Intermittent Fasting Kept Some Weight Off for a Year, but Muscle Loss Remained
A 12-week trial found lasting weight reductions after intermittent fasting, while early eating better preserved fat loss and lean mass remained a concern.
Intermittent fasting’s longer-term result may depend on more than whether the scale stays down. In a study of adults who were overweight or obese, early and late eight-hour eating windows were linked to greater weight reduction than usual eating patterns one year after the programme ended. But muscle loss during the intervention was not fully recovered, and early eating produced a more favorable balance of fat loss.
Researchers at the University of Granada followed 99 adults through a 12-week intervention and then checked in 12 months after it concluded. Everyone received education about the Mediterranean diet. Participants were assigned to a control group that kept usual eating patterns or to one of three groups using an eight-hour daily eating window. The study appeared in Clinical Nutrition.
What the follow-up found
The fasting groups differed in when participants chose to eat. The early group selected a window that began before 10:00 a.m.; the late group chose one beginning after 1:00 p.m. A third group could pick its preferred eight-hour window. The control group ate across 12 hours or more.
During the year after the formal programme, participants were no longer required to keep a strict schedule. At the 12-month follow-up, the early and late groups had maintained significantly greater weight loss than the control group. They retained roughly half of their initial weight loss, with an average overall reduction of 2.5%.
That finding matters because the study looked beyond the end of a structured intervention. Short-term weight reduction alone can’t show whether a routine remains useful when participants are no longer following a prescribed schedule. Here, the group differences were still evident a year later, although the reported average reduction was modest.
Body composition adds an important qualification. Only the early-window group maintained a statistically significant reduction in fat mass compared with the control group at the 12-month mark. Both early and late schedules were associated with sustained weight reduction, but the results suggest that the timing of an eating window may affect what kind of weight is lost.
“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,” said lead author Dr Alba Camacho Cardeñosa.
Muscle loss complicates the result
The study also found that some of the initial weight reduction in the fasting groups came from fat-free mass, which includes muscle tissue. That lean tissue loss had not been fully recovered at the one-year follow-up. The concern was especially pronounced in the late-window group, where weight reduction was driven predominantly by lean mass reductions. The early group showed a better balance of fat loss.
For cyclists, scale weight doesn’t tell the whole story. Lower body weight may be one goal, but losing muscle can work against the strength and power needed for riding. These findings don’t establish that every person who fasts will lose muscle, or that one eating schedule will suit every athlete. They do show why tracking body composition and maintaining adequate support for muscle should be part of any weight-loss plan.
The article’s practical suggestions are to place the eating window earlier in the day, and to pair time-restricted eating with resistance work and protein intake. It gives 9:00 a.m. to 5:00 p.m. as an example of an early window and recommends upwards of 1.6 g of protein per kg of body weight during the eight-hour eating period. Those figures are reported recommendations in the source article; the trial details provided here don’t establish that they were tested as a specific muscle-preserving programme.
Adherence without a required schedule
During the follow-up year, participants received no coaching or enforcement around fasting. Roughly one in three participants—26%—chose to continue practising intermittent fasting on their own. That offers a glimpse of how the approach fit into daily routines for some people, though it doesn’t show why they continued or whether continued fasting caused the weight differences observed at follow-up.
For active readers considering time-restricted eating, the clearest takeaway is a trade-off: the study found that some weight reduction persisted after a short programme, while lean mass remained a concern. An earlier eating window was associated with sustained fat-mass reduction, but the results don’t amount to a guarantee of improved cycling performance. Any approach should leave room to eat enough to support training and recovery. The longer-term measure that matters is not only whether weight stays lower, but whether the change is compatible with strength and the work athletes want to do.
