Time restricted feeding (TRF) is a form of intermittent fasting that limits daily caloric intake to a six to 12 hour period. Recent randomized controlled trials (RCTs) have shown that TRF combined with exercise can improve body composition when compared to a normal diet (ND) with an equivalent amount of exercise. However, the effects of TRF compared with a ND on physical performance in healthy individuals with regular exercise habits present varying and inconsistent results. These discrepancies highlight the need for a systematic review to comprehensively evaluate the available evidence and provide a clearer understanding of the effects of TRF combined with various exercise modalities on physical fitness. Therefore, in this article, we will look at a systematic review with meta-analysis to examine the effects of TRF versus ND on physical performance and body composition in healthy adults with regular exercise habits.
Overview
- What did they test? The authors conducted a systematic review and meta-analysis of RCTs that explored the effects of TRF versus ND on physical performance and body composition in healthy adults with regular exercise habits.
- What did they find? Fifteen randomized controlled trials with 361 participants were included in the systematic review. In comparison with the ND group, TRF significantly decreased body weight and fat mass. However, there was no effect on physical performance-related variables.
- What does it mean for you? For healthy adults who exercise regularly, TRF may be an effective strategy to improve body composition, especially in terms of fat loss. However, its impact on physical performance is less clear.
What’s the problem?
Purpose
Surprisingly, no meta-analysis has ever systematically compared the effects of TRF versus ND on physical performance and body composition in healthy adults with regular exercise habits, even though TRF has shown to promote weight loss. Time-restricted feeding, a form of intermittent fasting, limiting daily caloric intake to a six to 12-hour window without the need for individuals to count calories or monitor food intake during the eating window 1. It has demonstrated efficacy in promoting weight loss, enhancing overall health and optimizing nutrient utilization without explicitly restricting energy intake, as well as reducing obesity, inflammation and insulin resistance 2. Recent RCTs have shown that TRF combined with exercise can significantly improve the fat mass (FM) and fat-free mass (FFM) ratio when compared with a normal diet (ND) combined with an equivalent amount of exercise 3. However, other RCTs have shown varying and inconsistent results. These discrepancies highlight the need for a systematic review to comprehensively evaluate the available evidence and provide a clearer understanding of the effects of TRF combined with various exercise modalities on physical fitness.
Hypothesis
The authors did not provide any formal hypotheses in the study.
What Did They Test and How?
Participants
The systematic review included a total of 15 RCTs involving 361 participants, all of whom were healthy adults. Among these studies, four specifically focused on athletes, such as professional runners and elite cyclists. Two studies included distance-trained individuals, three recruited in-school physical education students, four included physically active individuals and two studies enrolled a general population of healthy adults. Furthermore, two studies exclusively included women, while eleven studies included only men.
Eight studies were RCTs, and seven studies were randomized crossover studies. All the studies included an intervention group that followed a TRF diet and a control group that ate whenever they wanted. For the duration of the intervention, the studies ranged in length from 11 days to four weeks, eight weeks and 12 months.
Study Procedures
This systematic review and meta-analysis was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and was registered with PROSPERO.
Seven electronic databases (MEDLINE, PubMed, Embase, SPORTDiscus, Web of Science, CINAHL and Cochrane Central Register of Controlled Trials (CENTRAL)) were searched for relevant studies on 30 October 2023.
Studies that met the following criteria were included in the systematic review: (i) adults aged 18–64 years with regular exercise habits, (ii) the fasting protocol entailed a reduced eating window of time recurring daily (the usual length of fasting is 12–21 hours per day), (iii) the studies performed comparisons with ND in participants’ daily life, (iv) the outcomes included physical performance indicators (eg, one repetition maximums, maximal oxygen uptake (VO2max), peak power output, jump height) and body composition indicators (eg, FM, FFM), (v) the study adopted a randomized controlled design and randomized crossover design and (vi) studies were peer-reviewed and written in English. Studies were excluded if they (i) were comments, editorials or reviews and (ii) included another type of fasting strategy (eg, Ramadan).
Relevant data were extracted from each study, including:
- Participant characteristics (health status, number of participants, age, sex, body mass index)
- Study characteristics (sample size, design, duration)
- Intervention details (TRF protocols, training protocol, physical performance test)
- Outcomes measured (changes in body fat, muscle mass, strength, endurance)
The data extraction was completed independently by two reviewers. A third independent reviewer was consulted to settle any discrepancies during the data extraction process.
The flow diagram for the systematic review is shown in Figure 1.
Figure 1
