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A Personal Experiment in Fasting Mimicking, Nutritional Ketosis, Meditation and Heart Coherence

Recently I tried a personal experiment in fasting mimicking, which has been in the public eye recently. My motivation was to gain the health benefits it seems to offer, and yes to be honest lose a bit of belly fat, but also to see how it affected my meditation practice - and given that I use heart coherence biofeedback (HRV biofeedback) to support my meditation, I wanted to see what it did for my heart coherence levels, if anything.

Why should fasting mimicking benefit health, and why should I think it might benefit my meditation practice and maybe even my heart coherence?

First I need to say something about what it is. It's obviously not fasting, but it's a short-term diet designed to induce the same metabolic effects as fasting, at least to some degree. I followed a fasting mimicking diet for three days, and you probably wouldn't want to follow it for much more than about five days at a time. Beyond that there might be adverse effects - that's why I say short-term.

Metabolic Effects of Fasting

So what are the metabolic effects of fasting? Metabolism is the cellular process of burning fuels derived from food to create energy which can be utilised (for generally staying alive, etc.) The fuel is basically sugar (mainly glucose) which comes from carbohydrates in food, and fat. You can also burn protein for energy, but doing so to any significant extent is not ideal, and should be considered as one of the body's emergency responses.

When you fast, the body has to dip into its stores of energy. The body has a store of glycogen which is a form of carbohydrate, easily converted (back) into sugar. You typically have about 2,000 calories' worth of glycogen, which is enough for the best part of a day at least, but not that much more. So fasting longer than a day will shift you into fat burning - and most people have a much larger store of fat than glycogen.

Fat burning means mainly burning fatty acids (which are of course derived from fat) but it can also be said to include something called ketosis. Brain cells can't burn fatty acids directly, but they can burn ketone bodies, which are produced by the liver from fatty acids. So nutritional ketosis is a state where your liver is producing ketone bodies which are then used as the brain's primary fuel.

The interesting thing is that ketone metabolism seems to be more efficient, or runs cleaner. I don't claim to be an expert in the science of ketosis but it seems that fat burning generally produces less in the way of "exhaust fumes" in the form of (toxic) free radicals. Certainly a lot of people claim that they feel much better in ketosis, have a clearer mind and better cognitive performance. That's why I wanted to try it for myself.

So nutritional ketosis is the first major metabolic benefit of fasting, and a second is a process called autophagy. Autophagy is not to do with energy but is about proteins. The body uses many different types of protein for both structural and functional purposes - e.g. haemoglobin is a protein that transports oxygen. The body is continually building new protein molecules, from amino acids which have come from protein in the diet.

When you fast, your supply of amino acids runs low, so the body starts to cannibalise old worn-out protein molecules in the cells. This is autophagy - it literally means "self-eating" and it's healthy because effectively it renews yours cells' molecular machinery.

Fasting Mimicking

Fasting mimicking aims to reproduce these two key mechanisms, ketosis and autophagy, but without stopping eating altogether (which is challenging for most people). How? Essentially by limiting both carbohydrates and proteins (again I stress in the short-term). In practice you can do that by eating only vegetables and fat or oil. Not just any vegetables, you need to avoid starchy veg like potatoes. (Starch is a form of carbohydrate.) Other vegetables contain relatively little carbs and very little protein.

In my case I cooked up a pot of vegetable soup as my mainstay for the three days. I bulked it up using "rice" made from konjac which is a plant fibre, having very little nutritional content at all, and therefore very low in calories. You can by konjac noodles and rice in some supermarkets and also online. I used a brand called "bare naked".

I tried to keep the soup for lunch and dinner - for breakfast I had coffee in the "bullet-proof" style - i.e. made with butter and an extract of coconut oil called caprylic acid which is readily convertible into ketone bodies. So this drink contained fat only, and pretty much zero carbs and protein.

The Ketogenic Diet

As an aside, I'll briefly touch on the ketogenic diet, which is gaining in popularity. It's essentially a very low carb diet, designed to switch you into nutritional ketosis. Protein restriction and autophagy are not part of the ketogenic diet. Some people follow it full-time, but it seems there are risks with that, and a cyclical ketogenic diet is probably safer.

Testing for Ketosis

I mentioned that ketones are fairly easy to detect. You can measure them in blood, urine and even in the breath. In my case I bought a very cheap (chinese-made) ketone breathalyzer from ebay - I paid less than £10 for it. (Just search ebat for "ketone breathalyzer".) For that price I didn't expect a state of the art highly accurate scientific instrument, but I found it to work and to be at least relatively consistent (in the sense that consecutive measurements were the same or close).

ketone breathalyzer

When it arrived the packaging said it was an alcohol breathalyzer, which was disappointing and arguably mis-selling. I assume the numbers it reports (in grams per litre) are calibrated for alcohol, not acetone (which is the liver-produced ketone I assume it's able to detect). I'm not going to worry to much about the numbers, I only want to be able to detect ketosis or not. From that point of view it seems to work.

Over the course of my three days I tested myself frequently (it's very easy with the breathalyzer). I found that the reading, initially zero, started to rise from the first afternoon, which is what I would expect given I'd had my last significant carbs the previous evening. They rose steadily up till they hit the maximum the device was capable of detecting (about 1.9 g per l) on the third day. Interestingly the readings took several hours to go back down to zero after I ended the diet, which I guess makes sense too.

I didn't know what numbers I should have been getting, and again I guess it my device is calibrated for alcohol not acetone, but given the measurements I'm confident that I gradually went into ketosis over the three days.

My Experience

Even from the first day, I found myself feeling very good in terms of my mood, which to be honest normally isn't that great. I found I had plenty of energy, and sense of quiet contentment and well-being. (In honesty I did drink more coffee than usual, but only two cups per day.)

This was the second time I've done three days of fasting mimicking. The first time I found somewhat challenging during the evenings when I wanted to eat chocolate. I guess that was psychological craving rather than genuine hunger. This time was significantly easier - no hunger at all during the day time but a little craving (probably triggered by boredom) in the evening, and again I don't think this was genuine hunger. (Personally I judge it real hunger if my mouth waters when I think of eating - any food not just my favourites.)


I decided to make the three days into a mini urban retreat. I was still at home and going to work during the day time, but I found time to do more sits. I found my meditation reached an above-average level of focus (in terms of being able to stay one-pointed on the breath, with less distracting mental chatter). Of course, this is to be expected given my increased level of effort or commitment (i.e. doing more practice) but that said, I find it easy to believe the diet helped.

Heart Coherence

I track my heart coherence during meditation (and indeed use the measurement as biofeedback). I use software I developed myself, called Mind-Body Training Tools. It calculates a coherence score, and having used it for a long time I know what my numbers typically tend to be. On the second day of my diet I reached the highest coherence score I've ever measured - at 141, higher even than when I'm on retreat (when it is noticably higher in my experience). Here is the graph of this session.

heart coherence biofeedback chart

The coherence score from the biofeedback software has an arbitrary scale. I calibrated it such that a score of 100 represents very good coherence, but by no means a maximum.

For comparison, here is a more typical session, originating from one of the days shortly before my fasting mimicking diet.

heart coherence biofeedback chart

You can see that my maximum score in this session is about half of my best-ever.

As an aside, you might notice that in the typical chart the heart coherence score builds up gradually over the course of a session, while in the best-ever session it goes high very quickly. I think this is mainly because the typical session was recorded first thing in a morning, while the record session was in the middle of the day. This is the pattern I often see - that I have to work up to a good coherence lesson when I'm not long out of bed.

My record score was a big surprise. Prior to that I hadn't gotten above 130, so it was a big leap. I genuinely wasn't expecting the fasting mimicking to make such a difference - but I can't imagine it was a coincidence. On another occasion I scored 132, so I beat my record twice. I thought maybe I'd go from average scores to the upper part of my range, nothing more. I don't think it was merely the expectation that made the difference.

Background on Fasting Mimicking

I'd heard of fasting mimicking via a podcast on the internet. I was sufficiently interested to read the interviewee's book - "The Longevity Diet" by Valter Longo, who is a leading research scientist. The book doesn't go into specifics of what to eat - in fact the author advises caution because fasting mimicking won't suit everyone. But given I'm basically fit and healthy and not too old, I went ahead based on the understanding that I have - which is by no means expert status. If you're considering trying it out for yourself, please take some responsibility and do your research.


This personal "experiment" in fasting mechanism is not scientific research - far from it. But I so much enjoyed the response I got that I plan to repeat the experience - maybe once a month.

If you've tried fasting mimicking yourself, why not add a comment below saying something about your results.

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