Optimal Time Restricted Eating Window

Remember when I detailed one of the simplest, cheapest, easiest to implement strategies for body composition improvement and longevity? Over a year and a half ago I asked you, Are You Restricting Your Eating Window? Since then, lots of new studies have come out that I’m excited to share. Not only about fat loss, metabolic health, and inflammation but also regarding the optimal protocol that should be used. How long or short should your fasting window be? And does it matter what part of the day your fasting vs feeding window is in? What about the caloric distribution within that range? What is the optimal guideline and how has my meal timing changed over the past year and a half? Well, let’s get into it!

What is Time Restricted Eating?

Your eating window can be calculated by the determining the hours between your first caloric intake of the day and your last caloric intake of the day. This is your feeding state, or the anabolic state where eating and digestion occur. Oppositely, your fasting state, or catabolic state, is where you’re burning calories that have been stored during the anabolic state. No eating occurs during this time and it’s where most of your cell maintenance and DNA repair occurs. And the idea is, the longer you can extend that fasting state, and the shorter you can reduce your feeding state, the more optimally your body can function [1].

Well, nowadays people are eating around the clock with 98% of calories being consumed between 6am and midnight with the average person’s feeding window being 15 hours [2]. That’d be like eating breakfast at 7am and a bedtime snack at 10pm. And while that’s obviously relatable to many, that doesn’t mean it’s healthy to be in this constant anabolic state. That’s why many studies have now tested restricting people’s eating window to 12 hours or less and the results have been universally beneficial [3].

Why Time Restrict Eating?

Not only can time restricted eating help with weight reduction and fat loss while maintaining fat-free mass like muscle and bone, but large systematic reviews have praised its benefits for management of blood pressure, blood sugar, and cholesterol [4]. Those are my Top 3 Biomarkers for Health that I posted about a couple of weeks ago! And if you’re thinking these benefits occur because people might eat fewer total calories during that shortened eating window, it’s been found that these benefits persist even when caloric intake is unchanged [5]. You eat the same amount of food but just in a narrower window, and somehow magic. Like Disney. Your biomarkers improve and you lose fat.

And to top it off, even if you’re not worried about weight loss, studies have been done in elite athletes showing similar results. In one study they did time restricted eating with elite cyclists and found improvements in body composition, reduction in inflammation, and benefits to the immune system [6]. So even if your goal is to maintain muscle mass or strength, TRE can be a tool for you too [7].

Optimal Window Duration

So, TRE. Amazing. Magic. Disney. The next question becomes, what’s the optimal protocol. Let’s start with duration of the feeding window. As I mentioned earlier, time restricted eating usually occurs by reducing the feeding window to less than 12 hours a day. But could less be better? In a study that indirectly measured a 12-hour fasting window to a 14-hour fasting window, the 14-hour window appeared to do better with weight loss and blood sugar management [8]. What about an 18-hour fasting window? Again, better greater effects with weight loss, cell repair, and anti-aging effects [9]. What about 20 hours of fasting? Even when participants ate the same number of calories in that 4 hour daily eating window compared to the control group, they still had significantly improved blood pressure, blood sugar, and cholesterol all while dropping body fat [10]. It appears that despite how many calories you consume, the more you decrease your feeding window and increase your fasting window, the better the results [11].

But I should mention that one problem does arise from this. Even when consuming the same number of calories, the more you restrict your feeding window, the greater your feeling of hunger and desire for food [10]. While decreasing your window improves a whole host of health benefits, the more you restrict, the harder it is to comply and maintain. So, just keep this in mind if you’re interested in trying TRE.

Optimal Window Timing

Cool, so less is better with TRE but does it matter when my feeding window is? Should I eat more in the morning or at night? Well, there’s two main factors driving the benefits of time restricted eating. First, by restricting your feeding window, you’re more likely decreasing your caloric consumption by not eating as late into the evening. Late night eating usually involves more junk food, higher fat foods, and more high caloric foods. So just by improving your eating habits, we see benefits [12]. But second, independent of weight loss, a lot of these benefits are seen from the realignment of feeding with your circadian clock [5]. This is because your glucose tolerance, or ability to keep your blood sugar under control are greater in the morning than the evening. It’s why those who skip breakfast may eat fewer total calories throughout the day, but don’t lose weight, increase their risk for type 2 diabetes, and have worse cholesterol levels [13].

From these two mechanisms, we can assume that eating earlier in the day is likely healthier than eating later in the day. And we have a few studies to confirm this. One study had participants eat the same 2,000 calorie meal in the evening or in the morning. What they found was that those who ate the meal in the morning lost weight whereas the evening group maintained their weight [14]. Now because of practicality, you’re likely not going to be eating just one meal a day but we have another study comparing eating three meals a day during a 9-hour feeding window either earlier in the morning (8am to 5pm) or later in the evening (12pm to 9pm). What they found was that the group eating earlier had lower average fasting glucose levels [15]. Or better management of blood sugar.

But not only does shifting your eating window to earlier in the day have larger benefits but eating calories within that feeding window matters too! As in front loading your calories. If you give people the same 1,400 calorie diet, but one group eats more calories earlier in the day (700C breakfast, 500C lunch, 200C dinner) and another group eats more calories later in the day (200C breakfast, 500C lunch, 700C dinner), the group eating calories earlier do better with weight loss and markers for health like blood sugar and cholesterol [16]. Meaning not only should you shift your eating window earlier in the day, but probably the majority of your calories too.

Final Thoughts

Time restricted eating is a simple, cheap, and effective strategy to not only lower body fat while maintaining muscle, but also to improve overall markers of health. And the more you restrict that feeding window, the better the results you’re going to get. But the harder it may be to maintain. And for optimal results, shift that restricted feeding window earlier in the day with the majority of calories being consumed earlier too. The last time I posted about TRE, I was following a 10-hour feeding window between 11am and 9pm while fasting the other 14 hours. But over the past year, since learning about all the latest research, I’ve shifted that 10-hour feeding window earlier starting at 9am and concluding at 7pm. This feels like a beneficial and sustainable eating habit that’s allowing me to live healthier and happier.

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Hey, I am Brandon Zerbe

Welcome to myHealthSciences! My goal has always been to increase quality-of-life with healthy habits that are sustainable, efficient, and effective. I do this by covering topics like Fitness, Nutrition, Sleep, Cognition, Finance and Minimalism. You can read more about me here.


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