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The regulation of the circadian clock plays an important role in influencing physiological conditions. While it is reported that the timing and quantity of energy intake impact circadian regulation, the underlying mechanisms remain unclear. This study investigated the impact of dietary protein intake on peripheral clocks. Firstly, transcriptomic analysis was conducted to investigate molecular targets of low-protein intake. Secondly, mPer2::Luc knock-in mice, fed with either a low-protein, normal, or high-protein diet for 6 weeks, were analyzed for the oscillation of PER2 expression in peripheral tissues and for the expression profiles of circadian and metabolic genes. Lastly, the candidate pathway identified by the in vivo analysis was validated using AML12 cells. As a result, using transcriptomic analysis, we found that the low-protein diet hardly altered the circadian rhythm in the central clock. In animal experiments, expression levels and period lengths of PER2 were different in peripheral tissues depending on dietary protein intake; moreover, mRNA levels of clock-controlled genes and endoplasmic reticulum (ER) stress genes were affected by dietary protein intake. Induction of ER stress in AML12 cells caused an increased amplitude of Clock and Bmal1 and an advanced peak phase of Per2. This result shows that the intake of different dietary protein ratios causes an alteration of the circadian rhythm, especially in the peripheral clock of mice. Dietary protein intake modifies the oscillation of ER stress genes, which may play key roles in the regulation of the circadian clock. [ABSTRACT FROM AUTHOR]

Objectives: Metabolic syndrome is associated with an increased risk of diabetes, cardiovascular disease, and all-cause mortality. Some evidence suggests that the cardiometabolic health benefits of protein intake may vary by the source (animal or plant); however, the evidence is inconsistent. This study aimed to assess the risk of developing metabolic syndrome according to the protein source., Participants: Among a total of 3,310 participants aged 40 years or older in the Ansan and Ansung population based prospective cohort, 1,543 incident cases of metabolic syndrome were identified between 2007 and 2018., Measurements: Dietary intake was assessed using a validated food frequency questionnaire. Cox proportional hazards models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) by quintile (Q), adjusting for demographics and health-related lifestyle factors., Results: Higher intake of animal protein (HR quintile5 (Q5) vs quintile1 (Q1) [95% CIs]: 0.76 [0.59-0.96], P-trend ≤ 0.0307) and a higher relative intake of animal protein (HR Q5 vs.Q1 : 0.78 [0.64-0.95], P-trend ≤ 0.0017) were associated with a significantly decreased risk of developing metabolic syndrome. In subgroup analyses, associations between the risk of metabolic syndrome and the relative intake of animal and plant protein differed according to whether the total protein intake was within the recommended nutrient intake (RNI). Specifically, significant associations were observed only among those with a total protein consumption below the RNI (HR Q5vs Q1 [95% CIs]: 0.72 [0.56-0.93] for the relative intake of animal protein), but not among those consuming above the RNI. This association was more significant in women than in men., Conclusion: A higher absolute and relative intake of animal protein were associated with a significantly decreased risk of metabolic syndrome, particularly among those who consumed less than the RNI of protein., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2024. Published by Elsevier Masson SAS.)