Share on PinterestWhen is it best to eat and when to fast, to reap the most benefits? Image credit: mrs/Getty Images
- There has been an increase in the popularity of time-restricted eating, also known as intermittent fasting, over the last few years.
- Past studies show following time-restricted eating might improve certain health areas, including metabolic health.
- A new study found that when you eat when following time-restricted eating, and how large your eating window is, matters when it comes to metabolic health benefits.
With an increase in the popularity of time-restricted eating, which is a form of intermittent fasting, over the last few years researchers have been examining how this type of eating pattern might impact different areas of a person’s health.
For example, in addition to weight and fat loss, past studies show that following time-restricted eating might help a person’s blood sugar control, blood pressure, and insulin sensitivity.
Previous research has also tied time-restricted eating to possibly improving brain, metabolic, heart health.
Now, a new study published in the journal BMJ Medicine reports that when you eat when following time-restricted eating, and how large your eating window is, matters when it comes to metabolic health benefits.
Time-restricted eating: Time of day and eating window size
For this study, researchers analyzed health data from 41 previous randomized controlled trials, including more than 2,200 participants.
Scientists categorized time-restricted eating participants by the time of day they ate — early, mid, or late in the day, or self-selected — as well as how long their daily eating window was, including less or more than eight hours or exactly eight hours.
“Time-restricted eating has gained substantial public and scientific interest because it does not require calorie counting or specific food restrictions, which makes it easier for many people to follow,” Ling-Wei Chen, PhD, an associate professor in the College of Public Health-Institute of Epidemiology and Preventive Medicine at National Taiwan University and senior author of this study, told Medical News Today.
“However, existing studies have used different definitions of time-restricted eating, particularly with respect to eating timing,“ Chen noted. “We wanted to move beyond asking whether time-restricted eating works and instead examine how the timing and duration of the eating window shape metabolic outcomes.”
“Metabolic diseases such as obesity, type 2 diabetes, and cardiovascular disease continue to rise globally,” he continued.
“Many people struggle to sustain complex or highly restrictive diets, so identifying simpler, more practical strategies that fit real-world lifestyles is essential. Research that expands our understanding of how and when we eat, not just what we eat, can offer more accessible and scalable approaches to improving metabolic health.”
– Ling-Wei Chen, PhD
Eating early, mid-day best for metabolic outcomes
At the study’s conclusion, researchers found that participants following early and mid-day time-restricted eating experienced better outcomes, including a lowering of body weight, waist circumference, body mass index (BMI), fat mass, systolic blood pressure, and fasting glucose (blood sugar) levels, when compared to participants who ate late in the day.
“These findings highlight that aligning food intake earlier in the day, when metabolic processes such as insulin sensitivity are more favorable, may amplify the benefits of time-restricted eating,” Chen explained.
“The results suggest that not all time-restricted eating patterns are equal. Eating earlier appears to confer broader metabolic advantages compared with delaying food intake to later hours,” he added.
Additionally, scientists discovered that late-day eating, when combined with a longer eating window, was the least effective dietary pattern for the most metabolic benefits.
“This result underscores that simply labeling an eating pattern as time-restricted does not guarantee metabolic benefit,” Chen further noted.
“When eating is concentrated late in the day and spread over a still relatively longer window, it may conflict with circadian rhythms that regulate metabolism. This helps explain why some time-restricted eating trials show mixed results and reinforces the importance of considering both timing and duration together.”
– Ling-Wei Chen, PhD
Unsurprising findings on time-restricted eating
MNT had the opportunity to speak with Mir Ali, MD, a bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, about this study.
Ali, who was not involved in the research, commented that he was not surprised at all by the findings, as other studies have shown the benefits of time restricted eating and not eating later in the evening.
“With the rise in obesity, and therefore metabolic problems associated with obesity, the need to find better solutions will only increase,” he explained. “Unfortunately, no single method can work for all people, therefore, having multiple options and methods to improve metabolic health is essential.”
“Additional research into the most effective diets to pair with time restricted eating would also be greatly beneficial,” Ali added.
What is the best time for a time-restricted eating schedule?
For those who may want to give time-restricted eating a try, Monique Richard, MS, RDN, LDN, a registered dietitian nutritionist and owner of Nutrition-In-Sight, offered some tips on how to figure out the best time of the day and size of eating window that is best for each individual to follow.
First, Richard said, is to start with your natural rhythm, and not necessarily the clock:
“Observe your hunger and satiety cues, your schedule, what feels comfortable and supportive and what you tend to gravitate toward (type of food, liquid, solid, hot, cold, etc). The evidence suggests that aligning your eating window with your natural circadian rhythm — that is, earlier in the day when metabolism is more active — may offer more benefits than eating late. However, it is also important to consider what you may be experiencing in your body, life and current circumstances.”
Next, choose an eating window you can stick with, Richard advised.
“A consistent eating window, whether 8, 10, or 12 hours, that fits your lifestyle and sleep schedule is more important than picking an arbitrary number,” she explained.
“Consistency helps your body anticipate when food is coming, which supports metabolic regulation. For many people, earlier eating windows (e.g., 8:00am–6:00pm) align better with circadian biology, supporting glucose tolerance and metabolic flexibility,” she noted.
Additionally, Richard said it is important to keep in mind your sleep and activity schedule, and not to forget food quality within your eating window.
“Keep in mind as well that there are no ‘hard and fast rules’ or ‘right way’ to an individual’s eating pattern,” she continued. “Bringing judgment, unnecessary stress, and rigidity into our lives around feeding and nourishing our bodies is counterproductive to health. Time-restricted eating is not about eating less but about eating to complement your body’s internal clock and support functionality.”
