Time-restricted eating shows promising weight and metabolic benefits, study reveals

New research highlights the potential of time-restricted eating and calorie timing as effective, sustainable alternatives for weight management and improved blood sugar levels.

Study: Meal Timing and Anthropometric and Metabolic Outcomes. Image Credit: Pormezz / Shutterstock.com

In a recent study published in JAMA Network Open, researchers performed a systematic review and meta-analysis of randomized clinical trials (RCTs) to explore the impact of meal timing strategies on body weight management and metabolic outcomes.

The efficacy of modern approaches to weight loss

The global prevalence of obesity and overweight is sharply increasing, partly because of modifiable lifestyle risk factors, including unhealthy dietary patterns and physical inactivity, both of which are associated with an increased risk of diabetes, cardiovascular disease, cancer, and premature death.

Current estimates indicate that most individuals consume food for more than 14 hours each day and snack late at night, which further increases the risk of type 2 diabetes and worsens glycemic control. Comparatively, intermittent fasting, which involves consuming foods during a six—to ten-hour duration during the active phase of the day, has emerged as a popular weight loss strategy.

Dietary modification, including calorie restriction, is considered the primary strategy for body weight management. Meal timing strategies, such as time-restricted eating (TRE), a form of intermittent fasting, meal frequency reduction, and alteration of calorie distribution throughout the day, have emerged as promising alternatives for people who find it challenging to monitor daily calorie intake for weight loss.

In the current systematic review and meta-analysis, scientists analyze published RCTs to evaluate the long-term impact of meal timing strategies on anthropometric and metabolic outcomes in adults with or without metabolic disease.     

Study design

The scientists searched various electronic databases to identify RCTs that investigated within-day meal timing patterns for at least 12 weeks and reported anthropometric outcomes, such as body weight and body mass index (BMI).

The final analysis included 29 RCTs involving 2,485 participants. The risk of bias analysis showed that about 76% of the selected trials provided low-quality data.

Meal timing strategies evaluated in the reviewed RCTs included time-restricted eating, meal frequency, and daily calorie distribution.

Time-restricted eating

The meta-analysis of RCTs investigating the impact of time-restricted eating on weight management revealed that this strategy can significantly reduce both body weight and BMI. However, time-restricted eating was not found to impact lean body mass or waist circumference.

Study participants with high BMI at baseline lost more weight than those with lower BMI. Greater weight loss was observed with eight hours or less of consuming food every day as compared to feeding times that exceeded eight hours each day.

Regarding metabolic outcomes, time-restricted eating was associated with reductions in fasting blood glucose, glycated hemoglobin (HbA1c), low-density lipoprotein (LDL) levels, and energy intake.

Meal frequency

Lower meal frequency was associated with small reductions in body weight and BMI; however, meal frequency did not appear to impact lean mass or waist circumference measurements. Likewise, meal frequency was not found to impact fasting glucose, HbA1c, LDL levels, or energy intake.

Calorie distribution

Consuming most calories earlier in the day leads to greater weight reduction, lower BMI values, and reduced waist circumference measurements compared to calorie consumption later in the day. Like meal frequency, no clear association was observed between calorie distribution and metabolic outcomes.

Study limitations

A subgroup analysis of the current study confirmed that the weight-reducing effect of meal timing strategies is persistent and does not depend on the training level of clinicians who delivered the interventions. However, most of the reviewed clinical trials enrolled participants from clinical settings and involved clinicians with nutrition training, which may restrict the generalizability of the findings. Similarly, all clinical trials on calorie distribution involved only female participants.  

Another limitation of the current study is the low quality of evidence due to the risk of bias and inconsistency. Thus, additional clinical trials with larger sample sizes, similar intervention designs, and longer follow-up periods should be conducted to provide more conclusive results on the health benefits associated with time-restricted eating.

Conclusions

Meal timing strategies implemented for more than 12 weeks can moderately reduce body weight, BMI, and waist circumference measurements. Time-restricted eating was also found to reduce HbA1c and fasting glucose levels, thus indicating the potential utility of this strategy for the management of diabetes.

The strict nature of calorie counting in traditional weight loss interventions is one of the primary reasons contributing to its low adherence, in addition to its association with higher disinhibition, energy intake, and BMI. Comparatively, time-restricted eating may provide a simpler and more flexible approach for healthcare clinicians to support behavioral change in overweight or obese adults.