and between the 2 exercise trials. When accounting for the excess energy expended during exercise, relative energy intake during exercise in the heat was lower than the control (P = 0.002) but was similar between exercise in the neutral temperature and the control and between exercise in the heat and in the neutral temperature. The lower rel-ative energy intake after exercise in the heat was associated with an elevated tympanic temperature and circulating concentrations of peptide YY (P,0.05).
Conclusion: Exercise in a neutral environmental temperature is associated with higher energy intake in the subsequent meal com-pared with a control, whereas exercise in the heat is not. Am J Clin Nutrdoi: 10.3945/ajcn.2009.28162.
INTRODUCTION
Weight management is an issue of growing concern, partic-ularly in Western society where there is an abundant availability of energy-dense foods, as well as the use of modern technologies that promote a sedentary lifestyle. It is well established that maintenance of a healthy weight is achieved when there is a balance between energy (food) intake and the amount of energy expended to sustain bodily function and participate in physical activities (1). However, it is also now apparent that an acute bout of exercise itself may influence the total amount of energy consumed, the motivation to eat, and preferences for foods of specific macronutrient composition (2, 3). This acute effect of exercise on energy intake appears to be moderated by the sex (4–
6), body composition (7), and training status of the individual (8), as well as by the duration, mode, and intensity of the exercise session (8–10). Another factor that may influence the acute effect of exercise on subsequent energy intake is the environmental temperature at which exercise is performed. Dressendorfer (11) compared the acute effect of exercise (30 min cycling at 70%
_
VO2max) immersed in cold water (22°C), warm water (34°C), and on land (24°C) on energy intake during the postexercise meal in trained male participants. Energy intake was signifi-cantly greater after exercise in cold water in comparison with both warm water and on land. Similarly, White et al (12) showed that energy intake from a buffet-type meal was significantly greater after exercise while immersed in cold water (45 min cycling at 60%V_O2maxin 20°C) in comparison to energy intake after an equivalent bout of exercise immersed in warm water (33°C) in male college students. Taken together, these findings indicate that the environmental temperature in which exercise is performed may influence energy intake in the postexercise meal. However, it is important to note that these studies have focused primarily on the effect of low (cold) temperatures resulting from water immersion. In addition, the influence of environmental temperature during exercise on subsequent macronutrient se-lection and preferences for energy intake from solid foods or drinks remains unknown.
Therefore, the aim of the present study was to investigate the effect of land-based exercise, performed in the heat, on sub-sequent energy intake, macronutrient selection, and preferences for solid food or drinks from a buffet-type meal of precisely known quantity and nutrient composition from which participants could consume ad libitum. A secondary aim was to determine the effect of exercise in the heat on a range of hormones involved in the regulation of appetite.
1
From the School of Sport Science, Exercise and Health, The University of Western Australia, Perth, Australia.
2
Supported by a University of Western Australia Research Development Award. The hormone assays were carried out at the facilities at the Centre for Microscopy, Characterisation and Analysis, The University of Western Aus-tralia, which are supported by university, state, and federal government funding.
3
Address correspondence to K Guelfi, School of Sport Science, Exercise and Health, The University of Western Australia, 35 Stirling Highway, Craw-ley, WA 6009, Australia. E-mail: kguelfi@cyllene.uwa.edu.au.
Received June 3, 2009. Accepted for publication August 29, 2009. doi: 10.3945/ajcn.2009.28162.
Am J Clin Nutrdoi: 10.3945/ajcn.2009.28162. Printed in USA.Ó2009 American Society for Nutrition 1 of 7
AJCN. First published ahead of print September 30, 2009 as doi: 10.3945/ajcn.2009.28162.
SUBJECTS AND METHODS
Participants
Eleven healthy, physically active men [mean (6SD) age: 20.86 2.1 y; body mass index (in kg/m2): 24.162.3;V_O2peak: 53.86 8.9 mLkgmin21; basal metabolic rate: 778161226 kJd21] were recruited for this study. Participants had maintained a stable body weight (62 kg) for a period of 6 mo preceding the study and were not taking any medications or on any special diet that may influence food intake. To minimize any conscious al-teration in food consumption, the participants were not informed that their food intake would be monitored during the study, but were personally debriefed after the completion of all trials. The study was approved by the Institutional Human Ethics Com-mittee, and written consent was obtained from all participants.
Experimental design
Each participant attended our laboratory on 4 separate occa-sions, each separated by 1 wk. The initial visit was a familiar-ization session, followed by 3 experimental trials administered in a randomized counterbalanced design: exercise in the heat (HEAT), exercise in a neutral environmental temperature (NEUT), and a resting control (CON).
Familiarization session
On arrival to the laboratory, participants completed a ques-tionnaire detailing the typical foods that they consumed at breakfast to ensure that the foods provided in the experimental trials would be palatable. Next, aerobic capacity (V_O2peak) was measured by using an incremental treadmill protocol to de-termine the treadmill speed required to standardize exercise intensity during the subsequent experimental trials. This test consisted of 3-min stages with the speed of the treadmill pro-gressively increased at each stage by or 1–2 km h21 until voluntary exhaustion. During the test, participants breathed through a mouthpiece into a computerized gas analysis system. This system consisted of a ventilometer (Morgan, Kent, United Kingdom) to measure the volume of inspired air, as well as oxygen and carbon dioxide analyzers (Ametek Applied Elec-trochemistry S-3A/1 and CD-3A; AEI Technologies, Pittsburgh, PA) to measure the percentage of oxygen and carbon dioxide in expired air. After theV_O2peak test, participants were presented with a buffet-type meal and instructed to eat ad libitum until satiety. The purpose of this was to familiarize participants with the buffet-type meal to account for any novelty factor and pre-vent overfeeding when presented with a similar buffet-type meal in the subsequent experimental trials.
Experimental trials
Each participant completed the 3 experimental trials in-dividually with 7 d between visits. On the day before the first experimental trial, participants were required to record all foods consumed and the timing of meals and then to replicate this on the day before each subsequent trial. In addition, the participants were asked to refrain from alcohol consumption and vigorous physical activity in the 48 h before the experimental trials.
Participants were also instructed to wear the same clothing for each visit.
For each of the 3 experimental trials, the participants attended the laboratory at 0700 in a fasted state. On arrival, participants were weighed and their dietary records were reviewed. At 0715, the participants either rested (CON) or exercised for 40 min in the heat (HEAT) or in a neutral temperature (NEUT). After exercise, excess postexercise oxygen consumption (EPOC) was measured while lying quietly for 20 min. A buffet-type breakfast was provided at 0830 for 30 min.
Exercise trials
The exercise trials consisted of treadmill running for 40 min at 70% V_O2peak in a climate-controlled chamber. The environ-mental temperature was set at 36°C, with 30% relative humidity during HEAT and at 25°C with 30% relative humidity during NEUT. Expired air was sampled during exercise by using the same computerized gas analysis system used for the de-termination of V_O2peak. In addition, a heart rate monitor was worn by each participant while exercising, and tympanic tem-perature was recorded at regular intervals (Bruin, Germany). Body mass was measured without clothing pre- and postexercise to determine mass loss due to sweating. After the cessation of exercise, excess postexercise oxygen consumption (EPOC) was measured for 20 min. This required participants to lie supine on a bed while breathing through a mouthpiece to allow for the collection of their expired air for subsequent analysis.
Control trial
During the control trial, participants lay supine in the climate chamber (25°C with 30% relative humidity) for 40 min while breathing through a mouthpiece enabling the collection of their expired air for analysis. After the 40-min control period, participants remained rested until 0830 when breakfast was provided.
Assessment of energy intake
After each experimental trial, participants were presented with an array of breakfast foods for 30 min during which time they were instructed to eat ad libitum until satiety was reached. The buffet-type breakfast consisted of foods and drinks con-sidered regular choices for breakfast that were of varied mac-ronutrient composition (ie, breakfast cereals, milk, bread, croissants, spreads, yogurt, fruit, juice, cold meats, and cheese). The foods provided were in excess of expected consumption and of precisely known quantity and nutrient composition. Total energy intake from the breakfast meal was calculated by weighing all remaining food products after the participant had left the laboratory. This methodology has been shown to be a reliable method of assessing energy intake (13). Total kilo-joules, along with the quantity of consumed carbohydrate, protein, and fat and the percentage of energy intake from solid foods and drinks were recorded. In addition, relative energy intake (REI) was calculated by correcting postexercise energy intake for the energy cost of the exercise session above the resting energy expenditure (14).
Blood sampling
A series of capillary blood samples (500lL) were taken from a hyperaemic fingertip after warming the hand for 3 min in a heated water bath before exercise or control and before and after the breakfast meal. From these samples, blood glucose and lactate concentrations were measured by using a blood gas an-alyzer (35 lL; Radiometer, Copenhagen, Denmark), and the remaining blood was treated with EDTA and serine protease inhibitor before centrifugation at 1020 gfor 10 min, with the plasma obtained stored at 280°C until later analysis. Leptin, insulin, active ghrelin, pancreatic polypeptide, and peptide tyrosine-tyrosine (PYY) concentrations were subsequently de-termined by using a commercially available assay kit (Lincoplex Human Gut Hormone Multiplex Assay; Linco Research Inc, St Charles, MO).
Data analysis
Energy and macronutrient intake were compared between trials by using repeated-measures analysis of variance (ANOVA), with post hoc pairwise comparisons that used Bonferroni ad-justment to determine where any differences lay. Two-factor (time·trial) repeated-measures ANOVA was used to compare the response of blood variables (glucose, lactate, and appetite-related hormones) to the experimental trials. Statistical signifi-cance was accepted as a P value of , 0.05 (SPSS 16.0 for Windows computer software package; SPSS Inc, Chicago, IL).
RESULTS
Exercise sessions
All participants completed the exercise bout at the prescribed intensity. Overall, the characteristics of the HEAT and NEUT exercise sessions were similar, with no significant differences in oxygen consumption, respiratory exchange ratio, or total energy expenditure during exercise between the 2 trials (P.0.05;Table 1). However, heart rate during HEAT was significantly higher compared with NEUT (P= 0.001). During recovery from ex-ercise, there was no significant effect of trial on EPOC (P = 0.429). Both exercise protocols resulted in a significant decrease in body mass (NEUT: 0.656 0.21 g; HEAT: 0.6560.41 g), whereas there was no change after CON.
Total energy intake
There was a significant main effect of trial on total energy intake during the postexercise meal (P= 0.012;Figure 1A). Post hoc analysis revealed that energy intake was greater after NEUT in comparison to CON (P = 0.021). However, there was no significant difference in energy intake between HEAT and CON (P= 0.307) or between HEAT and NEUT (P= 0.399).
Relative energy intake
To further investigate the effect of exercise on subsequent energy intake, REI was calculated to account for the extra energy expended during exercise. There was a significant main effect of trial on REI (P = 0.009; Figure 1B). Relative energy intake during HEAT was lower than CON (P= 0.002). In contrast, no significant difference in REI was observed between the 2 exer-cise trials (P= 0.484) or between NEUT and CON (P= 0.427).
Macronutrient intake
There was a significant main effect of trial on energy intake from carbohydrate (P= 0.01; Table 2). During NEUT, carbo-hydrate intake was significantly higher compared with CON (P= 0.02), whereas there was no difference between HEAT and
TABLE 1
Descriptive characteristics of 40 min treadmill running performed in the heat (HEAT) or in a neutral temperature (NEUT)1
NEUT HEAT
Exercise intensity (%V_O2peak) 7267 7067 Heart rate (beats/min) 165612a 180610b Respiratory exchange ratio 0.9160.04 0.9160.03 Total exercise energy expenditure (kJ) 23756280 23286222 EPOC at 10 min (Lmin21) 0.1460.10 0.1260.08 EPOC at 15 min (Lmin21) 0.1260.20 0.0660.06 EPOC at 20 min (Lmin21) 0.1860.24 0.1660.18
1
All values are means6SDs;n= 11. EPOC, excess postexercise oxygen consumption. Values that do not share a common superscript letter are significantly different,P,0.05 (pairwise comparisons).
FIGURE 1.Mean (6SE) results showing the effect of exercise in the heat (HEAT), the effect of exercise in a neutral environmental temperature (NEUT), or a resting control (CON) on (A) total energy intake and (B) relative energy intake in the postexercise meal (n = 11). Values that do not share a common superscript letter are significantly different,P,0.05 (post hoc pairwise comparisons with Bonferroni adjustment when the significant main effect of trial was indicated by repeated-measures ANOVA).
CON (P= 0.196) or between the 2 exercise trials (P= 0.44). However, when carbohydrate intake was expressed as a per-centage of overall energy intake, there was no difference be-tween trials (P= 0.124). There was no significant main effect of trial on absolute or relative fat (P= 0.252,P= 0.435) or pro-tein intake (P= 0.105,P= 0.239).
Solid food and drink preferences
There was a main effect of trial on energy intake from solid foods (P= 0.031), although post hoc comparisons did not reach significance (Table 2). Likewise, there was a main effect of trial on energy intake from drinks (P= 0.031), with a tendency for a greater amount of energy to be consumed in the form of drinks during HEAT compared with CON (P = 0.055). Furthermore, a greater quantity of water was consumed throughout both HEAT and NEUT in comparison with CON (P= 0.003 andP= 0.026, respectively), although no significant difference was ob-served between HEAT and NEUT (P= 0.502).
Blood lactate and glucose concentrations
There was a significant interaction effect of trial and time on blood lactate concentrations (P= 0.003;Figure 2A). Post hoc analysis revealed similar blood lactate concentrations preexer-cise between trials, followed by an increase during both HEAT and NEUT, which resulted in significantly greater concen-trations on the completion of exercise compared with CON (P= 0.041 and P= 0.001, respectively). During recovery from ex-ercise, blood lactate concentrations returned rapidly to baseline, with no significant difference between trials immediately before the breakfast meal.
On the other hand, there was no significant interaction effect of trial and time on blood glucose concentrations (P= 0.159; Figure 2B), although there was a main effect of time irrespective of trial
(P= 0.001), with an increase in blood glucose concentrations after consumption of the breakfast meal.
Tympanic temperature
There was a significant interaction effect of trial and time on tympanic temperature (P = 0.001; Figure 2C). Preexercise tympanic temperature was similar in the 3 trials. However, temperature increased during HEAT, which resulted in higher levels immediately postexercise compared with both CON (P= 0.001) and NEUT (P= 0.001). Before breakfast, the tympanic temperature remained elevated after HEAT compared with NEUT (P= 0.023). After the breakfast meal, temperature was similar in the 3 trials.
Hormonal response
The concentrations of circulating insulin were similar between trials throughout the experimental period with no significant interaction of trial and time (P= 0.979;Figure 3A). However, there was a main effect of time, with a significant increase in insulin after the breakfast meal (P = 0.002). In contrast, the interaction of trial and time on leptin approached significance (P = 0.088; Figure 3B), and a main effect of time revealed a decline in leptin after the breakfast meal (P = 0.001). With respect to active ghrelin, the interaction of trial and time also approached significance (P= 0.072; Figure 3C). There was no significant interaction of trial and time on the circulating con-centrations of pancreatic polypeptide (P = 0.262; Figure 3D), although a main effect of time revealed an increase after con-sumption of the breakfast meal (P,0.001). Finally, there was an interaction effect of trial and time on circulating concentrations of PYY (P= 0.048; Figure 3E), with significantly higher concen-trations in HEAT compared with CON before the breakfast meal (P,0.001). After the breakfast meal, PYY increased in all trials (P= 0.008), with significantly higher concentrations observed in TABLE 2
Effect of a resting control (CON), exercise performed in the heat (HEAT), or exercise in a neutral temperature (NEUT) on absolute and relative macronutrient intake and energy intake from food and drink sources1
CON NEUT HEAT
Carbohydrate (kJ)2 17186642a 270661,182b 21526918a,b (% intake) 46610 51612 49610 Fat (kJ) 11786508 14266548 13086672 (% intake) 3269 29611 3068 Protein (kJ) 7126295 8636335 6986330 (% intake) 1965 1766 1665 Solid food (kJ)2 283661020 399261579 305361390 (g)2 2386107a 4016174b 2836150a,b Drinks (kJ)2 9086546 1,2016419 12736528 (g)2 5326316 7906247 8056291 Water intake (g)2 1006240a 3606299b 5056270b 1
All values are means6SDs;n= 11. Values that do not share a common superscript letter are significantly different,
P,0.05 (post hoc pairwise comparisons with Bonferroni adjustment).
2
HEAT compared with both CON (P= 0.004) and NEUT (P = 0.024).
DISCUSSION
The primary aim of this study was to investigate the effect of an acute bout of exercise, performed in the heat, on energy and macronutrient intake, as well as preferences for energy intake from solid food or drinks in the subsequent meal. Contrary to the main hypothesis, total energy intake after HEAT was not sig-nificantly different from that observed after NEUT. However, energy intake was significantly greater after NEUT compared with the resting CON trial, whereas there was no difference after HEAT compared with CON.
The lack of direct statistical difference between HEAT and NEUT is in contrast with previous research reporting a significant effect of the environmental temperature during exercise on FIGURE 2.Mean (6SE) results showing the effect of exercise in the heat (d), the effect of exercise in a neutral environmental temperature (s), or a resting control (:) on (A) blood lactate, (B) blood glucose, and (C) tympanic temperature (n = 11). The downward arrow (Y) indicates the timing of the breakfast meal. Values that do not share a common superscript letter are significantly different,P ,0.05 (post hoc pairwise comparisons with Bonferroni adjustment when significant interaction of trial and time was indicated by 2-factor repeated-measures ANOVA).
FIGURE 3.Mean (6SE) results showing the effect of exercise in the heat (HEAT), the effect of exercise in a neutral environmental temperature (NEUT), or a resting control (CON) on the circulating concentrations of (A) insulin, (B) leptin, (C) ghrelin, (D) pancreatic polypeptide (PP), and (E) peptide YY (PYY) (n= 10). Values that do not share a common superscript letter are significantly different,P,0.05 (post hoc pairwise comparisons with Bonferroni adjustment when significant interaction of trial and time was indicated by 2-factor repeated-measures ANOVA). An asterisk indicates a significant difference from baseline concentrations,P ,0.05 (post hoc pairwise comparisons with Bonferroni adjustment when significant main effect of time was indicated by 2-factor repeated-measures ANOVA).
subsequent energy intake (11, 12). However, the focus of these past studies was on exercise in a low (cold) temperature, which resulted from water immersion. This raises the possibility that alterations in postexercise energy intake may be triggered only when the environmental temperature is below a certain threshold or that immersion itself may influence subsequent energy intake (12). In support of the latter, Zeyl et al (15) reported decreased concentrations of the hormone leptin (high concentrations of which decrease appetite) in response to resting cold-water im-mersion. Furthermore, the difference in the environmental temperature between NEUT and HEAT in the current study was 11°C. Perhaps differences in postexercise energy intake would become more evident with a greater temperature contrast.
To further investigate the acute effect of exercise in the heat on subsequent energy intake, REI was calculated by subtracting the energy cost of the exercise session from total energy intake. Relative energy intake after NEUT was not significantly different from CON. In contrast, REI after HEAT was significantly lower than the resting control trial. Accordingly, exercise in the heat may have greater potential to create a negative energy balance, which, in theory, should be advantageous to weight loss and maintenance (16). Although REI was not significantly different between NEUT and HEAT, it is important to acknowledge that REI was’800 kJ less after HEAT compared with NEUT. If this difference continued to occur at each postexercise meal, with exercise performed 4 times a week, REI would be ’3200 kJ lower per week as a result of exercising in a warmer tempera-ture. Although this study would need to be extended over a prolonged period of time to confirm this pattern, arguably such a reduction in energy intake would be beneficial to an individual aiming to lose or maintain body mass.
The lower REI after exercise in the heat may be attributed to a variety of possible mechanisms. White et al (12) hypothesized that greater energy intake after exercise in cooler conditions may be related to a higher EPOC. However, contrary to this sug-gestion, they observed significantly higher EPOC after exercise in warm water in comparison to cold water. In the present study, there were no differences in EPOC between the 2 exercise trials, which indicates that this factor was unlikely to have played a role in the observed results. Other potential mechanisms that may assist in explaining the effect of the environmental temperature during exercise on subsequent energy intake include the circu-lating concentrations of blood glucose (17–19) and lactate (20), as well as changes in core body temperature after exercise (11, 21, 22). We observed similar concentrations of glucose between trials, which suggests that this factor did not notably affect energy intake in the present study. Likewise, the increase in blood lactate was similar between NEUT and HEAT, and concentrations quickly returned to baseline before meal ingestion. On the other hand, tympanic temperature was significantly elevated in the response to exercise in the HEAT and remained higher than NEUT before the breakfast meal. Although, it is important to acknowledge that the measurement of tympanic temperature does not provide an extremely accurate reflection of core body tem-perature (23), it is possible that the higher body temtem-perature resulting from exercise in the HEAT influenced the tendency for lower postexercise energy intake (21, 22).
With respect to the effect of exercise on appetite-related hormones, we observed significantly higher concentrations of circulating PYY before the breakfast meal after HEAT compared
with CON. Given the role of PYY in signaling satiety (24, 25), this observation may assist in explaining, in part, the lower REI (ie, lack of compensation) after HEAT. In contrast, it would appear that insulin, leptin, active ghrelin, and pancreatic poly-peptide did not contribute to the observed changes in energy intake in the present study because there was no significant difference in the concentrations of these hormones before the breakfast meal between trials.
In addition to assessing the effect of the environmental tem-perature during exercise on overall energy intake, macronutrient preferences were examined. Despite the higher carbohydrate intake after NEUT compared with CON, there were no significant differences in absolute carbohydrate, fat, or protein intake be-tween the exercise trials. In contrast, White et al (12) observed significantly greater consumption of fat after 45 min of cycling in cold water (20°C) compared with warm water (33°C) and a resting control. Again, the larger temperature contrast or the immersion itself may assist in explaining these conflicting findings. With respect to preferences for energy intake in the form of drinks, there was no significant difference between NEUT and HEAT. However, there was a tendency for a greater proportion of kilojoules to be consumed in the form of drinks during HEAT compared with CON. Likewise, Stubbs et al (26) reported significantly higher fluid intake after exercise compared with a resting control trial. This may be related to the need to replace water loss resulting from exercise-induced sweating. In support of this premise, water consumption was also signifi-cantly greater during the exercise trials compared with CON.
In summary, when accounting for the excess energy expended during exercise, energy intake is lower after exercise in the heat compared with rest in a neutral ambient temperature in healthy, active men. Conversely, REI is similar after exercise in a neutral temperature compared with rest. These observations are most likely attributed to higher concentrations of circulating PYY, together with an increase in body temperature when exercising in the heat. Although it is possible that the warm temperature itself may have favored a negative energy balance without exercise, there is no evidence for this suggestion in the current literature. Regardless, the present results are applicable given that most people stay relatively “cool” while “resting” by avoiding the sun or by using indoor cooling. If rather than resting, an individual chooses to exercise, our results suggest that exercising in a warmer environment may be preferable for achieving a short-term negative energy balance if the choice is available—for example, exercising outdoors in a warmer temperature as op-posed to an air-conditioned gym. However, care should be taken to avoid exercise in overly hot environments due to the risk of dehydration and heat illness. Whether similar findings would be observed in women, overweight, or sedentary individuals remains to be determined. In addition, future studies should extend past the immediate postexercise meal alone because alterations in subsequent meals may compensate for any acute changes.
The authors’ responsibilities were as follows—ALS: contributed to devel-oping the experimental design, to the acquisition, analysis, and interpretation of the data collected, and to the drafting of the manuscript; KEW: involved in developing the experimental design, the interpretation of results, and the re-vision of the manuscript; and KJG: involved in developing the experimental design, obtaining funding for the study, interpreting the results, conducting the hormone assays, and revising the manuscript. None of the authors had a con-flict of interest.
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