“Fasting: Improves mental clarity and concentration, induces weight and body fat loss” - Jason Fung
Introduction | Insulin Sensitivity | Fat & Weight Loss | Blood Pressure & Cholesterol | Autophagy | Brain Function | Energy Metabolism | Healthy Aging & Longevity | Final Thoughts | References | Disclaimer
Introduction
Intermittent fasting [IF] as well as periodic fasting have been extensively studied in recent decades. An increasing body of research has provided a lot of evidence for the mechanisms that this eating regimen triggers in the human body. Besides improving our understanding of how human systems work, it also uncovered the positive effects they generate when performed regularly.
Intermittent fasting improves Insulin Sensitivity
A 5-week-long study, performed on a group of 8 men diagnosed with prediabetes, inspected the outcomes of an early time-restricted feeding regimen on various metabolic markers, including insulin sensitivity[1]. The authors observed that intermittent fasting decreased mean and peak insulin levels as well as reduced insulin resistance in the fasting group.
Another study, conducted by Gable et al., measured the outcomes of alternate-day fasting [ADF] and calorie restriction [CR] diets on insulin levels in insulin-resistant adults[2]. The researchers followed their participants for 12 months and concluded that alternate-day fasting achieved the best results in decreasing fasting insulin levels. Furthermore, the ADF group experienced a great reduction in the HOMA-IR marker [insulin resistance marker] in comparison to the CR and control groups.
Lastly, a group of researchers compared the effects of a calorie-restriction diet and alternate-day fasting on insulin sensitivity and insulin resistance markers in overweight and obese adults[3]. The results revealed that the ADF group experienced a bigger reduction in both fasting insulin levels and insulin resistance markers when compared with the CR group.
Intermittent fasting for Fat and Weight Loss
Fat and weight loss are the best-known effects of intermittent fasting on the human body. Body mass reduction is one of the most common reasons for starting an IF journey. Multiple studies have confirmed the correlation between IF and weight loss. Researchers Tinsley and La Bounty concluded that intermittent fasting appears to be effective at inducing fat loss and decreasing body weight[4] in normal-weight, overweight, and obese people.
Another review of randomized trials looked at the studies that inspected different forms of intermittent fasting, such as ADF [alternate-day fasting] and TRF [time-restricted feeding], as potential treatments for obesity[5]. The authors found that IF was successful in both weight reduction and fat loss. Additionally, intermittent fasting was considered a safe and effective method to apply to both overweight and obese humans.
Furthermore, Welton et al. demonstrated, based on a review of 27 trials assessing the effects of intermittent fasting on overweight and obese participants[6], that IF is an effective weight-loss technique and had no adverse effects in these studies.
IF impacts Blood Pressure and Cholesterol levels
A 12-week-long study, performed on 19 participants with metabolic syndrome[7], followed the changes in various metabolic parameters, including cholesterol and blood pressure levels. The subjects of the study were asked to adhere to a 10-hour eating window [time-restricted eating] for 12 consecutive weeks. The results showed a significant decrease in both systolic and diastolic blood pressure by 3% and 8%, respectively. Additionally, total cholesterol and LDL cholesterol were measured and both were reduced by 7% and 11%, respectively.
Another crossover, randomized trial followed normal-weight men and women aged 40–50 for 8 weeks[8]. The study group was consuming a restricted amount of meals, which allowed them to achieve a 20-hour fasting window. The researchers observed that such eating patterns lowered both systolic and diastolic blood pressures by 6%. Additionally, a small decrease in total and LDL cholesterol was noted.
Intermittent Fasting triggers Autophagy
Numerous studies have looked at the link between IF and autophagy. Autophagy is a process where our body "recycles" old proteins and cells to renew itself. One group of researchers [Bagherniya et al.][9] concluded that autophagy can be triggered by the state of food deprivation and that it appears to take place in multiple organs and tissues throughout the body.
Another study on fast-induced autophagy[10], focused on the pathways that are utilized in the process of activating hepatic autophagy in mice. It was reported that the FGF21-JMJD3 signaling axis was activated by histone demethylase JMJD3 [an activator of hepatic autophagy]. This activator is naturally present in many mammals, including humans.
Intermittent fasting and Brain Function
Fasting induces a metabolic phenomenon called "the metabolic switch," which requires the body to replace its preferred source of energy [glucose] with fat stored in adipose tissue. The ketone production that takes place when the body utilizes its fat stores to fuel itself is very beneficial for the brain and cognitive function.
A group of researchers [Baik et al.][11] conducted a study on mice that were subjected to a fasting period of either 12, 24, or 36 hours. Baik et al. tested the impact of intermittent fasting on hippocampal neurogenesis. They concluded that such fasting-induced neurogenesis does take place, and it utilizes the Noch 1 pathway. This signaling pathway collaborates with two other pathways called BDNF [brain-derived neurotrophic factor] and CREB [cAMP response element-binding protein]. Together, they support the differentiation of stem cells into neurons.
Another study[12] examined the effects of alternate-day fasting on memory retention in mice. Adult hippocampal neurogenesis (AHN) and the K1 gene associated with longevity have shown involvement in IF's effects on long-term memory.
Intermittent Fasting and Energy Metabolism
The resting energy expenditure during fasting can provide insight into how IF affects metabolism. The research on a group of lean and healthy participants looked at the metabolic effects of an 84-hour fast[13]. The outcomes of this study revealed that resting energy expenditure increased from 3.97 [measured on day 1] to 4.53 [measured on day 4]. Moreover, the scientists associated this change in energy expenditure with increased norepinephrine levels.
Another group of researchers [Nas et al.] designed a study that examined the outcomes of meal skipping [either breakfast or dinner] on energy expenditure[14]. They recruited 17 participants and followed the changes in their energy expenditure for 24 hours after the intervention. Nas et al. concluded that meal skipping leads to an increased 24-hour energy expenditure [+41 and +91 kcal/d]. They noted that such an extension of night fasting impacts energy metabolism.
Intermittent Fasting contributes to Healthy Aging and Longevity
Intermittent fasting has been linked in various studies to having positive effects on the aging process. One study followed 17 healthy and normal-weight participants for 10 weeks and measured the expression of their genes related to aging[15]. In their study, researchers observed increased expression of the gene SIRT3, which they concluded was caused by intermittent fasting.
Additionally, a study conducted by Jamshed et al.[16] looked into the correlation between early time-restricted eating [eTRE] and longevity gene expression. The results of their study revealed increased SIRT1 gene expression in the early morning, which led them to conclude that eTRF may promote longevity in humans.
Final Thoughts
Time-restricted eating is the most extensively studied form of IF. The research conducted by the scientists ranges in length and the choice of participants, but they come to very solid and interesting conclusions that shed more light on the benefits of intermittent fasting. We now know that intermittent fasting can induce metabolic changes in the human body, regulate hormones such as insulin, impact gene expression, and aid weight loss, to mention a few. Based on current evidence, IF enhances our health in a variety of ways, as well as helping regulate our eating habits. However, there is a need for more scientific evidence providing insights into the effects and mechanisms of other forms of IF on our bodies. To further our understanding of the health outcomes of this eating regimen, there is a necessity for longer trials that go beyond 10 or 12 weeks of study.
References
This article contains 16 citations:
Disclaimer
Read carefully: