Experiments with Circadian Rhythm Fasting


I have been doing the Fast Diet for a couple of years now. It works wonderfully, without having to buy any special equipment or supplement, which is fantastic. However, even after all this time, the diet days still need getting some use to. This is especially true when I am on "maintenance" mode, which means you fast once instead of twice a week. Because I am doing it less frequently, the diet day becomes harder because the body takes more time to adjust.

Some time back, I came across an article talking about Circadian Rhythm Fasting, popularized by Dr Jason Fung and many others. Here's a more recent article on the topic. The main idea is to restrict eating to a small window of the day, effectively fasting for the rest of the time. Like the Fast Diet, it does not require any special equipment or supplement, and is very flexible with the timing. For example, you can choose to start at 7am and end at 3pm, or start at 12pm and end at 6pm. However, the common guideline is to stop all eating before 7pm, because the whole idea of Circadian Rhythm Fasting is the to follow the circadian rhythm of the body when it comes to eating, thereby allowing the body to manage its insulin levels, which is crucial to burning off excess fat as well as avoiding Type-2 diabetes.

So I chose a 6-hour window from 12pm to 6pm, and stuck with the diet for 30 days. Note that I was not 100% strict with it. Sometimes I do snack a teeny bit at night (for example, when my wife has baked a bread and wanted me to try it while it's warm), and generally on Sundays, I allow myself to have breakfast at 9am. But generally, I stuck to the schedule. Here are the results:
I measured my weight twice every day, once in the morning at around 10am, and once in the evening at around 7pm. As can be seen, there's a ~1kg difference between morning and evening measurement. The trendline indicates a definite downward trend.

Contrast that with the next 30 days, when I went back to eating normally:
The trend is clear. Note that during the 6-hour window, I did not deliberately constrain my diet. I did periodic light snacking as one is prone to, and generally ate whatever I felt like.

Some thoughts about Fast Diet versus Circadian Rhythm Fasting. The latter is definitely easier to do. Because I am pretty much adhering to the same schedule every day, there's less adjustment problem as experienced in the Fast Diet. It is also incredibly flexible. I can have lunch normally with colleagues, and if I am meeting someone earlier in the morning, I am not opposed to having a cup of social coffee. If I don't feel particularly hungry that day, I can delay lunch or dinner by as much as an hour.

I also found breakfast incredibly easy to forego. As mentioned in the articles, one's hunger level is actually the lowest in the morning. A lot of our desire to eat breakfast comes from habit and socialization. A cup of tea to start the morning does equally well and typically get me to 10~11pm before hunger starts to slowly creep in.

I also think Circadian Rhythm Fasting provides a very nice set of boundaries for one's eating habits. There is no guesswork any more. Every day is the same, and you simply try to avoid eating outside of those boundaries. Yet it provides one with the flexibility of "cheating" once in a while when the need arises (though, of course, it defeats the purpose if you cheat on yourself too much!).

I am currently trying Circadian Rhythm Fasting for another 90 days to see how well it performs.

Stay tuned...

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