Does Intermittent Fasting Actually Work Long Term? A New Study Has Answers

Intermittent fasting has become one of the most popular dietary strategies of the past decade, and one of its most accessible forms, time-restricted eating, has generated significant scientific interest. The concept is simple: Instead of eating whenever you want throughout the day, you confine all of your meals and snacks to an eight-hour window and fast for the remaining 16 hours. But one question has lingered over the research: Does it actually work in the long run, or do the benefits disappear once the structure is removed?

“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,” explained lead investigator Alba Camacho Cardeñosa, Ph.D., a researcher at the University Joint Institute for Sport and Health at the University of Granada.

A new randomized controlled trial published in Clinical Nutrition set out to answer exactly that, following participants for a full 12 months after a 12-week time-restricted eating intervention to see whether the weight loss held up over time. The results are encouraging.

How the Study Worked

Investigators recruited 99 adults with overweight or obesity, with an average age of 49 years and an average body mass index of 32. Participants were randomly assigned to one of four groups. The usual care group maintained their normal eating pattern of 12 or more hours per day. The early time-restricted eating group confined eating to an eight-hour window beginning before 10 a.m. The late time-restricted eating group used an eight-hour window starting after 1 p.m. The self-selected group chose their own preferred eight-hour window. All four groups also received education on the Mediterranean diet throughout the 12-week intervention period.

Body weight, fat mass and fat-free mass were measured at the start of the study, at six weeks, at 12 weeks when the intervention ended, and again at the 12-month follow-up.

What the Investigators Found

At the 12-month mark, both the early and late time-restricted eating groups had maintained significantly greater body weight loss compared to the usual care group. The early time-restricted eating group also showed significantly greater fat mass loss compared to usual care at 12 months. When all three time-restricted eating groups were combined and analyzed together, the advantages over usual care became even more pronounced.

One particularly noteworthy finding: Only about 26% of participants reported still actively practicing time-restricted eating during the 12-month follow-up period. That means the majority had stopped formally following the eating window, yet the weight loss benefits persisted. Researchers suggest that even a temporary period of structured time-restricted eating may produce lasting metabolic changes or establish habits that continue to support weight maintenance even after the formal intervention ends.

What This Means for You

The study suggests that a 12-week commitment to time-restricted eating, regardless of whether you prefer an early, late or self-selected eating window, may offer benefits that extend well beyond the intervention itself. You do not have to follow it perfectly forever to see lasting results.

It is worth noting that this was a relatively small study and all participants also received Mediterranean diet guidance, so the combination of both strategies may have contributed to the outcomes.

“By evaluating the participants 12 months after the intervention ended, we demonstrated that the changes in body weight persist,” Cardeñosa said. “A very positive finding is that 1 in 3 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.”