A longer fast

I’ve been doing intermittent fasting for some time now, a day at a time, and have found it very effective for losing weight, and probably for many other health improvements, not all which I’ve measured. I started off with 600 calories on the fasting days, and once I got used to it, found I could go under 100 calories (a tin of tomatos), and then tried some complete fasts (black coffee, green tea, etc, but nothing calorific) and they were easier than I expected. A bit over a year ago I tried some longer full fasts, 60 hours (two and half days) and 98 hours (just over four days, with the aim of reaching ketosis to find whether it felt any different for me), and they were much easier than I expected. I’d like to try a whole week sometime, and as I started writing this, I was embarking on the halfway mark between four days and a week: I’m aiming for five and a half days. This fitted in conveniently with my weekend routine being disrupted by the Cambridge half-marathon; instead of the early Eucharist, followed by a cafe breakfast, a walk, and a Quaker meeting, I’m going to stay at home, mostly tinkering with things. My next planned social eating after the fast was Wednesday lunchtime, when I go for a pub lunch with friends from a previous job, and so that’s the first eating occasion which people will notice if I miss. (I’m doing this fast a bit furtively, because when I did my four-day fast, friends I told in advance seemed to think I’d been in terrible danger, despite (or rather, because of) knowing nothing about fasting.)

A lot of precious, aren’t-I-special, must-be-careful stuff is written about fasting (and about eating, for that matter), and I simply don’t believe most of it; the bits I do believe are backed by scientific evidence or direct experience. But I do take some care; for example, I know that eating a full-size meal after a fast of more than a day is likely to cause indigestion (I tried it). And there’s a reasonably clearly established connection between eating red meat and an increased risk of cancer (and between eating vegetables and a reduced risk), so I didn’t want red meat to be sitting round in my digestive tract as the last thing I ate before the fast. So I forewent what I would have liked to eat just before the fast (a doner kebab), and instead stuffed myself with green salad with chicken and fish, so I’d be up-to-date on greens and on protein and fats beforehand. And to avoid a sugar rush after the fast, I got some bags of nuts to break it with, that I’ll probably follow with some yoghurt.

I was hungry intermittently for the first couple of days, but on the third day that had largely gone, as I had switched from running on sugars to running on fat reserves. I felt slightly different from how I normally do, but it wasn’t a problem; it did feel very strange not to feel hungry at all. I took my urinary ketone readings twice a day, and saw that I entered ketosis after two and a half days.

Towards the end of the fifth day, I went to a dancers’ club ball, and danced fairly energetically. Driving back, I did feel a bit odd, and very thirsty, so took a ketone reading when I got home, and it was twice what it had been before, so I decided to break the fast then, by eating nuts and a tin of creamed mushrooms (an odd late-night choice).

The next day, after having some yoghurt to start with, I ate normally from lunchtime onwards, which was probably a bad idea; I did feel more than full, and should have allowed more time to make the transition from fasting to normal eating.

The fast did get me down to what I had long thought would be my target weight, which I’d been persistently unable to reach. I realized I’ll have a little more to lose after that to get down to my actual lean weight (think six-pack) but it definitely brought me into range.

So, would I do it again? Will I ever go for a whole week? Yes, with some modifications. If I have a whole week clear of social eating occasions, and without any energetic events like dances, I’ll try it again, perhaps as an annual reset to my digestion, but given seven days available for it, I’d probably fast fully for the first four of them, then have three days of salad with fish and nuts, before returning to normal eating.


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