Time-restricted eating rivals Mediterranean diet but falls short for visceral fat loss

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Jan 8 2025

Despite high adherence and safety, time-restricted eating fails to beat the Mediterranean diet for visceral fat loss but shines in other areas like subcutaneous fat reduction and glucose control.

Study: Effects of early, late and self-selected time-restricted eating on visceral adipose tissue and cardiometabolic health in participants with overweight or obesity: a randomized controlled trial. Image Credit: goffkein.pro / Shutterstock

In a recent study published in the journal Nature Medicine, researchers evaluated the impacts of various time-restricted eating (TRE) windows in combination with usual care (UC) and a Mediterranean diet in managing visceral adipose tissue (VAT) in overweight or obese individuals.

The randomized controlled trial evaluated 197 adults across early TRE, late TRE, and self-selected TRE in combination with a 12-week-long UC program. Study findings revealed that TRE, while being a safe, feasible, and well-tolerated dietary approach, provided no additional benefits to participants' VAT management compared to Mediterranean diet-based UC education alone. These results suggest that caloric restriction and dietary adherence may play a more pivotal role than TRE timing in reducing VAT. These findings were consistent irrespective of the TRE timing investigated. Notably, the early TRE cohort depicted a marked reduction in their subcutaneous adipose tissue (SAT) compared to other TRE groups.

Background

Overweight (body mass index [BMI] > 25) and obesity (BMI > 30) are global public health concerns, affecting ~43% and 12.5% of adults (2022). Alarmingly, the prevalence of these conditions has more than doubled since 1990 and tripled since 1975, emphasizing the need for identifying and managing the condition. Obesity is associated with a host of potentially lethal comorbidities, including diabetes, cancers, and cardiovascular diseases (CVDs). Obesity manifestation has been linked to several genetic, behavioral (diet, sleep, etc.), and neurological conditions. Historically, dietary interventions form the first steps in obesity management, with healthier diets (e.g., the Mediterranean diet) and energy-restricted diets generally producing favorable outcomes. Unfortunately, the latter approach depicts low long-term adherence, resulting in relapses in patient weight gain.

Time-restricted diets (TREs) have recently emerged as feasible and promising alternatives to energy-restricted diets. These interventions involve food consumption during relatively short (<10 hours) periods, with the rest of the day comprising fasting. Given their novelty, however, the literature on the clinical benefits of TRE and the relative impacts of different TRE periods (early in the day, late in the day, or patient-selected) remain poorly understood. Moreover, adherence to TRE has varied in prior studies depending on cultural, lifestyle, and individual preferences, highlighting the need for context-specific insights.

About the Study

The present study aimed to shed light on TRE's benefits by evaluating the effects of three nonoverlapping TRE periods (early TRE, late TRE, and self-selected TRE) on participant's visceral adipose tissue (VAT). To establish the holistic utility of TRE in obesity management, the study incorporated bi-monthly sessions of Mediterranean diet-based nutritional education alongside usual care (UC).

The study recruited overweight or obese participants (n = 2,598; ages 30-60 years) between April and December 2022. Of these, 197 (99 men and 98 women) passed baseline screening and were included in the study. Participants were randomly enrolled into UC (n = 49), early TRE (n = 49), late TRE (n = 52), and self-selected TRE (n = 47) cohorts. The study lasted 12 weeks, during which the UC cohort continued their routine, non-TRE-based diet schedule, albeit with Mediterranean diet education.

Study assessments were conducted at baseline and once again at 12 weeks following the end of the intervention period. The primary outcome of interest (VAT) was measured using Magnetic Resonance Imaging (MRI). Secondary outcomes (intermuscular adipose tissue and SAT) were similarly evaluated (MRI scans). Additionally, ectopic fat depots were routinely recorded following a 4-5 hour-long fasting period. Finally, body weight and health were measured at both time points using a stadiometer and scale, respectively. High adherence rates (85–88%) across all TRE cohorts underscored the feasibility of these interventions, even in cultural settings with late dining patterns, such as Spain.

Study Findings

The study depicted a -3% to -6% reduction in VAT following the experimental intervention but could not reveal statistical VAT measurement differences between any combination of cohorts, suggesting that TRE does not impart additional benefits over a healthy dietary pattern (e.g., the Mediterranean diet) and UC. This lack of significant difference underscores the complex role of caloric intake and weight loss in VAT reduction. Surprisingly, intermuscular abdominal adipose tissue did not significantly differ between any cohort's baseline and final evaluations. This suggests that neither UC nor TRE can significantly manage unwanted weight in the waistline. Body composition and blood pressure measurements remained similarly unchanged throughout the study.

Substantial inter-cohort differences were observed in secondary outcome measurements – early TRE participants, on average, lost 5% more SAT than participants in the other cohorts (late TRE, self-selected TRE, and UC). Similarly, fasting glucose levels in early TRE participants were significantly lower than in the other groups (-6 mg dl-1 to -8 mg dl-1). All TRE groups lost considerably more body weight (-2.4 kg to -3.1kg) than UC participants. The findings highlight that meal timing may selectively influence specific fat depots and glycemic control but is unlikely to broadly impact overall fat distribution or body composition.

Conclusions

The present study unravels TRE's benefits (or lack thereof) compared to routine UC and healthy dietary adherence. While TRE (particularly early TRE) helped enhance SAT, fasting glucose, and weight management compared to UC alone, no benefits were observed in VAT measurements. VAT is strongly associated with cardiovascular diseases but may require alternative management interventions.

Encouragingly, adherence to TRE was found to be high, with minimal adverse effects reported, highlighting the intervention as safe, feasible, and well-tolerated. However, the study's limitations, such as its relatively short duration, modest sample size, and heterogeneity introduced by UC, suggest the need for cautious interpretation and further research.