Circadian rhythms in metabolic organs and the microbiota during acute fasting in mice.

The circadian clock regulates metabolism in anticipation of regular changes in the environment. It is found throughout the body, including in key metabolic organs such as the liver, adipose tissues, and intestine, where the timing of the clock is set largely by nutrient signaling. However, the circadian clocks of these tissues during the fasted state have not been completely characterized. Moreover, the sufficiency of a functioning host clock to produce diurnal rhythms in the composition of the microbiome in fasted animals has not been explored. To this end, mice were fasted 24 h prior to collection of key metabolic tissues and fecal samples for the analysis of circadian clock gene expression and microbiome composition. Rhythm characteristics were determined using CircaCompare software. We identify tissue-specific changes to circadian clock rhythms upon fasting, particularly in the brown adipose tissue, and for the first time demonstrate the rhythmicity of the microbiome in fasted animals.

Physiological Responses of Post-Dietary Effects: Lessons from Pre-Clinical and Clinical Studies.

Dieting regimens such as calorie restriction (CR) are among the most commonly practiced interventions for weight management and metabolic abnormalities. Due to its independence from pharmacological agents and considerable flexibility in regimens, many individuals turn to dieting as a form of mitigation and maintenance of metabolic health. While metabolic benefits of CR have been widely studied, weight loss maintenance and metabolic benefits are reported to be lost overtime when the diet regimen has been terminated-referred to as post-dietary effects. Specifically, due to the challenges of long-term adherence and compliance to dieting, post-dietary repercussions such as body weight regain and loss of metabolic benefits pose as major factors in the efficacy of CR. Intermittent fasting (IF) regimens, which are defined by periodic energy restriction, have been deemed as more flexible, compliant, and easily adapted diet interventions that result in many metabolic benefits which resemble conventional CR diets. Many individuals find that IF regimens are easier to adhere to, resulting in fewer post-dietary effects; therefore, IF may be a more effective intervention. Unfortunately, there is a severe gap in current research regarding IF post-dietary effects. We recognize the importance of understanding the sustainability of dieting; as such, we will review the known physiological responses of CR post-dietary effects and its potential mechanisms through synthesizing lessons from both pre-clinical and clinical studies. This review aims to provide insight from a translational medicine perspective to allow for the development of more practical and effective diet interventions. We suggest more flexible and easily practiced dieting regimens such as IF due to its more adaptable and practical nature.