Investigation of seasonality of human spontaneous physical activity and energy expenditure in respiratory chamber in Phoenix, Arizona.

OBJECTIVE: The existence of seasonal changes in energy metabolism is uncertain. We investigated the relationship between the seasons and spontaneous physical activity (SPA), energy expenditure (EE), and other components measured in a respiratory chamber. METHODS: Between 1985-2005, 671 healthy adults (aged 28.8 ± 7.1 years; 403 men) in Phoenix, Arizona had a 24-hour stay in the respiratory chamber equipped with radar sensors; SPA (expressed as a percentage over the time interval), the energy cost of SPA, EE, and respiratory exchange ratio (RER) were measured. RESULTS: In models adjusted for known covariates, SPA (%) was lower during summer (7.2 ± 2.9, p = 0.0002), spring (7.5 ± 2.9, p = 0.025), and fall (7.6 ± 3, p = 0.038) compared to winter (8.3 ± 3.5, reference). Conversely, energy cost of SPA (kcal/h/%) was higher during summer (2.18 ± 0.83, p = 0.0008), spring (2.186 ± 0.83, p = 0.017), and fall (2.146 ± 0.75, p = 0.038) compared to winter (2.006 ± 0.76). Protein (292 ± 117 kcal/day, ß = -21.2, p = 0.08) oxidation rates was lower in the summer compared to winter. Carbohydrate and lipid oxidation rates (kcal/day) did not differ across seasons. RER and 24-h EE did not differ by season. CONCLUSION: SPA, representing fidgeting-like behavior in the chamber, demonstrated a winter peak and summer nadir in humans living in a desert climate. These findings indicate that the physiological propensity for movement may be affected by seasonal factors. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov identifiers: NCT00340132, NCT00342732.

Hepatic Insulin Resistance Increases Risk of Gallstone Disease in Indigenous Americans in the Southwestern United States.

OBJECTIVES: Animal models indicate that hepatic insulin resistance (IR) promotes cholesterol gallstone disease (GSD). We sought to determine whether hepatic and whole-body IR are associated with incident GSD. METHODS: At baseline, 450 Southwestern Indigenous American adults without GSD were included. Participants had a 2-step hyperinsulinemic-euglycemic clamp with glucose tracer at submaximal and maximal insulin stimulation (240 and 2400 pmol/m2/min) for whole-body IR (M-low and M-high) and hepatic glucose production (HGP) before and during submaximal insulin infusion (HGP-basal and HGP-insulin). Incident GSD was identified during follow-up visits conducted at ∼2-year intervals. The associations of HGP (basal, insulin, and % suppression), M-low, and M-high with risk of GSD were assessed by Cox regression models adjusted for age, sex, body fat (%), glucose, and insulin. RESULTS: Sixty participants (13%) developed GSD (median follow-up: 11.6 years). Participants who developed GSD were of similar age and whole-body IR as those who did not (p's> 0.07), but were more likely to be female, have higher body fat, higher HGP-basal, and HGP-insulin, and lower % suppression of HGP (p's<0.02). In separate adjusted models, higher HGP-insulin and lower % suppression of HGP were associated with increased risk for GSD (hazard ratio [HR] per SD: HR 1.38, 95% CI 1.12, 1.69, p=0.002; HR 1.41 95% CI 1.16-1.72, p=0.0007). HGP-basal, M-low, and M-high were not associated with GSD in adjusted models (p's>0.22). CONCLUSIONS: Resistance to insulin suppression of HGP increases risk for GSD. Hepatic IR is a link between GSD and other conditions of the metabolic syndrome.

Reduced plasma interleukin-6 concentration after transcranial direct current stimulation to the prefrontal cortex.

OBJECTIVES: Transcranial direct stimulation (tDCS) targeted to the dorsolateral prefrontal cortex (DLPFC) reduces food intake and hunger, but its effects on circulating factors are unclear. We assessed the effect of repeated administration of tDCS to the left DLPFC (L-DLPFC) on concentrations of pro/anti-inflammatory and appetitive hormone concentrations. MATERIALS AND METHODS: Twenty-nine healthy adults with obesity (12 M; 42±11 y; BMI=39±8 kg/m2) received 3 consecutive inpatient sessions of either anodal or sham tDCS targeted to the L-DLPFC during a period of ad libitum food intake. Fasting plasma concentrations of IL-6, orexin, cortisol, TNF-α, IL-1ß, ghrelin, PYY, and GLP-1 were measured before the initial and after the final tDCS sessions. RESULTS: IL-6 (ß=-0.92 pg/ml p=0.03) decreased in the anodal group compared with sham, even after adjusting for kcal intake; there were no changes in other hormones. Mean kcal intake was associated with higher IL-1ß and ghrelin concentrations after the ad libitum period (ß=0.00018 pg/ml/kcal, p=0.03; ß=0.00011 pg/ml/kcal, p=0.02; respectively), but not differ by intervention groups. CONCLUSIONS: IL-6 concentrations were reduced following anodal tDCS to the L-DLPFC independent of ad libitum intake. IL-6 concentrations reflect the inflammatory state of adiposity and may affect eating behavior and weight gain. These findings provide evidence of therapeutic benefit of tDCS.