Georg Hafner PhD , 2025-08-29 14:00:00
Does the time of day that you eat affect the success of intermittent fasting? Spanish scientists explored whether the time of day you eat your meals helps or hinders weight loss. So can you hack hunger hormones by scheduling your dinner for late at night instead of early afternoon?
According to this Nature Medicine research paper, the time of day doesn’t matter; just stick to an eight-hour window for sustainable success.
Time-Restricted Eating (TRE), a type of intermittent fasting, is a simple and safe approach that limits meals to an 8-hour window. New clinical trial data out of Granada, Spain, reports it can lead to meaningful weight loss in overweight adults without strict dieting or complicated timetables.
Participants who stuck to an 8-hour eating window lost more weight than those who ate without time restrictions. It didn’t matter when they scheduled their eating window, whether early or late, the weight loss results were the same. Just as importantly, people on the time-restricted eating plan showed no signs of negative impact on their mood, sleep, quality of life or metabolic indicators.
The team concluded that intermittent fasting using a daily 8-hour window is a safe, flexible and sustainable approach to managing weight.
What is Time-Restricted Eating?
The idea behind Time-Restricted Eating is delightfully simple: you don’t need to control what you eat; you control when you eat. Time restricted eating is a type of Intermittent Fasting (IF) that has drawn a lot of attention in recent years. While IF has many forms – for example, the 5:2 diet or alternate day fasting – TRE focuses on having a single daily eating window. Usually, this window is eight hours long, and within these eight hours you are free to eat whatever you want1.
That’s it.
No complex rules, calorie-counting apps or guilty feelings for saying ‘yes’ to dessert. You don’t need to swap your grandma’s lasagna for an asparagus-broccoli-ginger smoothie to detox your kidneys. You simply dine during the eight hours you set for eating and then stop for the next 16 hours.
Is TRE backed by science?
So is TRE supported by science? It all sounds almost too good to be true, but in a recent, well-executed study published in Nature Medicine earlier this year, researchers put TRE to the test2.
Scientists from several universities and research centres in Spain came together to evaluate the effects carefully of TRE among overweight adults. The researchers designed experiments to answer important questions on TRE:
- Can TRE help you lose weight?
- Does the timing of the 8-hour eating window matter?
- Is TRE safe?
The investigators discovered that TRE helped participants lose an average of around 6 lbs each over the 12-week trial, versus the approximately 3 lb lost by participants in the control group. On average, people who followed time restricted eating ate 250 kcal fewer per day than the folk who could eat wherever they wanted.
The time of day when people scheduled their eating window did not matter. The weight loss was the same regardless of whether they ate early or late in the day2.
What’s more, weight loss due to time-restricted eating was safe. Participants didn’t report any change in their quality of life, their sleep or their mood3. Blood tests showed that, during the experiment, important metabolic indicators like fasting glucose, insulin or blood lipids were normal compared to the control group. So no need to worry that pushing breakfast back a few hours will disrupt your hormones or hurt your metabolism. In fact, fasting glucose even improved slightly, so this could be a plus for people struggling with insulin resistance.
All in all, the study shows that TRE is an effective, easy to implement and safe approach to weight loss.
Does Time of Day Affect Success of Intermittant Fasting?
How did they test the time restrictions? The beauty of this trial was its careful design. The simplicity of time restricted eating worked in favour of researchers. Rather than relying on self-reported food diaries, participants would only need to stick to their scheduled dining windows. Unlike in many other trials, forgetfulness and fibs would not be an issue-the food they ate did not matter, just when they ate it. This allowed the diet detectives to set up a randomized controlled trial to compare the effects directly of different eating windows.
The team recruited 197 overweight, adult men and women and assigned them to one of four groups:
1. Early TRE: Participants chose an 8-hour eating window that began no later than 10 a.m.
2. Late TRE: Participants chose an 8-hour eating window that began no earlier than 1 p.m.
3. Self-selected TRE: Participants chose their own 8-hour eating window
4. Control group (no TRE): Participants could eat whenever they wanted.
Importantly, all participants had to stick to their assigned dining schedule for 12 weeks. Everyone received nutritional education based on the Mediterranean diet. Folk in the time restricted eating groups were free to eat what they liked, so long as they stuck to the eight-hour window.
At the start of the study and the end, the scientists weighed all the participants, checked their body composition and took blood samples. At the close they repeated the measures so that they could see how each person’s vital statistics changed, and in such a way that they could compare the groups to each other.
Flexible Food for Busy Lives
After 12 weeks participants in the time-restricted eating groups lost an average of about 3 lbs more than those in the control group. It did not make a difference whether the 8-hour window was early, late or self-selected. The weight loss was roughly the same in all three TRE groups and significantly more than in the control group.
The important result of this study is that the researchers showed that restricting your eating to an 8-hour window is what’s important, not the time of day. This is great news for people with busy lives. If you are a morning person who needs an early breakfast, you can move your dinner to an earlier time. If you want to have a late supper after work with your family, you can push your breakfast later in the day. You don’t need to set the same time every day and you don’t need to split your time into complicated schedules. Set an alarm on your phone and you are good to go.
Despite the rather off-putting name, time-restricted eating didn’t make people cranky, miserable or tired. The researchers used questionnaires as part of a secondary analysis to check in with participants throughout the trial. Participants in the TRE groups did not report a lower quality of life; their quality and duration of sleep did not change, nor did it cause anxiety or bad mood. They didn’t find that their time-restricted eating disrupted their social lives or had them missing out on fun with friends and family. The length of the 8-hour time window helped to avoid the social pitfalls of rigid intermittent fasting schedules and forbidden foods.
How Does Time Restricted Eating Make You Lose Weight?
So how does time-restricted eating/intermittent fasting work? What is it about this method that gives it the edge over regular ‘healthy eating’ plans? So far there is no evidence that fasting for a specific amount of time or only eating at very specific times can turbo charge your metabolism. The truth seems so far to be more grounded in practicality than in metabolic mysteries. The data gathered during the trial did not point to any special changes taking place. Eating early or late did not change metabolic markers or how the body processed fat. In truth, the participants’ physiology did not look any different to people following a regular calorie controlled diet.
What’s really going on is that time restricted eating helps people to develop a more considerate approach to eating. They might plan their meals more intentionally and not follow their impulse to order a pizza when working late. Besides, fewer eating hours often means fewer opportunities to snack.
This more careful approach to eating might explain why participants in the TRE groups ate, on average, about 250 kcal less than the control group. Time restricted eating works because people reduce their overall daily calorie intake. Two hundred and fifty kilocalories might not sound a lot but maintained over weeks, months and years this small reduction adds up to a substantial weight loss.
In a Perfect World…
Before you toss out your measuring cups, let’s consider the limitations of this study. A 12-week duration is relatively short, especially when assessing more profound changes, like body composition or long-term metabolic health. Apart from weight loss, there might be more benefits to TRE that become apparent only after several months.
The study also comes with a cultural caveat. This study took place in Spain, where people tend to have dinner around 10 p.m., later than almost every other nation in the world. This means people in Granada already have an unusually wide eating window. Spaniards who took on TRE likely had to overhaul their eating routines more dramatically than people in other countries would. This would mean it’s easier to cut 250 kcal in Madrid than in Milwaukee.
The Best Diet is The Diet You Can Live With
Sustainable weight loss is a long-term process. Pushing back against the risk of cardiovascular illnesses and type 2 diabetes needs a metabolic marathon mindset rather than a beach body sprint. Switching diets like lanes on the highway is not a recipe for long-term success.
Dieting should not be carried by the-biggest-loser-mentality, where the most amount of weight in the shortest amount of time counts. A healthy diet is a lifelong commitment carried by consistent, daily habits.
The best diet is the diet you can live with, and TRE might be that diet. It doesn’t involve a fundamental change in what you eat, just a small change to when you eat. You can choose your 8-hour window of eating on a daily basis and structure your meals around it. When life throws a curve ball, you can just change the start time of your eating window to accommodate it.
Time restricted eating does not ask you to give up your favourite food, only to shift when you enjoy it. Done consistently, TRE might help you find an approach to eating that supports you to reach and maintain a weight that feels right for you.
References:
1: Dote-Montero M, Clavero-Jimeno A, Labayen I, Ruiz JR. Intermittent fasting and health: Does timing matter? Clin Transl Med. 2025 May;15(5): e70325. doi: 10.1002/ctm2.70325.
2: Dote-Montero, M., Clavero-Jimeno, A., Merchán-Ramírez, E. et al. Effects of early, late and self-selected time-restricted eating on visceral adipose tissue and cardiometabolic health in participants with overweight or obesity: a randomized controlled trial. Nat Med 31, 524–533 (2025). doi: 10.1038/s41591-024-03375-y
3: Clavero-Jimeno A, Dote-Montero M, Migueles JH, et al. Time-Restricted Eating and Sleep, Mood, and Quality of Life in Adults With Overweight or Obesity: A Secondary Analysis of a Randomized Clinical Trial. JAMA Netw Open. 2025;8(6): e2517268. doi:10.1001/jamanetworkopen.2025.17268