Fast Response Mk2

So, as promised here is a follow up on my relatively short fast of seven days.  Yes – I know, some people call that an ‘extended fast’ but this post is all about how I feel about it.  My current feeling is that skipping a meal or two isn’t really significant.

A number of friends have asked me to talk about how it felt and I can summarise that quite simply:  after about a day of feeling a little under the weather it felt absolutely fine.  The big lesson for me out of this is that the human body is designed/evolved/adapted to cope with the food supply being variable or unreliable.  Even someone like me with a BMI in the ‘normal’ range can continue a moderately active life without food for quite a long time.

The main ‘issues’ were around habit patterns.  Initially the body has a rhythm of expecting food and starts to prepare for the next meal and the time it normally arrives.  When that doesn’t happen we feel ‘hungry’ and our tummy grumbles.  Drinking a glass of water or some black tea sorts this out.

After a couple of days, when the body no longer expects food what I noticed is that the mind is still looking for it.  Food is a significant part of our self-reward system, a pastime, an entertainment.   I noticed this, but it really wasn’t a problem.  I simply did something else with the time.


After stored sugar levels are used up the body starts releasing fats to provide energy.  Most cells work well on these but I understand that the nerves, so of course the brain, and also the heart muscle, can’t use fat as a source of energy.  The body copes with this by producing ketones.  It seems as though when first switching system it produces rather more than is needed and the excess gets excreted in the urine.  Simple dip tests are available to check for this so I tracked this during the fast.  I also took a note of my weight at significant points.  If I were to do this again with some preparation I might get blood monitors for ketones and sugar levels, but this method was simple and cheap.


As you can see nothing happens for a couple of days and then ketone production kicks in big time.  Remembering that this is a measure of excess production it’s not surprising that after a short period the body reduces the excess.  I’ve no idea what caused the sudden second peak.  Naturally enough excess ketones dropped off pretty quickly once I started to eat.  I kept my diet very low in carbohydrates for a couple of days, which may explain why levels didn’t drop to zero immediately.

Despite consuming more water than usual during the fast it seems that initial weight loss is mostly water.  This is water used by the digestive system (some suggest it is specifically required for processing blood sugars) and of course that system is shutting down.  This explains why this weight is regained immediately on re-feeding.  Sure enough I immediately regained 2kg.  One reason for delaying publication of this post was to see how permanent that loss was.  After a month I was still around 66kg and now two months later I hover between 67 and 68kg.  I suspect this is because we are now into mince pie and Christmas cake season!



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