Alternate day calorie restriction seems to be one of the most effective ways of increasing my life expectancy, but it isn’t easy. I tried it about three years ago, but gave up because it interfered with my sleep. I started it again three weeks ago, and this time I seem to be adjusting to it.

One important difference is that this time I’m better informed about what it takes to adjust to the diet. I planned a strict induction phase of 7 down days (about 550 calories) and 7 up days (unlimited food), followed by a less strict pattern of 2-3 days per week on which I’m limited to around 1000 calories a day. (I ended up adding an extra up day after each of the first two down days, then switched to strict alternation for the remainder of the induction phase). The severity of the induction phase may be important at triggering adaptation to this kind of diet.

The second difference is that this time I’ve been obsessive about measuring my food intake to the nearest gram. I suspect that when I intended to eat 1200 calories a day in my prior attempt, I was actually getting at least 1400 calories and fooling myself into thinking I was following the diet. This time I’m using a good scale to weigh each serving.

After the first down day, I slept poorly (as expected), getting impatient for sunrise to bring me an excuse to get up for food. After about the fourth down day, waking with an empty stomach seemed normal enough that it doesn’t provide a motive to get out of bed, or to get food quickly when I do get out of bed. I hardly notice the feelings of hunger then, even though I ought to be hungrier than late in the previous day when I did notice some of the standard hunger feelings. My sleep isn’t quite back to normal, but it seems close to normal and improving.

I’ve been feeling full about 50% of the time. I felt noticeably hungry about 30% of the time at first, and now it’s more like 20% of the time. Hunger feels a bit less important now than it used to feel (i.e. it affects my attention less).

Weight loss wasn’t an important motive for changing my diet, but I hoped I would lose about 7 pounds. I lost at least 5 pounds by the end of the 5th down day (my weight fluctuated enough that it’s hard to evaluate it precisely). I couldn’t comfortably eat enough on the up days to make up for what I lost on the 550 calorie days, even when I became mildly alarmed at my rate of weight loss.

Then my weight rebounded within a few days, without any apparent change in my diet, to roughly what it was at the start. The obvious guess is that my metabolism slowed down to compensate for the reduced calories. I did feel noticeably colder in bed after down days. I also felt less mental energy, and when doing an easy hike on the day after the 6th down day I felt a need to take rest breaks that was unusual in that it wasn’t caused by anything like muscle fatigue.

During the induction phase, I practiced strict protein fasting (< 15 grams of protein per day) on down days due to guesses that protein restriction is more effective at causing beneficial metabolic changes, which might cause faster psychological adaptation. My results seem to provide weak evidence in support of this guess. My diet on down days was mostly sweet potato and lettuce, with modest amounts of other vegetables and sugar-free chocolate. This provided more bulk to fill my gut than is typical for this kind of diet, but that was likely offset by the lack of protein related satiety. I’m not restricting protein now that I’m out of the induction phase (although I expect to do so maybe once a month).

My heart rate variability mysteriously increased after the first down day, then declined to a much lower than average level after the fourth down day, and has fluctuated a lot since then (averaging somewhat below normal).

Why did I have enough willpower to get this far, when I probably didn’t have the willpower needed to do it right three years ago?

One factor is that I now consider the CFAR community to be an important tribe to belong to, so my sense of self-identity has changed to attach more importance to being able to make big changes to my life.

Another factor is having information that led me to be somewhat confident that by a specific, not too distant, date it would become a good deal easier.

A third factor is being more obsessive about measuring how well I was complying with the rules I set down.

The induction phase cost me a fair amount of productivity. For 17 days I wasn’t close to having enough willpower/ambition to start writing a blog post (and had similar problems with most other non-routine tasks). But now I feel that writing this post is easier than normal. It’s too early to tell whether that means I have more mental energy than before.

I don’t know how to get strong evidence about whether it is worth the effort. I seem to feel more self-efficacy. I now think I can set my weight to any reasonable target simply by changing my calorie target on 2 or 3 down days per week. But in order to be clearly worthwhile it needs to improve my long-term health. I won’t know that for quite a while.