Browsing by Author "Broussard, Josiane, advisor"

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Countermeasures to metabolic impairment during circadian misalignment
(Colorado State University. Libraries, 2024) Lowry, Catherine, author; Broussard, Josiane, advisor; Fling, Brett, advisor; DuBose, Lydnsey, committee member; Johnson, Sarah, committee member
People who work evening, night or rotating shifts (i.e. "nonstandard" work hours) represent one in five U.S. employees and are at a 44% increased risk for developing Type 2 diabetes (T2D) compared to people who work standard day shifts. Shift workers experience acute, repeated bouts of misalignment between their endogenous circadian system and external behavior/environmental factors such as sleep, energy intake, activity, and light. Circadian misalignment is one mechanism suggested to increases the risk of T2D in shift-working populations. To date, there have been limited attempts at identifying strategies or countermeasures to prevent the impact of such circadian misalignment on T2D risk in a sizeable proportion of the population. The following thesis aims to test a nutritional countermeasure known as time-restricted eating (TRE). TRE has previously shown metabolic benefits in people with obesity. The overall aims of the two studies compiled within this thesis are to determine the impact of TRE on (1) circulating and muscle lipid accumulation and (2) insulin sensitivity and glycemic homeostasis. Both studies follow a randomized crossover design with a rigorous inpatient diet-, activity and light-controlled protocol in 32 healthy men and women. In these studies, participants underwent a 6d randomized crossover inpatient study with at least 1 month between conditions. In one condition, participants ate during the biological night as typically done during night shift work (circadian misalignment). In the other condition, participants consumed meals only in the biological daytime (circadian misalignment + time restricted eating), while keeping sleep times and diet consistent. Consolidating food intake to the biological daytime, particularly in night shift work, was hypothesized to reduce the risk of T2D by reducing the mismatch between the endogenous circadian system and external behaviors. Findings from this study represent a critical advancement in the fields of translational circadian and metabolic physiology by identifying and testing a countermeasure to circadian misalignment. Achievement of our proposed aims could lead to the development of new intervention strategies for chronic disease prevention and management. The knowledge to be gained offers the potential to support cost-effective programs that may inform our healthcare approach to metabolic disease prevention in populations at risk for these diseases such as shift workers, individuals with sleep disorders and anyone who eats outside of daytime hours.
Open Access
The effects of sleep extension on physical and cognitive performance in AROTC cadets
(Colorado State University. Libraries, 2023) Wedderburn, J'Michael, author; Broussard, Josiane, advisor; Lipsey, Tiffany, committee member; Eakman, Aaron, committee member; Brager, Allison, committee member
College students and military personnel have limited sleep opportunities; Reserve Officer Training Corps (ROTC) cadets belong to both groups. Thus, cadets are at a heightened risk of insufficient sleep. Sleep loss can have deleterious effects on physical and cognitive health (Halson et al., 2014). In military professions, these impairments have potentially fatal consequences, as decreased performance will result in diminished operational readiness. Recent evidence suggests that sleep extension is a valid intervention to increase sleep duration (Bonnar et al., 2018). Thus, we aim to identify if sleep extension improves performance in chronically sleep-deprived ROTC cadets. This study examines the impact of 1-week of sleep extension on physical and cognitive performance in Army ROTC cadets. We recruited 16 healthy, active male and female participants aged 18-35 from Colorado State University's ROTC program. Participants were equipped with Actiwatches and completed daily sleep questionnaires and diaries during the habitual and sleep extension periods. Sleep extension was achieved by asking participants to spend 10 hours in bed to increase sleep by at least 1 hour per night. Cadets then completed a series of physical and cognitive tests to measure performance on tactically relevant tasks. The physical testing consisted of a vertical jump, 3-repetition maximal hexagon deadlift, 300-meter shuttle, and a 1-mile run; and cognitive test consisted of a psychomotor vigilance test, the Purdue pegboard test Tiffin (1948), the STROOP color-word test Jensen (1965), and a simulated shooting exercise. Wilcoxon Signed rank-test and two samples paired t-test statistical analysis compared baseline, physical, and cognitive testing data to post-intervention testing data. Cognitive and physical testing occurred after 1-week of habitual sleep and 1-week of sleep extension. The mean objective Total Sleep Time (TST) was 6.07 ± 0.15 hours during the baseline period and 7.03 ± 0.17 hours during the sleep extension period (P=<0.0001). The mean Epworth Sleepiness Scale (ESS) rating was outside of normal limits at 10.47 ± 1.16 during the habitual sleep period; it decreased to fall within the normal limits during the sleep extension period at 7.10 ± 0.79 (P <0.005) (Shattuck & Matsangas. 2014). There were statistically significant differences found on 2 of the 4 Purdue pegboard tests and deadlift performance from habitual sleep to the sleep extension period. The mean hands and assembly scores significantly improved (P = 0.038 and P=0.003, respectively). Performance on the 3-repetition maximal hexagon deadlift increased significantly during the habitual sleep period and sleep extension period (p = .007). The limited sleep opportunities ROTC cadets encounter have negative implications on physical and cognitive performance; based on our findings in the current study, it is plausible that sleep was not extended to an adequate duration to elicit cognitive and physical performance improvements in all of the tested cognitive and physical measure. Thus, more research is needed to investigate the relationship between sleep duration and sleep quality and their effect on cognitive and physical performance in tactical population.
Open Access
The impact of time-restricted eating on circulating factors, insulin sensitivity and circadian rhythms
(Colorado State University. Libraries, 2020) Kennedy, Devin, author; Broussard, Josiane, advisor; Braun, Barry, committee member; Stephens, Jaclyn, committee member
Purpose: Obesity has been steadily increasing over several decades. In 2008, prevalence rates of obesity were reported at over 300 million people, defined as a body mass index of >30kg/m2. For years, scientists have tried to find "solutions" to obesity. While obesity prevention measures taken in childhood might result in decreased adulthood obesity, childhood prevention measures are not common, and obesity is often a health issue in adulthood. Negative energy balance and caloric restriction is most effective for reducing body weight, and studies have reported beneficial effects such as reduced fasting glucose and insulin, reductions in body weight [1], significantly higher insulin sensitivity, significantly lower BMI [2], reduced β-cell sensitivity [3], and reduced fasting glycemia and fasting insulinemia [4]; however, long-term adherence to caloric restriction is low. Certain fasting practices are emerging as promising possible solutions to help combat obesity. Fasting practices have resulted in improvements in cardiometabolic health including but not limited to protection from obesity [5], improved LDL and HDL cholesterol, reduced HbA1c and c-reactive proteins, [6], cell proliferation, and body weight [7]. Intermittent fasting is one method by which an individual can reduce body weight but also improve numerous cardiometabolic factors. However, research exploring intermittent fasting (IF), specifically time-restricted eating (TRE), as a method of improving cardiometabolic health is limited. Circadian rhythms might be the reason that aligning feeding windows to earlier in the day is showing these benefits. Currently, a gap in the knowledge exists as to whether circadian rhythms play a role in contributing to the metabolic benefits that are conferred by TRE, or if the timing of the food intake/duration is what results in the benefits. Therefore, our objective was to examine the effects of TRE on 24-hour glucose homeostasis and nighttime patterns of circulating factors (glucose, insulin, free fatty acids, triglycerides, and glycerol) as well as insulin sensitivity and the central circadian clock. Methods and results: This study employed a consecutive design. Eight healthy adults (6F; 27±4 y; 22.6±2.1 kg/m2; mean ± SD) completed a 2-week protocol. During Week 1 participants were instructed to consume their daily calories over a 13h period (control condition). In Week 2, participants were instructed to consume their daily calories over an 8h period (TRE condition). Specified mealtimes were pre-determined based on the habitual sleep and wake time for each individual participant. At the end of each week, participants were admitted to the Sleep and Metabolism Laboratory for an overnight stay that involved hourly blood samples. Plasma samples were analyzed for glucose, insulin, free fatty acids (FFA), lactate, triglycerides, and glycerol. The plasma analyses indicated that TRE decreased glucose variability during sleep (p=0.03), reduced nighttime insulin concentrations (p=0.005), increased nighttime FFA levels (p=0.04), increased nighttime triglycerides (p=0.006) and increased nighttime glycerol (p=0.02). TRE did not impact glucose variability during wakefulness (p = 0.49), nighttime glucose (p = 0.39), insulin sensitivity (MATSUDA-ISI, p = 0.38), or central circadian rhythms. Conclusion: The observed changes in nighttime glucose variability and insulin levels could represent mechanisms by which TRE can improve metabolic homeostasis in healthy lean individuals. Future studies are warranted to determine whether TRE can improve metabolic homeostasis in people at risk for diabetes such as people with overweight and obesity, and impaired glucose tolerance.