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Benefits of Time-Restricted Eating

What's the difference between intermittent fasting and time-restricted eating? We’ll break it down for you in this blog post so you know the nuts and bolts, as well as the scientific research behind it.

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If you are hearing a lot of talk about intermittent fasting you aren’t alone. One type of intermittent fasting creating a bit of a stir recently is "time-restricted eating."

What Is Time-Restricted Eating?

Time-restricted eating (TRE) is a form of intermittent fasting (IF). TRE limits eating to an eating window, typically  8 hours or less every day. IF plans require fasting for the entire day, a few days a week with normal eating on the other days1.

Another big difference between the two plans is that most IF protocols incorporate calorie restrictions. TRE programs typically don’t. Instead, they focus on eating during a short window of time. Eating occurs only within a 6 - 8 hour window, usually during the most active part of the day.

Some time-restricted eating plans also adjust eating times to earlier in the day. The theory is to eat according to your individual internal circadian rhythm2. The idea is to maximize your calorie intake during your most active times of the day.

This stems from research with night shift workers. Those who consistently work off-hours tend to have a high risk for abdominal obesity3, even when compared to day workers with similar energy intakes. This suggests that the timing of meals may have a significant role in weight management4.

<p class="pro-tip"><strong>Learn about planning </strong> <a href="/blog/healthy-work-lunches-weight-loss">healthy work lunches for weight loss</a>.</p>

What Are the Benefits of Time-Restricted Eating?

Weight loss is one of the of the most popular reasons for trying TRE. The research so far has shown some promise for modest weight reduction when following a TRE plan5. Another reason for interests in time-restricted eating is that most TRE plans don’t require you to count calories. Many people find tracking calories to be a chore, so this makes TRE appealing.

Other benefits that people talk about are improvements in blood glucose control, stress reduction, better sleep, and increased longevity.

How much is true? Let’s take a look.

Weight Reduction

Calorie-restricted programs are the most common type of diet plans for weight loss. While many people follow these programs, most have shown only modest weight loss results, and long-term weight loss is often lacking. One reason may be that many people find counting and tracking calories hard to stick with.

In contrast, most TRE plans do not limit calories or require you to track your calories. They only limit the time you can eat to certain hours during the day. This type of eating pattern naturally reduces your calorie intake. This seems especially true when eating between a short 6 - 8 hour period early in the day.

TRE plans also seem to be easy for individuals to follow. Some research suggests that these protocols are easier to stick with than calorie counting6.

So how well do TRE programs work for weight loss? At this point, we don’t know much about long-term weight loss, but what has been shown so far is that a TRE pattern can help with modest weight loss.

One recent small study showed that limiting eating to an 8-hour period over 12 weeks resulted in an average of 2.6% weight loss5.

smiling woman standing on a scale with arms in victory pose
Studies of TRE programs suggest time-restricted eating may contribute to modest weight loss.

Another recent study in the New England Journal of Medicine looked at an 8-hour TRE program along with calorie restriction. They compared that to a calorie-restricted diet alone. They followed both groups for 12 months and saw similar amounts of weight loss in both. Neither group had large dropout rates, suggesting that both were easy to follow for the 12-month period7.

A downside of some TRE programs is that the dinner meal occurs in the early to late afternoon. This will likely mean you may have to skip dinner with your family, which may not be ideal.

A solution could be to shift your eating hours to a little later in the day. Have breakfast later in the morning so you can enjoy dinner with your family. Doing this along with a smaller dinner portion may make a plan like this more palatable and easier to follow.

<p class="pro-tip"><strong>Learn more about </strong> <a href="/blog/how-often-to-eat-for-metabolic-health">meal timing and metabolic health</a>.</p>

Blood Glucose Control

What about controlling blood glucose? In some animal studies, more steady and controlled blood glucose levels were shown when following a TRE program. This hasn’t translated to humans however. While some studies have shown improvements in insulin sensitivity with TRE, the impact on blood glucose levels is less clear.

A recent systematic review of healthy individuals found mixed results on fasting glucose during a TRE protocol, with the majority of individuals showing no change8.

Another small study in prediabetic men found no change in fasting glucose or body weight. They did, however, have a significant decrease in fasting insulin levels and improvements in insulin sensitivity9. This study followed an early TRE protocol and shifted all meals to before 3 PM. 

Other studies found eating over a 6-hour period reduced blood glucose levels slightly in the morning and overnight but had little effect on blood glucose during day10.

So, there may be some benefits with fasting insulin and insulin sensitivity when following a TRE diet, but little change in blood glucose.

<p><strong></strong><p class="pro-tip"><strong>Learn more about</strong> stable blood glucose levels<strong></strong></p></p>

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Increased Ketones

We know that during fasting your body moves from burning glucose and glucose stores (glycogen) to burning fat. Once those glycogen stores are used, ketones break down stored fat, which results in weight loss.

Other reported benefits of higher ketone levels are reduced oxidative stress, preservation of lean body mass and decreased hunger11. While TRE has short fasting windows, it may still lead to some ketosis12.

So, are ketones good for controlling and stabilizing blood glucose? A recent small study of individuals with type 2 diabetes found significantly lowered blood glucose in those following a ketogenic diet13. Increased levels of ketones also appear to suppress appetite, which helps with weight loss14.

What about TRE diets? In a study of 11 overweight adults, early TRE decreased the appetite hormones, ghrelin, and leptin but saw no change in the amount of energy expended. While they did not measure ketone levels the researchers suggested there may have been an increase in fat oxidation as well15.

So it is possible that weight loss while following a TRE diets happens because of a combination of reduced calorie intake, a decrease in appetite, and by burning more fat due to ketosis.

<p><strong></strong><p class="pro-tip"><strong>Read more about</strong> keto and intermittent fasting<strong></strong></p></p>

Lower Evening Cortisol

Another proposed benefit of TRE is a reduction in evening cortisol levels. There is some limited research that supports this theory16.

First of all, what is cortisol and why is it important? Cortisol is a steroid hormone that your body makes. You may have heard that it is helpful during stress because it is released during the “fight or flight” response to help you deal with stress17.

But cortisol does so much more.

Cortisol helps manage your circadian rhythms18. More cortisol is released in the morning to help you wake up and tackle the day. Less cortisol is released at night, helping you relax and get a good night’s sleep. The highest level of cortisol should occur around 9 AM and the lowest around midnight18

With cortisol you want a natural rise and decline during the day19. When cortisol remains elevated that is a sign of stress. Ongoing stress can lead to high blood pressure, obesity, anxiety, and gastrointestinal issues20

Are there other ways to support healthy cortisol levels beyond fasting? Absolutely! 

One of the easiest ways is to manage stress. Getting some daily exercise and following a Mediterranean-style diet are good places to start. Other great stress reducers are taking frequent breaks during the day, getting outside, and spending quality time with friends and loved ones.

two women smiling and preparing a salad
A Mediterranean-style diet and spending time with friends can promote healthy cortisol levels.

<p><strong></strong><p class="pro-tip"><strong>Read more about</strong> the physical effects of stress<strong></strong></p></p>

Higher Evening BDNF (Brain-Derived Neurotrophic Factor)

If you haven’t heard of BDNF, you aren’t alone. BDNF is a little-known protein in your brain that helps your neurons grow and develop21. As we age, we see a natural decline in the number of neural connections. Aging brains are also slower to develop new neurons and synapses. Higher levels of BDNF may be helpful with both of these because it helps keep the connections (synapses) between neurons sharp. These connections maintain your memory and learning abilities22.

What does this have to do with when you eat? We aren’t entirely sure, but there may be something to "eating like a king for breakfast." One small study found that people who followed a TRE program and restricted their eating to earlier in the day (until 2 PM) saw increases in BDNF levels in the evening10.

Are there other ways to increase your BDNF levels as you age? 

While the research in this area is very young, there is some evidence that lifestyle changes may improve BDNF levels as we age. Things you can do include focusing on stress reduction, controlling your weight and blood glucose, and getting more exercise23.

<p><strong></strong><p class="pro-tip"><strong>Read more about</strong> starting a healthy lifestyle<strong></strong></p></p>

Key Takeaway: 

It’s possible that restricting eating to a 6 - 8 hour window during the day may be helpful for weight loss in some people. You may see a small effect on your blood glucose levels and insulin sensitivity, and it may help you sleep better. The effects of TRE are highly individual and much more research is needed.

Finding the right eating program that is easy for you to follow is most important. While IF and TRE may be helpful for some people, more research is needed to study the long-term effects.

With a CGM, you can observe how your body responds to your eating and exercise program. A CGM can help you understand your individual response to time-restricted eating, and how time-restricted eating plans impact your blood glucose. 

<p><strong></strong><p class="pro-tip"><strong>Learn about</strong> getting started with a Signos CGM<strong></strong></p></p>

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References

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About the Author

Laura is an award-winning food and nutrition communications consultant, freelance writer, and recipe developer.
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