Glycemic control is impaired in the evening in prediabetes through multiple diurnal rhythms

Association of largest meal timing and eating frequency with body mass index and obesity

BACKGROUND AND AIMS

The circadian pattern of eating behaviors has garnered increasing interest as a strategy for obesity prevention and weight loss. It is believed that the benefits stem from aligning food intake with the body's natural daily rhythms. However, the existing body of evidence is limited in scale and scope and there has been insufficient evaluation of temporal eating behaviors, such as the specific time of day in which the highest calorie consumption occurs, meal frequency, and distribution. This research aims to explore the association between the timing of the largest meal of the day and eating frequency with Body Mass Index (BMI) and obesity.

METHODS

Participants (n = 2050, 18-65y) were part of an exploratory cross-sectional and population-based research, with data collection in a virtual environment. Linear regression analyses and restricted cubic splines evaluated differences in BMI associated with independent eating variables [timing of the largest meal, number of meals/day (as continuous and categorical: ≤3 or >3/day), and each largest meal of the day (breakfast/lunch/dinner)]. Logistic regression models were fitted to assess Odds Ratios (OR) and 95 % Confidence Intervals (CI) of obesity associated with the same independent variables.

RESULTS

Our main findings were that the timing of the largest meal and reporting dinner as the largest meal were associated with higher values of BMI (respectively, 0.07 kg/m2 and 0.85 kg/m2) and increased odds of obesity [respectively OR(95%CI):1.04(1.01,1.08), and OR(95%CI):1.67(1.18,2.38)]. Those who realized more than 3 meals/day presented lower values of BMI (-0.14 kg/m2) and 32 % lower odds of having obesity [OR(95%CI):0.68(0.52,0.89)]. Reporting lunch as the largest meal also protected against obesity [OR(95%CI):0.71(0.54,0.93)]. These associations were statistically significant and independent of sex, age, marital status, education level, diet quality, sleep duration, and weekly frequency of physical exercise.

CONCLUSION

Having the largest meal earlier in the day, concentrating the majority of caloric intake during lunch, and consuming more than three meals a day, may present a promising intervention for preventing and treating obesity/overweight.

Metabolic health tracking using Ultrahuman M1 continuous glucose monitoring platform in non- and pre-diabetic Indians: a multi-armed observational study

Continuous glucose monitoring (CGM) device adoption in non- and pre-diabetics for preventive healthcare has uncovered a paucity of benchmarking data on glycemic control and insulin resistance for the high-risk Indian/South Asian demographic. Furthermore, the correlational efficacy between digital applications-derived health scores and glycemic indices lacks clear supportive evidence. In this study, we acquired glycemic variability (GV) using the Ultrahuman (UH) M1 CGM, and activity metrics via the Fitbit wearable for Indians/South Asians with normal glucose control (non-diabetics) and those with pre-diabetes (N = 53 non-diabetics, 52 pre-diabetics) for 14 days. We examined whether CGM metrics could differentiate between the two groups, assessed the relationship of the UH metabolic score (MetSc) with clinical biomarkers of dysglycemia (OGTT, HbA1c) and insulin resistance (HOMA-IR); and tested which GV metrics maximally correlated with inflammation (Hs-CRP), stress (cortisol), sleep, step count and heart rate. We found significant inter-group differences for mean glucose levels, restricted time in range (70-110 mg/dL), and GV-by-SD, all of which improved across days. Inflammation was strongly linked with specific GV metrics in pre-diabetics, while sleep and activity correlated modestly in non-diabetics. Finally, MetSc displayed strong inverse relationships with insulin resistance and dysglycemia markers. These findings present initial guidance GV data of non- and pre-diabetic Indians and indicate that digitally-derived metabolic scores can positively influence glucose management.

Photoperiod and metabolic health: evidence, mechanism, and implications

Circadian rhythms are evolutionarily programmed biological rhythms that are primarily entrained by the light cycle. Disruption of circadian rhythms is an important risk factor for several metabolic disorders. Photoperiod is defined as total duration of light exposure in a day. With the extended use of indoor/outdoor light, smartphones, television, computers, and social jetlag people are exposed to excessive artificial light at night increasing their photoperiod. Importantly long photoperiod is not limited to any geographical region, season, age, or socioeconomic group, it is pervasive. Long photoperiod is an established disrupter of the circadian rhythm and can induce a range of chronic health conditions including adiposity, altered hormonal signaling and metabolism, premature ageing, and poor psychological health. This review discusses the impact of exposure to long photoperiod on circadian rhythms, metabolic and mental health, hormonal signaling, and ageing and provides a perspective on possible preventive and therapeutic approaches for this pervasive challenge.

Chrononutrition in traditional European medicine-Ideal meal timing for cardiometabolic health promotion

Meal timing plays a crucial role for cardiometabolic health, given the circadian regulation of cardiometabolic function. However, to the best of our knowledge, no concept of meal timing exists in traditional European medicine (TEM). Therefore, in this narrative review, we aim to define the optimal time slot for energy intake and optimal energy distribution throughout the day in a context of TEM and explore further implications. By reviewing literature published between 2002 and 2022, we found that optimal timing for energy intake may be between 06:00 and 09:00, 12:00 and 14:00, and between 15:00 and 18:00, with high energy breakfast, medium energy lunch and low energy dinner and possibly further adjustments according to one's chronotype and genetics. Also, timing and distribution of energy intake may serve as a novel therapeutic strategy to optimize coction, a concept describing digestion and metabolism in TEM. Please cite this article as: Eberli NS, Colas L, Gimalac A. Chrononutrition in traditional European medicine-Ideal meal timing for cardiometabolic health promotion. J Integr Med. 2024; 22(2);115-125.

Understanding temporal changes and seasonal variations in glycemic trends using wearable data

Seasonal variations in glycemic trends remain largely unstudied despite the growing prevalence of diabetes. To address this gap, our objective is to investigate temporal changes in glycemic trends by analyzing intensively sampled blood glucose data from 137 patients (ages 2 to 76, primarily type 1 diabetes) over the course of 9 months to 4.5 years. From over 91,000 days of continuous glucose monitor data, we found that glycemic control decreases significantly around the holidays, with the largest decline observed on New Year's Day among the patients with already poor glycemic control (i.e., <55% time in the target range). We also observed seasonal variations in glycemic trends, with patients having worse glycemic control in the months of November to February (i.e., mid-fall and winter, in the United States), and better control in the months of April to August (i.e., mid-spring and summer). These insights are critical to inform targeted interventions that can improve diabetes outcomes.

A micro-randomized pilot study to examine the impact of just-in-time nudging on after-dinner snacking in adults with type 2 diabetes: A study protocol

AIM

To determine whether a digital nudge soon after dinner reduces after-dinner snacking events as measured objectively by continuous glucose monitoring (CGM) in patients with type 2 diabetes (T2D).

METHODS

This is a single-site micro-randomized trial (MRT). People with T2D, aged 18-75 years, managed with diet or a stable dose of oral antidiabetic medications for at least 3 months, and who habitual snack after dinner at least 3 nights per week, will be recruited. Picto-graphic nudges were designed by mixed research methods. After a 2-week lead-in phase to determine eligibility and snacking behaviours by a CGM detection algorithm developed by the investigators, participants will be micro-randomized daily (1:1) to a second 2-week period to either a picto-graphic nudge delivered-in-time (Intui Research) or no nudge. During lead-in and MRT phases, 24-hour glucose will be measured by CGM, sleep will be tracked by an under-mattress sleep sensor, and dinner timing will be captured daily by photographing the evening meal.

RESULTS

The primary outcome is the difference in the incremental area under the CGM curve between nudging and non-nudging days during the period from 90 minutes after dinner until 04:00 AM. Secondary outcomes include the effect of baseline characteristics on treatment, and comparisons of glucose peaks and time-in-range between nudging and non-nudging days. The feasibility of 'just-in-time' messaging and nudge acceptability will be evaluated, along with the analysis of sleep quality measures and their night-to-night variability.

CONCLUSIONS

This study will provide preliminary evidence of the impact of appropriately timed digital nudges on 24 -hour intertitial glucose levels resulting from altered after-dinner snacking in people with T2D. An exploratory sleep substudy will provide evidence of a bidirectional relationship between after-dinner snacking behaviour, glycaemia and sleep. Ultimately, this study will allow for the design of a future confirmatory study of the potential for digital nudging to improve health related behaviours and health outcomes.

Can Circadian Eating Pattern Adjustments Reduce Risk or Prevent Development of T2D?

Type 2 diabetes (T2D) is a chronic condition that occurs in insulin-resistant people with reduced glucose uptake. It is contributed to and exacerbated by a poor diet that results in accumulation of adipose tissue, high blood sugar, and other metabolic issues. Because humans have undergone food scarcity throughout history, our species has adapted a fat reserve genotype. This adaptation is no longer beneficial, as eating at a higher frequency than that of our ancestors has had a significant effect on T2D development. Eating at high frequencies disrupts the circadian clock, the circadian rhythm, and the composition of the gut microbiome, as well as hormone secretion and sensitivity. The current literature suggests an improved diet requires meal consistency, avoiding late-night eating, low meal frequency, and fasting to increase metabolic health. In addition, fasting as a treatment for T2D must be used correctly for beneficial results. Early time-restricted eating (TRE) provides many benefits such as improving insulin resistance, cognitive function, and glycemic control. Alternate-day fasting (ADF), 5:2 fasting, and long-term fasting all have benefits; however, they may be less advantageous than early TRE. Therefore, eating pattern adjustments can be used to reduce T2D if used correctly.

Light modulates glucose metabolism by a retina-hypothalamus-brown adipose tissue axis

Public health studies indicate that artificial light is a high-risk factor for metabolic disorders. However, the neural mechanism underlying metabolic modulation by light remains elusive. Here, we found that light can acutely decrease glucose tolerance (GT) in mice by activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) innervating the hypothalamic supraoptic nucleus (SON). Vasopressin neurons in the SON project to the paraventricular nucleus, then to the GABAergic neurons in the solitary tract nucleus, and eventually to brown adipose tissue (BAT). Light activation of this neural circuit directly blocks adaptive thermogenesis in BAT, thereby decreasing GT. In humans, light also modulates GT at the temperature where BAT is active. Thus, our work unveils a retina-SON-BAT axis that mediates the effect of light on glucose metabolism, which may explain the connection between artificial light and metabolic dysregulation, suggesting a potential prevention and treatment strategy for managing glucose metabolic disorders.

Chrono-exercise: Time-of-day-dependent physiological responses to exercise

Exercise is an effective strategy to prevent and improve obesity and related metabolic diseases. Exercise increases the metabolic demand in the body. Although many of the metabolic health benefits of exercise depend on skeletal muscle adaptations, exercise exerts many of its metabolic effects through the liver, adipose tissue, and pancreas. Therefore, exercise is the physiological state in which inter-organ signaling is most important. By contrast, circadian rhythms in mammals are associated with the regulation of several physiological and biological functions, including body temperature, sleep-wake cycle, physical activity, hormone secretion, and metabolism, which are controlled by clock genes. Glucose and lipid tolerance reportedly exhibit diurnal variations, being lower in the evening than in the morning. Therefore, the effects of exercise on substrate metabolism at different times of the day may differ. In this review, the importance of exercise timing considerations will be outlined, incorporating a chrono-exercise perspective.

Complex physiology and clinical implications of time-restricted eating

Time-restricted eating (TRE) is a dietary intervention that limits food consumption to a specific time window each day. The effect of TRE on body weight and physiological functions has been extensively studied in rodent models, which have shown considerable therapeutic effects of TRE and important interactions among time of eating, circadian biology, and metabolic homeostasis. In contrast, it is difficult to make firm conclusions regarding the effect of TRE in people because of the heterogeneity in results, TRE regimens, and study populations. In this review, we 1) provide a background of the history of meal consumption in people and the normal physiology of eating and fasting; 2) discuss the interaction between circadian molecular metabolism and TRE; 3) integrate the results of preclinical and clinical studies that evaluated the effects of TRE on body weight and physiological functions; 4) summarize other time-related dietary interventions that have been studied in people; and 4) identify current gaps in knowledge and provide a framework for future research directions.

The association of indoor heat exposure with diabetes and respiratory 9-1-1 calls through emergency medical dispatch and services documentation

BACKGROUND

People with pre-existing medical conditions, who spend a large proportion of their time indoors, are at risk of emergent morbidities from elevated indoor heat exposures. In this study, indoor heat of structures wherein exposed people received Grady Emergency Services based care in Atlanta, GA, U.S., was measured from May to September 2016.

METHOD

ology: In this case-control study, analyses were conducted to investigate the effect of indoor heat on the odds of 9-1-1 calls for diabetic (n = 90 cases) and separately, for respiratory (n = 126 cases), conditions versus heat-insensitive emergencies (n = 698 controls). Generalized Additive Models considered both linear and non-linear indoor heat and health outcome associations using thin-plate regression splines.

RESULTS

Hotter and more humid indoor conditions were non-linearly associated with an increasing likelihood of receiving emergency care for complications of diabetes and severe respiratory distress. Higher heat indices were associated with increased odds of a diabetes (odds ratio for change from 30 to 31 °C: 1.12, 95% CI: 1.08-1.16) or respiratory 9-1-1 medical call versus control (odds ratio for change from 34 to 35 °C: 1.18, 95% CI: 1.09-1.28) call. Both diabetic and respiratory distress patients were more likely to be African-American and/or have comorbidities.

CONCLUSIONS

In this study, the statistical association of indoor heat exposure with emergency morbidities (diabetic, respiratory) was demonstrated. The study also showcased the value and utility of data gathered by emergency medical dispatch and services from inaccessible private indoor sources (i.e., domiciles) for environmental health.

Circadian clock, diurnal glucose metabolic rhythm, and dawn phenomenon

The circadian clock provides cue-independent anticipatory signals for diurnal rhythms of baseline glucose levels and glucose tolerance. The central circadian clock is located in the hypothalamic suprachiasmatic nucleus (SCN), which comprises primarily GABAergic neurons. The SCN clock regulates physiological diurnal rhythms of endogenous glucose production (EGP) and hepatic insulin sensitivity through neurohumoral mechanisms. Disruption of the molecular circadian clock is associated with the extended dawn phenomenon (DP) in type 2 diabetes (T2D), referring to hyperglycemia in the early morning without nocturnal hypoglycemia. The DP affects nearly half of patients with diabetes, with poorly defined etiology and a lack of targeted therapy. Here we review neural and secreted factors in physiological diurnal rhythms of glucose metabolism and their pathological implications for the DP.

Metabolic state switches between morning and evening in association with circadian clock in non‐diabetic humans

Aims/Introduction

Understanding morning–evening variation in metabolic state is critical for managing metabolic disorders. We aimed to characterize this variation from the viewpoints of insulin secretion and insulin sensitivity, including their relevance to the circadian rhythm.

Materials and Methods

A total of 14 and 10 people without diabetes were enrolled, and underwent a 75‐g oral glucose tolerance test (OGTT) and hyperinsulinemic‐euglycemic clamp study, respectively. Participants completed the OGTT or hyperinsulinemic‐euglycemic clamp at 08.00 hours and 20.00 hours in random order. Before each study, hair follicles were collected. In mice, phosphorylation levels of protein kinase B were examined in the liver and muscle by western blotting.

Results

Glucose tolerance was better at 08 .00 hours, which was explained by the higher 1‐h insulin secretion on OGTT and increased skeletal muscle insulin sensitivity on hyperinsulinemic‐euglycemic clamp. Hepatic insulin sensitivity, estimated by the hepatic insulin resistance index on OGTT, was better at 20.00 hours. The 1‐h insulin secretion and hepatic insulin resistance index correlated significantly with Per2 messenger ribonucleic acid expression. The change (evening value – morning value) in the glucose infusion rate correlated significantly with the change in non‐esterified fatty acid, but not with clock gene expressions. The change in non‐esterified fatty acid correlated significantly with E4bp4 messenger ribonucleic acid expression and the change in cortisol. In mice, phosphorylation of protein kinase B was decreased in the liver and increased in muscle in the beginning of the active period as, expected from the human study.

Conclusions

Glucose metabolism in each tissue differed between the morning and evening, partly reflecting lipid metabolism, clock genes and cortisol levels. Deeper knowledge of these associations might be useful for ameliorating metabolic disorders.

A scoping review of intermittent fasting, chronobiology, and metabolism

Chronobiology plays a crucial role in modulating many physiologic systems in which there is nutritional synergism with meal timing. Given that intermittent fasting (IF) has grown as a flexible dietary method consisting of delayed or early eating windows, this scoping review addresses the effects of IF protocols on metabolism as they relate to clinical nutrition and the circadian system. Although nocturnal habits are associated with circadian misalignments and impaired cardiometabolic profile-and nutritional physiology is better orchestrated during the day-most findings are based on animal experiments or human studies with observational designs or acute meal tests. Well-controlled randomized clinical trials employing IF protocols of delayed or early eating windows have sometimes demonstrated clinical benefits, such as improved glycemic and lipid profiles, as well as weight loss. However, IF does not appear to be more effective than traditional diets at the group level, and its effects largely depend on energy restriction. Thus, efforts must be made to identify patient biological rhythms, preferences, routines, and medical conditions before individual dietary prescription in clinical practice.

The Effect of Early Time-Restricted Feeding on Glycemic Profile in Adults: A Systematic Review of Interventional Studies

BACKGROUND

Early time-restricted feeding (eTRF) is a new dietary strategy, involving extended fasting (>14h) from midafternoon onwards with or without calorie restriction. Most of the published studies indicate controversial effects on several glycemic markers.

AIM

To evaluate the effect of non-calorie restricted eTRF on the glycemic profile of adults.

METHOD

this systematic review was designed according to PRISMA guidelines. Pubmed/ Medline, the Cochrane library and EBSCO electronic databases were systematically searched for eligible clinical trials. Studies with eTRF or with daily fasting regimens that presented all the characteristics of eTRF were selected and compared with regular diet schedules or delayed time-restricted feeding. Blood glucose and insulin markers were extracted from each study as the main outcome measures.

RESULTS

Five articles including 67 adult subjects in total were selected. The period of intervention varied between 3 days to 5 weeks. Three of the included studies were diet- controlled for weight maintenance, whereas the other two studies allowed for free living. Quality assessment identified two studies of low and three studies of high risk of bias. two studies showed clear positive effects of eTRF on both glucose and insulin markers, including fasting glucose levels, muscle glucose intake, glucose iAUC responses insulin levels, and insulin resistance (p<0.05). Two other studies showed beneficial effects on glucose markers only (fasting glucose, 24h mean glucose levels, and iAUC responses, p<0.05) and the fifth study showed positive effects on insulin markers only (insulin resistance, p<0.05).

CONCLUSIONS

eTRF seems to have positive effects on the glycemic profile mainly in healthy individuals with normal BMI. However, other factors should also be taken into account to address overweight, obese, and prediabetic individuals. Further research is required to clarify better the effectiveness of eTRF among individuals with different characteristics.

Diurnal variations in muscle and liver glycogen differ depending on the timing of exercise

It has been suggested that glycogen functions not only in carbohydrate energy storage, but also as molecular sensors capable of activating lipolysis. This study aimed to compare the variation in liver and muscle glycogen during the day due to different timing of exercise. Nine healthy young men participated in two trials in which they performed a single bout of exercise at 70% of their individual maximal oxygen uptake for 60 min in the post-absorptive (morning) or post-prandial (afternoon) state. Liver and muscles glycogen levels were measured using carbon magnetic resonance spectroscopy (13C MRS). Diurnal variations in liver and muscle glycogen compared to baseline levels were significantly different depending on the timing of exercise. The effect of the timing of exercise on glycogen fluctuation is known to be related to a variety of metabolic signals, and the results of this study will be useful for future research on energy metabolism.

Associations between Fasting Duration, Timing of First and Last Meal, and Cardiometabolic Endpoints in the National Health and Nutrition Examination Survey

Background: Research indicates potential cardiometabolic benefits of energy consumption earlier in the day. This study examined the association between fasting duration, timing of first and last meals, and cardiometabolic endpoints using data from the National Health and Nutrition Examination Survey (NHANES). Methods: Cross-sectional data from NHANES (2005–2016) were utilized. Diet was obtained from one to two 24-h dietary recalls to characterize nighttime fasting duration and timing of first and last meal. Blood samples were obtained for characterization of C-reactive protein (CRP); glycosylated hemoglobin (HbA1c %); insulin; glucose; and high-density lipoprotein (HDL), low-density lipoprotein (LDL), and total cholesterol. Survey design procedures for adjusted linear and logistic regression were performed. Results: Every one-hour increase in nighttime fasting duration was associated with a significantly higher insulin and CRP, and lower HDL. Every one-hour increase in timing of the last meal of the day was statistically significantly associated with higher HbA1c and lower LDL. Every one-hour increase in first mealtime was associated with higher CRP (β = 0.044, p = 0.0106), insulin (β = 0.429, p < 0.01), and glucose (β = 0.662, p < 0.01), and lower HDL (β = −0.377, p < 0.01). Conclusion: In this large public health dataset, evidence for the beneficial effect of starting energy consumption earlier in the day on cardiometabolic endpoints was observed.

A Time to Eat and a Time to Exercise

Analogous to exercise training, time-restricted eating may rescue some of the deleterious effects on metabolic health induced by our modern-day lifestyle.

This Perspective for Progress provides a synopsis for the potential of time-restricted eating (TRE) to rescue some of the deleterious effects on circadian biology induced by our modern-day lifestyle. We provide novel insights into the comparative and potential complementary effects of TRE and exercise training on metabolic health.

Will Delaying Breakfast Mitigate the Metabolic Health Benefits of Time-Restricted Eating?

Eating out of phase with the biological clock induces circadian misalignment in peripheral organs and impairs glucose tolerance in preclinical models. Time-restricted eating (TRE) is a dietary approach that consolidates energy intake to 6 to 10 hours during the biologically active phase of the day, without necessarily altering diet quality and quantity. TRE induces pleiotropic metabolic benefits in mice, flies, and humans. Most studies have initiated TRE early in the biological morning. This perspective discusses the potential challenges in translating early TRE to the community and considers the potential metabolic consequences of delaying TRE.

Diurnal Regulation of Peripheral Glucose Metabolism: Potential Effects of Exercise Timing

Diurnal oscillations in energy metabolism are linked to the activity of biological clocks and contribute to whole-body glucose homeostasis. Postprandially, skeletal muscle takes up approximately 80% of circulatory glucose and hence is a key organ in maintenance of glucose homeostasis. Dysregulation of molecular clock components in skeletal muscle disrupts whole-body glucose homeostasis. Next to light-dark cycles, nonphotic cues such as nutrient intake and physical activity are also potent cues to (re)set (dys)regulated clocks. Physical exercise is one of the most potent ways to improve myocellular insulin sensitivity. Given the role of the biological clock in glucose homeostasis and the power of exercise to improve insulin sensitivity, one can hypothesize that there might be an optimal time for exercise to maximally improve insulin sensitivity and glucose homeostasis. In this review, we aim to summarize the available information related to the interaction of diurnal rhythm, glucose homeostasis, and physical exercise as a nonphotic cue to correct dysregulation of human glucose metabolism.

Time-Restricted Eating: Benefits, Mechanisms, and Challenges in Translation

Eating out of phase with daily circadian rhythms induces metabolic desynchrony in peripheral metabolic organs and may increase chronic disease risk. Time-restricted eating (TRE) is a dietary approach that consolidates all calorie intake to 6- to 10-h periods during the active phase of the day, without necessarily altering diet quality and quantity. TRE reduces body weight, improves glucose tolerance, protects from hepatosteatosis, increases metabolic flexibility, reduces atherogenic lipids and blood pressure, and improves gut function and cardiometabolic health in preclinical studies. This review discusses the importance of meal timing on the circadian system, the metabolic health benefits of TRE in preclinical models and humans, the possible mechanisms of action, the challenges we face in implementing TRE in humans, and the possible consequences of delaying initiation of TRE.

Morning Mastication Enhances Postprandial Glucose Metabolism in Healthy Young Subjects

Postprandial glucose concentration is dependent on the time of day and its concentration in the morning is lower than in the evening. However, whether it is dependent on mastication at different times of the day has not been studied before. We hypothesized that mastication affects insulin-mediated glucose metabolism differently in the morning and evening in healthy individuals. Firstly, nine healthy male volunteers (22.0 ± 0.7 SEM years, body mass index 22.0 ± 1.0 kg/m²) performed a 75-g oral glucose tolerance test (OGTT). One week after the OGTT, they participated in a high-carbohydrate food (rice) consumption test with 10 or 40 chews per mouthful. Each experiment was conducted in the morning (0800 h) and evening (2000 h) on the same day. Blood samples were collected before and at 30-min intervals for 120 min after glucose or rice consumption. The incremental area under the curve (iAUC) for glucose in the OGTT was significantly lower in the morning than in the evening, whereas the iAUC for insulin was similar at both times. In participants who chewed 40 times, the iAUC for glucose after rice consumption was significantly lower in the morning than in the evening but was similar at both times in individuals who chewed 10 times. Chewing 40 times in the morning (but not the evening) significantly increased insulin secretion at 30 min. This suggests that morning mastication improves early-phase insulin secretion after rice consumption. This novel finding may aid in reducing the incidence of obesity and type 2 diabetes mellitus.

Effects of a 12-week moderate-intensity exercise training on blood glucose response in patients with type 2 diabetes: A prospective longitudinal study

BACKGROUND

The blood glucose response to moderate-intensity exercise remains unclear for patients with type 2 diabetes (T2DM). In addition, little is known about determinants of blood glucose response to a 12-week moderate-intensity exercise training. Therefore, this study aimed to explore trends in blood glucose in response to a 12-week moderate-intensity exercise training in patients with T2DM and to explore the predictors of post-exercise blood glucose (PEBG) and exercise-induced glucose response (EIGR).

METHODS

A prospective longitudinal study was conducted. Of the 66 participants with T2DM recruited from outpatient clinics of a medical center, 20 were eligible to enroll in a 12-week moderate-intensity exercise training. Participants were randomly assigned to 1 of 3 exercise times (morning, afternoon, or evening). Blood glucose were measured pre- and post-exercise. The EIGR was calculated by subtracting the PEBG from the before-exercise blood glucose (BEBG). Generalized estimating equations were used to examine the trends and predictors of PEBG and EIGR.

RESULTS

The BEBG declined progressively (β = -1.69, P < .001); while the PEBG (β = -0.18, P = .08) remained stable over time during the 12-week exercise training. Higher BEBG predicted higher (β = 0.53, P < .001) PEBG. Higher baseline maximum oxygen uptake (VO2max) contributed to a larger magnitude of EIGR; higher HgbA1c and BEBG predicted higher EIGR (β = 0.27, P = .02; β = 0.45, P < .001); afternoon or evening exercise predicted lower (β = -13.2, P = .04; β = -5.96, P = .005) EIGR than did morning exercise.

CONCLUSIONS

A 12-week moderate-intensity exercise training appears safe for patients with T2DM. Time of day for exercise, baseline VO2max, and baseline metabolic control may influence the impact of exercise for individuals with T2DM. These findings provide considerations for design of optimal exercise training for T2DM patients.

Effect of diurnal variations in the carbohydrate and fat composition of meals on postprandial glycemic response in healthy adults: a novel insight for the second-meal phenomenon

Background

Meals, particularly carbohydrate intake, determine diurnal blood glucose (BG) excursions. However, the effect of meals with variable carbohydrate content on diurnal BG excursions remains poorly understood, despite routine consumption of meals that vary daily.

Objective

The aim of this study was to verify our hypothesis that glycemic response is elevated when a meal with a higher carbohydrate content follows a meal with a lower carbohydrate content.

Design

This was a secondary analysis of a study whose primary endpoint was energy metabolism (e.g., energy expenditure and substrate oxidation). This crossover study was designed to test BG responses to 3 types of meals with different macronutrient contents [regular meals (R), meals with a high-carbohydrate breakfast (CB), and meals with a high-fat breakfast (FB)] using a continuous glucose monitoring system. The R test included 3 meals/d with the same macronutrient composition; the CB test, a high-carbohydrate meal at breakfast, a high-fat meal at lunch, and a high-carbohydrate meal at dinner; and the FB test, a high-fat meal at breakfast, a high-carbohydrate meal at lunch, and a high-carbohydrate meal at dinner. Each test had similar daily macronutrient compositions, except CB and FB had larger variations in carbohydrate content than R. Fourteen healthy young men were tested in random order and underwent whole-body indirect calorimetry.

Results

Daily peak BG concentrations were higher for the CB (mean ± SD: 143.9 ± 25.3 mg/dL) and FB (140.2 ± 24.8 mg/dL) conditions than for the R condition (127.5 ± 15.7 mg/dL). Postprandial BG peaks after a high-carbohydrate meal were ∼20 mg/dL higher when a previous meal was relatively high-fat than when not high-fat (P < 0.05 for all). A multiple regression analysis indicated that the postprandial glycemic response was negatively associated with the preprandial respiratory quotient.

Conclusions

Our findings indicate that switching from high-fat to high-carbohydrate meals contributes to larger postprandial BG excursions, along with alterations in prioritization of carbohydrate utilization. This study was registered at the UMIN Clinical Trials Registry as UMIN000028895.

Circadian dysrhythmia-linked diabetes mellitus: Examining melatonin’s roles in prophylaxis and management

Diabetes mellitus is a chronic, life-threatening metabolic disorder that occurs worldwide. Despite an increase in the knowledge of the risk factors that are associated with diabetes mellitus, its worldwide prevalence has continued to rise; thus, necessitating more research into its aetiology. Recent researches are beginning to link a dysregulation of the circadian rhythm to impairment of intermediary metabolism; with evidences that circadian rhythm dysfunction might play an important role in the aetiology, course or prognosis of some cases of diabetes mellitus. These evidences thereby suggest possible relationships between the circadian rhythm regulator melatonin, and diabetes mellitus. In this review, we discuss the roles of the circadian rhythm in the regulation of the metabolism of carbohydrates and other macronutrients; with emphasis on the importance of melatonin and the impacts of its deficiency on carbohydrate homeostasis. Also, the possibility of using melatonin and its analogs for the “prophylaxis” or management of diabetes mellitus is also considered.

Circadian regulation of glucose, lipid, and energy metabolism in humans

The circadian system orchestrates metabolism in daily 24-hour cycles. Such rhythms organize metabolism by temporally separating opposing metabolic processes and by anticipating recurring feeding-fasting cycles to increase metabolic efficiency. Although animal studies demonstrate that the circadian system plays a pervasive role in regulating metabolism, it is unclear how, and to what degree, circadian research in rodents translates into humans. Here, we review evidence that the circadian system regulates glucose, lipid, and energy metabolism in humans. Using a range of experimental protocols, studies in humans report circadian rhythms in glucose, insulin, glucose tolerance, lipid levels, energy expenditure, and appetite. Several of these rhythms peak in the biological morning or around noon, implicating earlier in the daytime is optimal for food intake. Importantly, disruptions in these rhythms impair metabolism and influence the pathogenesis of metabolic diseases. We therefore also review evidence that circadian misalignment induced by mistimed light exposure, sleep, or food intake adversely affects metabolic health in humans. These interconnections among the circadian system, metabolism, and behavior underscore the importance of chronobiology for preventing and treating type 2 diabetes, obesity, and hyperlipidemia.

Molecular clock as a regulator of β-cell function

Molecular clocks are important for the circadian regulation of ß-cell function. DBP/E4BP4 plays central roles among clock-related genes in the metabolic regulation.

[Chrono-nutrition and n-3 polyunsaturated fatty acid]

Circadian clock system has been widely maintained in many spices from prokaryote to mammals. "Circadian" means "approximately day" in Latin, thus circadian rhythm means about 24 hour rhythms. The earth revolves once every 24 hours, and our circadian system has been developed for adjusting to this 24 hour cycles, to get sun light information for getting their foods or for alive in birds or mammals. We have two different circadian systems so-called main oscillator located in the suprachiasmatic nucleus (SCN) of the hypothalamus, and local oscillator located in the various peripheral organ tissues such as liver, kidney and skeletal muscle. The SCN is directly entrained by light-dark information through retinal-hypothalamic tract, and then organizes local clock in peripheral tissues via many pathways including neural and hormonal functions. On the other hand, peripheral local clocks are entrained by feeding, exercise and stress stimuli through several cell signaling. Foods (protein, carbohydrate, and lipid) are important regulator of circadian clocks in peripheral tissues. Thus, controlling the timing of food consumption and food composition, a concept known as chrononutrition, is one area of active research to aid recovery from many physiological dysfunctions. In this review, we focus on molecular mechanisms of entrainment and the relationships between circadian clock systems and n-3 polyunsaturated fatty acid. We concentrate on experimental data obtained from cells or animals and humans and discuss how these findings translate into clinical research, and we highlight the latest developments in chrononutritional studies.

Cortisol: Mediator of association between Alzheimer's disease and diabetes mellitus?

Numerous epidemiologic studies have identified an independent association between Alzheimer's disease (AD) and diabetes mellitus (DM), which remains unexplained. This review contends that the association is mediated by mild hypercortisolemia that is manifested in AD by early stages, as empirical evidence indicates that hypercortisolemia is diabetogenic even at subclinical levels. Subclinical Cushing's syndrome is discussed as the paradigm. It is proposed that hypercortisolemia increases the risk of pre-diabetes and DM during early AD and the preceding decades. That hypercortisolemia is exhibited during the AD prodromal stage has yet to be determined, but may be inferred from concurrent metabolic parameters as documented in the literature. Studies refuting association between AD and DM also are evaluated, and the relationship between AD and DM is deduced to be more complex than directly causal, with DM of longstanding duration having a protective role. Association between DM and AD may require reappraisal by APOE ε4 carrier status, in view of newly identified roles of APOE ε4 in pre-diabetes. That association of APOE ε4 with DM in AD may have been underestimated in epidemiologic studies also is highlighted. At the core of arguments and mechanisms presented in this review is the circadian rhythm of cortisol secretion, which is the main determinant of glycemic control in humans. Alterations to that rhythm and to the hypothalamic-pituitary-adrenal axis occurring in AD are examined. Consequently the cause of hypercortisolemia in AD, and therefore of association between AD and DM, is proposed to be adrenal hyper-responsiveness to adrenocorticotropic hormone.

Carbohydrates from Sources with a Higher Glycemic Index during Adolescence: Is Evening Rather than Morning Intake Relevant for Risk Markers of Type 2 Diabetes in Young Adulthood?

Background: This study investigated whether glycemic index (GI) or glycemic load (GL) of morning or evening intake and morning or evening carbohydrate intake from low- or higher-GI food sources (low-GI-CHO, higher-GI-CHO) during adolescence are relevant for risk markers of type 2 diabetes in young adulthood. Methods: Analyses included DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study participants who had provided at least two 3-day weighed dietary records (median: 7 records) during adolescence and one blood sample in young adulthood. Using multivariable linear regression analyses, estimated morning and evening GI, GL, low-GI-CHO (GI < 55) and higher-GI-CHO (GI ≥ 55) were related to insulin sensitivity (N = 252), hepatic steatosis index (HSI), fatty liver index (FLI) (both N = 253), and a pro-inflammatory-score (N = 249). Results: Morning intakes during adolescence were not associated with any of the adult risk markers. A higher evening GI during adolescence was related to an increased HSI in young adulthood (p = 0.003). A higher consumption of higher-GI-CHO in the evening was associated with lower insulin sensitivity (p = 0.046) and an increased HSI (p = 0.006), while a higher evening intake of low-GI-CHO was related to a lower HSI (p = 0.009). Evening intakes were not related to FLI or the pro-inflammatory-score (all p > 0.1). Conclusion: Avoidance of large amounts of carbohydrates from higher-GI sources in the evening should be considered in preventive strategies to reduce the risk of type 2 diabetes in adulthood.

Priming Effect of a Morning Meal on Hepatic Glucose Disposition Later in the Day

We used hepatic balance and tracer ([³H]glucose) techniques to examine the impact of "breakfast" on hepatic glucose metabolism later in the same day. From 0-240 min, 2 groups of conscious dogs (n = 9 dogs/group) received a duodenal infusion of glucose (GLC) or saline (SAL), then were fasted from 240-360 min. Three dogs from each group were euthanized and tissue collected at 360 min. From 360-600 min, the remaining dogs underwent a hyperinsulinemic (4× basal) hyperglycemic clamp (arterial blood glucose 146 ± 2 mg/dL) with portal GLC infusion. The total GLC infusion rate was 14% greater in dogs infused with GLC than in those receiving SAL (AUC_360-600min 2,979 ± 296 vs. 2,597 ± 277 mg/kg, respectively). The rates of hepatic glucose uptake (5.8 ± 0.8 vs. 3.2 ± 0.3 mg ⋅ kg^-1 ⋅ min^-1) and glycogen storage (4.7 ± 0.6 vs. 2.9 ± 0.3 mg ⋅ kg^-1 ⋅ min^-1) during the clamp were markedly greater in dogs receiving GLC compared with those receiving SAL. Hepatic glycogen content was ∼50% greater, glycogen synthase activity was ∼50% greater, glycogen phosphorylase activity was ∼50% lower, and the amount of phosphorylated glycogen synthase was 34% lower, indicating activation of the enzyme, in dogs receiving GLC compared with those receiving SAL. Thus, morning GLC primed the liver to extract and store more glucose in the presence of hyperinsulinemic hyperglycemia later in the same day, indicating that breakfast enhances the liver's role in glucose disposal in subsequent same-day meals.

Clock Gene Dysregulation Induced by Chronic ER Stress Disrupts β-cell Function

In Wfs1^-/-A^y/a islets, in association with endoplasmic reticulum (ER) stress, D-site-binding protein (Dbp) expression decreased and Nuclear Factor IL-3 (Nfil3)/E4 Promoter-binding protein 4 (E4bp4) expression increased, leading to reduced DBP transcriptional activity. Similar alterations were observed with chemically-induced ER stress. Transgenic mice expressing E4BP4 under the control of the mouse insulin I gene promoter (MIP), in which E4BP4 in β-cells is expected to compete with DBP for D-box, displayed remarkable glucose intolerance with severely impaired insulin secretion. Basal ATP/ADP ratios in MIP-E4BP4 islets were elevated without the circadian oscillations observed in wild-type islets. Neither elevation of the ATP/ADP ratio nor an intracellular Ca2+ response was observed after glucose stimulation. RNA expressions of genes involved in insulin secretion gradually increase in wild-type islets early in the feeding period. In MIP-E4BP4 islets, however, these increases were not observed. Thus, molecular clock output DBP transcriptional activity, susceptible to ER stress, plays pivotal roles in β-cell priming for insulin release by regulating β-cell metabolism and gene expressions. Because ER stress is also involved in the β-cell failure in more common Type-2 diabetes, understanding the currently identified ER stress-associated mechanisms warrants novel therapeutic and preventive strategies for both rare form and common diabetes.

The effect of diurnal distribution of carbohydrates and fat on glycaemic control in humans: a randomized controlled trial

Diurnal carbohydrate and fat distribution modulates glycaemic control in rodents. In humans, the optimal timing of both macronutrients and its effects on glycaemic control after prolonged consumption are not studied in detail. In this cross-over trial, 29 non-obese men were randomized to two four-week diets: (1) carbohydrate-rich meals until 13.30 and fat-rich meals between 16.30 and 22.00 (HC/HF) versus (2) inverse sequence of meals (HF/HC). After each trial period two meal tolerance tests were performed, at 09.00 and 15.40, respectively, according to the previous intervention. On the HF/HC diet, whole-day glucose level was increased by 7.9% (p = 0.026) in subjects with impaired fasting glucose and/or impaired glucose tolerance (IFG/IGT, n = 11), and GLP-1 by 10.2% (p = 0.041) in normal glucose-tolerant subjects (NGT, n = 18). Diet effects on fasting GLP-1 (p = 0.009) and PYY (p = 0.034) levels were observed in IFG/IGT, but not in NGT. Afternoon decline of glucose tolerance was more pronounced in IFG/IGT and associated with a stronger decrease of postprandial GLP-1 and PYY levels, but not with changes of cortisol rhythm. In conclusion, the HF/HC diet shows an unfavourable effect on glycaemic control in IFG/IGT, but not in NGT subjects. Consequently, large, carbohydrate-rich dinners should be avoided, primarily by subjects with impaired glucose metabolism.

Matching Meals to Body Clocks-Impact on Weight and Glucose Metabolism

The prevalence of type 2 diabetes continues to rise worldwide and is reaching pandemic proportions. The notion that this is due to obesity, resulting from excessive energy consumption and reduced physical activity, is overly simplistic. Circadian de-synchrony, which occurs when physiological processes are at odds with timing imposed by internal clocks, also promotes obesity and impairs glucose tolerance in mouse models, and is a feature of modern human lifestyles. The purpose of this review is to highlight what is known about glucose metabolism in animal and human models of circadian de-synchrony and examine the evidence as to whether shifts in meal timing contribute to impairments in glucose metabolism, gut hormone secretion and the risk of type 2 diabetes. Lastly, we examine whether restricting food intake to discrete time periods, will prevent or reverse abnormalities in glucose metabolism with the view to improving metabolic health in shift workers and in those more generally at risk of chronic diseases such as type 2 diabetes and cardiovascular disease.

Endocrine and metabolic diurnal rhythms in young adult men born small vs appropriate for gestational age

OBJECTIVE

Sleep disturbances and alterations of diurnal endocrine rhythms are associated with increased risk of type 2 diabetes (T2D). We previously showed that young men born small for gestational age (SGA) and with increased risk of T2D have elevated fat and decreased glucose oxidation rates during nighttime. In this study, we investigated whether SGA men have an altered diurnal profile of hormones, substrates and inflammatory markers implicated in T2D pathophysiology compared with matched individuals born appropriate for gestational age (AGA).

METHODS

We collected hourly blood samples for 24 h, to measure levels of glucose, free fatty acids (FFA), triglycerides (TG), insulin, C-peptide, leptin, resistin, ghrelin, plasminogen activator inhibitor-1 (PAI-1), incretins (GLP-1 and GIP), and inflammatory markers (TNF-α and IL-6) in 13 young men born SGA and 11 young men born AGA.

RESULTS

Repeated measurements analyses were used to analyze the diurnal variations and differences between groups. The SGA subjects had increased 24-h glucose (P=0.03), glucagon (P=0.03) and resistin (P=0.003) levels with no difference in diurnal rhythms compared with AGA controls. We found significant diurnal variations in levels of blood glucose, plasma TG, FFA, insulin, C-peptide, GLP-1, GIP, leptin, visfatin, TNF-α, IL-6 and PAI-1. The variation in FFA levels differed between the groups during the evening. Plasma ghrelin and glucagon levels did not display diurnal variations.

CONCLUSIONS

Young men born SGA exhibit elevated 24-h blood glucose, and plasma glucagon and resistin levels with no major differences in diurnal rhythms of these or other key metabolic hormones, substrates or inflammatory markers implicated in the origin of adiposity and T2D.

Circulating cell-free mitochondrial DNA as the probable inducer of early endothelial dysfunction in the prediabetic patient

Recent evidence has shown that 346million people in the world have diabetes mellitus (DM); this number will increase to 439million by 2030. In addition, current data indicate an increase in DM cases in the population between 40 and 59years of age. Diabetes is associated with the development of micro- and macro-vascular complications, derived from chronic hyperglycemia on the endothelium. Some reports demonstrate that people in a prediabetic state have a major risk of developing early endothelial dysfunction (ED). Today, it is accepted that individuals considered as prediabetic patients are in a pro-inflammatory state associated with endothelial and mitochondrial dysfunction. It is important to mention that impaired mitochondrial functionality has been linked to endothelial apoptosis and release of mitochondrial DNA (mtDNA) in patients with sepsis, cardiac disease, or atherosclerosis. This free mtDNA could promote ED, as well as other side effects on the vascular system through the activation of the toll-like receptor 9 (TLR9). TLR9 is expressed in different cell types (e.g., T or B lymphocytes, mastocytes, and epithelial and endothelial cells). It is localized intracellularly and recognizes non-methylated dinucleotides of viral, bacterial, and mitochondrial DNA. Recently, it has been reported that TLR9 is associated with the pathogenesis of lupus erythematosus, rheumatoid arthritis, and autoimmune diabetes. In this work, it is hypothesized that the increase in the levels of circulating mtDNA is the trigger of early ED in the prediabetic patient, and later on in the older patient with diabetes, through activation of the TLR9 present in the endothelium.