The Effects of Exclusive Walking on Lipids and Lipoproteins in Women with Overweight and Obesity: A Systematic Review and Meta-Analysis

Abstract

Objective

To evaluate the effects of walking, independent of diet and weight-loss, on lipids and lipoproteins in women with overweight and obesity.

Data Source

Academic Search Complete, Alternative Health Watch, Global Health, Health Source, CINAHL, MEDLINE, EMBASE, SportDiscus, and ProQuest.

Study Inclusion and Exclusion Criteria

(1) experiment-control design; (2) women with overweight or obesity; (3) walking as the experiment’s independent variable; (4) four or more weeks; and (5) pre- to post-assessment of lipids and/or lipoproteins. Excluded studies reported use of lipid-lowering medication, diet or other modes of physical activity, and alternative interventions as the control.

Data Extraction

Data extraction and study quality were completed by the first 2 authors using the Cochrane review protocol and risk of bias assessment.

Data Synthesis

Raw mean difference between the experiment and control groups using a random effects model.

Results

Meta-analyses of 21 interventions (N = 1129) demonstrated exclusive walking improves total cholesterol (raw mean difference = 6.67 mg/dL, P = .04) and low-density lipoproteins (raw mean difference = 7.38 mg/dL, P = .04). Greater improvement in total cholesterol, triglycerides, high-density lipoproteins, and low-density lipoproteins existed in women with obesity.

Conclusions

Exclusive walking aids in normalizing total cholesterol and LDLs in women with overweight and obesity. Exclusive walking can be used as a non-pharmacologic therapy, which may have positive clinical outcomes for individuals who especially struggle with diet and weight-reduction.

Keywords

body mass index lipids total cholesterol triglycerides lipoproteins raw mean difference

Introduction

Overweight and obesity are global public health disorders.¹ Women are affected by these conditions more than men,² with two-thirds of women in the United States accounting for the disorders.³ Further, overweight and obesity are risk factors for cardiovascular disease (CVD),⁴ and dyslipidemia is highest among adults with overweight and obesity.⁵ The negative effects of dyslipidemia are of special concern for women as they are more likely than men to succumb to their first myocardial infarction, and women who survive their first coronary incident are twice as likely to develop heart failure.⁶ When compared to men, higher mortality risks for women are partly attributed to physiological differences such as smaller cardiovascular anatomy and underlying hormone-related mechanisms.^7,8 Aerobic physical activity elicits positive effects on lipids and lipoproteins in individuals with overweight and obesity.⁹ Physical activity is thus especially critical for this population, yet physical inactivity is more common among women than men.^10,11 Therefore, interventions for women that focus on increasing physical activity are needed to combat CVD.

Researchers who reported improved lipid and lipoprotein profiles also reported weight-loss among participants. Additionally, weight-loss is a common goal of lifestyle interventions for adults with overweight and obesity.^12,13 While weight-loss is optimal for preventing CVD,⁴ weight-loss and weight-loss maintenance are often difficult for individuals with overweight and obesity due to several physiological and psychological factors.^4,14 If individuals are encouraged to focus on improving lipid and lipoprotein profiles to reduce their risk of developing CVD, aside from weight-loss, the risk of developing CVD may be reduced.

Walking is a simple and generally safe form of physical activity,¹⁵ and due to its practicality, it has been used as the modality of exercise for large intensive lifestyle interventions, such as the Diabetes Prevention Program.¹⁶ Walking interventions, independent of diet and weight-loss, for women with overweight and obesity have resulted in differing lipid and lipoprotein outcomes. For example, total cholesterol, low-density lipoproteins, and triglycerides improved in some studies, but did not improve in others.^17-19 We observed that intensity (moderate vs vigorous or combined) and duration (1 session vs 12 weeks) varied among the studies, and these are variables that can ultimately moderate outcomes.²⁰ Therefore, a meta-analysis is warranted to provide a more precise estimate of the effects of exclusive walking on lipids and lipoproteins in this population, and the relationships that exists between the effects and potential mediating variables.

Previous meta-analyses have calculated the effects of walking on lipids and lipoproteins. One meta-analysis demonstrated significant improvement in low-density lipoproteins and total cholesterol to high-density lipoproteins ratio (TC: HDL), but not in total cholesterol,²¹ and another only demonstrated improvement in total cholesterol.²² The difference in findings between the studies may be due to differences in their methodology, such as their exclusion criteria.^21,22 However, both meta-analyses were for general populations and were not limited to overweight and obese adults.

Another meta-analysis calculated the combined effects of aerobic exercise (walking, jogging, running, and cycle ergometry) and diet used to improve lipids and lipoproteins (e.g., low-saturated fat diet) in overweight and obese adults. The authors reported significant improvement in total cholesterol, low-density lipoproteins, and triglycerides.²³ However, sub-group analyses for men and women could not be substantially completed due to some of the included studies not reporting separate data for the genders. Additionally, due to the nature of the meta-analysis, the independent effects of aerobic exercise and diet could not be determined. Therefore, this meta-analysis builds upon previous work by providing the independent effects of a single aerobic activity (walking) on lipids and lipoproteins in overweight and obese women.

Objective

The purpose of this study was to complete a systematic review and meta-analyses to examine the effects of walking, independent of diet and weight-loss, on lipids and lipoproteins in women with overweight and obesity. A secondary aim was to determine the relationship that exists between the effects of exclusive walking and the following: walking duration, intensity, and body mass index (BMI). Additionally, due to different measurements of walking activity, the relationship between this variable and the effects of exclusive walking were determined.

Methods

Data Source

An extensive search of the scientific and medical research literature was systematically conducted using the PRISMA statement²⁴ and the Cochrane review guidelines.²⁵ Academic Search Complete, Alternative Health Watch, Global Health, Health Source, CINAHL, MEDLINE, EMBASE, SportDiscus, and ProQuest dissertations and theses databases were searched. Three sets of extensive search terms were entered using Boolean logic to identify all possible literature. Search terms were: (women) AND (lipids or lipoproteins or [additional terms]) AND (walk or walking or [additional terms]). Also, reference lists from fully reviewed publications were searched for additional studies not found in the search of databases. The search of literature was not restricted to a timeframe in which the studies were completed.²⁵

Inclusion Criteria

Studies were initially selected for review based on titles and abstracts. Studies that met the following inclusion criteria were fully reviewed: (1) experiment-control design; (2) sample of women (≥18 years) with overweight (average BMI: 25.0 kg/m² to 29.9 kg/m²) or obesity (average BMI: ≥ 30.0 kg/m²); (3) walking as the experiment’s independent variable; (4) period of four or more weeks²⁶; and (5) pre-to post-assessment of lipids and/or lipoproteins.

Exclusion Criteria

Studies that reported participants taking lipid-lowering medication (e.g., statins), intervention groups that included diet or other modalities of physical activity, and studies that used any type of alternative intervention as the control (e.g., diet counseling and other physical activity) were excluded. Also, to quantify data, the selected studies had to include the sample size along with the test statistics (e.g., means and standard deviations) for the control and intervention groups. For studies that reported insufficient data, attempts to obtain the necessary data were completed by contacting the corresponding author prior to exclusion.

Selection of Studies

A total of 1508 studies were identified from the search of databases and review of reference lists. An initial search was completed in 2019, with a return of 948 citations, spanning from 1985 to 2019, and an additional 9 studies were identified from the search of reference lists. A second search was completed in 2021, with a return of 550 citations, spanning from 2019 to 2021, and 1 additional study was identified from the search of reference lists. Of the 1508 studies, 1422 were excluded after reviewing titles and abstracts. The remaining 86 studies were fully reviewed for eligibility. Upon full review of the remaining studies, 29 were excluded due to non-experiment design, and 31 were excluded due to not meeting other inclusion criteria (e.g., walking plus diet or other modalities of physical activity and average BMI less than 25 kg/m²). Last, 2 studies were excluded due to duplicate data and 3 were excluded due to unsuccessful attempts to retrieve data from corresponding authors, leaving 21 studies for analysis. The selection of studies is summarized in Appendix A.

The first 2 authors independently searched the databases and identified studies for potential inclusion. After each author completed the search of databases and selection of studies, the authors compared their lists of selections to identify differences in exclusion or inclusion of the selected studies. When there were differences, the authors assessed the papers that were excluded/included on their opposing lists and together decided if the papers should be excluded or included in the final sample of studies.

Data Extraction and Risk of Bias Assessment

Sample size, and baseline and post-intervention data (means and standard deviations) for total cholesterol, triglycerides, low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs) were extracted from the 21 studies. Data provided in the form of millimoles per liter (mmol/L) were converted to milligrams per deciliter (mg/dL). Data extraction was independently completed by the first 2 authors. Once independently completed, the authors assessed the articles together to confirm correct and accurate data extraction.²⁵

The first 2 authors also independently completed a risk of bias assessment on the 21 studies. The risk of bias assessment was based on selection, performance, detection, attrition, and reporting. Each category was rated as high, low, or unclear risk of bias.²⁵

Data Synthesis

Data for the lipids and lipoproteins were entered in the Comprehensive Meta-Analysis software (CMA, version 3.0; Biostat Inc.). Most of the studies reported multiple variables (e.g., total cholesterol and HDLs) (Table 1), and the data from these studies were separately entered and calculated in the software. Some of the studies also had more than 1 intervention group (e.g., a moderate-intensity group and a vigorous intensity group, or a 12-week group and a 24-week group) (Table 1), which were also entered and calculated separately in the software.

Table 1.

Sample Characteristics.

Reference	Number of Subjects	Mean BMI	△ in Mean BMI^a	TC	Outcome	Variable	LDL	Number of Weeks	Intensity	Total Dose (minutes)
Reference	Number of Subjects	Mean BMI	△ in Mean BMI^a	TC	TRG	HDL	LDL	Number of Weeks	Intensity	Total Dose (minutes)
Ahn, 2007⁴²	36	25.2	NR	X	X	X	X	12	Moderate	1800
Aldred et al., 1995⁴³	24	25.8	−1.0				X	12	Moderate	1440
Asikainen et al., 2003⁴¹	204	25.8	−1.2	X	X	X	X	15	Moderate	3375
								24	Low	3600
								24	Moderate	3600
Buyukyazi, 2008¹⁷	37	28.6	−1.48	X	X	X	X	8	Moderate	1600
Buyukyazi, 2008¹⁷	37	28.6	−1.48	X	X	X	X	8	Vigorous	1600
Cauley et al., 1987⁴⁴	204	25.1	−0.74	X	X	X		104	Moderate	13 000
Davison and Grant, 1995⁴⁵	62	25.9	−0.76	X	X	X		14	Vigorous	1680
Guessogo et al., 2016³⁹	139	34.1	−0.72	X	X	X	X	24	Moderate	4800
Habibzadeh, 2010⁴⁶	20	30.5	−1.71	X				8	Moderate	720
Hinkleman and Nieman, 1993⁴⁷	36	28.3	−3.5	X	X		X	15	Moderate	3375
Hopewell, 1989⁴⁸	11	27.7	NR	X	X	X	X	12	Moderate	1500
Hopewell, 1989⁴⁸	11	27.7	NR	X	X	X	X	24	Moderate	2400
Keller and Trevino, 2001⁴⁹	36	34.6	0	X	X	X	X	24	Moderate	2160^b
Keller and Trevino, 2001⁴⁹	36	34.6	0	X	X	X	X	24	Moderate	3600^c
Kim, 2004⁵⁰	29	30.4	+0.31	X	X	X		12	Moderate	1440
Mezghanni et al., 2012¹⁸	20	33.6	−3.1	X	X	X	X	12	Moderate	2700
Miller, 1995⁵¹	37	25.1	−0.95	X	X	X	X	14	Moderate	2100^d
Miller, 1995⁵¹	37	25.1	−0.95	X	X	X	X	14	Moderate	4200^e
Nieman et al., 1993⁵²	30	26.0	+0.3	X	X	X	X	5	Moderate	875
Nieman et al., 1993⁵²	30	26.0	+0.3	X	X	X	X	12	Moderate	2100
Nieman et al., 2002⁵³	43	32	−1.0	X	X	X	X	12	Vigorous	2700
Ready et al., 1995⁵⁴	25	30.7	−1.9	X	X	X	X	24	Moderate	7200
Ready et al., 1996⁵⁵	53	26.5	−0.3	X	X	X	X	24	Moderate	4320^b
Ready et al., 1996⁵⁵	53	26.5	−0.3	X	X	X	X	24	Moderate	7200^c
Seals et al., 2001⁵⁶	35	28.5	−0.1	X	X	X	X	13	Vigorous	2600
Verity and Ismail, 1989³⁰	10	30.3	−2.1	X		X		16	Vigorous	2880
Woolf-May et al., 1999³¹	38	26.2	NR	X		X		18	Vigorous	2772^f

Note. NR = not reported. TC = total cholesterol. TG = triglycerides. HDL = high-density lipoproteins. LDL = low-density lipoproteins.

^aChange in mean BMI (kg/m²) of the walking groups.

^b3 days per week.

^c5 days per week.

^d30 minutes per day.

^e60 minutes per day.

^fAverage minutes of groups that walked multiple distances.

Separate meta-analyses were completed for the lipids (total cholesterol and triglycerides) and lipoproteins (HDLs and LDLs). For each meta-analysis, the difference in pre- and post-intervention raw means within each walking group, and the difference in pre- and post-intervention raw means within each control group were calculated. After calculating the difference in pre- to post- means within each group, the software calculated the between-group raw mean difference (RMD) of each paired intervention-control group for each study. Finally, the random effects model was used to calculate the overall RMD of each meta-analysis. Standard error (SE), confidence interval (CI), level of significance (P), and heterogeneity of RMD (Q-df, I²) were also calculated.²⁷

To explain heterogeneity between the studies of each meta-analysis, subgroup and meta-regression analyses were completed. Meta-regression analyses were used to explain the relationship between the effects of walking (RMD) and covariates that were continuous variables.²⁷ Subgroup analyses were used to assess variables that were nominal.

Coding of Variables

The variables that potentially explained heterogeneity between the studies were: total walking dose (duration variable), walking intensity, BMI, and measurements of walking activity. The variables were coded and entered in the CMA software.

Total walking dose (e.g., 2400 minutes) was coded by calculating the total minutes per week times the number of weeks. Walking intensity was coded as low, moderate, or vigorous. Coding was based on reported intensity, reported maximal heart rate (HR_max),²⁸ or pace description (e.g., “brisk walking”).²⁹ BMI was coded as the average BMI of the control and intervention groups. Measurements of walking activity was coded as self-reported (participants self-recorded and reported their activity to the assessors), supervised (assessors observed or monitored and recorded participant activity), or both (self-reported and supervised methods were used weekly, or methods were used during a specific term of the intervention [e.g., supervised activity during the first 2 weeks, and self-reported activity during the remaining four weeks of a 6-week intervention]).

Assessment for Publication Bias

A funnel plot for each lipid and lipoprotein meta-analysis was used to determine if the effect of any individual study was overestimated. When asymmetry of a funnel plot was detected, the Duvall and Tweedie’s trim and fill was used to assess the magnitude of impact the bias may have on the meta-analysis.²⁷

Results

Sample Characteristics

The meta-analyses were comprised of 21 studies published between 1987 and 2016. The studies investigated changes in lipids and lipoproteins in exclusive walking interventions among women with overweight and obesity. Nineteen of the studies were published in peer-reviewed articles, and 2 of the studies were doctoral dissertations.

The sample of 21 studies consisted of 1129 participants. Mean age ranged from 22 to 73 years, with a median age of 49 years. Mean BMI ranged from 25.1 kg/m² to 34.6 kg/m², with a median value of 27.0 kg/m². Change in mean BMI, from pre-to post-intervention, for the control groups ranged from −2.9 kg/m² to +6.9 kg/m², with a median value of +0.2 kg/m². Change in mean BMI, from pre-to post-intervention, for the walking groups ranged from −3.5 kg/m² to +0.31 kg/m², with a median value of −0.95 kg/m². The interventions ranged from 8 to 104 weeks. Most of the studies were moderate intensity (N = 15; 71%), and most (N = 15; 71%) included supervised sessions. Over half of the studies (N = 13; 62%) reported all the lipid and lipoprotein variables (total cholesterol, triglycerides, HDLs, LDLs). The characteristics of the sample of studies are summarized in Table 1. Cochrane risk of bias assessment was completed on all 21 studies. The overall risk of bias was determined to be low. In the specific categories of bias, 2 studies were found to have high-risk for selective reporting,^30,31 and most of the studies had unclear selection bias for allocation concealment (N = 19; 90%). However, this appeared to be due to study reporting, and not due to the methodology of the studies.

Baseline Lipids and Lipoproteins

The median value for total cholesterol was abnormal (206.06 mg/dL), the median value for triglycerides was normal (116.01 mg/dL), the median value for HDLs was normal (54.05 mg/dL), and the median value for LDLs was abnormal (125.91 mg/dL) (Table 2).^32,33

Table 2.

Baseline Lipids and Lipoproteins.

Sample Mean
Outcome Variable	N	Minimum (mg/dL)	Maximum (mg/dL)	Median Value (mg/dL)	Normal Value^32,33 (mg/dL)
Total cholesterol	20	177.88	258.70	206.06	< 200
Triglycerides	17	82.38	176.26	116.01	< 150
High-density lipoproteins	18	40.61	64.97	54.05	> 60
Low-density lipoproteins	15	110.00	181.63	125.91	< 100

Note. mg/dL = milligrams per deciliter.

Meta-Analyses

Total Cholesterol

Twenty of the 21 studies examined total cholesterol. The RMD between the control and walking groups ranged from −21.95 mg/dL to +50.0 mg/dL (Figure 1). The first 6 studies resulted in negative RMDs, meaning the control groups exhibited better results than the walking groups in those studies. Conversely, 14 of the 20 studies resulted in positive RMDs, meaning the walking groups demonstrated better results than the control groups in these studies. Meta-analysis of the 20 studies yielded an overall RMD of +6.67 mg/dL, (P = .04; SE = 3.19; 95% CI: +0.42 to +12.92) (Table 3); which indicates the walking groups improved an average of 6.67 mg/dL more than the control groups. Heterogeneity of the total cholesterol studies was moderate (I² = 64%; Q-df = 54.04, P< 0.01).

Figure 1.

Forests plots of the raw mean difference (RMDs) between the control groups and walking groups of each study for each meta-analysis. The RMDs are effects of walking on each lipid and lipoprotien. A square in the plot represents the RMD for the given study with the size of the square being proportional to the weighing of the study in the meta-analysis. The horizontal line is the 95% confidence interval (CI) for the study’s RMD. Studies are arranged from lowest to highest RMD. The diamond at the bottom represents the overall RMD calculated using a random effects model. The width of the diamond represents the 95% CI for the overall RMD.

Table 3.

Summary of Overall Results of Meta-Analyses.

Outcome Variable	N	RMD Range (mg/dL)	RMD (mg/dL)	Standard Error	Confidence Interval (mg/dL)	P value
Total cholesterol	20	−21.95 to +50.0	+6.67	3.19	+0.42, +12.91	.04
Triglycerides	17	−16.9 to +45.0	+2.22	5.41	−8.40, +12.83	.68
High-density lipoproteins	18	−4.41 to +15.0	+1.46	.94	−0.38, +3.30	.12
Low-density lipoproteins	15	−5.95 to +40.0	+7.38	3.64	0.26, +14.51	.04

Note. RMD = raw mean difference. mg/dL = milligrams per deciliter.

Triglycerides

Seventeen of the 21 studies examined triglycerides. The RMD between the control and walking groups ranged from −16.9 mg/dL to +45.0 mg/dL (Figure 1). The first 11 studies resulted in negative RMDs, which indicates control groups exhibited better results than the walking groups. Conversely, 6 of the 17 studies resulted in positive RMDs, which indicates the walking groups demonstrated better results than the control groups. Meta-analysis of the 17 studies yielded an overall positive RMD for triglycerides, but this was not statistically significant (overall RMD = +2.22 mg/dL, P = 0.68; SE = 5.41; 95% CI: −8.40 to +12.83) (Table3). Heterogeneity of the triglyceride studies was moderate (I² = 63%; Q-df = 43.08, P < 0.01).

HDLs

Eighteen of the 21 studies examined HDLs. The RMD between the control and walking groups ranged from −4.41 mg/dL to +15.0 mg/dL (Figure 1). The first 5 studies resulted in negative RMDs, which indicates the control groups exhibited better results than the walking groups. Conversely, 11 of the 18 studies resulted in positive RMDs, which indicates the walking groups demonstrated better results than the control groups; and 1 study exhibited no RMD in HDLs between the walking and control groups. Meta-analysis of the 18 studies yielded an overall positive RMD for HDLs, but not statistically significant (overall RMD = +1.46 mg/dL, P = .12; SE = 0.94; 95% CI: −0.38 to +3.30) (Table 3). Heterogeneity of the HDL studies was small (I² = 39%; Qdf = 28.0, P = .05).

LDLs

Fifteen of the 21 studies examined LDLs. The RMD between the control and walking groups ranged from −5.95 mg/dL to +40.0 mg/dL (Figure 1). The first 3 studies resulted in negative RMDs, meaning the control groups exhibited better results than the walking groups. Conversely, 11 of the 15 studies resulted in positive RMDs, which indicates the walking groups demonstrated better results than the control groups; and 1 study exhibited no RMD in LDLs between the walking and control groups. The 15 studies yielded an overall positive RMD for LDLs (overall RMD = +7.38 mg/dL, P = .04; SE = 3.64; 95% CI: +0.26 to +14.51) (Table 3); indicating the walking groups improved an average of 7.38 mg/dL more than the control groups. Heterogeneity of the LDL studies was large (I² = 79%; Q-df = 67.8, P < .01).

Subgroup Analyses

Subgroup analysis for each lipid and lipoprotein compared the difference in effect size between moderate intensity (MI) and vigorous intensity (VI) groups; and the difference in effect size for measurements of walking of self-reported (SR), supervised (SPV), and both (B) activities. For walking intensity, there was no significant difference between the comparative groups for either lipid (total cholesterol [(MI) N = 16, RMD = +5.33 mg/dL, (VI) N = 6, RMD = +3.32, P = .81]; triglycerides [(MI) N = 16, RMD = +1.02 mg/dL, (VI) N = 4, RMD = +0.84 mg/dL, P = .99]) or lipoprotein (HDLs [(MI) N = 13, RMD = +1.95 mg/dL, (VI) N = 6, RMD = +1.33 mg/dL, P = .77]; LDLs [(MI) N = 13, RMD = +8.57 mg/dL, (VI) N = 3, RMD = +0.52 mg/dL, P = .35]) (Table 4). For measurements of walking activity, there was no significant difference between the comparative groups for either lipid (total cholesterol [(SR) N = 6, RMD = +3.67 mg/dL, (SPV) N = 11, RMD = +7.75, (B) N= 3, RMD= +4.70, P = .81]; triglycerides [(SR) N = 5, RMD = −2.12 mg/dL, (SPV) N = 10, RMD = +9.99 mg/dL, (B) N = 3, RMD = +0.44 mg/dL, P = .66]) or lipoprotein (HDLs [(SR) N = 5, RMD = +0.28 mg/dL, (SPV) N = 11, RMD = +2.30 mg/dL, (B) N = 3, RMD = +1.21 mg/dL, P = .70]; LDLs [(SR) N = 3, RMD = +1.90 mg/dL, (SPV) N = 8, RMD = +10.44 mg/dL, (B) N = 4, RMD = +4.90 mg/dL, P = .68]) (Table 5).

Table 4.

Summary of Subgroup Analyses for Walking Intensity.

Variable	Walking Intensity	N	RMD mg/dL	CI mg/dL	P value
Total cholesterol	Moderate	16	+5.33	−2.51, +13.18	.81
Total cholesterol	Vigorous	6	+3.32	−11.27, +17.92	.81
Triglycerides	Moderate	16	+1.02	−10.10, +12.13	.99
Triglycerides	Vigorous	4	+0.84	−21.85, +23.54	.99
High-density lipoproteins	Moderate	13	+1.95	−0.45, +4.35	.77
High-density lipoproteins	Vigorous	6	+1.33	−2.25, +4.91	.77
Low-density lipoproteins	Moderate	13	+8.57	+1.09, +16.06	.35
Low-density lipoproteins	Vigorous	3	+0.52	−14.62, +15.67	.35

Note. RMD = raw mean difference. CI = confidence interval. mg/dL = milligrams per deciliter.

Table 5.

Summary of Subgroup Analyses for Measurements of Walking Activity.

Variable	Collection Method	N	RMD mg/dL	CI mg/dL	P value
Total cholesterol	Self-reported	6	+3.67	−4.59, +11.94	.81
	Supervised	11	+7.75	−2.02, +17.54
	Both	3	+4.70	−5.64, +15.06
Triglycerides	Self-reported	5	−2.12	−25.05, +20.81	.66
	Supervised	10	+9.99	−5.72, +25.71
	Both	3	+0.44	−31.46, +32.34
High-density lipoproteins	Self-reported	5	+0.28	−3.89, +4.46	.70
	Supervised	11	+2.30	−0.06, +4.66
	Both	3	+1.21	−4.43, +6.85
Low-density lipoproteins	Self-reported	3	+1.90	−16.60, +20.42	.68
	Supervised	8	+10.44	−0.40, +21.30
	Both	4	+4.90	−10.02, +19.83

Note. RMD = raw mean difference. CI = confidence interval. mg/dL= milligrams per deciliter.

Meta-Regression Analyses

Total walking dose did not result in a significant relationship with the effects of exclusive walking on total cholesterol (P = .42), triglycerides (P = .34), HDLs (P = .92), or LDLs (P = .65) (Figure 2). However, mean BMI resulted in a significant relationship with the effects of exclusive walking on each lipid (total cholesterol [P = .02]; triglycerides [P < .01]) and lipoprotein (HDLs [P < .01]; LDLs [P = .03]) (Figure 3). As BMI increased, the difference in means between the control and experiment groups increased. Therefore, a positive and significant relationship existed between BMI and the effects of walking for each lipid and lipoprotein.

Figure 2.

Scatterplots of the meta-regression of difference in means on total dose for lipids and lipoproteins.

Figure 3.

Scatterplots of the meta-regression of difference in means on mean BMI for lipids and lipoproteins.

Discussion

The primary purpose of this study was to determine if walking, independent of diet and weight-loss, significantly improves total cholesterol, triglycerides, HDLs, and LDLs in women with overweight and obesity. The meta-analyses were also used to determine the influence of intensity, duration, BMI, and measurements of walking of activity on the lipid and lipoprotein outcomes. Total cholesterol and LDLs resulted in significant improvement, whereas there was no significant improvement in triglycerides and HDLs. Subgroup analyses for each lipid and lipoprotein did not result in a significant difference between the effects of moderate intensity and vigorous intensity; and they did not result in a significant difference between the effects of self-reported, supervised, and both activities combined. Meta-regression analyses for duration (total walking dose) of the interventions did not result in a significant relationship with either lipid or lipoprotein, but a significant relationship between the effects of exclusive walking and BMI existed for total cholesterol, triglycerides, HDLs, and LDLs.

For each lipid and lipoprotein, the effect (RMD) of exclusive walking increased as BMI increased. Similarly, in a large cohort study where individuals with overweight and obesity met physical activity guidelines that included vigorous activity, the individuals with obesity demonstrated a lower hazard ratio for cardiovascular disease mortality than individuals with overweight.³⁴ Therefore, cardiorespiratory activity appears to have increased effects for improving dyslipidemia and lowering atherogenic risks in individuals with obesity. Individuals with obesity have the highest prevalence of dyslipidemia,⁵ and the independent therapeutic effects of cardiorespiratory activity can aid in reducing atherogenic risks,^35,36 particularly for women.

There was no significant difference between the walking intensity groups or the walking measurement groups in the subgroup analyses, and the meta-regression analyses did not result in duration (total walking dose) having a significant relationship with the effects of exclusive walking. It is important to concede that most of the studies in this meta-analysis met physical activity duration and intensity recommendations (≥150 minutes per week, moderate or vigorous intensity).²⁹ The findings support recommendations of the physical activity guidelines and imply that the recommendations are effective for normalizing lipids and lipoproteins in women with overweight and obesity. However, because walking may be used as leisure-time physical activity (LTPA), to improve lipids or lipoproteins, it has been suggested that vigorous intensity be included with LTPA for individuals with obesity.³⁵ For measurements of walking activity, the effects of walking were not significantly different between the subgroups potentially due to social desirability bias. Social desirability bias is a limitation of self-reported data,³⁷ and future studies should consider designing experiments with fully supervised activity.

The meta-analyses of the current studies overall resulted in the walking groups having greater improvement than the control groups, which implies that exclusive walking is beneficial for improving lipids and lipoproteins, particularly total cholesterol and LDLs. Therefore, this study supports promotion of walking for women with overweight and obesity, which may positively impact clinical outcomes. More specifically, these findings are implications for promotion of walking when enhanced risk of developing atherosclerotic cardiovascular disease (ASCVD) is not present.

Although the median value for LDLs in this sample was abnormal, the value is not indicative of enhanced risk of ASCVD (≥160 mg/dL).³⁸ For adults who do not have LDLs of ≥160 mg/dL, clinicians are advised to recommend lifestyle habits that will improve abnormal conditions (e.g., engaging in at least 150 minutes per week of moderate intensity aerobic activity) as opposed to treatment with pharmacological therapy.³⁸ The guidelines do not specify recommended LDL reductions for non-pharmacological therapy, but it is clear the goal is to normalize the lipoprotein. Also, although the median baseline value for total cholesterol was relatively normal, the improvement in total cholesterol supports clinical guidance for advising regular physical activity to prevent ASCVD.³⁸

Previous meta-analyses investigated the effects of walking on lipids and lipoproteins, and they demonstrated similar results in terms of significant improvement for total cholesterol and LDLs.^21,22 However, either the relationship between BMI and the effects of physical activity on the lipid or lipoprotein was not determined,²² or BMI did not have a significant relationship with the effects.²¹ This may be due to the meta-analyses not being limited to populations with overweight and obesity. By investigating this population, this study revealed that dyslipidemia is improved by exclusive walking, with improvement being greater in individuals with obesity. This finding is especially relevant for promotion of physical activity by clinicians, particularly for women with obesity who may struggle with diet or weight-loss. The findings also provide evidence that will support future development of public health interventions and policies that promote physical activity to reduce the risks of CVD in populations with obesity.

Limitations

Due to the inherent nature of a systematic review, some qualifying studies may not have been identified for article inclusion. However, the authors completed a thorough search of literature per the Cochrane Review guidelines.²⁵ Also, the specificity of this topic limited the number of available studies. To identify additional studies, a second search of literature was later completed. One additional study was identified that met the inclusion criteria, but the authors were unable to extract data from the article and were unable to retrieve the dataset upon request from the corresponding author. Another limitation is one study dominated the overall effects for total cholesterol and LDLs. The Guessogo et al. study³⁹ primarily contributed to the total cholesterol and LDL meta-analyses having larger and significant effects. The study was unique due to its observation of a population with moderate obesity (mean BMI= 34.23 kg/m²) who walked a total of 200 minutes per week for 24 weeks. In addition, all of the walking activity was supervised.³⁹ Per the American College of Sports Medicine, 200 to 300 minutes of moderate intensity physical activity per week is recommended for populations with overweight and obesity.⁴⁰ Therefore, it is possible that this intervention dominated the overall results due to the volume of walking completed under full supervision. If more of the studies in this meta-analysis would have had a similar design, the Guessogo et al study³⁹ may not have dominated the main findings.

A limited number of low-intensity studies, lack of reported intervention-compliance, and lack of reported ethnicity were also limitations. Only one study reported low-intensity,⁴¹ which did not permit for a low-intensity comparative group in the subgroup analyses. Very few studies reported intervention-compliance or values for the number of minutes that were completed by the participants. The walking prescription (e.g., 30 minutes per day and 5 days per week) was relied upon for most of the studies to determine the amount of activity. Future physical activity interventions should ensure reporting of the actual number of minutes completed. Less than half of the studies reported participant ethnicity, which did not permit for subgroup analyses to determine if this variable moderated the main findings.

Another limitation is some of the studies did not indicate whether biometric samples were collected under a fasting state. Therefore, fasting lipids and lipoproteins could not be accounted for in this meta-analysis.

Conclusions

Walking aids in normalizing total cholesterol and LDLs in women with overweight and obesity, independent of diet and weight-loss. The effects of exclusive walking improved lipids and lipoproteins, with the greatest improvement resulting in women with obesity. Exclusive walking can be used as a non-pharmacologic therapy, which may have positive clinical outcomes for individuals who especially struggle with diet and weight-reduction.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Anjulyn M. Ballard

Brett Wong

PRISMA Flowchart of Review and Selection of Studies.

So What? What is already known on this topic?

For substantial health benefits, the second edition of the Physical Activity Guidelines for Americans recommends 150 to 300 minutes per week of moderate-intensity physical activity, with an emphasis on engaging in aerobic activity. Brisk walking is a moderate-intensity aerobic activity that can be used to reduce the risk of cardiovascular disease and other adverse health outcomes. Previous meta-analyses for general populations have demonstrated moderate-intensity walking is effective for improving lipids and lipoproteins.

What does this article add?

This systematic review and meta-analyses are the first that synthesize and quantify the effects of walking on lipids and lipoproteins, independent of diet and weight-loss, in an overweight and obese population. Findings from the meta-analyses support promotion of exclusive walking as a non-pharmacologic therapy, which may reduce cardiovascular incidents and mortality within high-risk populations.

What are the implications for health promotion practice or research?

The current study can aid in the advancement of physical activity promotion for populations with overweight and obesity in clinical practice, public health programs, and policy implementation.

References

World Health Organization . Obesity and overweight. Geneva, Switzerland: WHO; 2020. Available at: https://www.who.int/newsroom/fact-sheets/detail/obesity-and-overweight#:%7E:text=In_2016%2C_more_than_1.9_billion_adults_aged_18_years,women)_were_obese_in_2016. Accessed November 10, 2020.

Ritchie

Roser

M. Obesity

. 2017. Available at: https://ourworldindata.org/obesity. Accessed November 10, 2020.

U.S. Department of Health and Human Services . Overweight & obesity statistics. Washington, DC: USDHHS; 2017. Available at: https://www.niddk.nih.gov/health-information/health-statistics/overweight-obesity. Accessed January 7, 2020.

Centers for Disease Control and Prevention . Adult obesity causes & consequences. Atlanta, GA: CDC; 2020. Available at: https://www.cdc.gov/obesity/adult/causes.html. Accessed January 7, 2020.

Saydah

Bullard

Cheng

, et al. Trends in cardiovascular disease risk factors by obesity level in adults in the United States, NHANES 1999-2010. Obesity. 2014;22(8):1888-1895.

Cífková

Krajčoviechová

. Dyslipidemia and cardiovascular disease in women. Curr Cardiol Rep. 2015;17(7):609.

Papakonstantinou

Stamou

Baikoussis

Goudevenos

Apostolakis

. Sex differentiation with regard to coronary artery disease. J Cardiol. 2013;62(1):4-11.

Gerdts

Regitz-Zagrosek

. Sex differences in cardiometabolic disorders. Nat Med. 2019;25(11):1657-1666.

Nassef

Nfor

Lee

Chou

Liaw

. Association between aerobic exercise and high-density lipoprotein cholesterol levels across various ranges of body mass index and waist-hip ratio and the modulating role of the hepatic lipase rs1800588 variant. Genes. 2019;10(6).

10.

Ding

. Surveillance of global physical activity: progress, evidence, and future directions. Lancet Glob Health 2018;6(10):e1046-e1047.

11.

Centers for Disease Control and Prevention . Physical activity and health: a report of the surgeon general. Atlanta, GA: Centers for Disease Control and Prevention; 2018. Available at: https://www.cdc.gov/nccdphp/sgr/women.htm. Accessed January 7, 2020.

12.

Fayh

Lopes

Da Silva

Reischak-Oliveira

Friedman

. Effects of 5 % weight loss through diet or diet plus exercise on cardiovascular parameters of obese: a randomized clinical trial. Eur J Nutr. 2013;52(5):1443-1450.

13.

Namjou

Taheri

Binabaj

Nejabat

Gerey

Rizi

. Comparison of the effects of diet with and without physical activity on serum lipid profile of obese women. Med Lab J. 2017;11(1):711.

14.

American Psychological Association . Obesity. Washington, DC: APA; 2020. Available at: https://www.apa.org/topics/obesity. Accessed January 16, 2020.

15.

American Heart

Association.

Why is walking the most popular form of exercise? Dallas, TX: AHA; 2020. Available at: https://www.heart.org/en/healthy-living/fitness/walking/why-is-walking-the-most-popular-form-of-exercise. Accessed January 16, 2020.

16.

The Diabetes Prevention Program . The diabetes prevention program (DPP): description of lifestyle intervention. Diabetes Care 2002;25(12):2165-2171.

17.

Buyukyazi

. The effects of eight-week walking programs of two different intensities on serum lipids and circulating markers of collagen remodelling in humans. Sci Sports. 2008;23(3):162-169.

18.

Mezghanni

Chtourou

Lahyani

, et al. Effect of exercise intensity on body composition and cardiovascular disease risk factors in sedentary young obese women. Int J Sports Med. 2014;15(4):415-424.

19.

Wooten

Biggerstaff

Ben-Ezra

. A single 1-h session of moderate-intensity aerobic exercise does not modify lipids and lipoproteins in normolipidemic obese women. Appl Physiol Nutr Metabol. 2011;36(5):715-722.

20.

Pescatello

Arena

Riebe

Thompson

. General Principles of Exercise Prescription. ACSM’s Guidelines for Exercise Testing and Prescription. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins; 2013:166-177.

21.

Kelley

Tran

. Walking, lipids, and lipoproteins: A meta-analysis of randomized controlled trials. Prev Med 2004;38(5):651-661.

22.

Hanson

Jones

. Is there evidence that walking groups have health benefits? A systematic review and meta-analysis. Br J Sports Med. 2015;49(11):710-715.

23.

Kelley

Roberts

Haskell

. Combined effects of aerobic exercise and diet on lipids and lipoproteins in overweight and obese adults: a meta-analysis. J Obes 2012;1-16.

24.

Moher

Liberati

Tetzlaff

, et al. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med. 2009;151(4):264-269.

25.

Higgins

JPT

Thomas

Chandler

, et al. Cochrane Handbook for Systematic Reviews of Interventions. 2nd ed.. Chichester, UK: John Wiley & Sons; 2019.

26.

Pattyn

Cornelissen

Eshghi

SRT

Vanhees

. The effect of exercise on the cardiovascular risk factors constituting the metabolic syndrome. Sports Med. 2013;43(2):121-133.

27.

Borenstein

Hedges

Higgins

JPT

Rothstein

. Introduction to Meta-Analysis. Hoboken, NJ: John Wiley & Sons, Ltd; 2009.

28.

Centers for Disease Control and Prevention . Physical Activity: Target Heart Rate and Estimated Maximum Heart Rate. Atlanta, GA: Centers for Disease Control and Prevention; 2020. Available at: https://academized.com/heart-disease-and-physical-health. Accessed January 7, 2020.

29.

Piercy

Troiano

Ballard

, et al. The physical activity guidelines for Americans. J Am Med Assoc. 2018;320(19):2020-2028.

30.

Verity

Ismail

. Effects of exercise on cardiovascular disease risk in women with NIDDM. Diabetes Res Clin Pract. 1989;6(1):27-35.

31.

Woolf-May

Kearney

Owen

Jones

Davison

RCR

Bird

. The efficacy of accumulated short bouts versus single daily bouts of brisk walking in improving aerobic fitness and blood lipid profiles. Health Educ Res. 1999;14(6):803-815.

32.

Centers for Disease Control and Prevention. Cholesterol : High cholesterol facts. Atlanta, GA: CDC; 2020. Available at: https://www.cdc.gov/dhdsp/data_statistics/fact_sheets/fs_cholesterol.htm. Accessed May 12, 2020.

33.

Mayo

Clinic.

Cholesterol test. 2020. Available at: https://www.mayoclinic.org/testsprocedures/cholesterol-test/about/pac-20384601. Accessed November 10, 2020.

34.

O'Donovan

Stamatakis

Stensel

Hamer

. The importance of vigorous-intensity leisure-time physical activity in reducing cardiovascular disease mortality risk in the obese. Mayo Clin Proc. 2018;93(8):1096-1103.

35.

Ozemek

Laddu

Lavie

, et al. An update on the role of cardiorespiratory fitness, structured exercise and lifestyle physical activity in preventing cardiovascular disease and health risk. Prog Cardiovasc Dis. 2018;61(5-6):484-490.

36.

Barry

Caputo

Kang

. The joint association of fitness and fatness on cardiovascular disease mortality: A meta-analysis. Prog Cardiovasc Dis 2018;61(2):136-141.

37.

Van de Mortel

. Faking it: Social desirability response bias in self-report research. Aust J Adv Nurs 2008;25(4):40-48.

38.

Arnett

Blumenthal

Albert

, et al. 2019 ACC/AHA guideline on the primary prevention of cardiovascular disease: Executive summary: A report of the American college of cardiology/American heart association task force on clinical practice guidelines. J Am Coll Cardiol 2019;74(10):1376-1414.

39.

Guessogo

Temfemo

Mandengue

, et al. Effect of 24-week repeated short-time walking based training program on physical fitness of black Cameroonian obese women. J Exe Rehabilit. 2016;12(2):90-98.

40.

Deborah Riebe

JKE

Gary

Meir

American College of Sports Medicine . ACSM’s Guidelines for Exercise Testing and Prescription. 10th ed.. Philadelphia, PA: Wolters Kluwer; 2018.

41.

Asikainen

T-M

Miilunpalo

Kukkonen-Harjula

, et al. Walking trials in postmenopausal women: Effect of low doses of exercise and exercise fractionization on coronary risk factors. Scand J Med Sci Sports 2003;13(5):284-292.

42.

Ahn

. Effects of walking on cardiovascular risk factors and psychosocial outcomes in postmenopausal obese women. J Korea Acad Nurs. 2007;37(4):519-528.

43.

Aldred

Hardman

Taylor

. Influence of 12 weeks of training by brisk walking on postprandial lipemia and insulinemia in sedentary middle-aged women. Metab Clin Exp. 1995;44(3):390-397.

44.

Cauley

Kriska

LaPorte

Sandler

Pambianco

. A two year randomized exercise trial in older women: effects on HDL-cholesterol. Atherosclerosis. 1987;66(3):247-258.

45.

Davison

RCR

Grant

. The physiological effects of a 14-week walking programme on sedentary middle-aged women. J Sports Sci. 1995;13:24-25.

46.

Habibzadeh

. Effect of aerobic exercise on some of selected metabolic syndrome in young obese women. Acta Kinesiol. 2010;4(2):24-27.

47.

Hinkleman

Nieman

. The effects of a walking program on body composition and serum lipids and lipoproteins in overweight women. J Sports Med Phys Fit. 1993;33(1):49-58.

48.

Hopewell

. The effect of fiber and exercise on weight loss and blood lipids in moderately overweight women [Dissertation]. Morgantown, WV: West Virginia University; 1989.

49.

Keller

Treviño

. Effects of two frequencies of walking on cardiovascular risk factor reduction in Mexican American women. Res Nurs Health 2001;24(5):390-401.

50.

Kim

. The effects of aerobic exercise on hormones, blood lipids and body composition in middle-aged obese women according to 3-adrenergic receptor gene polymorphisms. J Korea Acad Nurs. 2004;34(6):1108-1116.

51.

Miller

. The effects of various caloric expenditures per week at moderate levels of exercise training intensity on coronary risk factors in women [Dissertation]. Pittsburgh, PA: University of Pittsburgh; 1995.

52.

Nieman

Warren

O'Donnell

Dotson

Butterworth

Henson

. Physical activity and serum lipids and lipoproteins in elderly women. J Am Geriatr Soc. 1993;41(12):1339-1344.

53.

Nieman

Brock

Butterworth

Utter

Nieman

. Reducing diet and/or exercise training decreases the lipid and lipoprotein risk factors of moderately obese women. J Am Coll Nutr. 2002;21(4):344-350.

54.

Ready

Drinkwater

Ducas

Fitzpatrick

Brereton

Oades

. Walking program reduces elevated cholesterol in women postmenopause. Can J Cardiol. 1995;11(10):905-912.

55.

Ready

Naimark

Ducas

, et al. Influence of walking volume on health benefits in women post-menopause. Med Sci Sports Exerc. 1996;28(9):1097-1105.

56.

Seals

Tanaka

Clevenger

, et al. Blood pressure reductions with exercise and sodium restriction in postmenopausal women with elevated systolic pressure: Role of arterial stiffness. J Am Coll Cardiol 2001;38(2):506-513.