Insufficient sleep is associated with obesity, yet little is known about how repeated nights of insufficient sleep influence energy expenditure and balance. We studied 16 adults in a 14-to 15-d-long inpatient study and quantified effects of 5 d of insufficient sleep, equivalent to a work week, on energy expenditure and energy intake compared with adequate sleep. We found that insufficient sleep increased total daily energy expenditure by ∼5%; however, energy intake-especially at night after dinner-was in excess of energy needed to maintain energy balance. Insufficient sleep led to 0.82 ± 0.47 kg (±SD) weight gain despite changes in hunger and satiety hormones ghrelin and leptin, and peptide YY, which signaled excess energy stores. Insufficient sleep delayed circadian melatonin phase and also led to an earlier circadian phase of wake time. Sex differences showed women, not men, maintained weight during adequate sleep, whereas insufficient sleep reduced dietary restraint and led to weight gain in women. Our findings suggest that increased food intake during insufficient sleep is a physiological adaptation to provide energy needed to sustain additional wakefulness; yet when food is easily accessible, intake surpasses that needed. We also found that transitioning from an insufficient to adequate/recovery sleep schedule decreased energy intake, especially of fats and carbohydrates, and led to −0.03 ± 0.50 kg weight loss. These findings provide evidence that sleep plays a key role in energy metabolism. Importantly, they demonstrate physiological and behavioral mechanisms by which insufficient sleep may contribute to overweight and obesity.calorimetry | misalignment | dysregulated eating | deprivation | restriction M ore than 1.4 billion adults, 150 million school-aged children, and 43 million preschool children are estimated to be overweight or obese worldwide (1-3), substantially raising risk for cardiovascular diseases (4) hyperlipidemia (5), diabetes (5, 6), osteoarthritis (6), sleep apnea (7), depression (8), and cancer (9). Excessive food consumption and inadequate physical activity are primary factors contributing to the obesity epidemic. When daily energy intake is in excess of energy expenditure (EE) a state of positive energy balance occurs. Over weeks, months, or years, a small cumulative impact of sustained positive energy balance results in weight gain and obesity (10). Alongside the rise in obesity there has been a decline in the number of individuals who report obtaining the recommended 7-9 h of sleep, with many obtaining less than 6 h per night (11). Insufficient sleep is a risk factor of weight gain and obesity (11-13), yet how insufficient sleep contributes to this risk is unclear. Sleep influences energy metabolism (14, 15), and one function of sleep is to conserve energy (16). Proposed mechanisms that associate insufficient sleep and higher body mass index (BMI) include changes in satiety and hunger hormones altering food intake and changes in EE (17). Insufficient sleep is associated with decreases...

The TODAY cohort is predominantly from racial/ethnic minority groups, with low socioeconomic status and a family history of diabetes. Clinical and biochemical abnormalities and comorbidities are prevalent within 2 yr of diagnosis. These findings contribute greatly to our understanding of American youth with type 2 diabetes.

Eating at a time when the internal circadian clock promotes sleep is a novel risk factor for weight gain and obesity, yet little is known about mechanisms by which circadian misalignment leads to metabolic dysregulation in humans. We studied 14 adults in a 6-d inpatient simulated shiftwork protocol and quantified changes in energy expenditure, macronutrient utilization, appetitive hormones, sleep, and circadian phase during day versus nightshift work. We found that total daily energy expenditure increased by ∼4% on the transition day to the first nightshift, which consisted of an afternoon nap and extended wakefulness, whereas total daily energy expenditure decreased by ∼3% on each of the second and third nightshift days, which consisted of daytime sleep followed by afternoon and nighttime wakefulness. Contrary to expectations, energy expenditure decreased by ∼12-16% during scheduled daytime sleep opportunities despite disturbed sleep. The thermic effect of feeding also decreased in response to a late dinner on the first nightshift. Total daily fat utilization increased on the first and second nightshift days, contrary to expectations, and carbohydrate and protein utilization were reduced on the second nightshift day. Ratings of hunger were decreased during nightshift days despite decreases in 24-h levels of the satiety hormones leptin and peptide-YY. Findings suggest that reduced total daily energy expenditure during nightshift schedules and reduced energy expenditure in response to dinner represent contributing mechanisms by which humans working and eating during the biological night, when the circadian clock is promoting sleep, may increase the risk of weight gain and obesity.insufficient sleep | melatonin | diet-induced thermogenesis | eating at night | appetite E merging evidence from nonhuman animal models indicates a fundamental interplay between circadian and metabolic physiology (1, 2) with implications for health and disease (3-5). Eating at inappropriate circadian times (e.g., at night) is considered a novel risk factor for weight gain and obesity, yet little research has been conducted in humans on this topic. The circadian time-keeping system in humans modulates energy metabolism so that wakefulness, activity, and food intake are promoted during the solar day and sleep, inactivity, and fasting occur during the solar night (2). With the widespread use of electrical lighting, however, work and social activities are capable of being extended further into the night (6, 7). Being awake during the biological night leads to disturbed physiology and behavior, because it creates a state of desynchrony between the circadian clock and wakefulness-sleep cycle known as circadian misalignment. Circadian misalignment is common in shiftwork. More than 20% of adults in the United States work nontraditional hours (8) and eat some of their meals during the biological night (9), which can increase blood glucose and triacylglycerol levels in response to a high-carbohydrate versus high-fat diet (10) and increase low-dens...

Metabolic adjustments occur with weight loss that may contribute to a high rate of weight regain. We have previously observed in obesity-prone, obese rats that weight reduction is accompanied by a suppression in resting metabolic rate beyond what would be predicted for the change in metabolic mass. In the present study, we examine if this adjustment in metabolic efficiency is affected by the length of time in weight maintenance and if it contributes to the propensity to regain after weight loss. Twenty-four-hour, nonresting, and resting energy expenditure (REE) were obtained by indirect calorimetry and normalized to metabolic mass estimated by dual-energy X-ray absorptiometry. A 10% loss in body weight in weight-reduced rats was accompanied by a 15% suppression in adjusted REE. This enhancement in metabolic efficiency was not altered with either 8 or 16 wk of weight maintenance, but it did resolve when the forced control of intake was removed and the weight was regained. The rate of weight regain increased with the time in weight maintenance and was exceptionally high early during the relapse period. During this high rate of weight gain, the suppression in REE persists while consumption increases to a level that is higher than when they were obese. In summary, an enhanced metabolic efficiency and an elevated appetite both contribute (60% and 40%, respectively) to a large potential energy imbalance that, when the forcible control of energy intake is relieved, becomes actualized and results in an exceptionally high rate of weight regain.

Weight regain after weight loss is the most significant impediment to long-term weight reduction. We have developed a rodent paradigm that models the process of regain after weight loss, and we have employed both prospective and cross-sectional analyses to characterize the compensatory adaptations to weight reduction that may contribute to the propensity to regain lost weight. Obese rats were fed an energy-restricted (50-60% kcal) low-fat diet that reduced body weight by 14%. This reduced weight was maintained for up to 16 wk with limited provisions of the low-fat diet. Intake restriction was then removed, and the rats were followed for 56 days as they relapsed to the obese state. Prolonged weight reduction was accompanied by 1) a persistent energy gap resulting from an increased drive to eat and a reduced expenditure of energy, 2) a higher caloric efficiency of regain that may be linked with suppressed lipid utilization early in the relapse process, 3) preferential lipid accumulation in adipose tissue accompanied by adipocyte hyperplasia, and 4) humoral adiposity signals that underestimate the level of peripheral adiposity and likely influence the neural pathways controlling energy balance. Taken together, long-term weight reduction in this rodent paradigm is accompanied by a number of interrelated compensatory adjustments in the periphery that work together to promote rapid and efficient weight regain. These metabolic adjustments to weight reduction are discussed in the context of a homeostatic feedback system that controls body weight.