Association between insulin sensitivity and lean mass loss during weight loss.

OBJECTIVE: The study objective was to assess the relationship between insulin sensitivity and changes in total lean mass (LM) and appendicular LM (ALM) during weight loss. METHODS: Individuals were randomly assigned to either a standard or a moderately reduced carbohydrate diet for 16 weeks. Body composition was assessed using dual-energy x-ray absorptiometry and insulin sensitivity index (SI) using an intravenous glucose tolerance test. Multiple linear regression was used to determine whether baseline SI was predictive of changes in total LM and ALM. RESULTS: Participants (n = 57; baseline BMI 32.1 ± 3.8 kg/m2) lost an average of 6.8 ± 3.2 kg of body weight (p < 0.001), with 1.5 ± 2.6 kg coming from LM (p < 0.05) and 0.5 ± 0.73 kg from ALM (p < 0.05). Multiple regression analysis demonstrated that SI was inversely associated with changes in total LM (kilograms; ß = 0.481, p < 0.001), after adjusting for baseline LM, fat mass, acute insulin response to glucose, and weight loss. Similar results were seen when assessing ALM loss (ß = 0.359, p < 0.05). CONCLUSIONS: Identifying individuals with low insulin sensitivity prior to weight loss interventions may allow for a personalized approach aiming at minimizing LM loss.

Association of periodic fasting lifestyles with survival and incident major adverse cardiovascular events in patients undergoing cardiac catheterization.

AIMS: Animal models repeatedly show fasting increases longevity. Human data, though, are limited to anecdotal claims. This study evaluated the association of routine fasting with survival and, secondarily, with incident major adverse cardiovascular events. METHODS AND RESULTS: Cardiac catheterization patients enrolled in the Intermountain INSPIRE longitudinal cohort (n = 2785) during 2013-2015 were followed through March 2019. A fasting survey was completed in n = 2025 (73%) of this cohort and 1957 were included in the final data analysis after 68 participants were removed (24 for data issues and 44 for fasting less than 5 years). Self-reported routine fasting behaviour, years of participation in fasting, and other fasting characteristics were surveyed. Mortality was the primary outcome and incident myocardial infarction (MI), stroke, and heart failure (HF) were secondary. Routine fasters (n = 389, mean age 64 ± 14 years, 34% female) averaged 42 ± 18 years of routine fasting (minimum 5 years). Non-fasters (n = 1568, aged 63 ± 14 years, 36% female) included never fasters (n = 1120 with 0 years of fasting) and previous fasters (n = 448 who averaged 32 ± 21 years of prior fasting but had stopped prior to enrolment). Routine fasters had greater survival vs. non-fasters [adjusted hazard ratio (HR) = 0.54, 95% confidence interval (CI) = 0.36-0.80; P = 0.002] and lower incidence of HF (adjusted HR = 0.31, CI = 0.12-0.78; P = 0.013), but not MI or stroke after adjustment. CONCLUSIONS: Routine fasting followed during two-thirds of the lifespan was associated with higher survival after cardiac catheterization. This may in part be explained by an association of routine fasting with a lower incidence of HF. CLINICAL STUDY REGISTRATION: The Intermountain INSPIRE registry https://clinicaltrials.gov/, NCT02450006.

The impact of exercise intensity on neurophysiological indices of food-related inhibitory control and cognitive control: A randomized crossover event-related potential (ERP) study.

Food-related inhibitory control, the ability to withhold a dominant response towards highly palatable foods, influences dietary decisions. Food-related inhibitory control abilities may increase following a bout of aerobic exercise; however, the impact of exercise intensity on both food-related inhibitory control and broader cognitive control processes is currently unclear. We used a high-powered, within-subjects, crossover design to test how relative intensity of aerobic exercise influenced behavioral (response time, accuracy) and neural (N2 and P3 components of the scalp-recorded event-related potential [ERP]) measures of food-related inhibitory and cognitive control. Two hundred and ten participants completed three separate conditions separated by approximately one week in randomized order: two exercise conditions (35% VO2max or 70% VO2max) and seated rest. Directly following exercise or rest, participants completed a food-based go/no-go task and a flanker task while electroencephalogram data were recorded. Linear mixed models showed generally faster response times (RT) and improved accuracy following 70% VO2max exercise compared to rest, but not 35% VO2max; RTs and accuracy did not differ between 35% VO2max exercise and rest conditions. N2 and P3 amplitudes were larger following 70% VO2max exercise for the food-based go/no-go task compared to rest and 35% VO2max exercise. There were no differences between exercise conditions for N2 amplitude during the flanker task; however, P3 amplitude was more positive following 70% VO2max compared to rest, but not 35% VO2max exercise. Biological sex did not moderate exercise outcomes. Results suggest improved and more efficient food-related recruitment of later inhibitory control and cognitive control processes following 70% VO2max exercise.

The Effects of Exercise on ß-Hydroxybutyrate Concentrations over a 36-h Fast: A Randomized Crossover Study.

PURPOSE: This study assessed ß-hydroxybutyrate (BHB) concentration during a short-term fast and the degree to which an initial bout of exercise influences the rate of ketogenesis. METHODS: Twenty subjects (11 male, 9 female) completed two 36-h fasts, with one protocol requiring the subject to complete a treadmill exercise session at the beginning of the fast. BHB levels were assessed via portable meter every 2 h, along with mood and hunger ratings. Venipuncture was performed every 12 h. RESULTS: The mean (SD) areas under the curve for BHB concentration were 19.19 (2.59) mmol·L-1 (nonexercised) and 27.49 (2.59) mmol·L-1 (exercised), yielding a difference of 8.30 mmol·L-1 between conditions (95% posterior probability interval (PPI), 1.94 to 14.82 mmol·L-1; posterior probability (PP) = 0.99). The mean (SD) times to BHB concentration of 0.5 mmol·L-1 were 21.07 (2.95) h (nonexercised) and 17.5 (1.69) h (exercised), a 3.57-h difference (95% PPI, -2.11 to 10.87 h; PP = 0.89). The differences in area under the curve between conditions were 5.07 µU·mL-1 (95% PPI, -21.64 to 36.18 µU·mL-1; PP = 0.67) for insulin, 97.13 pg·mL-1 (95% PPI, 34.08 to 354.21 pg·mL-1; PP = 0.98) for glucagon, and 20.83 (95% PPI, 4.70 to 24.22; PP = 0.99) for the insulin/glucagon ratio. CONCLUSIONS: Completing aerobic exercise at the beginning of a fast accelerates the production of BHB throughout the fast without altering subjective feelings of hunger, thirst, stomach discomfort, or mood. Insulin and the insulin/glucagon ratio experience a marked reduction within the first 12 h of fasting and was not altered with exercise. Thus, exercising at the beginning of a fast may improve the metabolic outcomes of fasting.

Randomized controlled trial of once-per-week intermittent fasting for health improvement: the WONDERFUL trial.

Aims: Low-density lipoprotein cholesterol (LDL-C) predicts heart disease onset and may be reduced by intermittent fasting. Some studies, though, reported that fasting increased LDL-C; however, no study evaluated LDL-C as the primary endpoint. This randomized controlled trial evaluated the effect of low-frequency intermittent fasting on LDL-C and other biomarkers. Methods and results: Adults aged 21-70 years were enrolled who were not taking a statin, had modestly elevated LDL-C, had ≥1 metabolic syndrome feature or type 2 diabetes, and were not taking anti-diabetic medication (N = 103). Water-only 24-h fasting was performed twice weekly for 4 weeks and then once weekly for 22 weeks; controls ate ad libitum. The primary outcome was 26-week LDL-C change score. Secondary outcomes (requiring P ≤ 0.01) were 26-week changes in homeostatic model assessment of insulin resistance (HOMA-IR), Metabolic Syndrome Score (MSS), brain-derived neurotrophic factor (BDNF), and MicroCog general cognitive proficiency index (GCPi). Intermittent fasting (n = 50) and control (n = 53) subjects were, respectively, aged 49.3 ± 12.0 and 47.0 ± 9.8 years, predominantly female (66.0% and 67.9%), and overweight (103 ± 24 and 100 ± 21 kg) and had modest LDL-C elevation (124 ± 19 and 128 ± 20 mg/dL). Drop-outs (n = 12 fasting, n = 20 control) provided an evaluable sample of n = 71 (n = 38 fasting, n = 33 control). Intermittent fasting did not change LDL-C (0.2 ± 16.7 mg/dL) vs. control (2.5 ± 19.4 mg/dL; P = 0.59), but it improved HOMA-IR (-0.75 ± 0.79 vs. -0.10 ± 1.06; P = 0.004) and MSS (-0.34 ± 4.72 vs. 0.31 ± 1.98, P = 0.006). BDNF (P = 0.58), GCPi (P = 0.17), and weight (-1.7 ± 4.7 kg vs. 0.2 ± 3.5 kg, P = 0.06) were unchanged. Conclusions: A low-frequency intermittent fasting regimen did not reduce LDL-C or improve cognitive function but significantly reduced both HOMA-IR and MSS. Trial registration: clinicaltrials.gov, NCT02770313.

Evaluating Relationships Between Sleep and Next-Day Physical Activity in Young Women.

BACKGROUND: To evaluate the relationship between sleep and next-day physical activity (PA) under free-living conditions in women. METHODS: Sleep and PA were measured objectively for 7 consecutive days by accelerometry in 330 young adult women (aged 17-25 y). A structural equation model was used to evaluate the relationship between the driving factor of sleep (total sleep or morning wake time) and the amount of nonsleep sedentary (SED) and moderate to vigorous physical activity (MVPA) each day. RESULTS: With sleep duration as the driving factor, the estimates of ßSED and ßMVPA were -0.415 and -0.093, respectively (P ≤ .05). For every hour slept, a 24.9-minute reduction in SED time and a 5.58-minute reduction in MVPA were observed. With wake time as the driving factor, the estimates of ßSED and ßMVPA were -0.636 and -0.149, respectively. For every wake time that was 1 hour later, a 38.2-minute decrease in SED and a 8.9-minute decrease in MVPA (P ≤ .05) were observed. CONCLUSIONS: Women who wake later or who sleep longer tend to get less MVPA throughout the day. Getting up earlier and going to bed earlier may support behaviors that improve PA and lifestyle.

The Impact of Step Recommendations on Body Composition and Physical Activity Patterns in College Freshman Women: A Randomized Trial.

Purpose: Transitioning from high school to college generally results in reduced physical activity and weight gain at a rate that is higher than the general population. The purpose of this study was to examine the effects of three progressively higher step recommendations over 24 weeks on changes in body weight and body composition. Methods: Ninety-two freshmen college women wore a multifunction pedometer for 24 weeks after being randomly assigned to a daily step level: 10,000, 12,500, or 15,000. Pedometer data were downloaded every two weeks and participants were counseled on meeting their step recommendation. Body weight and body composition were assessed at baseline and 24 weeks. Body composition was assessed by dual X-ray absorptiometry. Results: On average, women took 10,786 ± 1501, 12,650 ± 2001, and 13,762 ± 2098 steps per day for the 10,000-, 12,500-, and 15,000-step groups, respectively (F = 15.48, P < 0.0001). Participants gained 1.4 ± 2.6, 1.8 ± 2.1, and 1.4 ± 2.1 kg for the 10,000-, 12,500-, and 15,000-step groups, respectively (F = 37.74, P < 0.0001). Weight gain was not significantly different between groups (F = 0.18, P=0.8385). There was also no difference in fat weight gain (F = 0.41, P=0.7954). Discussion: A step recommendation beyond 10,000 does not prevent weight or fat gain over the first year of college. Future research should focus on either intensity of physical activity or the addition of dietary interventions to prevent weight gain during the first year of college.