The rising prevalence of obesity, particularly among postmenopausal women, has become a significant health concern in the United States. Overweight, characterized by a body mass index (BMI) between 25 and 30 kg/m2, and obesity, defined as a BMI above 30 kg/m2, often lead to severe health complications. These include diabetes, atherosclerotic vascular disease (potentially causing stroke, heart attack, or pulmonary thromboembolism), respiratory failure, and cancer. Consequently, mortality risk increases with rising obesity levels.
In addition to common obesity causes such as low physical activity and overeating, menopause and the associated decline in estradiol contribute to weight gain in women. This hormonal shift often results in the redistribution of body fat from subcutaneous, gluteal, and femoral areas (the gynoid pattern) to an android pattern, marked by increased abdominal subcutaneous (SC) and visceral fat (VF) deposits. The android fat distribution is strongly linked to metabolic complications like hypertension, diabetes, coronary heart disease, blood hypercoagulability, and a higher risk of death, highlighting the importance of effective fat loss strategies for postmenopausal women.
Understanding the role of walking speed in facilitating fat loss among postmenopausal women is a key focus. Previous research on the same group of subjects demonstrated that higher walking speeds, combined with a 45-minute daily exercise session, effectively suppressed bone mineral loss and moderately increased leg and whole-body bone mineral density. Subsequent studies have reinforced this finding, emphasizing the importance of a pre-exercise meal and a 40- to 45-minute exercise duration for anabolic bone responses. This raises the question of whether different exercise features are necessary to achieve specific physiological effects. For example, longer exercise sessions (170 minutes vs. 115 minutes) have been found more effective than exercise intensity (75% vs. 45% of VO2 peak) in increasing insulin sensitivity.
Meta-analyses and reviews indicate that the effectiveness of exercise in producing total and regional fat loss is not well understood. Unresolved issues include why exercise-induced body fat loss rarely exceeds 3 kg or 2 to 3% of initial body weight, regardless of training duration. Additionally, it remains unclear whether a definitive dose-response relationship exists between exercise frequency, volume, and intensity and total body fat loss. Claims that larger exercise doses produce proportional increases in total fat loss are weakened by studies showing similar fat loss results with different weekly frequencies of moderate-intensity exercise.
The role of exercise intensity or walking speed in total body fat loss also yields conflicting results. Some studies show no difference in fat loss with isocaloric exercise at different intensities, while others indicate that fat loss is inversely proportional to exercise speeds. For instance, one study involving a 4.8 km daily walk at varying speeds (8 km/h, 6 km/h, and 4 km/h) found that the greatest fat loss occurred at 4 km/h. However, other studies report greater fat loss at higher walking speeds or intensities, and some at lower speeds or intensities.
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Information regarding the differing effects of exercise on SC abdominal and VF depots requires re-examination due to the postmenopausal redistribution of SC fat from peripheral gynoid to abdominal android SC and VF sites. This redistribution carries serious health risks for postmenopausal women. Studies have focused on exercise features affecting abdominal SC and VF. One study demonstrated that increasing daily steps by 1800 above 7000 significantly decreased SC and VF. Other studies indicate that abdominal SC fat declines more than VF with higher walking speed, intensity, or weekly frequency, whereas VF responds to negative energy balance regardless of how it is achieved.
In subjects exercising at either low intensity (below the ventilatory threshold (VT)) or high intensity (above the VT) for 16 weeks, abdominal fat did not change after low-intensity exercise but declined significantly after high-intensity exercise. Additionally, longer exercise session durations at the same moderate intensity produced twice as much VF loss with 195 min/week compared to 135 min/week. Studies have shown that high exercise intensity produces greater SC fat loss than lower intensity, and when combined with a longer session bout, SC fat loss at high intensity is amplified.
Given the contradictory data on the direction and magnitude of total and regional fat loss, two hypotheses were proposed. The first, prompted by evidence suggesting that lower exercise intensity facilitates body fat loss while higher walking speed suppresses it, is supported by data indicating that exercise intensity affects the rate of body lipid utilization. During exercise lasting more than one hour at a relative effort of between 25% and 45%, approximately 90% of energy expenditure (EEE) is supplied by free fatty acids (FFA) and fat oxidation, though the energy utilization rate is low.
Study Methodology
Subject Recruitment and Screening
Forty-two healthy sedentary postmenopausal women were recruited from the Ann Arbor area over five years through the web page UMClinicalStudies.com and newspaper advertisements for an early-morning mall-walking program. The study included the same 25 subjects who exercised for 15 weeks for bone mineral loss measurements reported previously. Sixteen residual subjects continued exercising for an additional 15 weeks, totaling 30 weeks.
Inclusion criteria were:
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- 50-70 years old
- Surgical or natural menopause with no menstrual periods for at least one year
- No metabolic disease
- BMI less than 35 kg/m2
- Non-smoker
- Absence of musculoskeletal disabilities preventing mall walking
- Sedentary status (<60 min of regular exercise per week)
Exclusion criteria included hormonally uncorrected hypothyroidism and any deviations from inclusion criteria. Training started upon enrollment. Twenty-five subjects completed 15 weeks of training after 17 dropouts. Reasons for dropout included pre-menopausal status, participation in a dieting program, failure to adhere to DXA measurement requirements, inconvenience, lack of time, relocation, and other personal reasons. Sixteen subjects completed 30 weeks of training after nine further dropouts due to similar reasons.
The study was conducted in accordance with the Declaration of Helsinki, and the protocols were approved by the University of Michigan Medical School Institutional Review Board (IRB-MED). All subjects signed informed consent forms approved by the IRB-MED. Baseline subject characteristics did not differ between the 15-week (n = 25) and 30-week (n = 16) groups. Age, years post-menopause, weight, BMI, VO2 max, VT, and relative efforts at VT did not differ between slow and fast walkers in the 15-week and 30-week groups.
Data Collection
All subjects underwent health screenings by their healthcare providers, completed a health history questionnaire, and had body composition assessments and treadmill fitness tests. Height, weight, and total body fat were measured using dual-energy X-ray absorptiometry (DXA) (model Prodigy, Lunar Radiation Corporation, Madison, WI, USA) at the Michigan Clinical Research Center (MCRU) and the Ann Arbor Veteran’s Administration Hospital. Anthropometric measurements of regional fat distribution were performed by the same skilled technician at the University of Michigan Exercise Endocrinology Laboratory.
Exercise Protocol
Subjects were matched by age, weight, BMI, and VT after VT determination. They were assigned to two different walking speeds, below or above their VTs. Participants were informed about the study's purpose, which involved supervised walking at a local mall at assigned speeds over a pre-measured 4.8 km distance five days a week for 15 or 30 weeks. The exercise was isocaloric, as the assigned distance was the same for slow and fast walkers, and the speed of locomotion over the same distance does not affect energy expenditure. Walking started either at 6:30 a.m. when the mall opened or at 8:00 a.m. New subject cohorts began morning mall walking at the beginning of academic semesters. Women received reminder cards with individually assigned speeds and target times.
Kira Miner's Personal Journey
Kira Miner, a Washougal resident, faced her own health challenges, including a Type-2 diabetes diagnosis and surgery for a broken foot. Despite previous unsuccessful attempts to lose weight, she found renewed inspiration after her daughter’s wedding to try again. Over the past year, Miner has lost more than 40 pounds and feels significantly better.
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Initial Struggles and Renewed Inspiration
Miner had struggled with her weight and found it difficult to prioritize her health. In the 11 years leading up to her weight loss journey, she underwent six surgeries on her thyroid, toe, knee, and foot, which further hindered her health goals. She felt discouraged because her body seemed resistant to weight loss despite her efforts to eat clean and work out.
The Turning Point
Miner’s turning point came when her son, who has autism, went through a physical, violent phase. She realized she needed to be strong to care for herself and her son. Although her initial efforts were not successful, she rededicated herself to a program that combined workouts, nutrition, and accountability.
Keys to Success
Miner found success through a comprehensive approach that included:
- Workouts: Regular physical activity tailored to her needs.
- Nutrition: A focus on healthy eating habits.
- Accountability: Support and guidance from a community.
She also found purpose and connection through becoming a leader in a local home-school community. This helped her focus on something outside of her job and family that was beneficial for her.
Overcoming Challenges
Miner faced additional challenges when her father-in-law’s cancer treatment stopped working, and her mother was diagnosed with cancer. During this difficult time, the online community provided support and encouragement, helping her manage stress, eat right, and continue working out.
Current Status
Miner is now a Team Beachbody coach, sharing her experiences and inspiring others. She emphasizes the importance of perseverance and moving forward despite setbacks.
Insights from Kira Miner's Experience
Kira Miner’s journey highlights several important aspects of weight loss and health improvement:
- Personalized Approach: Finding a program that addresses individual needs and challenges is crucial.
- Comprehensive Strategy: Combining workouts, nutrition, and accountability can lead to better results.
- Community Support: Having a supportive community can provide encouragement and motivation during difficult times.
- Perseverance: Overcoming setbacks and continuing to move forward is essential for long-term success.
The Role of Walking Speed and Impulse in Fat Loss: Study Findings
Total Body Fat Loss
Slow walkers in the residual group progressively lost a significant percentage of total body fat over 30 weeks, while no such loss occurred after 15 weeks in fast walkers, supporting the hypothesis that a longer exercise impulse at a lower speed initially produces greater total fat loss. However, the 20% higher starting body fat in the residual slow walkers suggests that exercise fat loss is greater in overweight subjects. Fat loss did occur in fast walkers after 30 weeks of training.
Abdominal Fat Loss
The study did not support the hypothesis that faster walking speeds lead to greater abdominal subcutaneous (SC) and visceral fat (VF) loss. Instead, both walking speeds led to equal VF loss in the 30-week group, as estimated by waist circumference (CF), confirming that VF responds to the magnitude of energy expenditure and not walking speed.
Conclusions
Total body fat is lost through walking at all speeds, but the change is more rapid, clear, and initially greater with slow walking in overweight subjects. A longer exercise impulse at a lower speed initially produced greater total fat loss than a shorter one with fast walking speed. This contrasted with how the same exercise suppressed bone mineral loss. Data from other studies suggest that longer impulses may promote greater fat loss at both slow and high exercise speeds. The study's limited walking distance of 4.8 km may have constrained the walking impulse and the magnitude of fat loss.
Implications and Future Research
The study's findings have several implications for designing effective exercise programs for postmenopausal women:
- Individualized Exercise Prescription: Exercise prescriptions should consider individual factors such as body weight, fitness level, and preferences.
- Emphasis on Exercise Impulse: Longer exercise durations may be more effective for total fat loss, particularly in overweight individuals.
- Energy Expenditure for Visceral Fat Loss: Visceral fat loss appears to be primarily driven by energy expenditure, regardless of exercise intensity.
- Further Research: Additional studies are needed to investigate the optimal combination of exercise intensity, duration, and frequency for total and regional fat loss.
Other Inspiring Stories of Success at UTEP
Beyond the specific study, the University of Texas at El Paso (UTEP) has cultivated an environment where students thrive academically and personally. Several UTEP graduates exemplify this success:
Diana
Diana is a member of the College of Science “4 + 4” Club, indicating a GPA of 4.0 as a junior and senior. She is majoring in Cellular and Molecular Biochemistry with a minor in Nutrition and plans to pursue an MD with a specialty in pediatrics. Diana was born in El Paso and graduated third in her class from Silva Health Magnet High School. She received the BUILDing SCHOLARS research fellowship and the Terry Scholarship, a prestigious full-ride scholarship awarded to Texas high school graduates that show potential as future leaders, along with other scholarships.
While at UTEP, Diana is a member of the University Honors Program and the Texas Tech Collegiate Health Professions Honor Society. She has shadowed at various health centers and volunteered at multiple organizations. Her sophomore year, she performed undergraduate research with Dr. Charlotte Vines, studying the role of a protein called ERK5 on the migration of leukemic T-cells and interned at Baylor College of Medicine and the University of Connecticut Health Center.
Sebastian
Sebastian is graduating with a BS in Microbiology and a GPA of 4.00 and plans to become a physician in sports medicine where he will incorporate preventive medicine into his practice. He chose UTEP to stay close to family, engulf himself in volunteer and research opportunities. While maintaining a perfect GPA, Sebastian was involved in many projects and organizations at UTEP. He served as a General Chemistry Peer Leader, co-authored the General Chemistry resource workbook, and participated in numerous local outreach activities. He has been on the Dean’s List Plus since his enrollment in the fall of 2015 and the 4 + 4 Club for two years, while staying involved on the board of the university’s Peer Leader for Exceptional Chemistry Education (PLECE) organization, where he is currently Co-President.
Additionally, he participated in numerous local outreach activities, such as PBS Kids Fiesta, and local EPISD chemistry circuses, where he promoted the STEM field by sparking an interest in science and encouraging young students to pursue a science education in the future. He has been on the Dean’s List Plus since his enrollment in the fall of 2015 and the 4 + 4 Club for two years, while staying involved on the board of the university’s Peer Leader for Exceptional Chemistry Education (PLECE) organization, where he is currently Co-President.
Karina
Karina is graduating summa cum laude during the spring 2019 commencement with a baccalaureate in Biology - Biomedical Science Concentration. She chose UTEP because both of her parents graduated from this university. She created the “Women in STEAM” organization, was the head chemistry peer leader, historian of the MPO (Medical Professions Organization), member of the UTEP photography club, secretary for the UTEP chapter of the American Medical Student Association, a 21st Century Scholar, and part of the UTEP debate team as well as Dr. Zhang’s research lab. She also mentored numerous high school students want to have a future career in healthcare. In addition, she has her own photography business, El Paso Pop Shop, and works outside of UTEP.
Jose
Jose is completing a dual degree in Biology with a Biomedical Concentration and Psychology. He will be attending the Baylor School of Medicine in Houston, Texas in the fall of 2019. With his choice of US universities, he chose UTEP because of its undergraduate research program under the direction of COURI (Center of Undergraduate research Initiatives). As part of his preparation for medical school, he participated in the JAMP (Joint Admission Medical Program) where he completed summer internships at the University of North Texas Health Science Center and the University of Texas Southwestern Medical Center. He shadowed Dr. Oscar Aguilar of the El Paso Heart Center as a medical scribe, and he volunteered at Hospice El Paso.
Ysenia
Ysenia is graduating Summa Cum Laude with a BS in Biology - Biomedical Sciences Concentration with an overall GPA of 3.99. She plans to pursue a dual master’s degree in Business Administration and Public Health offered jointly by the University of Texas at San Antonio and the University Of Texas School Of Public Health. She chose UTEP because she was the recipient of the Presidential Scholarship.