Effects of continuous versus accumulated activity patterns on postprandial triacylglycerol concentrations in obese men

Transcription

1 (2008) 32, & 2008 Macmillan Publishers Limited All rights reserved /08 $ ORIGINAL ARTICLE Effects of continuous versus accumulated activity patterns on postprandial triacylglycerol concentrations in obese men Division of Sports Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki, Japan Objective: There is limited information regarding the effects of short (o10 min) bouts of activity on postprandial lipaemia and no studies are available regarding the effects of short bouts of activity on postprandial lipaemia in obese men. The objective of this study was to compare the effects of accumulating ten, 3-min bouts of exercise versus one 30 min bout of exercise on postprandial serum triacylglycerol (TAG) concentrations in obese men. Design: Each subject completed three 2-day trials at least 1 week apart in a randomized, repeated-measures design. On day 1, subjects rested (no exercise) or cycled at 60% of maximum heart rate in either ten, 3-min bouts (30 min rest between each), or one continuous 30-min bout. On day 2 of each trial, after an overnight fast, the subjects consumed a standardized test meal for breakfast. Venous blood samples were obtained in the fasted state (0 h), and 2, 4 and 6 h postprandially on day 2. Subjects: Eight sedentary men (age: 27±2 years) with body mass index between 25 and 37 kg/m 2. Measurements: Postprandial TAG, non-esterified fatty acids, 3-hydroxybutyrate, insulin and glucose were determined. Results: Total area under the postprandial serum TAG concentrations versus time curve was 18% (P ¼ 0.042) and 15% (P ¼ 0.032) lower throughout day 2 of both the accumulated exercise trial and the continuous exercise trial, respectively, compared with the control trial with little difference between exercise trials. Conclusion: At 30 min of moderate cycling (0.87 MJ per 30 min) accumulated in short bouts is equally effective in reducing postprandial serum TAG concentrations as one continuous 30 min bout of cycling in obese men. (2008) 32, ; doi: /ijo ; published online 27 May 2008 Keywords: accumulation; physical activity; postprandial lipaemia; triacylglycerol Introduction Physical activity recommendations advise that adults should engage in moderate-intensity physical activity for a minimum of 30 min on 5 or more days of the week. 1,2 The novel aspect of these reports was that the activity can be accumulated through a minimum of 10 min per bout to attain 30 min or more for general health benefit. The rationale behind the concept of accumulation for health is based on the assumption that the activities reported in many epidemiological studies are intermittent in nature (that is, walking, stair claming, gardening, occupational work). 3 However, if total energy expenditure is the most important factor for health benefits and a Correspondence: Dr, Division of Sports Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki , Japan. miyashita@stat.taiiku.tsukuba.ac.jp Received 18 February 2008; revised 8 April 2008; accepted 15 April 2008; published online 27 May 2008 reduction in coronary heart disease, 4 as is suspected, 3 then the duration of each bout of exercise should not matter provided that sufficient energy is expended in total. This issue is important to examine, because the partitioning of exercise sessions into multiple short bouts throughout the day may be easier to fit into everyday life as a previous study indicates that even people who follow the recommended physical activity guidelines of 30 min on most if not all days of the week 3 do not exercise continuously for 10 min at a time. 5 The effectiveness of accumulating short bout of exercise to reduce postprandial lipaemia (it is considered an emerging risk factor for cardiovascular disease 6 (CVD)) has been examined in previous studies Four studies have reported that the reduction in postprandial triacylglycerol (TAG) concentrations was comparable for accumulated (bouts lasting 3 30 min each bout) versus an equivalent volume of continuous activity 9 11 or even greater with accumulated (bouts lasting 10 min each bout) versus an equivalent volume of continuous exercise. 7 Although all four studies have provided support for the concept of accumulation, the

2 1272 acute effects of accumulating exercise in bouts shorter than 10 min per session throughout the day on postprandial TAG concentrations in obese individuals has not been determined. It is important to address this issue as the subjects in previous studies, 7,9,11 with exception of one study, 10 were healthy individuals. Thus, the findings needs to be generalized, to less active, overweight/obese individuals at more risk of CVD because perturbations in TAG concentrations following meals are more likely to be exaggerated in such individuals compared with their healthy peers Therefore, the purpose of the present study was to compare the effects of accumulating ten, 3-min bouts of cycling throughout a single day with those of one 30-min bout of cycling on postprandial TAG concentrations after a meal of moderate-fat content in obese men. An exercise volume of 30 min was chosen as this is consistent with current guidelines regarding physical activity and health. 1,2 Furthermore, previous studies have shown that this duration 11 and volume 16 of exercise performed both continuously (one, 30-min bout) and intermittently (10, 3-min bouts) is equally effective in reducing postprandial plasma TAG concentrations in young healthy men. Cycling was chosen because it is a low impact form of exercise and therefore suitable for heavy individuals to reduce joint stain and hence the risk of injury. 17 Methods Subjects After approval from the University of Tsukuba Ethics Committee, eight Japanese obese males aged years gave their written informed consent to participate in this study. The present study defined obesity as a body mass index (BMI) of 25 kg/m 2 and above. 18 The rationale behind this definition of obesity is based on findings that although the prevalence of obesity (defined as BMI of 30 kg/m 2 and above) is only 2 3% in Japan compared with 10 20% in Europe and North America, obesity-related health risk increases at BMI levels even lower than 30 kg/m 2 in a Japanese population. 18 All subjects were non-smoking and were not taking any medication known to influence lipid metabolism. They were also sedentary, not complying with current physical activity recommendations, 1,2 and had been weight stable (±2.5 kg) for at least 3 months before the study. Mean (±s.e.m.) values for the subjects age, height and weight were 26.5±1.5 years, 172.9±2.5 cm and 86.3±5.0 kg, respectively. Mean values for the subjects BMI, waist circumference, systolic blood pressure and diastolic blood pressure were 28.9±1.4 kg/m 2, 89.2±3.1 cm, 131±4 and 82±5 mm Hg, respectively. All applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during this research. Study design After preliminary testing, each subject underwent three 2-day trials: an accumulated exercise trial, a continuous exercise trial and a control trial. At 2-day, trials were used because skeletal muscle lipoprotein lipase activity is thought to peak48 h after exercise 19 and this enzyme facilitates the removal of TAG form the blood. 20 There was a 7-day gap between each trial and trials were performed in a randomized design. Preliminary exercise tests At 7 days before the first trial, each subject attended the laboratory for a submaximal-incremental exercise test performed on a cycle ergometer (Monark Exercise AB, Ergomedic 874E, Vansbro, Sweden). This test was to determine the steady-state relationship between power and heart rate. The test was 16 min in duration and was continuous in nature but was divided into four, 4 min stages. The initial power was set between 25 and 30 W depending upon each subject s activity level. The power was increased by 25 or 30 W at the end of each 4 min period depending upon each subject s activity level. The cadence was maintained at 60 r.p.m. and heart rate was monitored throughout the test using shortrange telemetry (Polar RS400, Kempele, Finland). Ratings of perceived exertion were assessed during the last 30 s of each incremental test using the Borg scale. 21 At the end of the test the power at each stage was plotted against heart rate to illustrate the power and heart-rate relationship. This regression line was used together with each subject s predicted maximal heart rate (220-age) to estimate the power eliciting 60% of predicted maximal heart rate. This power was used in the exercise sessions of the main trials. Main trials: day 1 On the accumulated exercise trial the subjects reported to the laboratory at 0900 hours having eaten breakfast. The subjects then performed 10, 3-min bouts of cycling throughout the day. A 30-min rest interval followed each bout. On the continuous exercise trial, the subjects reported to the laboratory at 1430 hours having eaten lunch. The subjects then performed one 30 min bout of cycling from hours. For both of these trials, the exercise was completed at 1530 hours so that the time interval between the cessation of exercise and the consumption of the test meal (on the following day) was the same (that is, 17 h). For the exercise trials, the exercise intensity for the cycling was 60% of maximum heart rate as determined by the preliminary exercise tests. Heart rate was measured every 15 s at 2 3 min of each bout in the accumulated exercise trial or 4 5, 9 10, 14 15, 19 20, and min during exercise in the continuous exercise trial using short-range telemetry. The subjects were blinded to their heart rate so as not to influence to their ratings of perceived exertion. Ratings of perceived exertion were assessed simultaneously with the

3 heart rate measurements during the exercise. The cadence was maintained at 60 r.p.m. Energy expenditure was estimated using the subject s body mass, heart rate and power. 17 On the control trial the subjects refrained from exercise. during or after the meal. The subjects consumed water ad libitum during the first trial, and the pattern and volume ingested was replicated in subsequent trials Main trials: day 2 In each trial, the subjects reported to the laboratory at 0800 hours after an overnight fast of at least 10 h (no food or drink except water). A fasting venous blood sample was collected in a seated position by venipuncture at 0830 hours. The subjects then consumed a standardized test meal for breakfast. A clock was started when subjects began eating, and they were required to rest (sitting reading, writing, working at a computer or watching television) in the laboratory for 6 h following the initiation of breakfast. Further venous blood samples were collected at 2, 4 and 6 h after the start of the test meal for the measurement of serum TAG, nonesterified fatty acids (NEFAs), 3-hydroxybutyrate (3-OHB), insulin, and plasma glucose. Standardization of diet and exercise The subjects weighed and recorded all food and drink consumed during the day before each trial and on day 1 of each trial. The subjects refrained from drinking alcohol during this period. The subjects were asked to replicate their dietary intake from the first trial on their subsequent trials. Food diaries were analysed using computerized software (Excel Eiyou-kun version 4.0, Kenpakusha, Tokyo, Japan) to determine caloric intake and macronutrient content. In addition, the subjects were asked to remain inactive on the day before day 1 of each trial and throughout the main trials (other than the exercise performed as part of the experiment). The subjects were also asked to wear a threedimensional pedometer (FB-720, Tanita Corporation, Tokyo, Japan) during the day before each trial and on day 1 of each trial, except the exercise performed as part of the experiment and sleep, for the measurement of steps. Test meal The test meal consisted of white bread, sliced cheese, butter, mayonnaise, lettuce, tomato, ham, whole milk, cocoa powder, and yogurt. The meal was prescribed according to body mass and provided 0.35 g fat, 1.17 g carbohydrate, 0.29 g protein and 37 kj energy per kilogram body mass. The macronutrient content of the test meal was 30.2±1.7 g fat, 101.0±5.8 g carbohydrate and 25.0±1.4 g protein that provided 3.23±0.16 MJ energy (energy derived was 35% from fat, 52% from carbohydrate and 13% from protein). The subjects were asked to consume the test meal within 20 min. The time taken to consume the test meal was recorded and replicated in subsequent trials. The time taken to consume the test meal was 10.5±0.9 min. None of the subjects reported nausea or any gastrointestinal discomfort Analytical methods For serum TAG, NEFA, 3-OHB and insulin measurements, venous blood samples were collected into 10-ml syringes and were then transferred into tubes containing clotting activators for isolation of serum. Thereafter samples were allowed to clot for 30 min at room temperature and then centrifuged at 1861 g for 10 min at 4 1C. Serum was removed, divided into aliquots, and stored at 35 1C for later analysis. For plasma glucose measurements, venous blood samples were collected into 10-ml syringes and were then transferred into tubes containing sodium fluoride and EDTA. Thereafter samples were immediately centrifuged and treated as above. TAG (Pure Auto S YG-N, Daiichi Pure Chemicals Co. Ltd, Tokyo, Japan), NEFA (NEFA-SS Eiken, Eiken Chemical Co. Ltd, Tokyo, Japan), 3-OHB (KAINOS 3-HB, KAINOS Laboratories, Inc., Tokyo, Japan) and glucose (Melcriauid Glu kit, Kanto Chemical Co. Inc., Tokyo, Japan) concentration were determined by enzymatic, colorimetric methods. Insulin was measured by enzyme-linked immunosorbent assay (Mercodia Insulin ELISA, Mercodia AB, Uppsala, Sweden). All samples from the same individual were assayed in a single run. Intra-assay coefficients of variation were 1.2% for TAG, 1.3% for NEFA, 4.1% for 3-OHB, 3.2% for insulin and 2.5% for glucose. Calculations and statistical analysis Data were analysed using the Statistical Package for the Social Science software version 16.0 for Windows (SPSS Japan Inc, Tokyo, Japan). Prior to analysis, all data were checked for normality of distribution using the Shapiro Wilk test and, if necessary, logarithmically transformed. The total area under the 6 h variable versus time curves (AUC) were calculated using the trapezium rule. The incremental AUC were calculated using the same method after correcting for fasting (0 h) concentrations. Student s t-tests for correlated data were used to compare physiological responses between exercise trials (estimated energy expenditure, percentage of maximal heart rate, heart rate, ratings of perceived exertion and power). One-factor analysis of variance (ANOVA) with repeated measures was used to examine differences among the three trials for fasting plasma or serum concentrations, AUC values and step counts. Two-factor ANOVA with repeated measures was used to examine differences among the three trials over time for plasma or serum constituents. Where a significant interaction was detected, post hoc pairwise comparisons were performed using the Bonferroni method. Statistical significance was accepted at the 5% level. Data are presented as mean±s.e.m.

4 1274 Results Responses during cycling Exercise data are shown in Table 1. There were no significant differences between exercise trials in the estimated gross energy expenditure or relative exercise intensity. Mean values for heart rate and ratings of perceived exertion were significantly higher on the continuous trial compared with the accumulated trial. Mean values for work rate were significantly lower on the continuous trial compared with the accumulated trial. Dietary and step counts data Analysis of food diaries revealed that energy intake did not differ significantly in the 48 h preceding day 2 of each trial. Energy intake for the day prior to the trials and for day 1 of the trials were 10.1±0.7 MJ (energy was derived 29±4% from fat, 56±4% from carbohydrate and 15±1% from protein) and 10.4±0.6 MJ (energy was derived 27±3% from fat, 52±5% from carbohydrate and 21±7% from protein), respectively. There were no significant differences in step counts in the 48 h preceding day 2 of each trial. Step counts for the day prior to the accumulated exercise, continuous exercise and control trials were 6455±1192, 5456±1084 and 6532±1330, respectively. Step counts for day 1 of the accumulated exercise, continuous exercise and control trials were 4553±582, 6158±820 and 5866±892, respectively. Plasma/serum concentrations in the postprandial state Postprandial serum TAG concentrations on day 2 of each trial are shown in Figure 1. Two-factor ANOVA revealed significant main effects of trial (P ¼ 0.010) and time (P ¼ 0.002) and a significant interaction (P ¼ 0.005). Serum TAG responses were lower on the exercise trials compared to the control trial (post hoc tests; accumulated exercise trial compared with control trial, P ¼ 0.039; continuous exercise trial compared with control trial, P ¼ 0.031) with little difference between the accumulated and continuous exercise trials. The postprandial TAG total and incremental AUC are given in Table 3. One-factor ANOVA revealed there was a main effect of trial for both of these variables. Post hoc tests showed that the TAG total AUC was 18% (P ¼ 0.042) and 15% lower (P ¼ 0.032) on the accumulated and continuous exercise trials, respectively, compared with the control trial. Post hoc tests also showed no significant between-trial Plasma/serum concentrations in the fasted state Fasting plasma and serum concentrations on day 2 of each trial are shown in Table 2. One-factor ANOVA revealed that there were no significant differences among trials in fasting serum TAG, NEFA, 3-OHB, insulin and plasma glucose concentrations. Figure 1 Mean (±s.e.m.) fasting and postprandial serum triacylglycerol concentrations in the accumulated exercise (K), continuous exercise (n) and control ( ) trials (N ¼ 8); the black rectangle indicates consumption of the test meal. Table 1 Estimated energy expenditure, %HRmax, heart rate, RPE and power during the accumulated and continuous exercise trials Trial Energy expenditure (MJ per 30 min) %HRmax Heart rate (beats per min) RPE Power (W) Accumulated exercise 0.83± ± ±1 11±1 69±7 Continuous exercise 0.85± ± ±1 a 12±0 a 64±7 a Abbreviations: HR, heart rate; %Hrmax, percentage of maximal heart rate; RPE, ratings of perceived exertion. N ¼ 8, values are mean±s.e.m. Means were compared using Student s t-test for correlated data. a Significantly different from the accumulated exercise trial, Pp Table 2 Fasting circulating concentrations of TAG, NEFAs, 3-OHB, insulin and glucose for the accumulated exercise, continuous exercise and control trials Trial TAG (mmol l 1 ) NEFA (mmol l 1 ) 3-OHB (mmol l 1 ) Insulin (pmol l 1 ) Glucose (mmol l 1 ) Accumulated exercise 1.65± ± ± ± ±0.17 Continuous exercise 1.70± ± ± ± ±0.16 Control 1.85± ± ± ± ±0.12 Abbreviations: NEFA, non-esterified fatty acids; 3-OHB, 3-hydroxybutyrate; TAG, triacylglycerol. N ¼ 8, values are mean±s.e.m. Means were compared using oneway analysis of variance for the main effect of trial followed by a Bonferroni multiple comparisons test.

5 differences for the TAG incremental AUC, but the values tended to be lowered in the exercise trials (accumulated exercise trial compared with control trial, P ¼ 0.052; continuous exercise trial compared with control trial, P ¼ 0.125) compared with the control trial. There were no significant differences in the postprandial TAG total and incremental AUC between exercise trials. Postprandial serum NEFA, 3-OHB, insulin and plasma glucose concentrations on day 2 of each trial are shown in Figure 2. Two-factor ANOVA revealed that there was a main effect of time for NEFA (Po0.0005), 3-OHB (P ¼ 0.045), insulin (P ¼ 0.001) and glucose (Po0.0005). For 3-OHB there was a main effect of trial (P ¼ 0.024). Post hoc tests revealed no significant between-trial differences for postprandial serum 3-OHB concentrations, but the values tended to be higher in both exercise trials (accumulated exercise trial Table 3 Six-hour areas under the serum concentration versus time curve for total TAG and incremental TAG (adjusted for fasting value) on the accumulated exercise, continuous exercise and control trials Trial Total TAG a (mmol l 1 for 6 h) Incremental TAG a (mmol l 1 for 6 h) Accumulated exercise 12.84±3.77 b 2.72±0.50 Continuous exercise 13.32±3.39 c 3.06±0.72 Control 15.70± ±0.78 Abbreviation: TAG, triacylglycerol. N ¼ 8, values are mean±s.e.m. Means were compared using one-factor analysis of variance followed by a Bonferroni multiple comparisons test. a Main effect of trial, Pp b Significantly different from the control trial, P ¼ c Significantly different from the control trial, P ¼ compared with control trial, P ¼ 0.059; continuous exercise trial compared with control trial, P ¼ 0.119) compared with the control trial. For insulin there was a main effect of trial (P ¼ 0.046). Post hoc tests revealed no significant betweentrial differences for postprandial serum insulin concentrations, but the values tended to be lower in both exercise trials (accumulated exercise trial compared with control trial, P ¼ 0.153; continuous exercise trial compared with control trial, P ¼ 0.237) compared with the control trial. Discussion The main finding of the present study is that accumulating 30 min of cycling in short (3 min) bouts is equally as effective in reducing postprandial serum TAG concentrations as one continuous 30 min bout in obese men. These findings suggest, but do not prove, that accumulating short bouts of activity may be an effective intervention against CVD and this is important as activities that are intermittent in nature often involve bouts lasting less than 10 min. 5 Previous studies have compared the effects of accumulated/intermittent exercise (bouts lasting min each bout) with an equivalent volume of one continuous exercise on postprandial TAG concentrations. 7,9,10 The reduction in postprandial TAG concentrations with both patterns of exercise demonstrated in the present study is consistent with the findings of previous studies employing young, active individuals 9 and middle-age, sedentary individuals. 10 To our knowledge, the present study is the first to examine 1275 Figure 2 Mean (±s.e.m.) fasting and postprandial circulating concentrations of (a) non-esterified fatty acids (NEFA), (b) 3-hydroxybutyrate (3-OHB), (c) insulin and (d) glucose in the accumulated exercise (K), continuous exercise (n) and control ( ) trials (N ¼ 8); the black rectangle indicates consumption of the test meal.

6 1276 the effects of accumulating short (3 min) bouts of activity on postprandial lipaemia in obese men. Data from the present study extend the findings of the previous study 11 by demonstrating that the recommended volume of activity (0.84 MJ ¼ 200 kcal) accumulated through multiple short bouts of moderate intensity activity is as effective in lowering postprandial TAG concentrations as 30 min of an equivalent volume of activity performed in one continuous bout in inactive obese men. This findings has previously been demonstrated for high volume of activity (2 MJ ¼ 476 kcal) in active, healthy men. 11 The present findings are also consistent with the findings of previous studies that a prior single bout of exercise reduces postprandial TAG concentrations in overweight/obese men 22,23 and overweight/obese men with other CVD risk factors. 24,25 Furthermore, the present findings extend the findings of the previous studies by demonstrating that 30 min of moderate-intensity cycling (0.9 MJ), as previously demonstrated for 90 min moderate-intensity walking (2.8 MJ), 22 (3.7 MJ), min of moderate-intensity running (2.6 MJ) 24 and 60 min of moderate/high-intensity running ( MJ), 25 performed the day before the test meal is effective at lowering postprandial TAG concentrations. The high volume of exercise used in the previous studies is not surprising because an increase in caloric expenditure through exercise is a general principle of exercise recommendations for obese individuals. 17 However, the volume of exercise performed in the present study may be attractive to obese individuals for the early stage of their exercise initiation. In the present study, there are two potential mechanisms underlying the reduction of postprandial TAG concentrations in the exercise trials relative to the control trial. One is increased activity of the enzyme lipoprotein lipase located in the capillaries supplying skeletal muscle which might enhance the uptake of TAG into the previously exercised muscle. 19 The other mechanism is a reduced rate of hepatic very low-density lipoprotein (VLDL)-TAG secretion. 26 It is difficult to tell which of these mechanisms predominates in the present study. NEFAs concentrations did not differ among trials in the present study suggesting that substrate delivery to the liver for TAG synthesis and secretion in VLDLs was not different among trials. However, there was a tendency for elevated postprandial serum 3-OHB concentrations in the exercise trials and this indicates that NEFA were being oxidized rather than esterified in the liver, thus reducing the availability of TAG for incorporation into VLDL. In contrast, the tendency for lower postprandial serum insulin concentrations in the exercise trials may suggest reduced insulin mediated inhibition of skeletal muscle lipoprotein lipase activity and thus enhanced TAG clearance at this site. 19 For consistency with the current guidelines regarding physical activity and health, 1,2 the present study employed moderate levels of activityfboth exercise intensity and exercise volume in this study are consistent with the guidelines. This is clearly demonstrated by the low heart rate, ratings of perceived exertion, and estimated energy expenditure of 0.84 MJ elicited by the exercise. In addition, accumulated bouts were separated by 30 min in the present study in contrast to 3 4 h in previous studies. 9,10 A 30 min rest interval was chosen because these intervals may more closely resemble lifestyle activities (that is, cycle/walk to/off a post office, shop, bus stop and so on), and frequent increases in muscle blood flow through multiple short bouts of exercise may enhance exposure of TAG to skeletal muscle lipoprotein lipase for reducing TAG concentrations. However, the subjects in the present study were young males. Thus, the findings may not be applicable to the public at large. Nonetheless, one study which supports the notion that the findings of the present study are applicable to the general public is that of Murphy et al. 10 Their study demonstrated that 30 min of brisk walking equivalent to 60% of maximum oxygen uptake accumulated throughout the day (10 min 3) or in one continuous session (30 min), performed by sedentary middle-aged individuals reduces postprandial plasma TAG concentrations measured over a 12-h period compared with a control trial. The reduction of postprandial TAG concentrations was comparable in both exercise trials as is the case in the present study. On the basis of the present findings this study provides further support for the concept of accumulation 1,2 and suggests that multiple short bouts of activity are also likely to be effective for health benefits at least in the case of postprandial lipaemia. Most studies examining postprandial TAG responses following exercise have employed a meal of high-fat content (over 60% total energy) (for a review of these studies see Gill and Hardman 27 and Petitt and Cureton 28 ). In the present study, a meal of moderate-fat content (35% total energy) was used to assess postprandial metabolism in response to exercises. The aim was to more accurately mimic a real life situation where the macronutrient composition of the test meal reflects the background diet consumed in over onethird of Japanese adults (38% of Japanese adults aged between 20 and 29 consumed daily meals containing over 30% of energy as fat), 29 and this is also shown by a 2-day diet recorded by some subjects in the present study. In agreement with previous studies using a meal(s) of moderate-fat content to examine the effect of exercise on postprandial TAG concentrations, 30,31 the present study found that both patterns of moderate exercise are effective in reducing postprandial TAG concentrations after a meal of moderatefat content in obese men. Thus, the findings of the present study may be applicable to the usual postprandial state in a real life situation. In the present study exercise was performed the day before postprandial testing rather than on the same day as postprandial testing. This is because such time interval may provide adequate time for maximizing skeletal muscle lipoprotein lipase activity, leading to lowered postprandial TAG concentrations. It is worth mentioning, however, that it has been suggested that only recent exercise appears to

7 facilitate exercise-induced postprandial TAG lowering effects. 25,32 In addition, although cross-sectional studies have shown that trained athletes tend to have a lower postprandial TAG response relative to sedentary individuals, 33 this exercise-induced suppressive effect on postprandial TAG concentrations is reduced by a short-period of detraining. 34,35 In respect to long-term exercise for health, taken together these emphasize the important role of regular physical activity for enhancing postprandial lipid metabolism through its role in weight control. Therefore, additional research is required to determine whether multiple short bouts of activity, performed on the same day as test meal(s) are consumed, is effective in lowering postprandial TAG concentrations. In summary, the findings of present study demonstrate that in obese men, postprandial serum TAG concentrations are reduced to a similar extent when 10, 3-min bouts of cycling are performed during the course of a day compared with one continuous 30 min bout of cycling. These findings suggest thatfas far as physical activity guidelines for health are concernedfthe duration of each activity bout may be unimportant for lowering at least postprandial TAG concentrations providing that sufficient energy is expended throughout the day. Further study is required to determine if exercise-induced reductions in postprandial lipaemia demonstrated in the present study also occur in other populations (that is, women, older age groups). Acknowledgements This study was supported by grants from the Japan Society for the Promotion of Science, Grant-in-Aid for young scientists (No , ) and the Health Promotion Foundation (Tokyo, Japan). References 1 Department of Health. Physical Activity, Health Improvement and Prevention. At Least Five a Week. Department of Health: London, UK, Haskell WL, Lee I-M, Pate RR, Powell KE, Blair SN, Franklin BA et al. Physical activity and public health: Updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc 2007; 39: Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C et al. Physical activity and public health. A recommendation from the centers for disease control and prevention and the American College of Sports Medicine. JAMA 1995; 273: Sesso HD, Paffenbarger RS, Lee I-M. Physical activity and coronary heart disease in men. The Harvard Alumni Health Study. Circulation 2000; 102: Whitt M, Kumanyika S, Bellamy S. Amount and bouts of physical activity in a sample of African-American women. Med Sci Sports Exerc 2003; 35: Stanner S. Cardiovascular Disease: Diet, Nutrition and Emerging Risk Factors. 1st edn. Blackwell: Oxford, Altena TS, Michaelson JL, Ball SD, Thomas TR. Single sessions of intermittent and continuous exercise and postprandial lipemia. Med Sci Sports Exerc 2004; 36: Burns SF, Miyashita M, Ueda C, Stensel DJ. Multiple bouts of resistance exercise and postprandial triacylglycerol and serum C- reactive protein concentrations. Int J Sport Nutr Exerc Metab 2007; 17: Gill JMR, Murphy MH, Hardman AE. Postprandial lipemia: effects of intermittent versus continuous exercise. Med Sci Sports Exerc 1998; 30: Murphy MH, Nevill AM, Hardman AE. Different patterns of brisk walking are equally effective in decreasing postprandial lipaemia. Int J Obes 2000; 24: Miyashita M, Burns SF, Stensel DJ. Exercise and postprandial lipemia: effect of continuous compared with intermittent activity patterns. Am J Clin Nutr 2006; 83: Miyashita M, Burns SF, Stensel DJ. Accumulating short bouts of running exercise throughout the day reduces postprandial plasma triacylglycerol concentrations and resting blood pressure in healthy young men. J Phys Act Health 2006; 3: Castro Cabezas M, Halkes CJM, Meijssen S, van Oostrom AJHHM, Erkelens DW. Diurnal triglyceride profiles: a novel approach to study triglyceride changes. Atherosclerosis 2001; 155: Fisher RM, Coppack SW, Gibbons GF, Frayn KF. Post-prandial VLDL subfraction metabolism in normal and obese subjects. Int J Obes Relat Metab Disord 1993; 17: Halkes CJM, Castro Cabezas M, van Wijk JPH, Erkelens DW. Gender differences in diurnal triglyceridemia in lean and overweight subjects. Int J Obes 2001; 25: Miyashita M, Stensel DJ. Accumulating short bouts of brisk walking reduces postprandial plasma triacylglycerol concentrations in young men. Atherosclerosis 2006; 188: S3. 17 American College of Sports Medicine. Guidelines for Exercise Testing and Prescription, 6th edn. Lippincott Williams and Wilkins: Philadelphia, The Examination Committee of Criteria for Obesity Disease in Japan, Japan Society for the Study of Obesity. New criteria for obesity disease in Japan. Circ J 2002; 66: Seip RL, Mair K, Cole TG, Semenkovich CF. Induction of human skeletal muscle lipoprotein lipase gene expression by short-term exercise is transient. Am J Physiol 1997; 272: E255 E Seip RL, Semenkovich CF. Skeletal muscle lipoprotein lipase: molecular regulation and physiological effects in relation to exercise. Exerc Sports Sci Rev 1998; 26: Borg GA. Perceived exertion: a note on history and methods. Med Sci Sports 1973; 5: Burton FL, Malkova D, Caslake MJ, Gill JMR. Energy replacement attenuates the effects of prior moderate exercise on postprandial metabolism in overweight/obese men. Int J Obes 2008; 32: Gill JMR, Al-Mamari A, Ferrell WR, Cleland SJ, Packard CJ, Sattar N et al. Effects of prior moderate exercise on postprandial metabolism and vascular function in lean and centrally obese men. J Am Coll Cardiol 2004; 44: Zhang JQ, Ji LL, Fretwell VS, Nunez G. Effect of exercise on postprandial lipemia in men with hypertriglyceridemia. Eur J Appl Physiol 2006; 98: Zhang JQ, Ji LL, Nunez G, Feathers S, Hart CL, Yao W-X. Effect of exercise timing on postprandial lipemia in hypertriglyceridemic men. Can J Apply Physiol 2004; 29: Gill JMR, Frayn KN, Wootton SA, Miller GJ, Hardman AE. Effects of prior moderate exercise on exogenous and endogenous lipid metabolism and plasma factor VII activity. Clin Sci 2001; 100: Gill JMR, Hardman AE. Exercise and postprandial lipid metabolism: an update on potential mechanisms and interactions with high-carbohydrate diets (Review). J Nutr Biochem 2003; 14:

8 Petitt DS, Cureton KJ. Effects of prior exercise on postprandial lipemia: a quantitative review. Metabolism 2003; 52: Ministry of Health, Labour and Welfare, Japan The National Health and Nutrition Survey in Japan. Ministry of Health, Labour and Welfare: Tokyo, Kolifa M, Petridou A, Mougios V. Effect of prior exercise on lipemia after a meal of moderate fat content. Eur J Clin Nutr 2004; 58: Kokalas N, Petridou A, Nikolaidis MG, Mougios V. Effect of aerobic exercise on lipaemia and its fatty acid profile after a meal of moderate fat content in eumenorrhoeic women. Br J Nutr 2005; 94: Herd SL, Hardman AE, Boobis LH, Cairns CJ. The effect of 13 weeks of running training followed by 9 d of detraining on postprandial lipaemia. Br J Nutr 1998; 80: Tsetsonis NV, Hardman AE, Mastana SS. Acute effects of exercise on postprandial lipemia: a comparative study in trained and untrained middle-aged women. Am J Clin Nutr 1997; 65: Gill JMR, Caslake MJ, Mcallister C, Tsofliou F, Ferrell WR, Packard CJ et al. Effects of short-term detraining on postprandial metabolism, endothelial function, and inflammation in endurance-trained men: dissociation between changes in triglyceride metabolism and endothelial function. J Clin Endocrinol Metab 2003; 88: Herd SL, Lawrence JEM, Malkova D, Murphy M, Mastana S, Hardman AE. Postprandial lipemia in young men and women of contrasting training status. J Apply Physiol 2000; 89: