- Intermittent fasting, or only eating food in certain time windows, is one practice that may carry certain health benefits and assist with weight loss.
- One type of intermittent fasting is time-restricted eating.
- Recent data suggest that combining time-restricted eating with exercise may be slightly more effective in reducing fat mass and body fat percentage than exercise without time-restricted eating.
Maintaining a healthy weight and body fat levels are essential components of health. Experts are continuing to research the best fitness plans and eating habits that promote optimal weight and body fat proportions.
One systematic review and meta-analysis published in the
The results suggest that time-restricted eating could help lower fat mass and body fat percentage better than exercising without restricting eating times. However, more research is required to explore and confirm the findings.
Time-restricted eating is a specific type of intermittent fasting. Intermittent fasting involves not eating or limiting calories at specific times while following regular dietary intake at other times. It may help achieve weight loss and fight insulin resistance.
The form of time-restricted eating assessed in this research was fasting for 12 to 20 hours a day, with 4 to 12 hours available for eating.
The review and meta-analysis included data from 15 studies looking at 338 participants. Researchers found studies via five different databases and the use of reference lists.
All the included studies were either randomized crossover studies or randomized controlled trials lasting at least 4 weeks. The studies included healthy adults and examined how time-restricted eating along with exercise affected body composition. They compared time-restricted eating groups to exercise-matched control groups without time-restricted eating.
Researchers conducted subgroup analyses to examine moderator variables like body mass index (BMI), exercise type, and energy intake.
They also considered the risk for bias in each of the examined studies. Of the studies analyzed, the average BMI of participants ranged from normal to overweight.
The allowed eating window was primarily mid-day, with eating between noon and 9 p.m., but varied across some of the studies. Exercise was performed during eating windows and the types of exercise included aerobic, resistance, or a combination of the two. In some studies, there was also a calorie restriction for both groups.
Overall, the meta-analysis found that, compared to control groups, participants in time-restricted eating groups appeared to reap more health benefits. While small, there was a significant average decrease in fat mass for participants who participated in time-restricted eating and exercise. This was estimated to translate to a possible 1.3 kilogram (kg) reduction in fat mass.
Time-restricted eating also appeared to lower body fat percentage better than exercise alone, as there was a small but significant average reduction for participants in this area. This was estimated to translate to a possible 1.3% reduction in body fat percentage.
Researchers did not observe significant changes in fat-free mass between engaging in time-restricted eating compared to controls.
The results indicate that the findings may not be impacted by BMI, exercise type, age, energy intake, or study duration. However, there were high levels of heterogeneity amongst the studies for fat mass, body fat percentage, and fat-free mass findings.
Overall, the results paint time-restricted eating in a positive light.
Remy Neville, MD, a board-certified internist at the Medical Offices of Manhattan, NY, who was not involved in the review, told Medical News Today:
“First, it is important to note that this study is a meta-analysis, which is actually a study comparing the findings of fifteen other separate studies. This study shows that combining time-restricted eating with exercise can help reduce body fat more than exercising without limiting eating times. I think it’s a simple and effective approach that could make a meaningful difference for my patients who are trying to improve their health and manage their weight.”
This research does have limitations. First, the researchers were limited in their data collection methods and their inclusion and exclusion criteria. For example, they only included studies written in English and focused on healthy adult participants, excluding those with problems like cardiometabolic conditions.
Second, the studies were not all of the same kind, which could affect the overall results. There was variety regarding components like diet, the specific exercise regimens, and body composition measuring. Researchers acknowledge that the body composition measurement tools “do not always reflect similar changes in body composition.”
Thirteen of the studies included participants who had BMIs of 25 or less. A BMI of 18.5 to under 25 is considered a
Kalyn True, RDN, LD, an outpatient dietitian with Memorial Hermann in Houston, who was not involved in the review, commented that, being published in an academic journal focused on obesity, “you’d think that the average BMI [of the participants] would be in the overweight to obese category.” However, she noted that the paper states that the average BMI was in the normal to overweight BMI ranges.
Thirdly, participants’ adherence to time-restricted eating and dietary intake were self-reported, which may lead to inaccuracies and underreporting of energy intake.
The studies had short durations, so the results cannot examine the long-term effects of time-restricted eating. Six of the studies lasted for 4 weeks, seven lasted for 8 weeks, and only one exceeded 12 weeks. True also noted that “typically, it will take at least 12 weeks to see proper body composition changes regardless of time-restricted eating.”
In the risk for bias assessment, there was some identified risk for bias. For example, most of the studies “were rated as unclear risk of bias for blinding of outcome assessment.” It was also noted that this sort of study cannot involve participant blinding because of the intervention type. The authors also identified possible publication bias when it came to fat mass and body fat percentage findings.
Researchers also only considered pre-post intervention values when it came to study outcomes, so this limits the data they considered. For example, this means the analysis did not look at any follow-up that happened after the studies’ main intervention periods.
About half of the studies were run in the United States. Additionally, nine of the studies had all-male participants. The average age of all participants was around twenty-nine years old. Thus, more diversity and examination of additional groups may be helpful in future research.
This analysis did not look at how dietary energy and protein intake affected body composition changes. The authors acknowledge that these factors can influence body composition changes in people who exercise.
Researchers acknowledge that some populations may not experience changes to fat mass or body fat percentages and that there may be variations in fat loss or gain. There may also be unaccounted-for variables that explain variations in the effect sizes of this analysis.
This research suggests a potential benefit for time-restricted eating. The authors note that more research is required.
For example, more research is needed to understand why time-restricted eating has certain effects. Future research can include more long-term studies and ones with more objective ways to measure food intake.
From True’s perspective:
“In an overall generality, I think that [time-restricted eating] combined with exercise could be a valuable tool for clinicians to incorporate into personalized weight management strategies for their patients with very close monitoring […] It is something that still needs a lot more research and tighter control analysis to really make an informed call on how [time-restricted eating] potentially could influence body composition.”
Ryan Glatt, CPT, NBC-HWC, senior brain health coach and director of the FitBrain Program at Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA, also noted that. “while [time-restricted eating] with exercise could complement weight management strategies, its application must be individualized.”
“Evidence remains inconclusive about whether [time-restricted eating] offers advantages over traditional calorie control and regular exercise routines. More rigorous, controlled trials are needed to confirm the effectiveness of [time-restricted eating] with exercise, particularly in diverse populations. Studies should also examine long-term adherence and real-world feasibility, as these factors heavily influence outcomes in practical settings,” he suggested.
