Trial finds benefits of 16-hour fasting are evident for at least 1 year, regardless of eating window timing

Three months of time-restricted eating (TRE), irrespective of whether it is earlier or later in the day, may be a promising strategy for sustaining long-term weight loss in adults with overweight or obesity, according to preliminary results of a randomized controlled trial being presented at this year’s European Congress on Obesity (ECO) in Malaga, Spain (11–14 May).

“Our study found that restricting the eating window to eight hours at any time of the day for three months can result in significant weight loss for at least a year,” said lead author Dr. Alba Camacho-Cardenosa, from the Instituto de Investigación Biosanitaria de Granada (ibs.GRANADA), Granada, Spain. “These benefits can be attributed to the 16-hour fasting window rather than the time of eating.”

Low-calorie diets are well-known ways to lose weight and improve cardiometabolic health. However, long-term adherence is typically low, even among highly motivated people.

TRE, which limits when, but not what people eat, is an increasingly popular intermittent fasting approach that may have greater long-term adherence and lead to better weight maintenance.

A previous randomized controlled trial by the same research team published in Nature Medicine found that reducing the eating window from 12 hours or more to eight hours per day decreases body weight and improves cardiometabolic health. However, the impact of eating window timing on the long-term maintenance of benefits remains unknown.

To find out more, researchers conducted a 12-month follow-up of the randomized controlled trial in 99 adults with overweight or obesity (50% women; average age 49 years; average BMI: 32 kg/m²) from Granada (Spain) to investigate whether the weight loss achieved after three months of TRE is sustained for 12 months.

Participants were randomly assigned to one of four groups for 12 weeks: habitual eating window of 12 hours or more; early TRE (eight-hour eating window starting before 10:00); late TRE (eight-hour eating window starting after 13:00); self-selected TRE (allowing participants to choose their own eight-hour eating window, which might improve adherence, acceptability, and efficacy). All groups also took part in a Mediterranean diet education program to encourage them to eat healthier.

Researchers measured body weight, waist and hip circumferences at the start of the trial, after the 12-week intervention, and 12 months after the intervention had ended.

After the 12-week intervention, the habitual eating group experienced an average weight loss of −1.4 kg (−1.5%). All TRE groups achieved significantly greater weight loss than the habitual eating group, with an average weight loss of −4.2 kg (−4.5%) in the early TRE group, −3.1 kg (−3.5%) in the late TRE group, and −3.8 kg (−3.9%) in the self-selected TRE group.

Additionally, the habitual eating group had a lower waist circumference (−1.1 cm) and hip circumference (−1.4 cm) after 12 weeks of intervention. In comparison, the early TRE group experienced significantly greater reductions in waist and hip circumferences (average −4.1 cm and −4.6 cm, respectively).

The late TRE group also achieved a significant reduction in waist circumference (average −4.1 cm), but there was no significant reduction in hip circumference (average −3.2 cm). Although not statistically significant, the self-selected TRE group also achieved reductions in waist and hip circumferences (average −3.7 cm and −3.6 cm respectively).

All TRE groups maintained greater weight loss than habitual eating at 12 months

Twelve months after the intervention ended, preliminary results reveal that the habitual eating group had an average body weight increase of 0.4 kg (+0.5%).

Both the early TRE and the late TRE groups maintained significantly greater weight loss compared to the habitual eating group (average −2.1% [−2.2 kg] and −2.0% [−2.0 kg] respectively). Although not statistically significant, the self-selected TRE group also maintained greater body weight loss than the habitual eating group (average −0.7% [−0.7 kg]).

At the same time, the habitual eating group showed an increase in waist circumference of +1.8 cm at 12 months, and a slight increase of +0.03 cm in hip circumference.

In comparison, both waist and hip circumferences remained significantly lower in the late TRE group (average −5.6 cm and −3.4 cm respectively) compared with the habitual eating group. Although not statistically significant, the early TRE group and self-selected TRE group also showed lower values in waist (average −0.5 cm and −1.3 cm respectively) and hip circumferences (average −1.0 cm and −1.8 cm respectively).

Importantly, there were no significant differences between the TRE groups in any measurement, indicating that the simple 3-month lifestyle intervention may be an effective long-term approach for sustaining weight loss, irrespective of the timing of the eating window.

No serious adverse events were reported during the 12-week intervention, and only five participants reported mild adverse events, all of whom chose to discontinue the intervention. Another important finding from the study was that TRE was well accepted by participants with adherence rates of 85−88%.

“This kind of intermittent fasting appears feasible for adults with overweight or obesity who wish to have a relatively simple way of losing and maintaining weight loss that is less tedious and more time-efficient compared with daily calorie counting, but it warrants further investigations in larger and longer-term studies,” said Dr. Jonatan R. Ruiz, study coordinator of the University of Granada, Instituto de Investigación Biosanitaria de Granada (ibs.GRANADA) and Centro de Investigacion Biomedica en Red Fisiopatologia de la Obesidad y Nutrición (CIBEROBN) in Spain.

Provided by
European Association for the Study of Obesity