A recent meta-analysis has provided insights into the potential benefits of combining intermittent fasting with exercise for weight loss. The study reviewed data from 15 separate studies, focusing on participants with an average age of 29 years. Most participants had a Body Mass Index (BMI) within the normal to overweight range, specifically below 25, considered a healthy weight. The analysis concluded that the strategy might be effective, but its application should be tailored to individual needs.
Intermittent fasting involves consuming food within specific time windows, and this study primarily observed eating windows from noon until 9 p.m. Exercise types varied across the studies, including aerobic and resistance training or a combination of both. The studies' durations ranged from four to over twelve weeks, yet despite varying methodologies and participant demographics, the findings suggested that the impact on weight loss might not depend on BMI, exercise type, age, energy intake, or study duration.
“While [time-restricted eating] with exercise could complement weight management strategies, its application must be individualized.” – Ryan Glatt, CPT, NBC-HWC
The meta-analysis revealed a possible reduction in body fat percentage by 1.3% and a reduction in fat mass by 1.3 kilograms (kg). However, these results come with a caveat due to the heterogeneity of the included studies. Thirteen of them involved participants with BMIs under 25, and nine studies focused exclusively on male participants. These limitations suggest that while promising, further research is required to solidify these findings.
“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.” – Ryan Glatt, CPT, NBC-HWC
The types of exercises being performed during eating windows varied widely across studies. This included aerobic exercise, resistance training, or a mixture of both. Importantly, the analysis noted that results might not differ significantly based on the type of exercise or the participants' BMI. However, this broad conclusion comes with the understanding that individual differences could play a significant role in effectiveness.
In terms of study duration, six of the examined studies lasted four weeks and seven extended to eight weeks. Only one study surpassed twelve weeks. This short duration poses questions regarding the sustainability and long-term effects of intermittent fasting combined with exercise.
“You’d think that the average BMI [of the participants] would be in the overweight to obese category.” – Kalyn True, RDN, LD
Despite these findings, experts urge caution. Some express skepticism regarding the short study durations and their ability to portray comprehensive results. Kalyn True, a Registered Dietitian Nutritionist (RDN), emphasized that significant body composition changes typically require at least 12 weeks to manifest.
“Typically, it will take at least 12 weeks to see proper body composition changes regardless of time-restricted eating.” – Kalyn True, RDN, LD
The meta-analysis adds to a growing body of evidence suggesting intermittent fasting as a viable component of weight management strategies. However, it highlights the necessity for personalization in dietary and exercise regimens to achieve optimal results. The diversity in study designs and participant characteristics underscores the need for more uniform and extensive research efforts.
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