Effect of physical activity on free fatty acids, insulin resistance, and blood pressure in obese older women

Article information

Phys Act Nutr. 2024;28(2):1-6

Publication date (electronic) : 2024 June 30

doi : https://doi.org/10.20463/pan.2024.0009

Woo-Hyeon Son ¹, Min-Seong Ha ², Tae-Jin Park ³^,

¹Institute of Convergence Bio-Health, Dong-A University, Busan, Republic of Korea

²Laboratory of Sports Conditioning: Nutrition Biochemistry and Neuroscience, Department of Sport, College of the Arts and Sports, University of Seoul, Seoul, Republic of Korea

³Department of Sports Healthcare, College of Humanities & Social Sciences, Inje University, Gimhae, Republic of Korea

*Corresponding author : Tae-Jin Park Department of Sports Healthcare, College of Humanities & Social Sciences, Inje University, 197 Inje-ro, Gimhae, 50834, Republic of Korea. Tel: +82-10-4550-5635 E-mail: ptj74@inje.ac.kr

Received 2024 March 6; Revised 2024 March 23; Accepted 2024 April 3.

Abstract

[Purpose]

Obesity is characterized by a progressive increase in body fat accompanied by insulin resistance (IR) and elevated blood pressure (BP), and presents significant health risks, particularly in aged individuals. This study aimed to evaluate the effects of physical activity (PA) on free fatty acid (FFA) levels, IR, and BP in obese older women.

[Methods]

Twenty-three participants were randomly assigned to either the control group (CON, n = 11) or the physical activity group (PA, n = 12). The PA group was provided with a target of achieving >7,000 steps/day for 5 days each week. Body composition, FFA levels, IR, and BP were measured at pre- and post- of the 12-week intervention.

[Results]

The analysis revealed a statistically significant interaction between FFA (p < 0.01), IR (p < 0.01), and SBP (p < 0.001). FFA (p < 0.5), IR (p < 0.5), and systolic blood pressure (SBP) (p < 0.01) were significantly decreased in the PA group compared to those in the CON group, which showed no significant changes in FFA, IR, and SBP.

[Conclusion]

PA significantly decreased FFA, IR, and SBP in older women with obesity. Therefore, PA is an effective intervention for the prevention and management of obesity and cardiovascular diseases in obese older women.

Keywords: obesity; physical activity; free fatty acid; insulin resistance; blood pressure

INTRODUCTION

Individuals aged ≥ 65 years constitute more than 9.6% of the global population. In the Republic of Korea, the older adults represented 14.2% of the population in 2018, and by 2025, we will have a super-aged society, with older adults exceeding 20% of the total population [1]. Concurrently, the prevalence of obesity in individuals aged ≥ 65 years has escalated to 40.6%, posing a health concerns [2]. Notably, the incidence of obesity is higher in older women than in men [3]. This disparity is largely attributed to diminished physical activity (PA) levels and a postmenopausal decline in estrogen levels, which contribute to decreased skeletal muscle mass and increased fat mass [4].

Increased adipose tissue leads to a greater release of FFA, resulting in higher FFA concentrations. Elevated plasma FFA levels are associated with increased risks of hypertension, thrombosis, and atherosclerosis [5,6]. Furthermore, increased plasma FFA concentrations inhibit hepatic glucose production and induce resistance to the effect of insulin on blood glucose, thereby reducing glucose uptake in skeletal muscle [7,8]. Therefore, elevated plasma FFA contribute to metabolic dysregulation and insulin resistance (IR) [9,10]. A previous study demonstrated the relationship between elevated FFA levels and IR [11].

IR is defined as a metabolic state in which insulin sensitivity is reduced compared to the normal state [12]. IR increases blood pressure (BP) and hypertension through hyperinsulinemia, which stimulates sodium metabolism in the kidney [13,14]. Castro et al. (2023) have corroborated the relationship between IR and hypertension [15].

Nonpharmacological interventions, such as regular PA, are advocated for managing obesity and metabolic disorders [16]. Regular PA, which results in weight loss and body fat reduction, is effective in ameliorating metabolic disorders [17]. Walking is a form of exercise that is highly manageable and requires no specialized equipment or training; therefore, it is a feasible option for the elderly who face constraints such as time and location [18]. Specifically, for older individuals, walking >7,000 steps/day reduces mortality and metabolic disorders [19,20].

Table 1.

Physical characteristics of the subjects.

Therefore, this study hypothesized that engaging in PA by walking >7,000 steps/day would have a positive effect on FFA levels, insulin resistance, and blood pressure in obese older women.

METHODS

Participants

This study included obese older women from B metropolitan city, all of whom met the criteria for obesity set by the Korean Society for the Study of Obesity (KSSO) [body mass index (BMI) ≥ 25 kg/m²] [21], no engagement in regular exercise within the preceding six months, and a willingness to participate in the intervention program. The participants were fully briefed on the study aims and procedures and provided written informed consent prior to inclusion. A total of 23 participants were randomly allocated to the physical activity group (PA; n = 12) or the control group (CON; n = 11). This randomization process was designed to impartially allocate participants to either group for the 12-week study period.

Measurement

Body composition, BP, and blood sampling were conducted at baseline and after completion of the 12-week intervention period. All assessments were performed under identical conditions to guarantee the consistency and control of potential confounding variables. Participants were instructed to fast for 12 h prior to evaluation to standardize their metabolic status, with all measurements scheduled between 8:00 and 10:00 AM to minimize the effects of diurnal variations. This protocol strictly followed for the pre-and post-intervention assessments to ensure accuracy and comparability of the data.

Body composition

Body composition was assessed with the participants wearing light clothing to ensure measurement accuracy. Height was accurately measured using a portable extensometer (InLabS50; Inbody, Republic of Korea), which facilitated precise acquisition of height for subsequent analyses. Weight and body fat percentage were quantified using an Inbody S10 (Inbody), a bioelectrical device for impedance analysis renowned for its reliability and accuracy in assessing body composition metrics. This method leverages the principle of bioelectrical impedance, providing a non-invasive and efficient means of determining body fat percentage and body weight, thereby contributing valuable data for the evaluation of physical health parameters.

Table 2.

Number of steps taken by the participants.

BP

BP was measured by using an automatic blood pressure monitor (HEM-1022; Omron, Tokyo, Japan). Prior to measurement, the participants were seated comfortably with back support for a minimum of 5 min to stabilize their cardiovascular parameters and ensure a resting state. This preparatory step is crucial for obtaining accurate and representative blood pressure readings. Following this rest period, two consecutive blood pressure measurements were obtained from each participant. The average of these two readings was calculated and used for the analysis to enhance the precision and mitigate the influence of transient fluctuations. This approach ensured that the data reflected a reliable and consistent measure of each participant’s blood pressure, thus contributing to the overall integrity of the study.

PA

Participants allocated to the PA group were advised to achieve a minimum walking goal of 7,000 steps/day, for five days each week. All participants were equipped with a Fitbit Charge 4 activity tracker (Fitbit, San Francisco, CA, USA) to facilitate the precise tracking of PA levels. This advanced wearable technology enabled continuous monitoring of step count, providing a detailed and accurate account of each participant’s daily activity. The participants were instructed to wear the activity tracker throughout the day, removing it only for sleep and water-based activities, such as bathing, to maintain integrity and consistency of the activity data. Weekly monitoring sessions were conducted to review the participants’ activity records, verify their adherence to the walking regimen, and provide feedback and encouragement. This protocol was designed to support participants in achieving the prescribed PA goals and gather robust data on their activity levels during the study period. The participants in the CON group were asked to maintain their usual lifestyle habits.

Table 3.

Change in FFA pre and post in control and physical activity group.

Table 4.

Change in insulin resistance pre and post in control and physical activity group.

Blood sampling

For biochemical analysis, 5 mL blood was collected from the brachial vein of each participant under aseptic conditions. Blood samples were immediately placed in plain tubes and centrifuged (Multifuge X1 R Pro; Thermo Fisher Scientific) at 3,000 rpm for 10 min to efficiently separate plasma from the cellular components of the blood. Plasma was carefully collected and stored at -70 °C to preserve the integrity of biomolecules until analysis. FFAs were quantified using an autoanalyzer (Hitachi 7150; Hitachi, Tokyo, Japan) to ensure the high precision and reliability of the measurements. Blood glucose level was determined using a Hitachi 7600 analyzer (Hitachi), and insulin concentration was measured using an Elecsys 2010 analyzer (Roche Diagnostics, Indianapolis, IN, USA), both of which are recognized for accuracy and consistency in clinical biochemistry. Homeostatic model assessment of insulin resistance was performed to evaluate the extent of IR using the following formula:

IR = Fasting insulin (μU/mL) × fasting glucose (mg/dL)/405 [22].

This calculation provides a reliable estimate of IR, which is a key factor in the metabolic profiles of participants.

Statistical analysis

Statistical analyses of the collected data were conducted utilizing SPSS/PC v.27.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics were calculated for each variable, and the data are presented as mean ± standard deviation. Repeated-measures analysis of variance (ANOVA) was used to assess the effects of the 12-week PA intervention, including the main effects of time (pre- vs. post-intervention), group (PA vs. control), and interaction between time and group, thereby elucidating the differential impact of the intervention. Post hoc analyses were performed using paired t-tests to assess within-subject differences between the pre- and post-intervention measurements, which allowed for a detailed investigation of the changes within individuals, contributing to a deeper understanding of the efficacy of the intervention. Statistical significance was set at p< 0.05. This criterion was applied to ensure that the findings were identified with a reasonable degree of confidence, minimizing the risk of Type I errors, while appropriately recognizing statistically meaningful differences and interactions.

RESULTS

Change in FFA content

A significant effect of time (F, 8.553; p<0.01) and group-by-time interaction (F, 11.075; p<0.01) for FFA levels were noticed. Specifically, FFA levels significantly decreased (p<0.05) in the PA group post-intervention, in contrast to that in the con group that showed no significant changes in FFA levels.

Change in IR

Significant changes in glucose levels over time (F, 8.553; p<0.01) with a notable group-by-time interaction (F, 11.075; p<0.01) was observed, indicating a significant reduction in glucose levels (p<0.01) in the PA group post-intervention. In contrast, the CON group exhibited no significant changes in glucose levels. Furthermore, a significant group-by-time interaction was observed for insulin levels (F, 7.114; p<0.05), with a marked decrease observed in the PA group (p<0.05), whereas the CON group showed no significant changes. The IR data also displayed a significant time effect (F, 4.712; p<0.05) and group-by-time interaction (F, 8.544; p<0.01). Unlike the CON group, the PA group exhibited a significant reduction in IR (p<0.01).

Change in BP

A significant effect of time (F, 10.384; p<0.01) and a substantial group-by-time interaction (F, 20.100; p<0.001) on SBP were noticed. The results indicated a significant decrease in SBP levels (p<0.01) in the PA group following intervention, in contrast to the stable SBP levels in the CON group that showed no significant changes. The analysis did not demonstrate a significant difference in diastolic BP (DBP), indicating that the intervention specifically influenced SBP.

Table 5.

Change in blood pressure pre and post in control and physical activity group.

DISCUSSION

This study evaluated the impact of regular PA on key health indicators, including FFA, IR, and SBP, in obese older women. Consistent with our hypothesis, the PA group demonstrated significant improvements in these parameters compared with the control group, suggesting that PA serves as a potent modulator of metabolic health and BP in this population.

FFAs play crucial physiological roles as major energy substrates in the liver and heart [23]. An increase in body fat due to obesity leads to an increased release of fatty acids, resulting in elevated plasma FFA levels, which potentially trigger metabolic syndrome. An increase in FFA levels inhibits glucose metabolism in skeletal muscle and directly impacts insulin secretion, leading to IR [24]. Additionally, it is a significant contributor to hypertension and cardiovascular diseases (CVD) [6]. Elevated fasting plasma FFA levels increase the risk of CVD [25].

However, regular PA participation decreased the plasma FFA levels [26]. A previous study reported a significant reduction in plasma FFA levels following increased PA in adolescent obese girls [27]. The decrease in FFA levels is attributed to the reduction in body fat through increased PA and increased utilization of fatty acids as the primary energy source in muscles during PA [28,29]. In our study, plasma FFA levels in the PA group significantly decreased, indicating that the reduction in BMI after PA contributed to the decrease in FFA levels. Therefore, participation in regular PA may improve plasma FFA levels associated with obesity.

Obesity impairs the cellular responses to insulin, which is a fundamental cause of IR [30,31]. IR is a state in which the response to insulin for glucose in tissues, such as the muscle and liver, is lower than normal [32]. It reduces energy expenditure and impairs glucose disposal, thereby increasing the risk of metabolic syndrome and CVD [33].

However, modifications in lifestyle and PA can improve IR [34], and elderly individuals engaged in regular PA exhibit higher glucose tolerance and lower IR than sedentary elderly individuals [35].

The reduction in plasma insulin concentrations through PA mobilizes fatty acids and glucose from adipose tissue and the liver, thereby improving insulin response and potentially ameliorating IR [36,37]. Fujieda (2023) have reported a significant reduction in IR after starting PA with a target of 10,000 steps/day in sedentary males [38]. Yokoyama et al. (2001) reported a decrease in IR following increased PA (average of 8,829±3,801 steps/day) in a study targeting patients with type 2 diabetes [39]. Increased PA promotes glucose uptake in muscles, enhances insulin responsiveness, and corrects the mismatch between fatty acid oxidation and uptake in skeletal muscles, thereby ameliorating IR [40-42].

In this study, IR was significantly decreased in the PA group, suggesting that the reduction in FFAs due to PA is a mechanism for ameliorating IR. Furthermore, the decrease in IR suggests the potential of PA to prevent the onset of type 2 diabetes mellitus. Increased activity of the sympathetic nervous system and endothelial dysfunction due to obesity contribute to elevated BP [43]. This elevated BP leads to the development of hypertension, which is a major cause of CVD [44]. In contrast, lowering BP significantly reduces the risk of CVD. A reduction in SBP by 5 mmHg decreases the occurrence of cardiovascular events [45].

Changes in lifestyle, particularly regular PA and medication, can improve BP [46]. Regular PA lowers BP and reduces cardiovascular risk [47]. Several studies have reported a decrease in SBP following an increase in PA (>10,000 steps/ day) [48,49]. A decrease in IR and improvement of the autonomic nervous system [50] owing to PA lead to an improvement in BP. Our study found that a decrease in SBP in the PA group. Therefore, PA is beneficial for improving BP in obese older women.

In conclusion, improvements in FFA level, IR, and SBP through increased PA may aid in addressing metabolic disorders and CVD in elderly obese population.

Acknowledgements

We are grateful to the participants in this study.

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Variables	PA (n=12)		CON (n=11)
Variables	Pre	Post	Pre	Post
Age (yrs)	69.80±1.23		69.90±0.94
Height (cm)	153.74±3.90		155.70±2.45
Weight (kg)	62.73±4.42	61.49±4.25	63.04±2.15	63.36±2.27
BMI (kg/m²)	26.22±1.03	26.02±1.23^***	26.04±1.14	26.15±1.17

Variables	PA (n=12)	CON (n=11)
Walking step	9380.18±959.64	1982.11±71.76
Sedentary time (min)	807.82±73.32	1218.22±126.74

Variable	PA (n=12)		CON (n=11)		Two-way repeated ANOVA
Variable	Pre	Post	Pre	Post	Time	Group	T×G
FFA (μEq/L)	512.20±72.18	460.40±61.92^*	553.56±71.73	582.90±79.02	0.978	8.796^**	10.922^**

Variable	PA (n=12)		CON (n=11)		Two-way repeated ANOVA
Variable	Pre	Post	Pre	Post	Time	Group	T×G
Glucose (mg/dLL)	104.30±6.45	101.20±5.92^**	105.60±8.60	105.80±5.51	8.553^**	0.798	11.075^**
Insulin (μU/mLg)	7.31±2.94	5.93±2.20^*	7.75±2.43	7.99±2.45	3.523	1.329	7.114^*
HOMA-IR	1.90±0.80	1.49±0.57^*	2.03±0.72	2.09±0.69	4.712^*	1.478	8.544^**

Variable	PA (n=12)		CON (n=12)		Two-way repeated ANOVA
Variable	Pre	Post	Pre	Post	Time	Group	T×G
SBP (mmHg)	142.50±5.91	137.80±7.42^**	143.20±8.83	143.60±10.49	10.384^**	1.451	20.100^***
DBP (mmHg)	83.80±7.73	82.40±7.66	84.03±5.08	84.50±5.42	1.580	0.200	2.810