High-intensity intermittent exercise attenuates ad-libitum energy intake

Subjects

Abstract

Objective:

To examine the acute effects of high-intensity intermittent exercise (HIIE) on energy intake, perceptions of appetite and appetite-related hormones in sedentary, overweight men.

Design:

Seventeen overweight men (body mass index: 27.7±1.6 kg m−2; body mass: 89.8±10.1 kg; body fat: 30.0±4.3%; VO2peak: 39.2±4.8 ml kg−1 min−1) completed four 30-min experimental conditions using a randomised counterbalanced design. CON: resting control, MC: continuous moderate-intensity exercise (60% VO2peak), HI: high-intensity intermittent exercise (alternating 60 s at 100% VO2peak and 240 s at 50% VO2peak), VHI: very-high-intensity intermittent exercise (alternating 15 s at 170% VO2peak and 60 s at 32% VO2peak). Participants consumed a standard caloric meal following exercise/CON and an ad-libitum meal 70 min later. Capillary blood was sampled and perceived appetite assessed at regular time intervals throughout the session. Free-living energy intake and physical activity levels for the experimental day and the day after were also assessed.

Results:

Ad-libitum energy intake was lower after HI and VHI compared with CON (P=0.038 and P=0.004, respectively), and VHI was also lower than MC (P=0.028). Free-living energy intake in the subsequent 38 h remained less after VHI compared with CON and MC (P0.050). These observations were associated with lower active ghrelin (P0.050), higher blood lactate (P0.014) and higher blood glucose (P0.020) after VHI compared with all other trials. Despite higher heart rate and ratings of perceived exertion (RPE) during HI and VHI compared with MC (P0.004), ratings of physical activity enjoyment were similar between all the exercise trials (P=0.593). No differences were found in perceived appetite between trials.

Conclusions:

High-intensity intermittent exercise suppresses subsequent ad-libitum energy intake in overweight inactive men. This format of exercise was found to be well tolerated in an overweight population.

Introduction

Exercise has a prominent role in improving the comorbidities of obesity,1 as well as contributing to a negative energy balance by increasing energy expenditure.2, 3 Importantly, exercise has also been shown to assist in weight management by directly influencing the total amount of energy consumed, the circulating concentration of a number of appetite-related hormones and feelings of hunger and satiety.4, 5, 6 In particular, manipulation of the intensity and type of exercise employed may alter appetite-related measures. In support of this view, a recent study reported reduced ad-libitum energy intake at a lunch and dinner meal following a bout of stationary cycling performed at high-intensity (75% VO2max) compared with an equicaloric bout of low-intensity exercise (40% VO2max) in obese adolescents.7 There is also evidence to suggest that the intensity of exercise may influence the circulating levels of appetite-related hormones. Erdmann et al.8 reported that cycling at 100 W was associated with lower ghrelin (hunger-stimulating hormone) compared with cycling at 50 W. Likewise, Ueda et al.9 showed a greater rise in the satiety hormone peptide tyrosine–tyrosine (PYY) in response to high (75% VO2max) compared with moderate-intensity (50% VO2max) exercise.

Prolonged and continuous high-intensity exercise may, however, not be sustainable in a sedentary overweight population. An alternative may be the use of high-intensity intermittent exercise (HIIE) that involves the performance of short bouts of high-intensity exercise interspersed with periods of exercise at lower intensities. This form of exercise has recently gained increasing popularity, given the significant improvements in many comorbidities of obesity.10 In support of the implementation of HIIE, we have recently shown that HIIE, consisting of maximal 4-s sprints repeated every minute with moderate-intensity exercise between sprints, suppressed post-exercise energy intake in overweight boys compared with a continuous bout of moderate-intensity exercise alone. In addition, participants reported that they preferred to participate in HIIE over the continuous moderate-intensity exercise, despite the fact that the HIIE involved a greater total amount of work.6 However, the role of the gastrointestinal hormones in regulating appetite following HIIE has not previously been examined, and whether similar suppression of appetite would be observed in overweight adults while performing a matched amount of total work is not known. Therefore, the aim of this study was to investigate the acute effects of HIIE compared with continuous moderate-intensity exercise of equicaloric cost on subsequent energy intake, appetite-related hormones and perceptions of appetite in a group of sedentary, overweight men.

Materials and methods

Participants

Seventeen overweight, inactive men (age: 30±8 years; body mass index: 27.7±1.6 kg m−2; body mass: 89.8±10.1 kg; body fat: 30.0±4.3%; VO2peak: 39.2±4.8 ml kg−1min−1; resting metabolic rate: 8021±843 kJ) volunteered from the community through advertisement (flyers, posters, social media and e-mail). Inclusion criteria were a body mass index of 25.0–29.9 kg m−2 and physical inactivity; defined as performing two or less 30-min exercise sessions of moderate to vigorous intensity per week.11 Exclusion criteria were a history of medical conditions and/or eating disorders known to affect appetite, or a score 3.5 on the restraint scale of the Dutch Eating Behaviour Questionnaire.12 Written consent was given by all participants, and the study was approved by the Human Research Ethics Committee at the University of Western Australia (UWA).

Study design

Participants attended the laboratory for an initial familiarisation session and collection of baseline data. Participants then completed four experimental trials using a randomised counterbalanced design. The experimental trials comprised 30 min of (i) MC: continuous exercise performed at moderate intensity (60% VO2peak), (ii) HI: intermittent exercise consisting of alternating high and lower intensity efforts performed at a ratio of 1:4 (60 s at 100% VO2peak: 240 s at 50% VO2peak), (iii) VHI: intermittent exercise consisting of alternating very-high and lower intensity efforts performed at a ratio of 1:4 (15 s at 170% VO2peak: 60 s at 32% VO2peak) and (iv) CON: control trial involving supine rest. The total mechanical work performed across each exercise protocol was matched. Experimental trials were performed at the same time of day and on the same day of the week, with a minimum of 1 week between visits. Primary outcome measures included post-exercise ad-libitum energy intake, changes in plasma concentrations of appetite-related hormones following a standard caloric load and ratings of perceived appetite.

Baseline testing and familiarisation

The initial laboratory session included measurement of height and body composition using a GE Lunar Prodigy Vision Dual-energy X-ray absorptiometry machine (GE Medical Systems, Madison, WI, USA). Each participant’s peak aerobic capacity (VO2peak) was assessed using a continuous incremental cycling test performed on a calibrated front access air-braked cycle ergometer (Model EX-10, Repco Cycle, Huntingdale, Victoria, Australia) that was interfaced with a customised software program (Cyclemax, School of Sport Science, Exercise and Health, UWA, Perth, Western Australia, Australia), which provided a continuous record and visual display of cycling power output. This test involved a starting workload of 50 W that increased by 30 W every 3 min until volitional exhaustion. Throughout this test, each participant wore a heart rate (HR) monitor and breathed through a mouthpiece that was connected to a calibrated computerised gas analysis system (previously described by West et al.13). Following this, participants were familiarised with the experimental protocols including a series of questionnaires to be administered during each trial and blood sampling. Using data from the VO2peak test, each participant’s VO2–power relationship was determined to calculate the cycling power output required to elicit the appropriate exercise intensity for the experimental trials. It should be noted that work intensities (that is, 170% VO2peak) were set based on a percentage of the power output at VO2peak. Participants then completed 2 min of each exercise protocol. Finally, to minimise the novelty of having a meal in a laboratory environment, participants were presented with a familiarisation breakfast test meal. To ensure that there was no hedonic bias related to the test meal, a standard nine-point hedonic scale was completed after its consumption (hedonic rating: 7±1).14

Experimental trials

In the 24 h leading up to each experimental trial, participants were required to refrain from vigorous physical activity and to document all food and drink consumption. The dietary information was reviewed by the investigator upon arrival to the laboratory, and participants were instructed to replicate their food and drink intake prior to each subsequent trial. A reminder was given prior to each trial and compliance was confirmed by inspection of the records upon arrival to the laboratory.

On the morning of each trial, participants arrived at 0700 hours, having fasted for 10 h (apart from consuming 250 ml of water between waking up and arriving at the laboratory). Participants then either performed the resting control protocol (CON) or one of the exercise protocols (MC, HI, VHI). The exercise intensities were confirmed by monitoring cycling power output and total work. HR was measured and participants’ ratings of perceived exertion (RPE) were measured periodically using the Borg scale.15 On completion of each trial, enjoyment of physical activity was assessed by using the Physical Activity Enjoyment Scale.16

Five minutes following exercise or CON, each participant was provided with a standardised liquid meal (350 ml, 1120 kJ; 61% carbohydrates, 15% protein and 30% fat; Up & Go liquid breakfast, Sanitarium, Berkeley Vale, NSW, Australia) to consume in a 2-min period to allow for subsequent comparison of the postprandial responses of appetite-related blood variables and perceived appetite between trials. During this time (60 min postprandial), participants sat quietly either reading or using a computer. Then, 70 min after consumption of the liquid meal, participants were provided with a second meal for a fixed duration of 20 min. During this period, participants were instructed to eat ad-libitum until a self-regulated satisfactory level of satiety was reached (that is, ‘eat till comfortably full’). This meal consisted of porridge made from a standardised mixture of instant oats (Oats Quick Sachet—Creamy Honey, Uncle Tobys, Nestle Australia, Sydney, NSW, Australia) and milk (HiLo Milk, Pura, Melbourne, VIC, Australia). A standardised bottle of plain drinking water (1000 ml) was also made available during this time. The breakfast porridge and drinking water were weighed before and re-weighed after consumption. To minimise the influence of environmental factors on eating behaviour,17 (i) participants always consumed from the same bowl, (ii) investigator left the nutrition laboratory during consumption, (iii) ambient temperature was controlled (21–23 °C), (iv) amount of porridge provided was the same in each trial and (v) more than a sufficient amount was provided (that is, eight serves of oats and milk mixture). This laboratory meal has been previously reported to have a test–retest correlation of 0.91.13

Assessment of perceptions of appetite

Perceptions of appetite were assessed using a modified visual analogue scale18 at (i) baseline, (ii) immediately post exercise/CON, (iii) 30 min post standard meal, (iv) 60 min post standard meal and (v) post ad-libitum meal. The visual analogue scale took the form of five straight lines (100 mm), each accompanied by a question anchored with words representing opposing extreme states of fullness, hunger, satiation, desire to eat and prospective food consumption at either end.

Assessment of appetite-related blood variables

To determine the endocrinal and metabolic factors reported to be involved in the regulation of energy intake, capillary blood was sampled at: (i) baseline, (ii) immediately post exercise/CON, (iii) 30 min post standard meal and (iv) 60 min post standard meal. Blood (500 μl) was collected from a fingertip using a sterile lancet (Unistick 2 Normal; Owen Mumford, Oxford, UK) after warming the entire hand in a box heated with warm air (60 °C). Blood glucose and lactate concentrations were measured using a blood gas analyzer (35 μl; Radiometer, Copenhagen, Denmark). The remaining blood was treated with EDTA (Microtainer tubes with K2E (K2EDTA), BD Microtainer, Franklin Lakes, NJ, USA) and serine protease inhibitor (20 μl per 500 μl of blood; Pefabloc SC, Roche Diagnostics, Sydney, New South Wales, Australia) before being centrifuged at 1020 g for 10 min. Plasma obtained was stored at −80 °C and later analysed for a range of appetite-related hormones: PYY, pancreatic polypeptide (PP), active ghrelin, leptin and insulin; using a commercially available assay kit (Milliplex Human Gut Hormone Panel; Millipore Corporation, Billerica, MA, USA).

Assessment of free-living energy intake and physical activity levels

Energy intake and physical activity levels were assessed for the remainder of the experimental day, as well as the next day using a self-recorded food diary and accelerometry (ActiGraph, Pensacola, FL, USA), respectively. Instructions on the use (including a 1-day example), and the necessity for accurate and detailed recordings of energy intake immediately after consumption were emphasised. Portable weighing scales were provided to assist recording. The total kilojoules ingested were calculated using commercially available software (Foodworks; Xyris Software, Kenmore Hills, QLD, Australia). The estimated energy expenditure through physical activity was determined using ActiLife software (ActiGraph).

Statistical analysis

One-way analysis of variance with repeated measures was used to assess the effect of trial on ad-libitum energy intake and physical activity enjoyment. Changes in blood variables, free-living energy intake and physical activity, and perceptions of appetite were compared using two-way (trial x time) repeated measures analysis of variance. Post hoc pairwise comparisons using Bonferroni adjustments were used to determine where any differences lay. Statistical significance was accepted at P0.05 (SPSS version 20, IBM Corporation, Armonk, NY, USA).

Results

Exercise characteristics

Energy intake and expenditure from physical activity 24 h prior to each experimental session were well-matched (energy intake: CON 9687±3565, MC 9619±3495, HI 9551±3597, VHI 9609±3488 kJ; P=0.852; energy expenditure: CON 1917±930, MC 1885±888, HI 1870±958, VHI 1907±995 kJ; P=0.914). Likewise, there were no differences in environmental characteristics between trials (temperature: CON 21.1±0.6, MC 21.1±0.4, HI 20.9±0.6, VHI 21.1±0.4 °C; P=0.624; humidity: CON 49±10, MC 47±8, HI 42.4±9, VHI 47±7%; P=0.146) or the total mechanical work performed (P0.05; Table 1). There was a main effect of trial for both HR and RPE (P<0.001), with a higher HR and RPE during the exercise trials compared with CON (P<0.001; Table 1). However, the increase was greater with HI and VHI compared with MC (P0.004), and RPE was greater in VHI compared with HI (P=0.028). Physical activity enjoyment was similar between the exercise trials (MC 85±13, HI 86±11, VHI 82±17; P=0.593).

Table 1 Descriptive characteristics of 30 min of rest (CON), MC, HI and VHI

Post-exercise ad-libitum energy intake

There was a main effect of trial on ad-libitum energy intake (P<0.001; Table 2). Post hoc analysis revealed that energy intake was lower following HI and VHI compared with CON (P=0.038 and P=0.004, respectively). Ad-libitum energy intake after VHI was also found to be lower compared with MC (P=0.028). Of note, there was a main effect of trial on water intake at the ad-libitum meal (P=0.003), with higher water intake following MC (327±164 ml) compared with CON (195±121 ml) (P=0.001).

Table 2 Ad-libitum energy intake following 30 min of rest (CON), MC, HI or VHI

Perception of appetite

There was no interaction of trial and time on ratings of perceived hunger (P=0.630), fullness (P=0.102), satiation (P=0.520), desire to eat (P=0.337) and prospective food consumption (P=0.157). However, there was a main effect of time for each of these variables (P<0.001; Figure 1), with increased fullness and satiation along with decreased hunger, desire to eat and prospective food consumption following the ad-libitum test meal.

Figure 1
figure1

Mean (±s.e.) perceived hunger (a), perceived fullness (b), perceived satiation (c), perceived desire to eat (d) and prospective food consumption (e) following 30 min of VHI, HI, MC or rest (CON) (n=17). The downward arrow (↓) and upward arrow (↑) indicate the timing of the standard liquid meal and ad-libitum meal, respectively. #Significantly different from baseline (P0.05).

Appetite-related blood variables

An interaction of trial and time on blood lactate (P<0.001) revealed higher levels after VHI, followed by HI, MC and CON (P0.014; Figure 2a). Blood lactate remained higher in VHI compared with the other trials (P0.014) following 35 min of recovery, and remained higher than CON up to 65 min post exercise (P=0.046). Likewise, there was an interaction effect of trial and time on blood glucose concentrations (P=0.004). Blood glucose was higher after VHI exercise compared with CON, MC and HI (P0.015; Figure 2b). There was also a significant main effect of time (P<0.001), with increased blood glucose in response to meal consumption.

Figure 2
figure2

Mean (±s.e.) response of lactate (a), glucose (b), active ghrelin (c), PP (d), leptin (e), insulin (f) and PYY (g) to 30 min of rest (CON), MC, HI or VHI. The downward arrow (↓) indicates the timing of the standard liquid meal. aSignificantly different from CON. bSignificantly different from MC. cSignificantly different from HI. #Significantly different from baseline. (P0.05).

There was an interaction effect of trial and time on the circulating levels of active ghrelin (P=0.001), with lower active ghrelin levels immediately post VHI compared with CON, MC and HI (P0.050; Figure 2c). There was also a main effect of time on active ghrelin (P=0.001), with a lower level at 35 min (P=0.007) and 65 min post exercise (P=0.007) compared with the baseline. In contrast, there was no interaction of trial and time on leptin (P=0.400), PP (P=0.281), insulin (P=0.705) or PYY (P=0.148). However, there was a main effect of time for each of these variables with increased PP (P0.004), insulin (P0.003) and PYY (P0.037) in response to caloric consumption, whereas leptin decreased over time (P0.007).

Free-living energy intake and physical activity

A main effect of trial (P<0.001) revealed lower daily energy intake (includes both standard and ad-libitum test meal) after VHI compared with CON and MC (P=0.003 and P=0.010, respectively; Figure 3a). There was also a main effect of time (day) (P=0.014), with higher total energy intake on the day of the trial compared with the day after the trial. In contrast, there was no effect of trial or time on the estimated energy expenditure from physical activity upon leaving the laboratory (P=0.710; Figure 3b).

Figure 3
figure3

Mean (±s.e.) estimated free-living energy intake (a) and estimated free-living physical activity (b) over 2 days (day of trial and day after trial) following 30 min of rest (CON), MC, HI or VHI. (n=17). aSignificantly different from CON. bSignificantly different from MC. #Significantly different between days (P0.05).

Discussion

The present study investigated the acute effects of HIIE compared with continuous moderate-intensity exercise or rest on subsequent energy intake in sedentary, overweight men. Total ad-libitum energy intake after HI and VHI was lower compared with CON, and energy intake following VHI was also lower than MC. These observations were associated with lower active ghrelin and higher blood glucose concentrations following VHI compared with the other trials, and higher blood lactate concentrations after HI and VHI compared with MC and CON. Importantly, the suppression of energy intake after VHI compared with CON and MC was maintained for more than 24 h.

This study is the first to demonstrate a suppression of energy intake following an acute bout of exercise consisting of very-high-intensity intermittent efforts (100% VO2peak) in overweight men. The experimental design of this study, in particular the use of distinctively different exercise intensities during equicaloric exercise trials (that is, MC, HI, VHI; 60, 100, 170% VO2peak, respectively), allowed us to examine the impact exercise intensity may have on post-exercise energy intake. Our results show that there was a more pronounced suppression of energy intake as the intensities employed increased (that is, VHI resulted in the greatest suppression of energy intake) and suggest that exercise intensity mediates subsequent energy intake, at least in the short term. To the authors’ knowledge, only one other study has investigated the effect of intermittent sprint efforts on energy intake and its regulation. Deighton et al.19 found no difference in energy intake after a bout of HIIE consisting of six 30-s sprints over 30 min compared with 60 min of endurance exercise and rest. However, these exercise protocols were not matched for work; they consisted of a lower volume of sprint efforts compared with the present study and was performed in normal-weight individuals. Surprisingly, we observed no difference in the perceived appetite ratings between trials, despite suppression of ad-libitum energy intake after HIIE. The reason for this is unclear, although previous research has shown that feelings of appetite may not always reflect actual food intake.20

A number of mechanisms may contribute to the lower energy intake following HI and VHI. In the current study, circulating active ghrelin was transiently lower following VHI compared with all other trials. Notably, the reduction in the circulating concentration of active ghrelin after VHI is consistent with the findings of Deighton et al.,19 who reported a suppression of active ghrelin after 30 min of sprint interval exercise. Given that active ghrelin has been shown to exert an orexigenic influence on energy intake and has a role in initiating feeding,21 the lower active ghrelin may partly explain the suppression of energy intake following VHI. Diversion of blood flow away from the gastrointestinal tract has been suggested to be the most likely cause of circulating active ghrelin suppression in response to exercise.22 Of relevance, it has been reported that gastrointestinal blood flow may be reduced by up to about 80% during maximal-intensity exercise.23 Although the plasma concentration of insulin and leptin were not different between conditions, it has been established that sensitivity to these hormones is increased post exercise.24, 25 Whether sensitivity to these appetite-related hormones is influenced by exercise intensity is yet to be determined. Further, although changes in PP and PYY in response to exercise have been reported,26, 27 no changes were detected between conditions in the present study. Possible reasons for this lack of response were the shorter duration of exercise performed (30 min in the present study compared with 60 min26, 27) and that blood in the present study was sampled before and after, but not during exercise.26 It should be noted that PP and PYY, although not significant, were highest following the VHI trial.

Another possible mechanism that may explain the effect of HIIE on energy intake is the circulating concentration of the two key metabolites, lactate and glucose. The HIIE trials adopted in the current study resulted in higher post-exercise blood lactate compared with MC and CON, which persisted 1 h post VHI compared with CON. Given that elevated blood lactate has been reported to suppress energy intake,28, 29 the comparatively higher levels of blood lactate during the HIIE sessions may, to some extent, have contributed to the suppressed ad-libitum energy intake. Blood glucose levels post exercise were also higher after VHI compared with CON, MC and HI. Specifically, an increase in circulating blood glucose levels has been shown to reduce short-term food intake.30, 31

Although acute changes in food intake are of interest, the persistence of these changes beyond the post-exercise meal is relevant to better understand how exercise affects free-living energy intake. Whereas no differences in daily physical activity were noted upon leaving the laboratory, differences were observed in daily energy intake between trials, with total energy intake over the subsequent 2 days after the VHI trial lower compared with CON and MC. This finding corroborates the observations of Thivel et al.,7 who reported that a single bout of high-intensity exercise suppressed spontaneous energy intake in the subsequent 24 h compared with either a single bout of lower-intensity exercise or rest in obese adolescents.

Finally, as enjoyment of physical activity has been reported to be a key factor in physical activity performance and exercise adherence,32, 33 the present study aimed to assess enjoyment of the different exercise trials. Whereas others have reported HIIE to be more enjoyable than moderate-intensity continuous exercise,34 the present study found similar enjoyment between trials. Importantly, enjoyment was not compromised in HI and VHI, despite higher mean RPE and HR during exercise compared with MC.

In summary, the key findings of this study are that (i) HIIE suppresses subsequent ad-libitum energy intake in overweight, inactive men compared with the rest; and (ii) HIIE is well tolerated in a sedentary and overweight population. The suppression of ad-libitum energy intake is greater with higher-intensity intermittent exercise and is likely attributable to increased levels of circulating blood lactate and blood glucose, together with a lower concentration of active ghrelin following the high-intensity exercise bouts. Whether these observations are maintained under chronic conditions (that is, training) and apply to women will need to be determined in future research. The findings of this study highlight the importance of appropriate exercise prescription, given the evidence both in this study and that of others that exercise intensity may alter important clinical measures. As such, findings of this study have implications for exercise guidelines and prescription for weight management, and are an important consideration for both the overweight individual living with major health risks, as well as for our community dealing with the burden of the current obesity pandemic.

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Acknowledgements

The hormone assays were carried out with the facilities at the Centre for Microscopy, Characterisation and Analysis, The University of Western Australia that are supported by the fundings of the University, State and Federal Government. TJF is in receipt of a McCusker Charitable Foundation grant, which was used to help defray costs of the Hormone assays.

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Correspondence to A Y Sim.

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Keywords

  • food intake
  • appetite
  • interval
  • ghrelin
  • overweight

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