Fasting 101

Fasting and Time Restricted Eating

Fasting has become incredibly popular in the fitness and health communities. But the subject is a bit of a minefield. With so many different forms of fasting and adherents of each making bold claims of their benefits, it’s hard to know which protocol to adopt and what to expect. In this week’s post I am going to outline my experience with a particular fasting regimen that I have been experimenting with for 6 months. I’ll tell you how to do it, what benefits I have experienced personally and what other benefits the research indicates are likely.

*Please note, as ever, that this post does not constitute a recommendation to implement fasting. Please consult your doctor before undertaking any protocol of fasting.

The What

There are a number of different fasting approaches. The approach I’m going to talk about is called time-restricted eating, or TRE for short. TRE involves adhering to daily eating and fasting windows. It is distinguished from intermittent fasting (IF) by the fact that TRE’s eating and fasting windows coincide with the circadian rhythm. In TRE your eating window occurs during day-time hours and your fasting window occurs in the evening and overnight. By contrast, IF often involves fasting throughout the morning.

TRE usually involves a daily eating window of between 8-10 hours and a fasting window of 14-16 hours. A typical structure might be to eat between 8am and 6pm and fast from 6pm to 8am the next morning. These, incidentally, are the timings I use.

During fasting windows, caloric intake should be zero. And you should also be careful to limit any non-caloric drinks that may still affect the digestive system.

I follow the TRE protocol from Sunday to Thursday and then ‘cheat’ on Friday and Saturday, allowing myself to eat with an unrestricted window. Luckily, the evidence suggests that TRE with weekends off is still effective.

The Why

So that’s how it works. But why bother with it? After all, it’s much more fun to just eat all the time, isn’t it?

From an evolutionary perspective, there is an intuitive case for TRE. Our hunter-gatherer forebears were forced to habitually deal with the limited availability of food. We have evolved as a species that underwent periods of fasting. It is, therefore, part of our inherited biology. We have adapted so that we can thrive in such conditions.

The fasting biology is part of our DNA and it turns out that certain physiological processes require or are vastly improved by being in an unfed state. Broadly speaking, our bodies appear to use the fasted state as an opportunity to undertake basic maintenance or organs and tissues. During fasting, processes of flushing-out dead and damaged cells (e.g. apoptosis, autophagy) are heightened and the following re-feed causes increased stem-cell production to replace these dysfunctional cells.

Beyond the evolutionary and scientific arguments, if my personal experience is anything to go by, there are some other very compelling reasons to give TRE a whirl.


This was the first effect I noticed and it occurred almost straight away. I found that I was able to go to bed earlier and sleep much more deeply. The length and quality of my sleep increased significantly. This is no small victory, especially considering I had no real difficulty with sleep to begin with. And remember how important sleep is for recovery and performance!

This is where the circadian rhythm aspect is so crucial (by contrast with IF). The theory is that our organs have internal clocks, just like our brain does. Food in the system is interpreted by organs as a signal of activity and day-time hours, in much the same way as light is interpreted (even artificial light). This causes a feedback loop in which hormones associated with sleep are inhibited and therefore sleep is harder to achieve. Restricting food at night prevents this breakdown of normal signalling, allowing your body to more effectively wind down.


This is commonly reported by people who fast and I experienced it myself. I have found that my focus and mental acuity have improved. I feel a sense of clarity. The research in animal models has indicated powerful effects in this area. Fasting in mice has been shown to increase memory as well as problem-solving ability. Fasting appears to increase the body’s ability to synthesise new neurons (by increasing neurotrophic factors) and enhances synaptic plasticity and the repair of damaged neurons.

In studies of mice, fasting protocols have been shown to be protective against a number of neurodegenerative diseases like Alzheimer’s and Parkinson’s. During fasted states, all organs apart from the brain shrink. The brain must turn to ketone bodies as a source of energy and it may be that this is a more efficient fuel source for cognition.


Look, I don’t necessarily want to get into the nitty gritty here, but suffice it to say that I have seen some indicators of digestive health improve dramatically since fasting. Again, this is not an area where I had previously identified a problem, but there has been an improvement nonetheless. According to Dr Satchin Panda, the world’s leading researcher on TRE, his project’s human data indicates strong anecdotal evidence that TRE alleviates digestive problems and gut health. This seems to make intuitive sense. Endlessly taxing the gut with relentless caloric intake can’t be a good thing. The gut needs time to rejuvenate and repair itself. Fasting gives it the opportunity to do so just like sleep gives the brain a chance to flush toxins.

All that being said, there are many reasons I fast that have little to do with what I have observed so far on a personal level. Although studies on humans are scarce for the time being, research does indicate some exciting prospects for those who fast.


This is the big one. In most animal models, fasting protocols have been shown to increase average lifetime, though this effect is not undisputed. Researches hypothesise that the probable mechanism for longevity is that fasting decreases IGF-1, suppresses the mTOR pathway and increases autophagy (the body’s mechanism for destroying cells with damaged DNA).

Look, I’m no biochemist either and I won’t pretend I fully understand those terms. But the short story is that IGF-1 and mTOR are involved in anabolic processes and appear to be related to ageing and certain chronic diseases such as cancer and Alzheimer’s. Suppressing mTOR signalling has been shown to increase average life-span in mice. At the same time, autophagy gives your body a better chance to get rid of cancerous cells before they divide and metastasise.

You may well have heard of these things in relation to muscle growth and it is true that you need functional mTOR signalling and IGF-1 to stimulate muscle synthesis. But you can have too much of a good thing. Have you ever noticed that ‘roid bros and olympic weightlifters look a lot older that their years? Well that may be because of overactive or dysfunctional mTOR signalling and its consequent ageing effect.

As well as regulating IGF-1 and mTOR, TRE has also been shown to reduce inflammation and improve insulin sensitivity and glucose metabolism in miceThere is strong evidence to suggest that TRE decreases blood pressure and resting heart rate in both animals and humans. In this way, there are hopes that fasting may contribute to preventing chronic diseases like diabetes and heart disease.


In mouse models, TRE has been shown to have robust protective effects against obesity. In experiments where two groups of mice ate the same diet and the same number of total calories, those that were restricted to a 9-hour feeding window gained 28% less weight than those that were left to eat as they pleased. Mice that ate within a 9-hour window put on 70% less fat mass than their freer counterparts. All on the same number of calories. That’s pretty crazy! And it strongly suggests that there is a relationship between when you eat and how lean you are. Eating within a day-time time window appears to protect against fat-gain and may promote accelerated fat-loss.

In Summary

In summary, there is reason to believe that time restricted eating can:

  • Aid cognition
  • Help prevent neurodegenerative diseases
  • Improve sleep quality
  • Improve gut health and digestion
  • Improve insulin sensitivity
  • Decrease chronic inflammation
  • Lower blood pressure and resting heart rate
  • Protect against chronic diseases like cancer and diabetes
  • Prevent weight-gain

Wooo! That’s quite a list. And it is worth mentioning that a lot of these hypotheses are far from being confirmed experimentally. But, I do think there is enough evidence to warrant a serious consideration of TRE as a lifestyle. What do you think?

If you want to learn more about the theory behind fasting, take a look at the resources below. If you guys are interested in this stuff, let me know and I will do another post shortly on practical implementation or TRE.

Learn more:

My Circadian Clock – Dr Panda’s website on TRE

Found My Fitness podcast episode with Dr Panda (part 1)

Found My Fitness podcast episode with Dr Panda (part 2)

Daily Eating Patterns and Their Impact on Health and Disease 

Time restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high fat diet

Fasting, circadian rhythms, and time restricted feeding in healthy lifespan

Fasting: Molecular Mechanisms and Clinical Applications