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.
CCH insights:
These are very encouraging results for the use of time-restricted eating (TRE) as a strategy for weight loss maintenance. It would be good to now see research into the use of TRE as a tool to prevent weight regain after cessation of GLP-1 therapy. If TRE is adopted during GLP-1RA treatment, and continued after stopping the medication, could it help maintain weight loss and cardiometabolic gains?
Helping patients hold on to their gains — during treatment and in the months after it ends — is exactly the terrain of our two-hour CPD course GLP-1RAs in Practice: Supporting Patients During Treatment, which covers nutrition, monitoring and preparing patients for life after treatment for any clinician managing the full arc of GLP-1RA care.
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New Cochrane Review Finds Intermittent Fasting Offers No Clear Weight Loss Advantage
Key Takeaways:
- A major Cochrane review found intermittent fasting did not lead to clinically meaningful weight loss compared with standard dietary advice or no structured diet.
- Evidence on safety and long-term outcomes remains limited due to small trials, inconsistent reporting, and short follow-up periods.
- Experts caution against overinterpreting social media claims and emphasise the need for individualised, long-term approaches to weight management.
Intermittent fasting under scrutiny
Intermittent fasting has become one of the most widely promoted dietary strategies for weight loss, often presented as a superior alternative to conventional calorie reduction. However, a new Cochrane review suggests that these claims may not be supported by robust evidence.
According to the review, intermittent fasting does not appear to deliver greater weight loss than standard dietary advice or even no specific diet plan. The findings challenge the widespread perception that structured fasting schedules offer a unique or clinically meaningful advantage for people who are overweight or living with obesity.
Obesity remains a global public health challenge
Obesity continues to represent a major public health concern worldwide and is now among the leading causes of death in high-income countries. Data from the World Health Organization show that global adult obesity rates have more than tripled since 1975. By 2022, an estimated 2.5 billion adults were classified as overweight, including around 890 million adults living with obesity.
Against this backdrop, intermittent fasting has gained substantial attention. Eating patterns such as alternate-day fasting, periodic fasting, and time-restricted feeding are widely promoted across social media platforms, often accompanied by claims of rapid weight loss and metabolic benefits.
What the review examined
To assess whether intermittent fasting truly offers an advantage, researchers analysed 22 randomised clinical trials involving 1,995 adults across North America, Europe, China, Australia, and South America. The studies evaluated a range of fasting approaches, including alternate-day fasting, periodic fasting, and time-restricted feeding. Most trials followed participants for up to one year.
When outcomes were compared with those of traditional dietary advice or no dietary intervention, intermittent fasting did not result in a clinically meaningful difference in weight loss. In practical terms, fasting-based approaches did not outperform more conventional strategies.
Limited evidence on safety and long-term outcomes
The review also highlighted substantial limitations in the available evidence. Reporting of side effects varied widely between studies, and many trials were relatively small. Inconsistent data collection made it difficult to draw firm conclusions about safety or potential long-term effects.
As a result, the overall certainty of the evidence was judged to be limited.
“Intermittent fasting just doesn’t seem to work for overweight or obese adults trying to lose weight,” said Luis Garegnani, lead author of the review from the Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre.
Social media enthusiasm outpaces the evidence
Garegnani also warned against the level of enthusiasm surrounding intermittent fasting online. “Intermittent fasting may be a reasonable option for some people, but the current evidence doesn’t justify the enthusiasm we see on social media.”
A further concern is the lack of long-term research. Few studies have examined outcomes beyond relatively short trial periods. “Obesity is a chronic condition. Short-term trials make it difficult to guide long-term decision-making for patients and clinicians,” Garegnani added.
Generalisability remains uncertain
Most of the studies included in the review primarily involved white participants living in high-income countries. Given that obesity prevalence is rising rapidly in low and middle-income countries, the findings may not fully reflect outcomes in more diverse global populations.
The authors note that responses to intermittent fasting could vary depending on sex, age, ethnic background, underlying health conditions, or existing eating behaviours and eating disorders.
Implications for clinical practice
Given the current state of evidence, the review’s authors advise caution when recommending intermittent fasting as a weight loss strategy.
“With the current evidence available, it’s hard to make a general recommendation,” said Eva Madrid, senior author from the Cochrane Evidence Synthesis Unit Iberoamerica. “Doctors will need to take a case-by-case approach when advising an overweight adult on losing weight.”
Overall, the findings reinforce the need for personalised, sustainable approaches to weight management rather than reliance on highly promoted dietary trends.
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