Effects of Intermittent Fasting in Human Compared to a Non-intervention Diet and Caloric Restriction: A Meta-Analysis of Randomized Controlled Trials

Intermittent fasting and health outcomes: an umbrella review of systematic reviews and meta-analyses of randomised controlled trials

Background

Benefits of Intermittent fasting (IF) on health-related outcomes have been found in a range of randomised controlled trials (RCTs). Our umbrella review aimed to systematically analyze and synthesize the available causal evidence on IF and its impact on specific health-related outcomes while evaluating its evidence quality.

Methods

We comprehensively searched the PubMed, Embase, Web of Science, and Cochrane databases (from inception up to 8 January 2024) to identify related systematic reviews and meta-analyses of RCTs investigating the association between IF and human health outcomes. We recalculated the effect sizes for each meta-analysis as mean difference (MD) or standardized mean difference (SMD) with corresponding 95% confidence intervals (CIs). Subgroup analyses were performed for populations based on three specific status: diabetes, overweight or obesity, and metabolic syndrome. The quality of systematic reviews was evaluated using A Measurement Tool to Assess Systematic Reviews (AMSTAR), and the certainty of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) system. This study is registered with PROSPERO (CRD42023382004).

Findings

A total of 351 associations from 23 meta-analyses with 34 health outcomes were included in the study. A wide range of outcomes were investigated, including anthropometric measures (n = 155), lipid profiles (n = 83), glycemic profiles (n = 57), circulatory system index (n = 41), appetite (n = 9), and others (n = 6). Twenty-one (91%) meta-analyses with 346 associations were rated as high confidence according to the AMSTAR criteria. The summary effects estimates were significant at p < 0.05 in 103 associations, of which 10 (10%) were supported by high certainty of evidence according to GRADE. Specifically, compared with non-intervention diet in adults with overweight or obesity, IF reduced waist circumference (WC) (MD = -1.02 cm; 95% CI: -1.99 to -0.06; p = 0.038), fat mass (MD = -0.72 kg; 95% CI: -1.32 to -0.12; p = 0.019), fasting insulin (SMD = -0.21; 95% CI: -0.40 to -0.02; p = 0.030), low-density lipoprotein cholesterol (LDL-C) (SMD = -0.20; 95% CI: -0.38 to -0.02; p = 0.027), total cholesterol (TC) (SMD = -0.29; 95% CI: -0.48 to -0.10; p = 0.003), and triacylglycerols (TG) (SMD = -0.23; 95% CI: -0.39 to -0.06; p = 0.007), but increased fat free mass (FFM) (MD = 0.98 kg; 95% CI: 0.18-1.78; p = 0.016). Of note, compared with the non-intervention diet, modified alternate-day fasting (MADF) reduced fat mass (MD = -0.70 kg; 95% CI: -1.38 to -0.02; p = 0.044). In people with overweight or obesity, and type 2 diabetes, IF increases high-density lipoprotein cholesterol (HDL-C) levels compared to continuous energy restriction (CER) (MD = 0.03 mmol/L; 95% CI: 0.01-0.05; p = 0.010). However, IF was less effective at reducing systolic blood pressure (SBP) than a CER diet in adults with overweight or obesity (SMD = 0.21; 95% CI: 0.05-0.36; p = 0.008).

Interpretation

Our findings suggest that IF may have beneficial effects on a range of health outcomes for adults with overweight or obesity, compared to CER or non-intervention diet. Specifically, IF may decreased WC, fat mass, LDL-C, TG, TC, fasting insulin, and SBP, while increasing HDL-C and FFM. Notably, it is worth noting that the SBP lowering effect of IF appears to be weaker than that of CER.

Funding

This work was supported by the National Key Research and Development Program of China (Q-JW), the Natural Science Foundation of China (Q-JW and T-TG), Outstanding Scientific Fund of Shengjing Hospital of China Medical University (Q-JW), and 345 Talent Project of Shengjing Hospital of China Medical University (T-TG).

Metabolic changes with intermittent fasting

BACKGROUND

The prevalence of obesity is rising globally and effective strategies to treat obesity are needed. Intermittent fasting, a dietary intervention for weight management, has received growing interest from the general public, as well as healthcare professionals, as a form of lifestyle intervention.

METHODS

We executed a rapid review using PUBMED database to identify systematic reviews that examined the impact of intermittent fasting on metabolic indices, published between 2011 and 2022.

RESULTS

Intermittent fasting leads to weight loss of a similar magnitude to continuous energy restriction. Most of the evidence shows that intermittent fasting leads to greater fat loss as measured by fat mass (kg) or body fat percentage compared to an ad libitum diet, but fat loss attained during intermittent fasting is not significantly different to continuous energy restriction, although recent evidence shows intermittent fasting to be superior. There is mixed evidence for the impact of intermittent fasting on insulin resistance, fasting glucose and lipid profile. Some studies focused on populations of Muslim people, which showed that Ramadan fasting may lead to weight loss and improvement of metabolic parameters during fasting, although the effects are reversed when fasting is finished.

CONCLUSIONS

Intermittent fasting is more effective than an ad libitum dietary intake, and equally or more effective as continuous energy restriction, for weight management. However, there is inconclusive evidence on whether intermittent fasting has a clinically beneficial effect on glucose and lipid metabolism.

Combined versus independent effects of exercise training and intermittent fasting on body composition and cardiometabolic health in adults: a systematic review and meta-analysis

INTRODUCTION AND AIM

Exercise training (Ex) and intermittent fasting (IF) are effective for improving body composition and cardiometabolic health overweight and obese adults, but whether combining Ex and IF induces additive or synergistic effects is less well established. We therefore, performed a systematic review and meta-analysis to compare the combined versus independent effects of Ex and IF on body composition and cardiometabolic health in adults.

METHOD

An electronic search was conducted in three main online databases including PubMed, Web of Science, and Scopus, from inception to March 9, 2023 for studies involving Ex plus IF trials versus standalone Ex and/or IF interventions in adults. Interventions had a duration of ≥ 2 weeks. Standardized (SMD) or weighted mean differences (WMD) and 95% confidence intervals were calculated in order to compare effects on body weight, body mass index (BMI), body fat lean body mass (LBM), visceral fat, and waist circumference. For cardiometabolic health, outcomes included fasting glucose, insulin, total cholesterol (TC), low-density lipoprotein cholesterol (LDL), triglycerides (TG), high-density lipoprotein cholesterol (HDL), systolic (SBP) and diastolic (DBP) blood pressure, and VO2max/peak.

RESULTS

Ex plus IF decreased body weight [WMD: -3.03 kg (95% CI: -3.44 to -2.61), p = 0.001], BMI [WMD: -1.12 kg.m2 (95% CI: -1.28 to -0.95), p = 0.001], body fat [SMD: -0.72 (95% CI: -1.23 to -0.21), p = 0.005], visceral fat [SMD: -0.34 (95% CI: -0.63 to -0.05), p = 0.01], and waist circumference [WMD: -2.63 cm (95% CI: -4.16 to -1.11), p = 0.001] more than Ex alone. However, changes in body composition and cardiometabolic health markers were not significantly different for Ex plus IF when compared with IF alone, with the exception of VO2max/peak [SMD: 0.55 (95% CI: 0.14 to 0.97), p = 0.009].

CONCLUSION

We demonstrate that a combination of Ex and IF produces superior changes in body composition, but not in markers of cardiometabolic health when compared with Ex or IF alone. Ex plus IF could therefore be effective for weight and fat loss but has no additive or synergistic effects for other cardiometabolic health markers.

Effect of intermittent fasting on lipid biokinetics in obese and overweight patients with type 2 diabetes mellitus: prospective observational study

BACKGROUND

Intermittent fasting (IF) is a commonly used dietary practice that alternates between periods of unrestricted dietary consumption and abstinence from caloric intake. IF reduces caloric intake along with metabolic switch from utilization of glucose to fatty acids and ketones and resulting in reduction in adiposity and subsequently insulin resistance. Thus, it has been hypothesized that IF regimens can improve body composition in obese and overweight individuals.

AIM

To assess the effect of IF on lipid biokinetics in obese and overweight patients with type 2 diabetes (T2D).

PATIENTS AND METHODS

Thirty overweight or obese T2D patients were recruited from the diabetes outpatient clinics at the Specialized Medical Hospital, Mansoura University. Patients were subjected to time restricted fasting for 16 h (from dawn to sunset) during Ramadan. Anthropometric data were measured for participants before and 3 weeks after Ramadan fasting. Fasting plasma glucose (FPG), HbA1c, lipid profile, leptin, beta hydroxybutyrate (βHB) and high sensitive CRP levels were measured 1 week before and 3 weeks after Ramadan fasting.

RESULTS

30 diabetic patients were recruited with a mean age of 54.3 ± 7.2 years. 24 (80%) were females. Obesity was diagnosed in 27 cases (90%). The median diabetes duration was 10 years. The study showed a statistically significant decrease in post-fasting body weight (BW), Body mass index (BMI), waist circumference (WC) & hip circumference (HC). There was a statistically significant decrease of post-fasting low density lipoprotein (LDL-C), Total cholesterol (TC), and leptin. The study also showed a statistically significant increase of post-fasting high density lipoprotein (HDL-C) and βHB. No significant change was found in post-fasting levels of HbA1c, FPG, triglycerides (TG) or high sensitive CRP. Post-fasting leptin was positively correlated with post-fasting BW, BMI, WC, and HC. Post-fasting βHB was positively correlated with post-fasting TG, HbA1c, and LDL-C. Leptin levels change (pre vs post fasting) was positively correlated with the change in LDL-C levels.

CONCLUSION

IF reduced leptin and increased β-hydroxybutyrate levels. IF is an effective tool for losing weight and visceral fat and improving lipid profile in obese and overweight patients with T2D.

The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans

The belief that the anabolic response to feeding during postexercise recovery is transient and has an upper limit and that excess amino acids are being oxidized lacks scientific proof. Using a comprehensive quadruple isotope tracer feeding-infusion approach, we show that the ingestion of 100 g protein results in a greater and more prolonged (>12 h) anabolic response when compared to the ingestion of 25 g protein. We demonstrate a dose-response increase in dietary-protein-derived plasma amino acid availability and subsequent incorporation into muscle protein. Ingestion of a large bolus of protein further increases whole-body protein net balance, mixed-muscle, myofibrillar, muscle connective, and plasma protein synthesis rates. Protein ingestion has a negligible impact on whole-body protein breakdown rates or amino acid oxidation rates. These findings demonstrate that the magnitude and duration of the anabolic response to protein ingestion is not restricted and has previously been underestimated in vivo in humans.

Intermittent Fasting and Its Effects on Weight, Glycemia, Lipids, and Blood Pressure: A Narrative Review

Metabolic syndrome (MetS) has become a significant public health concern globally. Weight managementis crucial in controlling MetS risk factors, making energy balance and weight loss strategies important in nutrition recommendations. Intermittent fasting (IF) has gained traction as a dietary approach for weight management and cardiovascular risk reduction. However, the effects of IF on cardiovascular risk factors have been inconsistent in previous studies. This review aims to summarize the effects of various types of IF on body mass index (BMI), glycemia, lipid profile, and blood pressure, while providing insights into their clinical implications. A comprehensive search of interventional studies and meta-analyses was conducted, and the results were analyzed. The findings indicate that different types of IF lead to mixed effects. Time-restricted eating (TRE) and alternate-day fasting (ADF) consistently showed decreases in BMI, while the outcomes of intermittent energy restriction (IER) were more uncertain. The effects of IF on glycemia and lipid profile were also variable, with TRE and ADF generally showing positive results. However, the impact of IER remained inconsistent. More research is needed to understand the long-term effects and optimal implementation of IF for managing metabolic syndrome and cardiovascular risk factors.

Mechanisms of ageing: growth hormone, dietary restriction, and metformin

Tackling the mechanisms underlying ageing is desirable to help to extend the duration and improve the quality of life. Life extension has been achieved in animal models by suppressing the growth hormone-insulin-like growth factor 1 (IGF-1) axis and also via dietary restriction. Metformin has become the focus of increased interest as a possible anti-ageing drug. There is some overlap in the postulated mechanisms of how these three approaches could produce anti-ageing effects, with convergence on common downstream pathways. In this Review, we draw on evidence from both animal models and human studies to assess the effects of suppression of the growth hormone-IGF-1 axis, dietary restriction, and metformin on ageing.

Eating, diet, and nutrition for the treatment of non-alcoholic fatty liver disease

Nutrition and dietary interventions are a central component in the pathophysiology, but also a cornerstone in the management of patients with non-alcoholic fatty liver disease (NAFLD). Summarizing our rapidly advancing understanding of how our diet influences our metabolism and focusing on specific effects on the liver, we provide a comprehensive overview of dietary concepts to counteract the increasing burden of NAFLD. Specifically, we emphasize the importance of dietary calorie restriction independently of the macronutrient composition together with adherence to a Mediterranean diet low in added fructose and processed meat that seems to exert favorable effects beyond calorie restriction. Also, we discuss intermittent fasting as a type of diet specifically tailored to decrease liver fat content and increase ketogenesis, awaiting future study results in NAFLD. Finally, personalized dietary recommendations could be powerful tools to increase the effectiveness of dietary interventions in patients with NAFLD considering the genetic background and the microbiome, among others.

Does Timing Matter? A Narrative Review of Intermittent Fasting Variants and Their Effects on Bodyweight and Body Composition

The practice of fasting recently has been purported to have clinical benefits, particularly as an intervention against obesity and its related pathologies. Although a number of different temporal dietary restriction strategies have been employed in practice, they are generally classified under the umbrella term "intermittent fasting" (IF). IF can be stratified into two main categories: (1) intra-weekly fasting (alternate-day fasting/ADF, twice-weekly fasting/TWF) and (2) intra-daily fasting (early time-restricted eating/eTRE and delayed time-restricted eating/dTRE). A growing body of evidence indicates that IF is a viable alternative to daily caloric restriction (DCR), showing effectiveness as a weight loss intervention. This paper narratively reviews the literature on the effects of various commonly used IF strategies on body weight and body composition when compared to traditional DCR approaches, and draws conclusions for their practical application. A specific focus is provided as to the use of IF in combination with regimented exercise programs and the associated effects on fat mass and lean mass.

Effects of Time-Restricted Feeding and Ramadan Fasting on Body Weight, Body Composition, Glucose Responses, and Insulin Resistance: A Systematic Review of Randomized Controlled Trials

Time-restricted feeding (TRF) and Ramadan fasting (RF) have been recently associated with several health outcomes. However, it is not yet clear if they are superior to existing treatments in terms of glucose metabolism, insulin action, and weight loss. This review aims to summarize the current data on the effects of these regimes on body weight, body composition, and glycemia. An electronic search was conducted in PUBMED and SCOPUS databases up to August 2022. Twenty-four records met the inclusion criteria and underwent a risk-of-bias assessment. The main outcomes were: (a) TRF may result in moderate weight loss in individuals with overweight/obesity; when TRF is combined with caloric restriction, weight loss is >5% of the initial body weight, (b) 14 h of fasting may be as effective as 16 h in terms of weight loss, and (c) TRF may lead to improved insulin sensitivity and glycemic responses/variability throughout the day in individuals with overweight/obesity. Concerning RF, only two studies were available and thus, conclusions were not drawn. TRF may be an effective nutritional approach for weight loss, and the amelioration of glycemic control and insulin sensitivity in individuals with overweight/obesity. However, more long-term, well-designed studies are needed.

Does intermittent fasting impact mental disorders? A systematic review with meta-analysis

Accumulating evidence supports the benefits of intermittent fasting (IF) as a dietary strategy for cardiometabolic health and weight control. However, little is known about the potential implications of IF on mental disorders. The aim of this review was to synthesize evidence regarding the effects of IF on mental disorders (depression, anxiety, and mood state) in the general population. We conducted a systematic search in five databases from inception to January 2022. Randomized and nonrandomized clinical trials (RCTs/nonRCTs) were included. A random effects method was used to pool standardized mean differences (SMDs) and 95% CIs. A total of 14 studies involving 562 individuals were included, of which 8 were RCTs and 6 were nonRCTs. IF showed a moderate and positive effect on depression scores when compared to control groups (SMD: 0.41; 95%CI: 0.05 to 0.76; I2=45%; n = 4). Conversely, within-group analyses did not show any significant effect of IF on anxiety (SMD: 0.10; 95%CI: -0.09 to 0.30; I2=0%; n = 5) or mood state (SMD: 0.14; 95%CI: -0.09 to 0.37; I2=59%; n = 7). IF modalities did not negatively impact mental disorders in the general population. In fact, IF showed a positive influence on diminishing depression scores, and did not modify anxiety or mood.