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The human circadian system regulates hunger independently of behavioral factors, resulting in a trough in the biological morning and a peak in the biological evening. However, the role of the only known orexigenic hormone, ghrelin, in this circadian rhythm is unknown. Furthermore, although shift work is an obesity risk factor, the separate effects of the endogenous circadian system, the behavioral cycle, and circadian misalignment on ghrelin has not been systematically studied. Here we show—by using two 8-day laboratory protocols—that circulating active (acylated) ghrelin levels are significantly impacted by endogenous circadian phase in healthy adults. Active ghrelin levels were higher in the biological evening than the biological morning (fasting +15.1%, P = 0.0001; postprandial +10.4%, P = 0.0002), consistent with the circadian variation in hunger (P = 0.028). Moreover, circadian misalignment itself (12-h behavioral cycle inversion) increased postprandial active ghrelin levels (+5.4%; P = 0.04). While not significantly influencing hunger (P > 0.08), circadian misalignment increased appetite for energy-dense foods (all P < 0.05). Our results provide possible mechanisms for the endogenous circadian rhythm in hunger, as well as for the increased risk of obesity among shift workers.

Context: Sleep restriction alters responses to food. However, the underlying neural mechanisms for this effect are not well understood. Objective: The purpose of this study was to determine whether there is a neural system that is preferentially activated in response to unhealthy compared with healthy foods. Participants: Twenty-five normal-weight individuals, who normally slept 7–9 h per night, completed both phases of this randomized controlled study. Intervention: Each participant was tested after a period of five nights of either 4 or 9 h in bed. Functional magnetic resonance imaging (fMRI) was performed in the fasted state, presenting healthy and unhealthy food stimuli and objects in a block design. Neuronal responses to unhealthy, relative to healthy food stimuli after each sleep period were assessed and compared. Results: After a period of restricted sleep, viewing unhealthy foods led to greater activation in the superior and middle temporal gyri, middle and superior frontal gyri, left inferior parietal lobule, orbitofrontal cortex, and right insula compared with healthy foods. These same stimuli presented after a period of habitual sleep did not produce marked activity patterns specific to unhealthy foods. Further, food intake during restricted sleep increased in association with a relative decrease in brain oxygenation level-dependent (BOLD) activity observed in the right insula. Conclusion: This inverse relationship between insula activity and food intake and enhanced activation in brain reward and food-sensitive centers in response to unhealthy foods provides a model of neuronal mechanisms relating short sleep duration to obesity.

Understanding the impact of rheological properties of food on postprandial appetite and glycemic response helps to design novel functional products. It has been shown that solid foods have a stronger satiating effect than their liquid equivalent. However, whether a subtle change in viscosity of a semi-solid food would have a similar effect on appetite is unknown. Fifteen healthy males participated in the randomized cross-over study. Each participant consumed a 1690 kJ portion of a standard viscosity (SV) and a high viscosity (HV) semi-solid meal with 1000 mg acetaminophen in two separate sessions. At regular intervals during the three hours following the meal, subjective appetite ratings were measured and blood samples collected. The plasma samples were assayed for insulin, glucose-dependent insulinotropic peptide (GIP), glucose and acetaminophen. After three hours, the participants were provided with an ad libitum pasta meal. Compared with the SV meal, HV was consumed at a slower eating rate (P = 0.020), with postprandial hunger and desire to eat being lower (P = 0.019 and P<0.001 respectively) while fullness was higher (P<0.001). In addition, consuming the HV resulted in lower plasma concentration of GIP (P<0.001), higher plasma concentration of glucose (P<0.001) and delayed gastric emptying as revealed by the acetaminophen absorption test (P<0.001). However, there was no effect of food viscosity on insulin or food intake at the subsequent meal. In conclusion, increasing the viscosity of a semi-solid food modulates glycemic response and suppresses postprandial satiety, although the effect may be short-lived. A slower eating rate and a delayed gastric emptying rate can partly explain for the stronger satiating properties of high viscous semi-solid foods.

Brain insulin sensitivity is an important link between metabolism and cognitive dysfunction. Intranasal insulin is a promising tool to investigate central insulin action in humans. We evaluated the acute effects of 160 U intranasal insulin on resting-state brain functional connectivity in healthy young adults. Twenty-five lean and twenty-two overweight and obese participants underwent functional magnetic resonance imaging, on two separate days, before and after intranasal insulin or placebo application. Insulin compared to placebo administration resulted in increased functional connectivity between the prefrontal regions of the default-mode network and the hippocampus as well as the hypothalamus. The change in hippocampal functional connectivity significantly correlated with visceral adipose tissue and the change in subjective feeling of hunger after intranasal insulin. Mediation analysis revealed that the intranasal insulin induced hippocampal functional connectivity increase served as a mediator, suppressing the relationship between visceral adipose tissue and hunger. The insulin-induced hypothalamic functional connectivity change showed a significant interaction with peripheral insulin sensitivity. Only participants with high peripheral insulin sensitivity showed a boost in hypothalamic functional connectivity. Hence, brain insulin action may regulate eating behavior and facilitate weight loss by modifying brain functional connectivity within and between cognitive and homeostatic brain regions.

Modern societies and their obesogenic environments expose individuals to persistent food stimulation. This frequent exposure can cause sensory systems to habituate or desensitize to food-related sensory stimulation. This can, in turn, lead to the reduction of pleasure associated with eating, which can elicit overeating behavior to attain the desired pleasurable effect. However, frequently engaging in overeating behavior can lead to excessive weight gain, which is associated with the development of metabolic and cardiovascular disease. Mindfulness training could serve as a tool to reduce the habituation response elicited by frequent food exposure while promoting mindful eating, emotion regulation, and reducing overeating behavior. To investigate this, the present study was registered as a clinical trial on the ISRCTN registry: trial ID ISRCTN12901054. In the study, meditation-naïve individuals with a tendency to stress-eat ( N  = 56) participated in either a 31-day, web-based, food-related mindfulness training or health training condition. Functional magnetic resonance imaging (fMRI) and behavioral data were acquired before and after the intervention. During the fMRI sessions, hungry and stressed participants were exposed to visual and olfactory high-calorie food stimuli. The results indicate that hunger and stress ratings increased in both groups during the fMRI sessions but that mindfulness training, in comparison to health training, may significantly reduce the habituation response to food stimuli. Our results demonstrate that the habituation response could be implicated through the increase of neural activity in brain regions involved in visual and olfactory processing as well as emotion regulation. This study, therefore, demonstrates that mindfulness training could improve the ability to attend to food stimuli, which may enhance the pleasurable experience of eating, thereby diminishing an individual’s tendency to engage in overeating behavior.

To investigate the effects of 8-weeks of full versus split body resistance training (RT) on appetite and energy intake in non-obese untrained men. The participants were pair-matched based on their initial fat mass and then randomly allocated into one of two treatment groups: Full body (FB, n = 20), in which all muscle groups were trained in every session, or Split body (SB, n = 15), in which upper and lower muscle groups were trained alternated per session; both groups trained in non-consecutive days, three times per week with total number of sets performed equated between groups. Energy intake, body composition, and strength performance were evaluated at pre-training, and after 8-weeks of RT, as well as self-reported hunger, fullness, and desire to eat, that were assessed at fasted and feed states pre- and post-intervention. FB and SB resistance training increased fat-free mass (FFM) (p < 0.001); and FB induced greater maximal strength improvement (p = 0.027). At fasted state self-reported hunger increased, and fullness decreased, while in feed state desire to eat something fatty increased in both groups. Carbohydrate intake (p = 0.011) decreased in both groups. In conclusion, FB and SB training increased orexigenic drive (increasing hunger and decreasing fullness), however, total energy intake and fat mass did not change after 8-weeks of RT in non-obese untrained men.Registered under Brazilian Registry of Clinical Trials no. RBR-3wkcvyw.

The worldwide obesity epidemic is a major health problem driven by the modern food environment. Recently, it has been shown that smell perception plays a key role in eating behavior and is altered in obesity. However, the underlying mechanisms of this phenomenon are not well understood yet. Since the olfactory system is closely linked to the endocrine system, we hypothesized that hormonal shifts in obesity might explain this relationship. In a within-subject, repeated-measures design, we investigated sensitivity to a food and a non-food odor in the hungry and sated state in 75 young healthy (26 normal weight, 25 overweight, and 24 obese) participants (37 women). To determine metabolic health status and hormonal reactivity in response to food intake, we assessed pre- and postprandial levels of insulin, leptin, glucose, and ghrelin. Odor sensitivity did not directly depend on body weight status/body mass index (BMI) or hunger state. However, we could establish a strong negative mediating effect of insulin resistance on the relationship between BMI/waist-hip ratio and olfactory sensitivity for the food odor. These findings indicate an impact of metabolic health status on sensitivity to food odors. Our results contribute to a better understanding of the mechanisms behind altered smell perception in obesity.

Examine the effect of experimental sleep restriction (SR) on adolescents' subjective hunger and perceived appeal of sweet/dessert foods versus other foods. A secondary goal was to replicate previous findings on the effects of SR on dietary intake. Randomized cross-over sleep restriction-extension paradigm. Sleep was obtained and monitored at home. Outcome measures were gathered during office visits. 31 typically-developing adolescents aged 14-17 years. The three-week protocol consisted of a baseline week, followed randomly by five consecutive nights of SR (6.5 hours in bed) versus healthy sleep duration (HS; 10 hours in bed), a 2-night wash-out period, and a 5-night cross-over. Sleep was monitored via actigraphy. The morning after each experimental condition, teens rated their hunger, underwent a 24-hour diet recall interview, and rated the appeal of a series of pictures of sweet/dessert foods (e.g., ice cream, candy) and non-sweets (meat, eggs, fruits, vegetables). Teens rated pictures of sweet/dessert foods to be more appealing after SR than after HS (Cohen's d = .41, t = 2.07, p = .045). The sleep manipulation did not affect self-reported hunger or the appeal of non-sweet foods (p >.10). Consistent with our prior work, intake of overall calories was 11% higher and consumption of sweet/dessert servings was 52% greater during SR than HS. Adolescent SR appears to increase the subjective appeal of sweet/dessert foods, indicating a potential mechanism by which SR might contribute to weight gain and the risk for obesity and chronic illness.

This study evaluated the impact of probiotic supplementation (Lactobacillus rhamnosus CGMCC1.3724 (LPR)) on appetite sensations and eating behaviors in the context of a weight-reducing program. Obese men (n = 45) and women (n = 60) participated in a double-blind, randomized, placebo-controlled trial that included a 12-week weight loss period (Phase 1) based on moderate energy restriction, followed by 12 weeks of weight maintenance (Phase 2). During the two phases of the program, each subject consumed two capsules per day of either a placebo or a LPR formulation (10 mg of LPR equivalent to 1.6 108 CFU/capsule, 210 mg of oligofructose, and 90 mg of inulin). The LPR supplementation increased weight loss in women that was associated with a greater increase in the fasting desire to eat (p = 0.03). On the other hand, satiety efficiency (satiety quotient for desire to eat) at lunch increased (p = 0.02), whereas disinhibition (p = 0.05) and hunger (p = 0.02) scores decreased more in the LPR-treated women, when compared with the female control group. Additionally, the LPR female group displayed a more pronounced decrease in food craving (p = 0.05), and a decrease in the Beck Depression Inventory score (p = 0.05) that was significantly different from the change noted in the placebo group (p = 0.02), as well as a higher score in the Body Esteem Scale questionnaire (p = 0.06). In men, significant benefits of LPR on fasting fullness and cognitive restraint were also observed. Taken together, these observations lend support to the hypothesis that the gut-brain axis may impact appetite control and related behaviors in obesity management.

Total sleep deprivation in rodents and in humans has been associated with hyperphagia. Over the past 40 years, self-reported sleep duration in the United States has decreased by almost 2 hours. To determine whether partial sleep curtailment, an increasingly prevalent behavior, alters appetite regulation. Randomized, 2-period, 2-condition crossover clinical study. Clinical Research Center, University of Chicago, Chicago, Illinois. 12 healthy men (mean age [+/-SD], 22 +/- 2 years; mean body mass index [+/-SD], 23.6 +/- 2.0 kg/m2). Daytime profiles of plasma leptin and ghrelin levels and subjective ratings of hunger and appetite. 2 days of sleep restriction and 2 days of sleep extension under controlled conditions of caloric intake and physical activity. Sleep restriction was associated with average reductions in the anorexigenic hormone leptin (decrease, 18%; P = 0.04), elevations in the orexigenic factor ghrelin (increase, 28%; P < 0.04), and increased hunger (increase, 24%; P < 0.01) and appetite (increase, 23%; P = 0.01), especially for calorie-dense foods with high carbohydrate content (increase, 33% to 45%; P = 0.02). The study included only 12 young men and did not measure energy expenditure. Short sleep duration in young, healthy men is associated with decreased leptin levels, increased ghrelin levels, and increased hunger and appetite.