- Intermittent fasting is the practice of eating during specific time frames while reducing calorie intake or abstaining from food at certain times, and research on its health benefits is ongoing.
- A recent secondary analysis found that participating in a form of intermittent fasting called time-restricted eating for 12 weeks maintained weight-loss effects at the one-year mark.
- These weight-loss benefits were observed regardless of when this 8-hour eating window occurred.
Research is ongoing on how what people eat and when they eat it affects weight loss and other aspects of health. A recent study published in Clinical Nutrition examined the effects of certain intermittent fasting methods on weight loss 1 year later.
This research explored eating within an 8-hour window, with that window starting at varying times.
The results showed that just 12 weeks of time-restricted eating helped maintain long-term weight loss. However, some participants also lost non-fat mass, raising concerns about health risks.
Testing time-restricted eating in 4 ways
The authors of this study note that keeping weight off after losing it can be difficult, so it’s critical to discover methods that support sustained weight loss. Time-restricted eating is a type of intermittent fasting in which people can eat what they want, but only within a specific time window of less than 10 hours.
The researchers wanted to see how time-restricted eating impacted weight loss in the long term. They did a secondary analysis of a randomized trial, focusing on a subsample of 99 participants.
These participants were between the ages of 30 and 60 and either had overweight or obesity. For 12 weeks, participants engaged in 1 of 4 eating patterns:
- Early time-restricted eatingwhere participants ate within an 8-hour window that started before 10 am
- Late time-restricted eatingwhere participants ate within an 8-hour window that started after 1 pm
- Self-selected time-restricted eatingwhere participants chose when they wanted their 8-hour eating window to be, before the intervention started
- Usual eating windowwhere participants ate at their typical times
In addition, all participants received education about following a Mediterranean dietary pattern and engaging in physical activity. Participants reported when they first and last ate using a mobile app.
Effects of time-restricted eating one year later
After 12 weeks, the researchers didn’t tell participants to stop or continue the timing pattern they had to use during the study, and there was a follow-up 1 year later. At the 1-year mark, participants reported whether they had practiced time-restricted eating since the intervention ended. Researchers also evaluated other components, such as body mass index and fat mass.
Among the 99 participants, only 65 completed the one-year follow-up assessment. Most participants in the time-restricted eating groups adhered to their eating schedule parameters throughout the intervention. At the one-year mark, 26% of participants reported using time-restricted eating on their own after the end of the intervention.
The results at the one-year mark showed a benefit to time-restricted eating. For the early and late time-restricted eating groups, there was a greater maintained loss of body weight compared to the control group that didn’t do time-restricted eating.
All three time-restricted groups also maintained a lower neck circumference. The late time-restricted eating group maintained larger decreases in waist and hip circumference, but also saw a decrease in fat-free mass.
Researchers also found that fat mass stayed lower in the early time-restricted eating group and that the group maintained “a tendency toward fat-free mass reduction.”
Pooling all 3 time-restricted eating groups showed better results as well. This group showed larger decreases in body weight, fat mass, and neck and waist circumference, and also larger decreases in fat-free mass than the usual care group.
Participants who said they did time-restricted eating after the intervention also maintained lower fat-free mass than participants who didn’t do time-restricted eating during this follow-up. Finally, researchers found that most of the weight loss that occurred happened in the first 6 weeks of the intervention.
Study authors Dr. Alba Camacho-Cardenosa, researcher at the Biosanitary Research Institute of Granada (ibs.GRANADA) and the Instituto Mixto Universitario Deporte y Salud (iMUDS), University of Granada, and Professor Jonatan R. Ruiz, Professor in the Department of Physical and Sports Education at the University of Granada, Principal Investigator of the project, and Co-Director of the PROFITH CTS-977 Research Group, explained the following:
“One year after completing the 12-week intervention, participants who had followed a TRE (time-restricted eating) schedule maintained greater weight loss than those who had received standard nutritional advice alone.”
“Interestingly, the benefits were observed regardless of whether the eating window was early in the day, late in the day, or self-selected, suggesting that reducing the daily eating window itself may be more important than the specific timing,” they told Medical News Today.
“One possible explanation is that TRE is a relatively simple strategy that people can easily summarize whenever they feel they are regaining weight,” they added.
What the study may be overlooking
How researchers chose to conduct their analysis may have affected the results, as well as any limitations in the original research. Researchers note that this secondary analysis focused solely on secondary outcomes and included only participants from one center in the original research.
There were a fairly small number of participants, and even fewer completed the one-year assessment. Each group’s size was small at follow-up, particularly the group that chose their 8-hour window for eating, limiting certain sensitivity analyses. Researchers admit that “the study may have been underpowered to detect small to moderate effects” in the group that chose their eight-hour eating window.
Some data relied on participant reporting. The authors note that they did not objectively measure changes in lifestyle factors, which could have influenced outcomes in the long term. Participants also used a mobile app to report information, which could have affected who participated in the study.
Body mass index was one measured component, which has its limits. Researchers note the limitations of their evaluation of changes in fat-free mass and caution about these results. They also note limits in how they assessed body composition. Some aspects, such as mid-thigh skeletal muscle tissue, were measured only during the initial intervention.
A number of participants reported continuing intermittent fasting after the intervention ended, suggesting ongoing benefits rather than effects that persist only after the intervention.
Finally, it’s worth noting that the weight loss in the late and self-selected time-restricted feeding groups was mainly due to fat-free mass loss, so timing may still be an important factor to consider when it comes to time-restricted eating.
Mir Ali, MD, bariatric surgeon, bariatric medicine specialist, and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, who was not involved in the study, noted the following about continued research in this area:
“Further research with larger patient cohorts and extended timeframes is necessary to better define both the long-term benefits and any potential negative effects.”
Intermittent fasting best supplements a healthy diet
Overall, the study suggests a weight loss benefit from time-restricted eating, even at the one-year mark. People interested in intermittent fasting should consult licensed medical professionals to determine whether it would be appropriate for their situation.
The researchers also note that some of their findings support the use of muscle-preserving strategies to improve body composition. Dr. Randa Abdelmasih, an endocrinologist with UTMB, who was not involved in the study, commented the following:
“The reduction in fat-free mass deserves attention. Preserving lean muscle is increasingly recognized as an essential component of healthy weight loss, particularly as we see more patients treated with highly effective anti-obesity medications. Any dietary strategy that promotes weight loss should also emphasize adequate protein intake and resistance exercise to minimize muscle loss.”
Ruiz and Camacho-Cardenosa also noted:
“Our findings suggest that TRE could become a useful and relatively simple lifestyle approach to help people sustain weight loss after completing a structured weight-management program.”
“Importantly, in our study, TRE was combined with nutritional education based on the Mediterranean diet. Therefore, we believe that time-restricted eating should not be viewed as a substitute for healthy eating, but rather as a strategy that can complement an overall healthy lifestyle.”
—Ruiz and Camacho-Cardenosa, study authors
