Restricting eating to an 8-hour window for three months led to sustained weight loss in people with overweight or obesity, regardless of the timing of that window. This is according to preliminary findings from a randomized controlled trial presented at the European Congress on Obesity (ECO) 2025 in Málaga, Spain.
The dietary method, known as time-restricted eating (TRE), involves limiting when people eat each day but not necessarily changing what they eat. According to Jonatan Ruiz, PhD, from the University of Granada and the Spanish Biomedical Research Centre in Madrid, the study suggests that the timing of the 8-hour window may not be as important as previously believed, offering flexibility for people adopting TRE.
The 12-month follow-up study involved 99 adults from Granada (average age 49, BMI 32), half of whom were women. Participants were randomly assigned to one of four groups: habitual eating (more than 12 hours), early TRE (eating window before 10 AM), late TRE (after 1 PM), or self-selected TRE (participants chose their own window). All groups also took part in a Mediterranean diet education program.
Measurements were taken at baseline, after the 12-week intervention, and 12 months later. After the initial 12 weeks, the habitual eating group lost 1.4 kg (1.5%), while all TRE groups lost more: 4.2 kg (4.5%) in the early group, 3.1 kg (3.5%) in the late group, and 3.8 kg (3.9%) in the self-selected group.
Reductions in waist and hip circumferences were also seen. The early TRE group showed the largest reductions (4.1 cm and 4.6 cm), while the late group lost 4.1 cm at the waist and 3.2 cm at the hips. The self-selected group saw smaller reductions, which were not statistically significant. Ruiz noted that allowing participants to choose their own window may have led to inconsistency, potentially affecting results.
After 12 months, only the habitual eating group regained weight (+0.4 kg). The early and late TRE groups maintained significant weight loss (–2.2 kg and –2.0 kg, respectively), while the self-selected group showed a modest, non-significant loss (–0.7 kg).
Waist circumference in the habitual group increased by 1.8 cm over the year. In contrast, the late TRE group maintained reductions of 5.6 cm (waist) and 3.4 cm (hip), while other TRE groups showed smaller but lower values.
Ruiz explained that TRE could be a low-cost, sustainable method for weight management, especially for those struggling with calorie counting or strict diets. He added that future studies would explore combining TRE with exercise.
Adam Collins, PhD, from the University of Surrey, noted that while TRE may affect nutritional adequacy, more data on eating behaviour and nutrient intake is needed. Maria Chondronikola, PhD, from the University of Cambridge, emphasized the need for data on adherence and metabolic outcomes.
Ruiz confirmed high adherence rates (85–88%) and no serious side effects.
The dietary method, known as time-restricted eating (TRE), involves limiting when people eat each day but not necessarily changing what they eat. According to Jonatan Ruiz, PhD, from the University of Granada and the Spanish Biomedical Research Centre in Madrid, the study suggests that the timing of the 8-hour window may not be as important as previously believed, offering flexibility for people adopting TRE.
The 12-month follow-up study involved 99 adults from Granada (average age 49, BMI 32), half of whom were women. Participants were randomly assigned to one of four groups: habitual eating (more than 12 hours), early TRE (eating window before 10 AM), late TRE (after 1 PM), or self-selected TRE (participants chose their own window). All groups also took part in a Mediterranean diet education program.
Measurements were taken at baseline, after the 12-week intervention, and 12 months later. After the initial 12 weeks, the habitual eating group lost 1.4 kg (1.5%), while all TRE groups lost more: 4.2 kg (4.5%) in the early group, 3.1 kg (3.5%) in the late group, and 3.8 kg (3.9%) in the self-selected group.
Reductions in waist and hip circumferences were also seen. The early TRE group showed the largest reductions (4.1 cm and 4.6 cm), while the late group lost 4.1 cm at the waist and 3.2 cm at the hips. The self-selected group saw smaller reductions, which were not statistically significant. Ruiz noted that allowing participants to choose their own window may have led to inconsistency, potentially affecting results.
After 12 months, only the habitual eating group regained weight (+0.4 kg). The early and late TRE groups maintained significant weight loss (–2.2 kg and –2.0 kg, respectively), while the self-selected group showed a modest, non-significant loss (–0.7 kg).
Waist circumference in the habitual group increased by 1.8 cm over the year. In contrast, the late TRE group maintained reductions of 5.6 cm (waist) and 3.4 cm (hip), while other TRE groups showed smaller but lower values.
Ruiz explained that TRE could be a low-cost, sustainable method for weight management, especially for those struggling with calorie counting or strict diets. He added that future studies would explore combining TRE with exercise.
Adam Collins, PhD, from the University of Surrey, noted that while TRE may affect nutritional adequacy, more data on eating behaviour and nutrient intake is needed. Maria Chondronikola, PhD, from the University of Cambridge, emphasized the need for data on adherence and metabolic outcomes.
Ruiz confirmed high adherence rates (85–88%) and no serious side effects.
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