Minimum fasting length to see benefits from time restricted eating

Time restricted eating (TRE) is the practice of consuming your daily calories within a short time period each day, typically in an 8 – 10 hour window.

When I first  heard about TRE, I knew I could make it work for me. Unlike diets that restrict what you eat, time restricted eating tells you when to eat but doesn’t stop you from having that piece of after-dinner chocolate if you want it.

According to the experts, practising time restricted eating gives you a long list of benefits but I was confused about how long I actually needed to fast to start reaping these amazing benefits. I love food so I obviously didn’t want to fast longer than I have to.

If you’re like me and you only want to fast as long as you need to, let’s take a deep dive into what the research shows:

Weight loss

When I first started time restricted eating, I felt the need to eat just a little bit more at dinner in case I got hungry later. But this feeling quickly subsided over a few days and I eventually found I consumed less calories when I didn’t have the luxury of eating 24-7. We all know eating less contributes to eventual weight loss.

However, studies also found that even if you ate the same amount of calories, but within a shorter time frame, you still lose weight.

Based on the studies I read, you’ll need to eat within an 8- to 10-hour time frame (14 to 16 hour fast) for at least 8 weeks to lose weight.

Improved heart health

TRE lowered fat mass, blood pressure, triglyceride levels and markers of oxidative stress. All these, including obesity, are important risk factors for cardiac disease.

These improvements occured when the study subjects confined their eating windows to a maximum of 10 hours a day.

Improved blood sugar levels

If you manage to eat only once a day or at least much earlier in the day in a 6 to 8 hour window, TRE can improve your fasting sugar and decrease insulin levels. It also increases insulin sensitivity, average 24-hour blood sugar levels, and even your desire to eat after a while.


I admit that autophagy was what intrigued me the most about time restricted eating and intermittent fasting.

In case you were wondering, autophagy is a natural mechanism by which the cells in our body ‘self-eats’ or degrades any unnecessary or damaged components within it. This process helps clean up harmful material in the cell and rejuvenates them.

Autophagy happens naturally all the time in the cell, but less when you’re well-fed and more when you (or your cells) are under stress.

I was really sad to read that depending on your metabolism, significant autophagy may take two to four days of fasting. This is because it is triggered when glucose and insulin levels drop considerably.

A study in humans found that even with only 4 days of early time restricted eating (a 6-hour window between 8am and 2pm), 6 out of 8 circadian clock gene expression improved for the better.

LC3A expression was increased by 22% in the morning at the end of an 18-hour fast. LC3A is an autophagy gene. However, gene expression is not an indicator of protein activation. In other words, we still don’t really know if an 18 hour fast is enough time to actually trigger increased autophagy.

Despite the claims, I suspect time restricted eating is just not long enough a fasting time to induce any kind of significant autophagy. To achieve that, we might need to incorporate other strategies as well like a longer fast, exercise or a keto diet.

If your kids don’t allow you to exercise, check out how I work out with my toddlers.

Increases lifespan

The same study also showed that SIRT1 expression increased in the morning with early time restricted eating. SIRT1 is the longevity gene that protects against inflammation and DNA damage, increases telomere stability and extends lifespan.

An interesting animal study in fruit flies found that when they were fasted for 20 hours, lifespan increased for the flies that fasted at night and broke their fast around lunchtime. Healthspan – better muscle and neuron function, also increased in the same flies.

All the other beneficial effects of time restricted eating also contributes to better health, reduced risk of disease and therefore, longevity.

To wrap up

After digging around looking at all the research, I found  that in order to reap some benefits from time restricted eating like weight loss, better sugar control and better heart health, we would need to eat within a less than 8 to 10 hour window.

However, to really see significant benefits in our healing and healthspan, at the very least, we would need to fast for 18 to 20 hours, limiting our eating window to about 4 to 6 hours earlier in the day.

Check out my beginners guide to starting time restricted eating.


4 thoughts on “Minimum fasting length to see benefits from time restricted eating”

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