Intermittent Fasting Maintains Long-Term Weight Loss Irrespective of Meal Timing, Study Shows

Key Takeaways: 

• Adults living with overweight or obesity who followed a 16:8 fasting pattern for 12 weeks kept off significantly more weight a full year after the intervention ended.
  
• The benefit held whether the eight-hour eating window fell early or late in the day, giving people the freedom to fit fasting around their own routines.
  
• One in three participants chose to carry on fasting unprompted during the follow-up year, pointing to a habit that is relatively easy to sustain.
  
  
  

A twelve-week habit with lasting results

New research has shown that confining daily food intake to an eight-hour window helps people living with overweight or obesity maintain their weight loss 12 months after a structured intervention comes to an end. The work was carried out by scientists from the University of Granada (UGR), the Granada Institute for Biomedical Research (ibs.GRANADA), the Public University of Navarra and the Biomedical Research Networking Center (CIBER), and was recently published in the journal Clinical Nutrition.

The trial followed 99 adults, half of them women, all of whom were living with overweight or obesity. It focused on intermittent fasting, and specifically the approach widely known as 16:8, in which people fast for 16 hours and eat only during the remaining eight. The findings indicate that this pattern is an effective way to hold on to weight loss over the medium term.

Crucially, the researchers found that the benefits endured a year later regardless of when the eating window fell. Whether participants ate early in the day, between 9 a.m. and 5 p.m. (early fasting), or later on, between 1 p.m. and 9 p.m. (late fasting), they fared better than people who kept to their usual routine of eating across a window of 12 hours or more. Both the early- and late-fasting groups sustained significantly greater weight loss at 12 months, and the early-fasting group also held on to a greater reduction in fat mass. According to the team, this suggests that the approach is not only feasible and effective in the short term but also produces effects that last.

Body composition assessed one year later

For the first 12 weeks, participants were split into four groups, each of which took part in a Mediterranean diet education programme. A control group kept its usual eating window of 12 hours or longer. An early-fasting group used an eight-hour window that began before 10 a.m., while a late-fasting group used an eight-hour window that started after 1 p.m. A fourth, self-selected group chose its own eight-hour window.

Weight, fat mass and fat-free mass were measured before and after the 12-week intervention, and again a year after the study finished. The work forms part of a larger project whose principal results appeared in the journal Nature Medicine. That analysis found that people who practised time-restricted eating (TRE), whatever their eating schedule, lost an average of 3–4 kilograms (6.6–8.8 pounds) more than those given nutritional advice alone.

Dr Alba Camacho Cardeñosa, a researcher at the University Joint Institute for Sport and Health (iMUDS) at the University of Granada and a postdoctoral fellow at ibs.GRANADA in the Endocrinology and Nutrition Department at San Cecilio University Clinical Hospital, is the study’s first author. She explains that “to date, although we knew that intermittent fasting promotes modest weight loss in the short term, it was unclear whether its effects were sustained over time. By evaluating the participants 12 months after the intervention ended, we demonstrated that the changes in body weight persist.”

The researchers also point to the strength of ongoing adherence, noting that “a very positive finding is that one in three people decided to continue practicing intermittent fasting on their own during that year of follow-up, suggesting that it is a relatively easy habit to integrate into daily life.”

A flexible strategy against obesity

The study was led by researchers from ibs.GRANADA belonging to the PROFITH CTS-977 research group at the University of Granada, headed by Professor Jonatan Ruiz Ruiz. It was conducted in collaboration with the San Cecilio University Clinical Hospital and the Virgen de las Nieves University Hospital in Granada, the Public University of Navarra, the CIBER on Obesity (CIBEROBN) and the CIBER on Frailty and Healthy Aging (CIBERFES).

The team emphasises that as little as 12 weeks of intermittent fasting may serve as an effective medium-term strategy for weight management in adults living with overweight or obesity. Because both early- and late-day regimens proved effective, the findings give people the flexibility to choose the schedule that best fits their lifestyle, which may in turn improve adherence and support more successful obesity treatment.