Therapeutic Potential of Various Intermittent Fasting Regimens in Alleviating Type 2 Diabetes Mellitus and Prediabetes: A Narrative Review

Intermittent fasting has drawn significant interest in the clinical research community due to its potential to address metabolic complications such as obesity and type 2 diabetes mellitus. Various intermittent fasting regimens include alternate-day fasting (24 h of fasting followed by 24 h of eating), time-restricted fasting (fasting for 14 h and eating within a 10 h window), and the 5:2 diet (fasting for two days and eating normally for the other five days). Intermittent fasting is associated with a reduced risk of type 2 diabetes mellitus-related complications and can slow their progression. The increasing global prevalence of type 2 diabetes mellitus highlights the importance of early management. Since prediabetes is a precursor to type 2 diabetes mellitus, understanding its progression is essential. However, the long-term effects of intermittent fasting on prediabetes are not yet well understood. Therefore, this review aims to comprehensively compile existing knowledge on the therapeutic effects of intermittent fasting in managing type 2 diabetes mellitus and prediabetes.

Intermittent Fasting: Myths, Fakes and Truth on This Dietary Regimen Approach

Intermittent fasting (IF) has been indicated as a valuable alternative to the classical caloric restriction dietary regimen for lowering body weight and preventing obesity-related complications, such as metabolic syndrome and type II diabetes. However, is it effective? In this review article, we analyzed over 50 clinical studies in which IF, conducted by alternate day fasting (ADF) or time-restricted feeding (TRF), was compared with the caloric restriction approach. We evaluated the different roles of IF in treating and preventing human disorders such as metabolic syndrome, type II diabetes, and some types of cancer, as well as the usefulness of IF in reducing body weight and cardiovascular risk factors such as hypertension. Furthermore, we explored the cellular pathways targeted by IF to exert their beneficial effects by activating effector proteins that modulate cell functions and resistance to oxidative stress. In contrast, we investigated concerns regarding human health related to the adoption of IF dietary regimens, highlighting the profound debate surrounding weight loss regimens. We examined and compared several clinical trials to formulate an updated concept regarding IF and its therapeutic potential.

Effects of Early and Late Time-Restricted Feeding on Parameters of Metabolic Health: An Explorative Literature Assessment

Chrono-nutrition (meal timing) aligns food consumption with one's circadian rhythm. The first meal (e.g., breakfast) likely promotes synchronization of peripheral circadian clocks, thereby supporting metabolic health. Time-restricted feeding (TRF) has been shown to reduce body weight (BW) and/or improve cardiovascular biomarkers. In this explorative literature assessment, 13 TRF randomized controlled trials (RCTs) were selected from PubMed and Scopus to evaluate the effects of early (eTRF: first meal before 10:30 a.m.) and late TRF (lTRF: first meal after 11:30 a.m.) on parameters of metabolic health. Although distinct variations in study design were evident between reports, TRF consistently decreased energy intake (EI) and BW, and improved insulin resistance as well as systolic blood pressure. eTRF seemed to have a greater beneficial effect than lTRF on insulin resistance (HOMA-IR). Importantly, most studies did not appear to consider chronotype in their evaluation, which may have underestimated TRF effects. TRF intervention may be a promising approach for risk reduction of human metabolic diseases. To conclusively determine benefits of TRF and identify clear differences between eTRF and lTRF, future studies should be longer-term (≥8 weeks) with well-defined (differences in) feeding windows, include participants chronotypically matching the intervention, and compare outcomes to those of control groups without any dietary limitations.

The Effect of Early Time-Restricted Eating vs Later Time-Restricted Eating on Weight Loss and Metabolic Health

CONTEXT

It remains controversial whether the choice of the daily eating window early or later in time-restricted eating (TRE) intervention (early or later TRE) has different effects on weight loss and metabolic health.

OBJECTIVE

A network meta-analysis was performed to evaluate the efficacy between early and later TRE in adults with obesity or overweight.

METHODS

We searched PubMed, Embase, Web of Science, and Cochrane Library for randomized controlled trials (RCTs) published until October 16, 2022. We conducted a network meta-analysis to evaluate the efficacy of early and later TRE on body weight and metabolic parameters, including glycemic metabolism, blood pressure, and lipid profiles.

RESULTS

Twelve RCTs with 730 obese or overweight adults were included in this meta-analysis. Early TRE and later TRE both elicited moderate reductions in body weight and insulin resistance (IR) (homeostasis model assessment of IR) when compared to non-TRE. Interestingly, early TRE showed more effectiveness than later TRE in improving IR (early vs later TRE: -0.44; 95% CI, -0.86 to -0.02; P < .05), whereas no statistically significant difference was detected in weight loss (early vs later TRE: -0.31 kg; 95% CI, -1.15 to 0.53 kg; P >.05). In addition, early TRE rather than later TRE showed significant benefits in glycemic metabolism and blood pressure when compared to non-TRE. No significant differences between early and later TRE were observed for fasting blood glucose, blood pressure, and lipid profiles.

CONCLUSION

This meta-analysis suggests that people may choose early TRE for more effective weight management and metabolic benefits. Nevertheless, further large-scale RCTs are warranted to verify our findings.

Influence of Aging, Macronutrient Composition and Time-Restricted Feeding on the Fischer344 x Brown Norway Rat Gut Microbiota

Both ketogenic diets (KD) and time-restricted feeding (TRF) regimens have the ability to influence several parameters of physical health, including gut microbiome composition and circulating cytokine concentration. Moreover, both of these dietary interventions prevent common impairments associated with the aging process. However, significantly altering macronutrient intake, which is required for a KD, may be unappealing to individuals and decrease compliance to dietary treatments. In contrast to a KD, TRF allows individuals to continue eating the foods they are used to, and only requires a change in the time of day at which they eat. Therefore, we investigated both a KD and a diet with a more Western-like macronutrient profile in the context of TRF, and compared both diets to animals allowed access to standard chow ad libitum in young adult and aged rats. While limited effects on cytokine levels were observed, both methods of microbiome analysis (16S sequencing and metagenomics) indicate that TRF and KDs significantly altered the gut microbiome in aged rats. These changes were largely dependent on changes to feeding paradigm (TRF vs. ad libitum) alone regardless of macronutrient content for many gut microbiota, but there were also macronutrient-specific changes. Specifically, functional analysis indicates significant differences in several pathways, including those involved in the tricarboxylic acid (TCA) cycle, carbohydrate metabolism and neurodegenerative disease. These data indicate that age- and disease-related gut dysbiosis may be ameliorated through the use of TRF with both standard diets and KDs.

Effects of Early vs. Late Time-Restricted Eating on Cardiometabolic Health, Inflammation, and Sleep in Overweight and Obese Women: A Study Protocol for the ChronoFast Trial

Background: Time-restricted eating is a promising dietary strategy for weight loss, glucose and lipid metabolism improvements, and overall well-being. However, human studies demonstrated contradictory results for the restriction of food intake to the beginning (early TRE, eTRE) or to the end of the day (late TRE, lTRE) suggesting that more carefully controlled studies are needed.

Objective: The aim of the ChronoFast trial study is to determine whether eTRE or lTRE is a better dietary approach to improve cardiometabolic health upon minimized calorie deficits and nearly stable body weight.

Methods: Here, we present the study protocol of the randomized cross-over ChronoFast clinical trial comparing effects of 2 week eTRE (8:00 to 16:00 h) and lTRE (13:00 to 21:00 h) on insulin sensitivity and other glycemic traits, blood lipids, inflammation, and sleep quality in 30 women with overweight or obesity and increased risk of type 2 diabetes. To ensure timely compliance and unchanged dietary composition, and to minimize possible calorie deficits, real-time monitoring of dietary intake and body weight using a smartphone application, and extensive nutritional counseling are performed. Continuous glucose monitoring, oral glucose tolerance test, 24 h activity tracking, questionnaires, and gene expression analysis in adipose tissue and blood monocytes will be used for assessment of study outcomes.

Discussion: The trial will determine whether eTRE or lTRE is more effective to improve cardiometabolic health, elucidate underlying mechanisms, and contribute to the development of recommendations for medical practice and the wider population.

Clinical Trial Registration:www.ClinicalTrials.gov, Identifier [NCT04351672]

The Window Matters: A Systematic Review of Time Restricted Eating Strategies in Relation to Cortisol and Melatonin Secretion

Time-Restricted Eating is an eating pattern based on the circadian rhythm which limits daily food intake (usually to ≤12 h/day), unique in that no overt restriction is imposed on the quality, nor quantity, of food intake. This paper aimed to examine the effects of two patterns of TRE, traditional TRE, and Ramadan fasting, on two markers of circadian rhythm, cortisol and melatonin. PubMed and Web of Science were searched up to December 2020 for studies examining the effects of time restricted eating on cortisol and melatonin. Fourteen studies met our inclusion criteria. All Ramadan papers found statistically significant decrease in melatonin (p < 0.05) during Ramadan. Two out of the three Ramadan papers noted an abolishing of the circadian rhythm of cortisol (p < 0.05). The non-Ramadan TRE papers did not examine melatonin, and cortisol changes were mixed. In studies comparing TRE to control diets, Stratton et al. found increased cortisol levels in the non-TRE fasting group (p = 0.0018) and McAllister et al. noted no difference. Dinner-skipping resulted in significantly reduced evening cortisol and non-significantly raised morning cortisol. Conversely, breakfast skipping resulted in significantly reduced morning cortisol. This blunting indicates a dysfunctional HPA axis, and may be associated with poor cardio-metabolic outcomes. There is a paucity of research examining the effects of TRE on cortisol and melatonin. The contrasting effect of dinner and breakfast-skipping should be further examined to ascertain whether timing the feeding window indeed has an impact on circadian rhythmicity.

Identification of factors influencing motivation to undertake time-restricted feeding in humans

The interaction between time of day and energy intake, termed chrono-nutrition, has received considerable recent interest. One aspect of chrono-nutrition with potential to benefit long-term cardio-metabolic health is time-restricted feeding (TRF). Current support for TRF primarily derives from animal research, although recent small-scale human studies indicate possible translational benefit. Whether free-living humans, however, can incorporate TRF into their daily lives is poorly understood. This study reports data from participants (n = 608) who completed an online questionnaire to investigate daily routine, likelihood of TRF incorporation within work vs free-days, and key considerations influencing TRF uptake. The majority of participants reported a typical daily feeding window (time between first and last energy intake) of between 10 and 14 h on workdays and free days, 62.7 and 65.5% respectively. Likelihood of adherence to TRF declined with an increase in the proposed restriction of the feeding window by 0.5 to 4-h per day. We then examined data from participants with a typical daily feeding window of 12+ h on workdays (n = 221) and free-days (n = 223) to investigate the likelihood of using TRF, and the most important considerations in making this decision. Of these participants, (n = 132) on workdays and (n = 125) on free days would likely reduce their feeding window by 3-h. Multiple regression analysis revealed that key considerations determining the likelihood of adopting TRF were: cost, time availability, and perceived health benefits (on workdays); wake time, bed time, time availability, motivation to change and perceived health benefits (on free-days). These data provide novel information regarding public attitudes towards TRF and highlight important aspects to be considered when translating controlled laboratory studies to public dietary advice.