An introduction to time-restricted eating

11/8/2022

Introduction

Concepts like time-restricted eating (TRE) and intermittent fasting (IF) are all the rage right now. In this post we will dive into time-restricted eating specifically. What is it? What does the research say? What is my experience with it?

What is time-restricted eating?

First off, what is time-restricted eating? Well, the concept is pretty self-explanatory. It simply means that you eat and drink all your calories within a so-called feeding window every day. A feeding window has a start time and an end time.

For example, a feeding window could be between 11 am and 7 pm. This would be an 8-hour feeding window. The start and end times can vary, as can the length of the window. Different durations and start/end time combinations can have different effects.

Intermittent fasting and time-restricted eating

You may have also heard of the term intermittent fasting. Time-restricted eating and intermittent fasting are related concepts, but not entirely equal. The explanation that I usually reach for is that time-restricted eating is a subset of intermittent fasting. While time-restricted eating allows you to have a feeding window every day, other intermittent fasting practices like the 5:2 diet would have you eat normally five days of the week, while restricting your calories the other two. Another intermittent fasting practice could have you fasting an entire day every week, and eating normally the other six. So intermittent fasting is a much broader term than time-restricted eating. There’s also no defined focus on calories when doing time-restricted eating, as the smaller feeding window is a natural delimiter of calories. But at the same time, you should not eat junk food when doing time-restricted eating “just because you can”. Then the entire point of doing TRE is lost in my opinion. This post will only explore the time-restricted eating part of intermittent fasting. Other types of intermittent fasts will be covered in other posts.

What does the research say?

When you dive into the research of health-related concepts, the results and findings are often contradictory and confusing. There are a myriad of reasons for this in my opinion. First of all, it’s really hard to conduct studies on health-related concepts. It’s hard to get people to follow a diet or whatever it is that is being researched for a long period of time without slip-ups. It’s also hard to isolate the one specific lifestyle-factor that you are trying to research, which means that it’s hard to find causative relationships. Oftentimes correlations are the only result of a study, and correlations need to be taken with a grain of salt since they do not show a cause-and-effect relationship. Blinded randomized control trials (RCTs) are the gold standard of nutritional and lifestyle-related research, but they are often very expensive and time-consuming to conduct. In an RCT, factors that are not under direct experiment but that can still impact the result of the study are controlled for, meaning that the only thing that varies in the experiment is the factor under experiment. The blinding part simply means that participants are not aware of the intervention they received. This can for example be used to control for placebo effects. In addition, when researching health and lifestyle, you often want to show the long-term effects of lifestyle factors, which means that you have to conduct the study for a very long time, sometimes 10, 20 years or even longer. Also, a lot of companies and organizations pay for studies and use research to carry out their agendas, which further adds to the contradicting nature of this field of research.

Three studies on TRE

Keeping all this in mind, let’s look at this study, which turned some heads when it was published in the New England Journal of Medicine in April 2022. The authors conducted a yearlong study in which they had just over 100 obese participants randomly divided in two groups. The two groups both ate the same (low) amount of calories, with one group having a time-restricted eating window between 8AM and 4PM, and the other group could eat throughout the day according to their normal schedule. They concluded that no significant changes in weight loss, waist circumferences, BMI, body fat, blood pressure or other metabolic risk factors could be found between the groups, meaning that they awarded the results to the calorie restriction factor and not the time-restricted eating. However, there are some glaring problems with this study. First of all, they should have controlled for the eating window of the group that only did calorie restriction. According to their data, the group that only did calorie restriction had a median eating window of roughly 11 hours. So in a nutshell, this study is a comparison between an 8-hour feeding window and an 11-hour feeding window. Does a difference of three hours really do that much? It would have been better to have the non-TRE group have a feeding window of 14-16 hours. Second of all, they did not control for physical activity, which of course can skew the results as well.

Furthermore, let’s take a look at this meta-analysis, in which the authors sourced almost 500 articles in search of time-restricted eating’s effects on human health. They found that TRE induced fat loss independently of caloric restriction. They also concluded that TRE produced beneficial metabolic effects independently of weight loss, which would suggest that TRE has an intrinsic effect on human health that is disconnected from weight loss.

Last but not least, let’s look at an article that discusses different timings of the eating window. This article suggests that an early feeding window is more beneficial with regard to insulin resistance and other metabolic parameters in comparison with a midday feeding window. It has also been suggested that early time-restricted eating works better with our body’s circadian rhythm. The circadian rhythm is the daily cycle that our body naturally carries out each day, and is controlled by a group of nerve cells called the suprachiasmatic nucleus, or SCN for short.

Summary

To sum up, according to the research, time-restricted eating might lead to:

  • Increased cardio metabolic health
  • Weight loss
  • Fat loss
  • Improved blood sugar levels
  • Lower insulin resistance

But whether this is due to the natural calorie restriction that comes with TRE or the actual timing of the meals seems to be a bit unclear, and the jury is still out on that one. As is the case for a lot of health-related things, the only way to find out if something really works for you is to actually try it.

My experience with TRE

When I was younger, I had a really strong urge to eat breakfast. I really had to have breakfast within the first 20 minutes of waking up, otherwise I would start to panic. I believed that I would not be able to function at all without eating breakfast. Today, I can eat breakfast whenever I want. Or not at all. It’s not unusual for me to skip breakfast and go straight for lunch. Sometimes at 2 or 3 PM. Being awake for 7-8 hours before eating is now a piece of cake (no pun intended) for me. People often say to me that they would never be able to do what I do, skipping breakfast and all that. They feel like they would literally die if they did that. But little do they know that I used to be exactly like them. If you were to zoom out a little bit, it’s very easy to understand that the human body is designed to survive without food for longer periods of time. Food used to be scarce. It’s not like hunter-gatherers woke up and had a bowl of cheerios for breakfast while downing a liter of orange juice. They often had to wake up and go hunting for food. This is also why the body is made to perform well when in a fasted state. Hunting food is a task that used to require both mental clarity and physical prowess. Since the body is very smart, we have evolved to perform well in such a state, but it can take some getting used to. Speaking from my own experience, the first week or so when trying time-restricted eating, I did struggle a bit. The feeling of hunger was substantial, but manageable. For every day that I completed my 16-hour fast, it got easier. And I started to notice some benefits. My mental performance in the morning got a lot better. Usually after eating breakfast, I would crash and get tired shortly after. By skipping breakfast, I was able to maintain my mental clarity and energy throughout the morning. Oftentimes I would feel worse after eating lunch, but that might depend on what I was actually eating. I think for people that are new to intermittent fasting and time-restricted eating, simply aiming for an eating window of 12 hours is a good starting point. That means that you would fast for 12 hours every day as well. For example, eating between 8AM and 8PM would be a 12-hour feeding window. Then you could gradually decrease the feeding window, either by starting to eat later in the day or eating your last meal earlier. Preferably both. Happy fasting!

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Disclaimer: The contents of this site is for informational purposes only and should not be seen as medical advice