Time-Restricted Feeding Regulates Circadian Rhythm of Murine Uterine Clock

Effects of Intermittent Fasting on Female Reproductive Function: A Review of Animal and Human Studies

PURPOSE OF REVIEW

Intermittent fasting has gained significant attention, yet a comprehensive understanding of its impact on female reproductive health is lacking. This review aims to fill this gap by examining various intermittent fasting regimens and their effects on female reproductive function, along with potential mechanisms.

RECENT FINDINGS

In healthy non-overweight/obese or pregnant animal models, alternate-day fasting (ADF) and an 8-h time-restricted feeding (TRF) window may have adverse effects on reproductive function. However, these regimens show potential to mitigate negative consequences induced by a high-fat diet (HFD) or environmental exposure. A 10-h TRF demonstrates benefits in improving fertility in both normal-weight and HFD-fed animal models. In women with overweight/obesity or polycystic ovary syndrome (PCOS), the 5:2 diet and TRF significantly reduce the free androgen index while elevating sex hormone binding globulin, promising improvements in menstrual regulation. For pregnant Muslim women, available data do not strongly indicate adverse effects of Ramadan fasting on preterm delivery, but potential downsides to maternal weight gain, neonatal birthweight, and long-term offspring health need consideration. Factors linking intermittent fasting to female reproductive health include the circadian clock, gut microbiota, metabolic regulators, and modifiable lifestyles. Drawing definitive conclusions remains challenging in this evolving area. Nonetheless, our findings underscore the potential utility of intermittent fasting regimens as a therapeutic approach for addressing menstruation irregularities and infertility in women with obesity and PCOS. On the other hand, pregnant women should remain cognizant of potential risks associated with intermittent fasting practices.

Impact of daily breakfast intake on the outcomes of assisted reproductive technology procedures

OBJECTIVE

To assess the relationship between meal consumption frequency and assisted reproductive technology (ART) outcomes among female patients with infertility.

RESEARCH METHODS & PROCEDURES

This cohort study was conducted from February 2022 to January 2024 at Tokyo Medical University Hospital. Overall, 101 female patients with infertility issues and without a history of stroke, heart disease, cancer, or type 1 or type 2 diabetes were enrolled in this study. The factors extracted from the questionnaire included demographic information, meal consumption frequency before ART and at 20 years of age, smoking status, and alcohol consumption status. Data on other factors, including age, body mass index, anti-Müllerian hormone level, and parity history, were collected from medical records. The assessed clinical outcomes included number of transplanted embryos, clinical pregnancies, ongoing pregnancies, live births, and miscarriages.

RESULTS

After adjusting for potential confounding factors, including age, smoking status, alcohol consumption status, body mass index, anti-Müllerian hormone level, and parity history, a multivariate analysis of ART outcomes was performed. Patients were categorized into groups based on the frequency of weekly consumption of breakfast, lunch, and dinner. Patients who consumed breakfast 6-7 times a week were significantly more likely to have higher rates of live birth and lower rates of miscarriage in pregnancies conceived through ART.

CONCLUSIONS

Consumption of breakfast 6-7 times a week before ART was associated with increased success rates following ART. This highlights the potential importance of regular breakfast consumption for optimizing ART outcomes.

Comparison of the Effects of Inappropriate Meal Timing-Induced and Genetic Models of Circadian Clock Disruption on Uterine mRNA Expression Profiles

BACKGROUND

Accumulating evidence reveals that inappropriate meal timing contributes to the development of lifestyle-related diseases. An underlying mechanism is thought to be the disruption of the intracellular circadian clock in various tissues based on observations in both systemic and tissue-specific clock gene-deficient mice. However, whether the effects of conditional clock gene knockout are comparable to those of inappropriate meal timing remains unclear.

OBJECTIVES

This study aimed to compare the effects of a recently developed 28-h feeding cycle model with those of a core clock gene Bmal1 uterine conditional knockout (Bmal1 cKO) model on uterine mRNA expression profiles.

METHODS

The models were generated by subjecting C57BL/6J mice to an 8-h/20-h feeding/fasting cycle for 2 wk and crossing Bmal1-floxed mice with PR-Cre mice. Microarray analyses were conducted using uterine samples obtained at the beginning of the dark and light periods.

RESULTS

The analyses identified 516 and 346, significantly 4-fold and 2-fold, up- or downregulated genes in the 28-h feeding cycle and Bmal1 cKO groups, respectively, compared with each control group. Among these genes, only 7 (1.4%) and 63 (18.2%) were significantly up- or downregulated in the other model. Moreover, most (n = 44, 62.9%) of these genes were oppositely regulated. These findings were confirmed by gene set enrichment analyses.

CONCLUSIONS

This study reveals that a 28-h feeding cycle and Bmal1 cKO differently affect gene expression profiles and highlights the need for considering this difference to assess the pathophysiology of diseases associated with inappropriate meal timing.

Exenatide administration time-dependently affects the hepatic circadian clock through glucagon-like peptide-1 receptors in the central nervous system

Accumulating evidence indicates that disruption of the circadian clock contributes to the development of lifestyle-related diseases. We have previously shown that exenatide, a glucagon-like peptide-1 (GLP-1) receptor agonist, can strongly affect the molecular clocks in the peripheral tissues. This study aimed to investigate the effects of its dosing time and the central nervous system-specific GLP-1 receptor knockdown (GLP1RKD) on the hepatic clock in mice treated with exenatide. Male C57BL/6J and GLP1RKD mice were housed under a 12-h/12-h light/dark cycle, and feeding was restricted to either the light period (L-TRF) or the first 4 h in the dark period (D-TRF). In parallel, exenatide was administered 4-5 times, once daily either at the beginning of the dark (ZT 12) or light period (ZT 0), and we assessed the mRNA expression rhythms of clock genes in the liver thereafter. Exenatide administration at ZT 12 counteracted the phase shift effect of the L-TRF on the hepatic clock of wild-type mice, whereas the dosing at ZT 0 enhanced its effect. However, exenatide did not influence the phase of the hepatic clock under D-TRF regardless of the dosing time. The effect of exenatide in wild-type mice weakened in GLP1RKD mice. These results showed that exenatide dosing time-dependently affects the hepatic circadian clock through the central GLP-1 system. Exenatide administration at the beginning of the active period (i.e., in the morning for humans) might prevent disruption of the peripheral clocks caused by irregular eating habits.

Desynchronization between Food Intake and Light Stimulations Induces Uterine Clock Quiescence in Female Mice

BACKGROUND

Dysmenorrhea is associated with breakfast skipping in young women, suggesting that fasting in the early active phase disrupts uterine functions.

OBJECTIVES

To investigate the possible involvement of the uterine clock system in fasting-induced uterine dysfunction, we examined core clock gene expressions in the uterus using a 28-h interval-fed mouse model.

METHODS

Young female mice (8 wk of age) were divided into 3 groups: group I (ad libitum feeding), group II (time-restricted feeding, initial 4 h of the active period every day), and group III (time-restricted feeding for 8 h with a 28-h cycle). Groups II and III have the same fasting interval of 20 h. After analyzing feeding and wheel running behaviors during 2 wk of dietary restriction, mice were sacrificed at 4-h intervals, and the expression profiles of clock genes in the uterus and liver were examined by qPCR.

RESULTS

The mice in group I took food mainly during the dark phase and those in group II during the initial 4 h of the dark phase, whereas those in group III delayed feeding time by 4 h per cycle. In all groups, spontaneous wheel running was observed during the dark phase. There was no difference in the quantity of feeding and the amount of running exercise among the 3 groups during the second week. The mRNA expressions of peripheral clock genes, Bmal1, Clock, Per1, Per2, Cry1, Nr1d1, and Dbp and a clock-controlled gene, Fabp1, in the uterus showed rhythmic oscillations with normal sequential expression cascade in groups I and II, whereas their expressions decreased and circadian cycles disappeared in group III. In contrast, liver core clock genes in group III showed clear circadian cycles.

CONCLUSIONS

Fluctuations in the timing of the first food intake impair the uterine clock oscillator system to reduce clock gene expressions and abolish their circadian rhythms.

Association between frequency of breakfast intake before and during pregnancy and infant birth weight: the Tohoku Medical Megabank Project Birth and Three-Generation Cohort Study

BACKGROUND

Low birth weight is associated with an increased risk of developing chronic diseases in adulthood, with a particularly high incidence in Japan among developed countries. Maternal undernutrition is a risk factor for low birth weight, but the association between the timing of food intake and infant birth weight has not been investigated. This study aimed to examine the association between breakfast intake frequency among Japanese pregnant women and infant birth weight.

METHODS

Of all pregnant women who participated in the Tohoku Medical Megabank Project Three Generation Cohort Study, 16,820 who answered the required questions were included in the analysis. The frequency of breakfast intake from pre- to early pregnancy and from early to mid-pregnancy was classified into four groups: every day and 5-6, 3-4, and 0-2 times/week. Multivariate linear regression models were constructed to examine the association between breakfast intake frequency among pregnant women and infant birth weight.

RESULTS

The percentage of pregnant women who consumed breakfast daily was 74% in the pre- to early pregnancy period and 79% in the early to mid-pregnancy period. The average infant birth weight was 3,071 g. Compared to women who had breakfast daily from pre- to early pregnancy, those who had breakfast 0-2 times/week had lower infant birth weight (β = -38.2, 95% confidence interval [CI]: -56.5, -20.0). Similarly, compared to women who had breakfast daily from early to mid-pregnancy, those who had breakfast 0-2 times/week had lower infant birth weight (β = -41.5, 95% CI: -63.3, -19.6).

CONCLUSIONS

Less frequent breakfast intake before and mid-pregnancy was associated with lower infant birth weight.

The Circadian Clock, Nutritional Signals and Reproduction: A Close Relationship

The circadian rhythm, which is necessary for reproduction, is controlled by clock genes. In the mouse uterus, the oscillation of the circadian clock gene has been observed. The transcription of the core clock gene period (Per) and cryptochrome (Cry) is activated by the heterodimer of the transcription factor circadian locomotor output cycles kaput (Clock) and brain and muscle Arnt-like protein-1 (Bmal1). By binding to E-box sequences in the promoters of Per1/2 and Cry1/2 genes, the CLOCK-BMAL1 heterodimer promotes the transcription of these genes. Per1/2 and Cry1/2 form a complex with the Clock/Bmal1 heterodimer and inactivate its transcriptional activities. Endometrial BMAL1 expression levels are lower in human recurrent-miscarriage sufferers. Additionally, it was shown that the presence of BMAL1-depleted decidual cells prevents trophoblast invasion, highlighting the importance of the endometrial clock throughout pregnancy. It is widely known that hormone synthesis is disturbed and sterility develops in Bmal1-deficient mice. Recently, we discovered that animals with uterus-specific Bmal1 loss also had poor placental development, and these mice also had intrauterine fetal death. Furthermore, it was shown that time-restricted feeding controlled the uterine clock's circadian rhythm. The uterine clock system may be a possibility for pregnancy complications, according to these results. We summarize the most recent research on the close connection between the circadian clock and reproduction in this review.

Effects of whole-body vibration on reproductive physiology in a rat model of whole-body vibration

Findings from epidemiological studies suggest that occupational exposure to whole-body vibration (WBV) may increase the risk of miscarriage and contribute to a reduction in fertility rates in both men and women. However, workers exposed to WBV may also be exposed to other risk factors that contribute to reproductive dysfunction. The goal of this experiment was to examine the effects of WBV on reproductive physiology in a rat model. Male and female rats were exposed to WBV at the resonant frequency of the torso (31.5 Hz, 0.3 g amplitude) for 4 hr/day for 10 days. WBV exposure resulted in a significant reduction in number of developing follicles, and decrease in circulating estradiol concentrations, ovarian luteinizing hormone receptor protein levels, and marked changes in transcript levels for several factors involved in follicular development, cell cycle, and steroidogenesis. In males, WBV resulted in a significant reduction in spermatids and circulating prolactin levels, elevation in number of males having higher circulating testosterone concentrations, and marked alterations in levels of transcripts associated with oxidative stress, inflammation, and factors involved in regulating the cell cycle. Based upon these findings data indicate that occupational exposure to WBV contributes to adverse alterations in reproductive physiology in both genders that may lead to reduction in fertility.

Skipping breakfast during pregnancy and hypertensive disorders of pregnancy in Japanese women: the Tohoku medical megabank project birth and three-generation cohort study

BACKGROUND

Hypertensive disorders of pregnancy (HDP) adversely affect the prognosis of mother and child, and the prognosis depends on the subtype of HDP. Skipping breakfast may be associated with increased blood pressure due to disruption of the circadian clock, but the association with the development of HDP has not been studied. The purpose of this study was to examine the association between skipping breakfast and the development of HDP and HDP subtypes in Japanese pregnant women.

METHODS

Of the pregnant women who participated in the Tohoku Medical Megabank Project Three-Generation Cohort Study, 18,839 who answered the required questions were included in the analysis. This study had a cross-sectional design. The breakfast intake frequency from pre-pregnancy to early pregnancy was classified into four groups: daily, 5-6 times per week, 3-4 times per week, and 0-2 times per week. HDP was classified into gestational hypertension (GH), chronic hypertension (CH), preeclampsia (PE), and severe preeclampsia (SuPE). Multiple logistic regression analysis and multinomial logistic analysis were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for breakfast intake frequency and development of HDP or HDP subtypes. We performed a stratified analysis based on energy intake.

RESULTS

Of the participants, 74.3% consumed breakfast daily, and 11.1% developed HDP. Women who consumed breakfast 0-2 times per week had a higher risk of HDP (OR: 1.33, 95% CI: 1.14-1.56), CH (OR: 1.63, 95% CI: 1.21-2.19), and PE (OR: 1.68, 95% CI: 1.27-2.21) than those who consumed breakfast daily. No association was found between skipping breakfast and the risk of developing GH (OR: 1.26, 95% CI: 0.99-1.61) and SuPE (OR: 0.91, 95% CI: 0.55-1.49). Stratified analysis showed that the risk of developing HDP due to skipping breakfast was highest in the group with the highest daily energy intake.

CONCLUSIONS

Skipping breakfast during pre-to early pregnancy is associated with the development of HDP. Further longitudinal studies are required to clarify the causal association between skipping breakfast and HDP.

Sustained effect of habitual feeding time on daily rhythm of core body temperature in mice

Background and aim

Circadian clocks in most peripheral tissues are entrained mainly by feeding. Therefore, this study aimed to investigate whether the daily rhythm of core body temperature (CBT), including the effect of diet-induced thermogenesis, varies according to habitual feeding time.

Methods

Wild-type and uncoupling protein 1 (UCP1) knockout mice were fed only during the first 4 h (Breakfast group) or the last 4 h of the dark period (Dinner group) for 17 days. On day 18, both groups were fed twice for 2 h, at the same starting times. Locomotor activity and CBT were measured continuously during the experiment.

Results

On day 18, CBT increased at the beginning of each feeding period, regardless of the group and strain. However, the CBT increase induced by the first meal decreased sharply in the Breakfast group and mildly in the Dinner group; the opposite was observed after the second meal. In UCP1 knockout, but not wild-type, mice, the total amount of CBT was significantly lower in the Dinner group than in the Breakfast group. These effects were mostly independent of the locomotor activity and food intake.

Conclusion

These results reveal that the effect of habitual feeding time on the daily rhythm of CBT is sustained at least until the following day. These effects may be mediated by both UCP1-dependent and -independent mechanisms.

Uterine Deletion of Bmal1 Impairs Placental Vascularization and Induces Intrauterine Fetal Death in Mice

Recently, it was demonstrated that the expression of BMAL1 was decreased in the endometrium of women suffering from recurrent spontaneous abortion. To investigate the pathological roles of uterine clock genes during pregnancy, we produced conditional deletion of uterine Bmal1 (cKO) mice and found that cKO mice could receive embryo implantation but not sustain pregnancy. Gene ontology analysis of microarray suggested that uterine NK (uNK) cell function was suppressed in cKO mice. Histological examination revealed the poor formation of maternal vascular spaces in the placenta. In contrast to WT mice, uNK cells in the spongiotrophoblast layer, where maternal uNK cells are directly in contact with fetal trophoblast, hardly expressed an immunosuppressive NK marker, CD161, in cKO mice. By progesterone supplementation, pregnancy could be sustained until the end of pregnancy in some cKO mice. Although this treatment did not improve the structural abnormalities of the placenta, it recruited CD161-positive NK cells into the spongiotrophoblast layer in cKO mice. These findings indicate that the uterine clock system may be critical for pregnancy maintenance after embryo implantation.

Randomized controlled trial for time-restricted eating in healthy volunteers without obesity

Time-restricted feeding (TRF) improves metabolic health. Both early TRF (eTRF, food intake restricted to the early part of the day) and mid-day TRF (mTRF, food intake restricted to the middle of the day) have been shown to have metabolic benefits. However, the two regimens have yet to be thoroughly compared. We conducted a five-week randomized trial to compare the effects of the two TRF regimens in healthy individuals without obesity (ChiCTR2000029797). The trial has completed. Ninety participants were randomized to eTRF (n=30), mTRF (n=30), or control groups (n=30) using a computer-based random-number generator. Eighty-two participants completed the entire five-week trial and were analyzed (28 in eTRF, 26 in mTRF, 28 in control groups). The primary outcome was the change in insulin resistance. Researchers who assessed the outcomes were blinded to group assignment, but participants and care givers were not. Here we show that eTRF was more effective than mTRF at improving insulin sensitivity. Furthermore, eTRF, but not mTRF, improved fasting glucose, reduced total body mass and adiposity, ameliorated inflammation, and increased gut microbial diversity. No serious adverse events were reported during the trial. In conclusion, eTRF showed greater benefits for insulin resistance and related metabolic parameters compared with mTRF. Clinical Trial Registration URL: http://www.chictr.org.cn/showproj.aspx?proj=49406.

Time-restricted eating, both early (eTRF) and mid-day (mTRF), have been shown to have metabolic benefits. Here the authors report a randomized controlled trial to compare the effects of eTRF and mTRF in healthy volunteers without obesity, and find that eTRF is more effective in improving the primary outcome insulin sensitivity.

Chronic Treatment with Metformin Has No Disrupting Effect on the Hepatic Circadian Clock in Mice

Background and Objectives: The antidiabetic agent metformin is known to activate AMP-activated protein kinase (AMPK) in various tissues. Because AMPK can modulate intracellular circadian clocks through regulating the stability of clock components, a single dose of metformin has been reported to affect circadian clocks in the peripheral tissues. In this study, therefore, we investigated whether chronic treatment with metformin causes the impairment of circadian clocks, especially if given at an inappropriate time. Materials and Methods: Non-diabetic C57BL/6J mice were allowed access to food only during 4 h at the beginning of the dark period, and repeatedly i.p. injected with a nearly maximum non-toxic dose of metformin, once daily either at 4 h after the beginning of the dark period or at the beginning of the light period. Diabetic ob/ob mice were given free access to food and treated with metformin in drinking water. Results: Under the controlled feeding regimen, 8-day treatment with metformin did not alter the mRNA expression rhythms of clock genes in both liver and adipose tissue of C57BL/6J mice, regardless of dosing time. In addition, chronic treatment with metformin for 2 weeks affected hepatic AMPK activation rhythm but did not disrupt the circadian clocks in the liver and adipose tissues of the ob/ob mice. Conclusions: These results mitigate concerns that treatment with metformin impairs peripheral circadian clocks, although confirmation is needed in humans.