Circadian Rhythms

The Benefits of Time-Restricted Eating: A Simpler Dietary Intervention

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Discover why time-restricted eating has become one of the most popular nutrition strategies over the last few years.

What is Time-Restricted Eating?

Depending on who you ask, you’ll get wildly different answers as to what to eat for optimal health – and these pundits’ answers seem to change every few years.

Thankfully, through this new area of research, it is becoming increasingly clear that “when you eat” is as important as “what you eat”.

Time-restricted eating (TRE) is a practice in which you eat all your calories within a compressed window of time each day, typically eight to twelve hours. As you will be fasting for the remaining twelve to sixteen hours, this allows organs and tissues in the digestive system more time for vital repair processes to occur, leading to a host of health benefits.

From an evolutionary standpoint, it makes perfect sense. It is highly unlikely that our ancestors were eating much beyond a ten to twelve hour time period each day. This has only become feasible very recently, with the widespread use of refrigeration and artificial light.

Thus, our bodies are not equipped to handle the twenty-four hour access to food we now enjoy – and perhaps abuse.

In this article you’ll discover:

the potential health benefits of time-restricted eating
the possible mechanisms at work
why time-restricted eating is easier to follow than other diet strategies
information to help you pick your eating window
whether coffee breaks your fast or not
and more

Confusion about terms

Before we get to the details of time restricted eating, I want to provide some definitions. Although you’ll often find the below terms used interchangeably, there appears to be some difference in how the scientific community uses them:

Time-restricted eating (TRE) vs. time-restricted feeding (TRF)

The term time restricted eating is generally used for humans whereas time restricted feeding is reserved for animals – the mice in lab studies for example have to be fed by the researchers.

Time-restricted eating vs. intermittent fasting

Time-restricted eating refers to fasting periods less than twenty-four hours, that occur every day (or almost every day). The term intermittent fasting is more often reserved for fasting periods of twenty-four hours or more, that are repeated on a periodic basis (i.e. fast for five days every quarter, fast one day per week, etc.).

Other names

The 16:8 diet, the warrior diet, and the OMAD (one meal a day) diet are all forms of time-restricted eating.

Discovery and results from mice

I first came across TRE from the work of Satchin Panda, Professor at the SALK Institute for Biological Studies and one of the world’s leading experts on circadian rhythms.

His team compared mice that ate all their calories within an eight to twelve hour window with mice that ate over a larger period of time. The TRE mice showed a wide range of health benefits – this despite the fact that both groups ate the same high-fat, high-sugar diet, as well as the same amount of calories.

Below are some images that sum up his findings nicely

Benefits of time-restricted feeding in animal models

Lower blood cholesterol
Lower fasting blood sugar
Lower body weight
Lower body fat
Lower levels of inflammation
Reduction in dysbiosis (microbial imbalance)
Improved cardiac function
Improved sleep
Improved endurance
Improved motor control
Improved energy expenditure

But how does time-restricted eating affect humans?

The health benefits of TRF in animal models are well confirmed and truly amazing. Unfortunately the case is less clear for humans. This can partially be explained by a simple lack of data, but could also be attributed to the heterogeneity of humans when compared to lab mice – not everyone is going to respond the same.

That being said, evidence is mounting for metabolic improvements in obese and overweight individuals[1][2]. TRE has shown beneficial effects in healthy adults as well[3][4].

There is also plenty of anecdotal evidence. Participants in Panda’s ongoing studies report losing weight, sleeping better, and feeling more energetic during the day.

In a recent podcast where Dr. Peter Attia interviews Dr. Jason Fung, they shared their experiences with putting patients on a TRE regimen. Fung sees a lot of people benefit from TRE, even with little attention paid to diet. Attia, on the other hand, has seen mixed results: significant improvements in some, no improvement whatsoever in others. Though Attia acknowledges that his patients are starting from a much healthier baseline than Fung’s.

Below we’ll detail some of the findings from Panda’s team, as well as other studies and possible explanations for improvements in human health.

Circadian rhythm component

As detailed in my post about circadian rhythms, most peripheral clocks, including those in adipose tissue, gut, liver, muscle and pancreas, use food intake as the primary zeitgeber. Keeping a consistent daily eating window, which allows adequate time for repair processes, is essential to nurturing your natural rhythms.

Perceived vs. actual eating window

Researchers in Panda’s lab discovered that people were eating for much longer than they realized. While most people thought they were eating all their food within a twelve hour time period, actual data showed that fifty percent of adults eat for fifteen hours or longer.

Experts in this area, such as the aforementioned Panda as well as Dr. Valter Longo, suggest everyone eat within a twelve-hour window to minimize adverse health effects.

When eating periods extend beyond this, you start to see problems.

You start seeing people overweight, not being able to sleep, metabolic syndrome, insulin resistance, etc.

– Dr. Valter Longo [5]

Time of day and food choices

Panda’s lab also discovered that people were eating more calories in the final three hours of their eating window, than during the first eight. This increase was caused by poor choices at this time of day. Late night indulgences more often included things like ice cream, nachos and alcohol.

This is important because glucose regulation follows a circadian rhythm; glucose tolerance is much better in the morning than in the evening[6].

So should I choose an earlier eating window? Not necessarily

For those of you who find it easier to skip, or at least delay breakfast as the means to shortening your window, you’ll be happy to hear that recent studies indicate there is some flexibility in determining your eating window.

Researchers compared two different nine-hour TRE windows (8am to 5pm and 12pm to 9 pm) for men at risk for type 2 diabetes. The results showed a thirty-six percent reduction in glycemic response to a meal, as well as reduced fasting triglycerides, regardless of which window was chosen[7].

Although glucose regulation is better in the morning and gets worse as the day progresses, there are other factors to consider when choosing a window.

Adherence may be better with later eating windows because dinner is the meal that most often has a social component to it, i.e., sitting down to eat with family and friends. Also, it is entirely possible that regularly skipping breakfast could prolong your insulin sensitivity to the time you start eating – something that has yet to be studied.

Caloric restriction component

Some benefits of TRE may be a result of reduced calorie intake. Caloric restriction has shown potential to slow aging and protect against age-related disease[8][9]. But caloric restriction is hard to adhere to. Who wants to keep track of all calories consumed and stop eating once a specified number is reached?

Through TRE, caloric intake is often reduced as a consequence of the eating window alone, without the requirement of counting calories. It’s pragmatically harder to eat the same amount of food in a shorter period of time.

Benefit compared to diet change

Another benefit to TRE is the ease of adopting it compared to diet change. Just like it’s much easier to pick an eating window and stick to it when compared to counting and limiting calories, TRE is also much easier than diet strategies that have people limiting certain types of food, e.g., counting how many grams of carbs you eat in a day and keeping that amount below a certain percentage of total food intake.

TRE allows you to derive benefits without changing your diet – though the greatest health benefits will come when you adopt a healthier diet alongside TRE.

It should be noted that, in Panda’s studies, food choices were inadvertently improved since the types of calories usually consumed outside of a TRE window more often included the late-night indulgences mentioned earlier in this post (alcohol, ice cream, nachos, etc.).

What about cheat days?

For those of you who can’t make diet adjustments without the fall back of a cheat day, you’ll be happy to hear that this has been tested as well.

Mice subjected to a nine-hour time restricted feeding window were temporarily allowed ad libitum access to food on the weekends[10]. These mice still showed health benefits as long as TRF was maintained the other five days. Surprisingly, the gene expression pattern of these mice looked similar to mice on a seven-day TRF schedule.

The optimum is no doubt to maintain TRE all the time, but this data suggests you won’t completely reverse all your hard work with that weekend binge.

What about coffee?

There is some debate about whether coffee breaks the fast or not. On one hand, black coffee contains no calories, so consumption won’t affect any weight loss or caloric restriction goals. On the other hand, the caffeine in coffee activates metabolic processes in the gut and liver, preventing these tissues from resting and repairing themselves. So it depends on what your goals are.

One side benefit to drinking coffee is that it may actually suppress appetite, making adherence to a TRE window easier.

Ketogenesis

Some of the benefits of TRE are thought to be the result of elevated ketones in the blood. Your body starts to produce ketones after about ten hours of fasting. About two to four hours after that, ketones start showing up in the blood.

Some of the health benefits of time-restricted feeding may be mediated by this increase in ketone bodies.

– Dr. Satchin Panda [11]

The ketogenic diet has been a hot topic over the last few years, and while many people have benefited from it, I can attest to the fact that it’s not an easy diet to adhere to.

Rather than alienating family and friends with your super restrictive diet, you may derive some of the same benefits simply by sticking to a TRE schedule. It’s much easier to limit the amount of time you’re eating than to remove entire food groups from your diet.

Minor stress and hormesis

Another theory as to the mechanism of action is hormesis. This is when the body responds favourably to low doses of something – in this case fasting – when high doses would be harmful. The low levels of stress imposed by fasting forces cells to adapt, becoming stronger and more resilient against more severe stress.

Are smaller eating windows better?

If you’re starting from an unhealthy baseline – if you have metabolic syndrome for example – the evidence suggests you’ll see greater health benefits from shorter windows.

A recent pilot study[12] compared an early six-hour (8 a.m. to 2 p.m.) TRE window with a twelve-hour window (8 a.m. to 8 p.m.). The researchers found that when the participants followed the six-hour schedule, they had lower 24-hour blood glucose, lower evening cortisol, increased brain-derived neurotrophic factor (important for long-term memory), and higher ketone levels. The findings also suggest eighteen-hour fasting windows may lead to increased autophagy, which is the body’s way of cleaning out damaged cells, and replacing them with new, healthier cells.

Caution is needed though as some experts, such as Dr. Longo, advise against extremely short eating windows. According to Longo, if you limit food intake to four to six hours per day, “then you start to see gallstone formation [and] increase the chance that you’re [going to] need your gallbladder removed.”[13]

Though it appears Panda doesn’t view this as a big concern:

Couple of papers from 70s and 80s found a small number of women (not men) who abruptly reduced caloric intake and ate within a smaller window for rapid weight loss may have bile sludge. Those studies lack data on hydration level, smoking and what they ate.
— Satchin Panda (@SatchinPanda) July 24, 2018

The bottom line is this: If you’re going to shorten your eating window beyond eight hours, it would be prudent to get your doctor involved to ensure you aren’t causing any harm.

Adjustment period

Due to the compressed eating period, most TRE schedules will have you abstaining from food for at least two or three hours before bed. Difficulty sleeping due to hunger is a common complaint from people first trying this protocol – especially those accustomed to late-night snacking. However, after two to three weeks, your body should adapt and you’ll no longer feel hungry at bedtime.

Conclusion

Panda and others continue to research whether the benefits of time-restricted eating apply to humans as well as mice.

While the data for health benefits in humans isn’t as conclusive, it still seems that most people will benefit from fasting for at least twelve hours every twenty-four hour period. And you can rest easy knowing there is no evidence of any adverse health effects for twelve-hour eating windows.

The evidence suggests the greatest health benefits will come with longer fasting windows. However, fasting periods beyond sixteen hours may increase the risk of other issues and should only be adopted after consultation with your doctor.

Featured image by Aron Visuals on Unsplash

References:

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