The effects of diurnal Ramadan fasting on energy expenditure and substrate oxidation in healthy men.

The study aimed to examine the effects of diurnal Ramadan fasting (RF) on substrate oxidation, energy production, blood lipids and glucose as well as body composition. Nine healthy Muslim men (fasting (FAST) group) and eight healthy non-practicing men (control (CNT) group) were assessed pre- and post-RF. FAST were additionally assessed at days 10, 20 and 30 of RF in the morning and evening. Body composition was determined by hydrodensitometry, substrate oxidation and energy production by indirect calorimetry, blood metabolic profile by biochemical analyses and energy balance by activity tracker recordings and food log analyses. A significant group×time interaction revealed that chronic RF reduced body mass and adiposity in FAST, without changing lean mass, whereas CNT subjects remained unchanged. In parallel to these findings, a significant main diurnal effect (morning v. evening) of RF on substrate oxidation (a shift towards lipid oxidation) and blood metabolic profile (a decrease in glucose and an increase in total cholesterol and TAG levels, respectively) was observed, which did not vary over the course of the Ramadan. In conclusion, although RF induces diurnal metabolic adjustments (morning v. evening), no carryover effect was observed throughout RF despite the extended daily fasting period (18·0 (sd 0·3) h) and changes in body composition.

Accuracy of the vivofit activity tracker.

The purpose of this study was to examine the accuracy of the vivofit activity tracker in assessing energy expenditure and step count. Thirteen participants wore the vivofit activity tracker for five days. Participants were required to independently perform 1 h of self-selected activity each day of the study. On day four, participants came to the lab to undergo BMR and a treadmill-walking task (TWT). On day five, participants completed 1 h of office-type activities. BMR values estimated by the vivofit were not significantly different from the values measured through indirect calorimetry (IC). The vivofit significantly underestimated EE for treadmill walking, but responded to the differences in the inclination. Vivofit underestimated step count for level walking but provided an accurate estimate for incline walking. There was a strong correlation between EE and the exercise intensity. The vivofit activity tracker is on par with similar devices and can be used to track physical activity.

Problematic drinking and physiological responses among female college students.

Problematic drinking is a widespread problem among college students, and can contribute to alcohol dependence during later adulthood, particularly among females. The current study assessed vulnerability for alcohol-related consequences by comparing self-reported drinking with coping styles and physiological and behavioral stress responses during a challenging task. Cardiovascular measurements and saliva samples were taken from 88 female students at the beginning of the experiment and after the task. Hypothalamic-pituitary-adrenal (HPA) activity was measured by assessing cortisol and dehydroepiandrosterone (DHEA) salivary levels. The behavioral task consisted of a set of three anagrams of increasing difficulty, the last of which had no possible solution, to test the distress tolerance of the participants. Results showed that the majority of participants (70%) reported drinking in the six months prior to data collection, most of whom reported at least one incident of binge drinking. Excessive alcohol use was related to an impaired physiological response to stress during the impossible task. College students who drank to cope with stress had significantly higher basal levels of cortisol and DHEA, an indication of HPA axis over-regulation, while their stress response remained remarkably flat. Self-reported consequences of drinking were related to motives for drinking and lower DHEA levels. Regression analysis indicated that higher cortisol levels mediated the relationship between motives for drinking and problematic drinking.