Most advocates for intermittent fasting promote a restrictive eating window as low as six hours, but the findings from this study show that eating in a less restrictive eating window of ten hours still has positive health benefits such as changes in hunger, mood, and energy levels. Those who were consistent with their eating window experienced greater benefits than those who varied their eating windows.
“This is the largest study outside of a tightly controlled clinic to show that intermittent fasting can improve your health in a real-world setting. What’s really exciting is that the findings show that you don’t have to be very restrictive to see positive results. A ten-hour eating window, which was manageable for most people, improved mood, energy levels, and hunger. We found for the first time that those who practised time-restricted eating, but were not consistent day to day, did not have the same positive health effects as those who were dedicated every day,” said Dr. Sarah Berry, from the School of Life Course & Population Sciences and chief scientist at ZOE
This study involved 37,545 participants who were enrolled in the ZOE Health App and who completed the core intervention period for three weeks. The participants were asked to eat as they normally would for the first week and then begin an IF schedule with a ten-hour eating window for two weeks. More than 36,231 participants opted to continue for additional weeks, and 27,371 were classified as being highly engaged in the program. Of the highly engaged participants, 78% were female with a mean age of 60 and a BMI of 25.6. Additionally, those with a longer eating window before the intervention experienced even greater health benefits.
Kate Bermingham PhD, from King’s and ZOE, said: “This study adds to the growing body of evidence showing the importance of how you eat. The health impact of food is not just what you eat but the time at which you choose to consume your meals, and eating window is an important dietary behaviour that can be beneficial for health. Findings shows that we don’t need to be eating all the time. Many people will feel satiated and even lose weight if they restrict their food to a ten-hour window.”
According to the ZOE website, on average the participants reduced their eating windows by two hours, and 16 weeks later more than 5,000 of the participants were still maintaining the 10-hour eating window. On average participants had an 11% increase in mood positivity (reduced anxiety/nervousness), a 6% reduction in feelings of hunger, and a 22% increase in energy levels compared to before starting IF. Those who extended the eating window beyond the 2-week mark also experienced other benefits, close to 64% reported improved gut health with symptoms of bloating improving by an average reduction of 11%.
Overall, 58% of the participants consumed fewer snacks during IF with participants consuming on average less than one snack per day. However, there was variation depending on the timing of the eating window and when the window closed. Those who closed their windows later tended to eat more snacks, and those who were night owls also tended to be more unpredictable snackers.
