Effect of a Long Bout Versus Short Bouts of Walking on Weight Loss During a Weight‐Loss Diet: A Randomized Trial

This study aimed to evaluate the effect of different daily physical activity (PA) frequencies, while maintaining the same daily volume of PA, on weight loss, carbohydrate metabolism, and lipid metabolism in women with overweight or obesity throughout a 24‐week intervention.


Introduction
The worldwide epidemic of obesity has resulted in calls for prevention and treatment strategies. Clinical trials on weight reduction through diet have shown only modest long-term efficacy (1). It is recommended that physical activity (PA) should be an integral part of the management of weight loss, weight maintenance (2), and the treatment of abdominal obesity (3). It appears that weight-loss interventions containing PA are more effective than dietary instruction alone for long-term weight management (4,5).
There is evidence of the need to maintain a physically active lifestyle, which should include more than 50 min/wk of PA to manage body weight (6,7), whereas 200 to 300 min/wk is recommended for long-term weight loss (8,9). Since 1995, PA guidelines have included the concept that health benefits of exercise or PA may be accumulated in bouts spread over the course of the day (10). Lack of time was frequently cited as a barrier to PA (11), which led to short bouts of activity throughout the day being recommended rather than a continuous time slot in a busy schedule (12).
The results of studies of the impact of accumulated versus continuous exercise on weight loss have been contradictory and inconclusive. Some studies have indicated that weight loss was similar between accumulated and continuous exercise training (13)(14)(15), whereas other studies have indicated superior health benefits gained from PA in multiple bouts (16,17), and some studies have indicated more weight loss and superior health benefits gained from one continuous PA bout (18)(19)(20). Available evidence has also been contradictory and insufficient to determine whether accumulated exercise is as effective as continuous exercise for outcomes such as adiposity, blood lipids, and indicators of psychological well-being (21).
To our knowledge, clinical studies that have looked at continuous versus multiple short bouts of exercise during a weight-loss intervention are scarce. So, the primary objective of the present study was to compare the effect of a daily brisk walking program with a fixed total duration per day, undertaken over either 50 continuous minutes (longer bout) or two 25-minute periods (shorter bouts), on weight loss and anthropometric measures in healthy women with obesity or overweight while following a comprehensive 24-week weight-loss program. The secondary objective was to examine the effect of the daily pattern of PA on biochemical indicators of cardiometabolic risk.

Participants
Healthy women with overweight or obesity were recruited between February 2015 and July 2015 from participants attending the NovinDiet Clinic for weight loss in Tehran, Iran. Inclusion criteria were the following: female sex (18-40 years of age; BMI = 27-35 kg/m 2 ), sedentary lifestyle (reported exercising fewer than 3 d/wk and <20 min/d for the previous 6 months) (22,23), and being ready to introduce a dietary change to lose weight. For additional inclusion criteria, participants were required to be nonsmokers and free of established cardiovascular diseases, stroke, diabetes, liver disease, kidney disease, depression, cancer, or autoimmune disease. Only participants with a BMI of 27 to 35 kg/m 2 were selected to reduce the effect of confounding factors of a more extreme diet and more extreme PA behaviors because it is likely that food intake behaviors and PA abilities of those in other classes of obesity may influence the results. Moreover, participants were only included if they could show that they were able to keep an adequate 4-day food record as part of the screening process and record details of their total daily steps and if they were considered by the study physician to be fit to participate in the physical exercise program. Exclusion criteria were pregnancy or lactation during the prior 6 months or planned pregnancy in the next 6 months; depression defined by using the Beck Depression Inventory (24); weight loss of ≥10% of body weight within the 6 months before enrollment in the study; participation in any weight-loss research project in the previous 6 months; taking medication to lower lipids and/or cholesterol or that could affect metabolism or change body weight; and a self-reported history of heart disorders, frequent chest pains, or faintness or dizziness on the Physical Activity Readiness Questionnaire (25).
The study was approved by the Ethical Committee of The Digestive Research Institute at Tehran University of Medical Science. All participants provided their signed consent before study enrollment.

Study design and interventions
The study was a 24-week, two-arm randomized clinical trial. Eligible participants were randomly assigned, after baseline measurements, by the project director and by using a computer-generated randomnumbers method. The allocation was obscured from the participants and dietitians until randomization was revealed to the study participants at the first intervention clinic appointment. To control the effects of menstrual cycle on measurements, participants started the study at the same phase of their menstrual cycle. Sixty-five participants were randomly assigned to one of the two study groups: (1) diet plus short bouts of moderate physical activity (SBP) (n = 32) and (2) diet plus a long bout of moderate physical activity (LBP) (n = 33). Participants in the LBP group were requested to perform brisk walking for 50 min/d, 6 d/wk (300 min/wk), whereas participants in the SBP group were instructed to perform brisk walking in two 25-minute bouts per day 6 d/wk (300 min/wk) (9,26).
To become conditioned to the level of exercise, a week before the start of the study, participants were asked to increase their daily step count and record the step count in a diary. To standardize the intensity of the PA sessions, participants were asked to walk at least 100 steps/min during the brisk walking sessions (27) and to do the walking on a flat surface outdoors in their neighborhood or a park with loose-fitting and comfortable clothing appropriate for the weather conditions.
To encourage participants to achieve the requested PA goal, they were encouraged to recruit one PA partner from their group of friends and family members to participate in the PA part of the study with them. Weekly visits to the dietitian and exercise coach were required in order to promote adherence to the hypoenergetic diet and recommended PA protocol. To promote adherence to the PA intervention, participants were provided with a three-dimensional pedometer (JT626; SunnyLife Limited, London, United Kingdom) and were instructed to wear the pedometer for the whole day except when bathing or showering or going to bed and to write their daily step counts and time of their structured PA in their log book. Both groups were guided on the hypoenergetic diet according to the NovinDiet protocol.

Dietary and activity intervention sessions
The NovinDiet Clinic is a private weight-loss clinic that uses an integrated approach (dietary, behavioral, exercise, and medical treatments). The NovinDiet protocol is based on helping each member develop their own problem-solving approach. In this study, the program was designed to enable weight loss of 7% to 10% of initial body weight at a rate of 0.5 to 1 kg/wk over 24 weeks. The individual diet programs were based on the participant's food diary records as a reflection of their food preferences. Gradual modifications were made to bring their diet in line with the NovinDiet protocol. Participants were instructed to consume a hypoenergetic diet with a mainly high-carbohydrate and low-saturated-fat content (15% of energy from protein, 30% from fat [<10% from saturated fat], and 55% from carbohydrates). The diet program was designed to introduce a 500-to 600-kcal/d energy deficit based on estimated energy requirements at the start of the study. Participants were encouraged to eat mainly foods with low energy density to achieve satiety, some low-fat dairy products, fiber-rich foods, and controlled amounts of foods with high energy density. The main behavior-change strategies applied included assessing and discussing stages of change, goal setting, self-monitoring with food diaries, and giving feedback on waist measurement changes (7).
At weekly sessions, the participants discussed with their dietitian any problems they had in complying with their weight-loss program. Home booklets that included their dietary and PA goals were provided as resources for each participant. During the intervention period, participants completed a feedback form regarding their adherence to diet and PA. At weekly clinic visits, the dietitian reviewed their progress and also checked their PA adherence and their log during the previous week. Participants also had access to a website, weekly Internet magazines, and one-on-one telephone and/or online support from a physician if they felt that they had difficulty with compliance.

Measurements
Anthropometric measurements of all subjects were taken at baseline and at 24 weeks (except height, which was taken only at the screening visit) by the dietitian.
Energy and macronutrient intake at baseline and at the last week of the intervention (week 24) was analyzed by Nutritionist IV software (version 4.1; Hearst, San Bruno, California). Estimated daily PA measurements of all participants were taken at the start of the intervention and at weeks 4, 8, 12, 16, 20, and 24 by using the three-dimensional pedometer. Blood samples were taken from all subjects after an overnight (10-12 hours) fast (between 7:00 am and 9:00 am) at baseline and after 24 weeks. Blood samples from an antecubital vein via a venipuncture were taken while the participants were in a sitting position, according to the standard protocol, and were centrifuged within 30 to 45 minutes. Blood samples were also taken 2 hours after ingesting 75 g of glucose according to the standard method for 2-hour postprandial (2-hpp) glucose (28). Blood samples were analyzed for biochemical, cellular, and hormonal variables.

Anthropometric measurements
Body weight was measured to the nearest 0.1 kg by using a digital calibrated scale (Omron Health Care, Hoofddorp, Netherland) while the participant wore light clothing with no shoes. Body height was measured to the nearest 0.1 cm by using a wall-mounted stadiometer (seca, Hamburg, Germany) while participants were shoeless and in a freestanding position. Waist circumference (WC) was measured with a flexible but nonstretching measuring tape and recorded to the nearest 0.5 cm. WC was measured halfway between the lower rib and the iliac crest (29). BMI was calculated as measured weight in kilograms divided by height in meters squared.

Blood sample measurements
Fasting plasma glucose (FPG) and 2-hpp glucose levels were measured by using an enzymatic colorimetric method. Insulin was measured by using a radioimmunoassay with 125 I-labeled human insulin and a human insulin antiserum in an immunoradiometric assay (Biosource, Dorest, Belgium) with a gamma counter system (Gamma I; Genesys, Daly City, California). Fasting insulin resistance was evaluated by homeostatic model assessment of insulin resistance (HOMA-IR), which was calculated by using the following formula: HOMA-IR = (fasting insulin [milliunits per liter] × FPG [millimoles per liter]) ÷ 22.5 (30). Glycated hemoglobin (HbA1c) was measured by a colorimetric method after an initial separation by ion exchange chromatography (Biosystems, Barcelona, Spain).

Statistical methods
Baseline values of cardiovascular risk factors (including weight, WC, LDL-c, HDL-c, TC, FPG, and TG), fasting insulin, HOMA-IR, HbA1c, 2-hpp glucose, food intake, and step-count data were compared between the SBP and LBP groups by using unpaired t tests.
At baseline, distribution was normal for all variables. All participants who were randomly assigned and completed an initial assessment were included in the final results by using an intention-to-treat analysis. Multiple imputations with the use of linear regression were used to impute missing values from 24 weeks and were based on the assumption that data were missing at random. We used analysis of covariance (ANCOVA) to compare the means of postintervention outcomes between the two groups using baseline values as covariates. Repeatedmeasures two-factor analysis of variance (ANOVA) with intervention groups (SBP and LBP) and time (weeks 0, 4, 8, 12, 16, 20, and 24) as within-subject factors was used to assess the effects of the interventions on the PA level measured by using the step-count data between the groups over time.
The primary outcome addressed in this study was the difference in body weight loss after the 24-week weight-loss program. The power calculation was based on the prior data (α = 0.05; power (1 − β) = 0.9), which were based on expected differences in weight loss between the intervention groups (1.3; SD = 2.1 kg), to determine the targeted final sample size (n = 57). Considering a drop-out rate of 10%, the sample size required was 63, therefore 65 subjects were randomly assigned in the two groups of the intervention.
Statistical significance was set at P ≤ 0.05. All data are presented as mean ± SD unless otherwise stated. All statistical analyses were performed by using SPSS software version 22.0 for Windows (IBM Corp., Armonk, New York).

Baseline characteristics
Of 65 recruited participants with overweight or obesity, 57 completed the 24-week intervention (88% of the randomly assigned population; Figure 1). At screening, five people decided that they were not interested in being in the study, and one participant was excluded from the study because of the results of the Beck depression questionnaire. Five were excluded because they failed to keep the dietary record reliably. Blood test results at screening showed that nine were ineligible because they had one or more of the exclusion criteria.
The remaining 65 eligible participants gave written consent, and then 32 participants were allocated randomly to the SBP group and 33 to the LBP group. After starting the intervention, a total of eight participants dropped out for different reasons (one in the LBP group because of illness, four because of loss of interest in completing the study [three in the LBP group and one in the SBP group], one in the LBP group because of an unexpected pregnancy, one in the SBP group because of relocation, and one in the SBP group without giving any reason).
At baseline, there were no statistically significant differences in physical characteristics or biochemical measurements between the two groups (

Body weight, BMI, and WC
As shown in Table 2, there was a significant weight reduction in both groups (P < 0.001) and a significant difference in body weight between the groups (P = 0.019) after 24 weeks of the intervention. The weight change (mean ± SD) was −8.08 ± 2.20 kg in the SBP group and −6.39 ± 2.28 kg in the LBP group.
BMI reduction in each group was in the expected direction, with significant effects over 24 weeks for both groups (P < 0.001). However, the decline in BMI was larger in the SBP group than in the LBP group after 24 weeks (P = 0.027; Table 2).
In both groups, WC had decreased significantly after the 24-week intervention (P < 0.001). There was a significant difference in the decrease in WC between the two groups after 24 weeks (−8.78 ± 2.62 cm in the SBP group and −5.76 ± 2.03 cm in the LBP group; P = 0.026), as shown in Table 2.

Lipid profiles
Reductions in TC, LDL-c, and TG concentrations and an increase in HDL-c levels were seen over the 24 weeks in each group (P < 0.001). However, there were no significant differences in these results between the groups (Table 2).  Glucose metabolism measurement FPG, 2-hpp glucose, HbA1c, fasting serum insulin, and HOMA-IR all declined over the 24-week study in each group (P < 0.001). However, there were no significant differences in the reductions of these glucose metabolism variables between the two groups at 24 weeks (Table 2).

Food intake
At baseline, there was no significant difference in energy and macronutrient intakes Table 3. Estimated energy intakes showed a significant reduction over time in both groups (P < 0.001 for time effect), but there were no significant differences between the two groups at the end of the 24-week intervention.

PA measurements
As shown in Figure 2, at baseline, both groups had similar mean (±SD) daily steps (3,990 ± 651 in the SBP group and 3,925 ± 701 in the LBP group). Compared with baseline, both groups had higher mean daily steps over time (P < 0.001 for time effect). Furthermore, the step-count increase (mean ± SD) was higher in the SBP group compared with the LBP group over the 24-week intervention (SBP: +2,965 ± 795 steps per day; LBP: +2,196 ± 789 steps per day; P < 0.001; two-way ANOVA).
Regarding the PA adherence of participants, the mean values calculated from the exercise log book showed that the SBP group attended 92% of the prescribed 288 sessions, whereas the LBP group attended 89% of the 144 prescribed sessions. In addition, total duration for the structured PA was 280 ± 65 min/wk in the SBP group versus 247 ± 54 min/wk in the LBP group, which was not significantly different.

Discussion
The aim of the current study was to evaluate the effect of different daily PA frequencies, while aiming to maintain the same total period of activity, on weight loss and anthropometric measures in healthy women with obesity or overweight following a comprehensive 24-week weight-loss program. The secondary objective was to examine the effect of the daily pattern of PA on biochemical indicators of cardiometabolic risk. The main finding of the present study was that those in the SBP group with two 25-minute PA sessions per day for 6 d/wk had significantly greater weight loss than those in the LBP group with 50 min/d of PA for 6 d/wk, although they were prescribed to have the same total of 300 min/wk of PA. However, no significant differences in the changes in carbohydrate metabolism characteristics and lipid profiles were seen after the weight-loss intervention between the groups.
In the current study, participants in the SBP group, who were asked to perform two 25-minute bouts of PA 6 d/wk, lost 1.7 kg more weight than those in the LBP group, who performed one bout of PA for 50 min/d 6 d/wk. Our results are consistent with previous studies with results of greater weight loss in short bouts versus long bouts of exercise (16,17). However, our results are in contrast with others that have shown either no differences in weight loss between accumulated and continuous exercise training (13)(14)(15) or more weight loss when activity was performed in one continuous PA bout (18)(19)(20). The contrast between our results and those of previous studies may be related to the different designs in terms of the duration of PA, which was less in the previous studies than in the current guideline recommendations (8,9), and/or the absence of an integrated weight-loss diet in their programs (13)(14)(15)18,19).
In the present study, the average percentage of weight loss during a 6-month intervention was similar to that of other behavioral lifestyle modification programs (32-34) and our previous study, which encompassed a similar dietary component and PA weekly duration (i.e., 300 min/wk) (35). Furthermore, the results of the present study are in agreement with the Jakicic et al. (36) study, which indicated that the combination of changes in eating and PA behaviors can improve long-term weight loss compared with changing either behavior alone. The participants of the present study were walking ≤5,000 steps/d, which defines a sedentary lifestyle. They increased PA during the intervention, and the increase was significantly higher in the SBP group compared with the LBP group over the 24-week intervention (SBP: +2,965 ± 795 steps/d; LBP: +2,196 ± 789 steps/d; P < 0.001).
The present results are also consistent with previous evidence that small changes in daily PA (an increase of 3,000 steps/d accrued across time) as part of a nutritional changes program is linked with modest, consistent, and sustained weight loss (37). However, the majority of our participants, especially those in the LBP group, did not achieve 7,000 to 8,000 steps a day and so were below the threshold of free-living PA recommended in current public health guidelines (38).
The results of the current study also showed a higher overall PA, assessed by mean daily steps, in the SBP group compared with the LBP group. These results are consistent with previous studies (39) that have indicated that prescribing short bouts of PA may increase long-term exercise adherence or may actually lead to participants undertaking higher-intensity PA and/or more than the prescribed exercise duration. However, these results are inconsistent with the outcome of the study by Jakicic et al. (20), which showed that the duration of PA was only significantly greater in the SBP compared with LBP in the first 4 weeks, but no significant differences were seen among the groups after that. It seems that further studies are required to measure the adherence to PA recommendations in the longer term.
There were no significant differences in estimated energy intake between the groups. Therefore, the significant difference in weight loss after 24 weeks between the groups may be due to a difference of PA energy expenditure between the two groups, but to find an accurate explanation for the greater weight loss in the SBP group than in the LBP group, further studies are needed.
In the present study, as would be expected according to the weight loss during the intervention, significant, potentially beneficial changes in lipid profiles and carbohydrate metabolism characteristics were observed, but these changes were similar in both groups over time.
The findings of the present study may have clinical implications for the prescription of PA that are consistent with the current guidelines, which indicate combining >250 min/wk of PA with an energy-restricted diet for weight-loss management. In addition to overcoming the lack of time for doing continuous PA in a busy lifestyle, the current study suggests  that having two shorter bouts of PA rather than one continuous bout during a day may lead to more weight loss. However, further research is required to examine whether the weight-loss benefits of SBP compared with LBP are sustained in the long term.
The principal strength of this study is that it was a randomized outpatient clinical trial while participants were on a comprehensive diet plan for weight control in a longer-term intervention (i.e., 24 weeks). Second, participants wished to lose weight and included middle-aged women with overweight or obesity who were able to comply with a weight-loss plan; hence, they demonstrated that they were motivated to adhere to the weight-loss diet protocol (40).
There are some limitations to this study that should be considered when interpreting the results. First, this study was designed to test whether LBP would result in greater weight loss than would SBP. However, accurate objective measurements of PA characteristics, e.g., intensity and length of PA in the intervention groups, were not made during the structured PA sessions or over the rest of the day. These should be included in future studies. Second, because the majority of PA attained in this study was brisk walking, the effect of other forms of activity on weight loss could not be determined. Third, not measuring energy expenditure is a limitation of this study, and further studies using more robust objective measurements of energy expenditure are certainly indicated. Also, the method used to measure energy intake may also be a limitation, and this would be an important component of future work.

Conclusion
PA performed in two short bouts per day appears to have a beneficial impact on weight loss in women with overweight or obesity who adhere to a weight-loss diet. Longer-term studies are now required to investigate whether these differences are sustained.O Figure 2 Mean ± SEM step calculations with the use of a three-dimensional pedometer over the 24week intervention. At baseline, there were no differences in step counts between the SBP (n = 32) and LBP (n = 33) groups. There was a significant group × time interaction for the mean daily steps over 24 weeks (P = 0.001; two-factor ANOVA). LBP, diet plus a long bout of moderate physical activity; SBP, diet plus short bouts of moderate physical activity.