Intermittent Fasting, Intermittently?

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❝Have you come across any research on alternate-day intermittent fasting—specifically switching between one day of 16:8 fasting and the next day of regular eating patterns? I’m curious if there are any benefits or drawbacks to this alternating approach, or if the benefits mainly come from consistent intermittent fasting?❞

Short and unhelpful answer: no

Longer and hopefully more helpful answer:

As you probably know, usually people going for approaches based on the above terms either

• practise 16:8 fasting (fast for 16 hours each day, eat during an 8-hour window) or
• practise alternate-day fasting (fast for 24 hours, eat whenever for 24 hours, repeat)

…which latter scored the best results in this large meta-analysis of studies:

Effects of different types of intermittent fasting on metabolic outcomes: an umbrella review and network meta-analysis

There is also the (popular) less extreme version of alternate-day fasting, sometimes called “eat stop eat”, which is not a very helpful description because that describes almost any kind of eating/fasting, but it usually refers to “once per week, take a day off from eating”.

You can read more about each of these (and some other variants), here:

Intermittent Fasting: What’s The Truth?

What you are describing (doing 16:8 fasting on alternate days, eating whenever on the other days) is essentially: intermittent fasting, just with one 16-hour fast per 48 hours instead of per the usual 24 hours.

See also: International consensus on fasting terminology ← the section on the terms “STF & PF” covers why this gets nudged back under the regular IF umbrella

Good news: this means there is a lot of literature into the acute (i.e., occurring the same day, not long-term)* benefits of 16:8 IF, and that means that you will be getting those benefits, every second day.

You remember that meta-analysis we posted above? While it isn’t mentioned in the conclusion (which only praised complete alternate-day fasting producing the best outcomes overall), sifting through the results data discovers that time-restricted eating (which is what you are doing, by these classifications) was the only fasting method to significantly reduce fasting blood glucose levels.

(However, no significant differences were observed between any IF form and the reference (continuous energy restriction, CER, i.e. calorie-controlled) diets in fasting insulin and HbA1c levels)

*This is still good news in the long-term though, because getting those benefits every second day is better than getting those benefits on no days, and this will have a long-term impact on your healthy longevity, just like how it is better to exercise every second day than it is to exercise no days, or better to abstain from alcohol every second day than it is to abstain on no days, etc.

In short, by doing IF every second day, you are still giving your organs a break sometimes, and that’s good.

All the same, if it would be convenient and practical for you, we would encourage you to consider either the complete alternate-day fasting (which, according to a lot of data, gives the best results overall),or time-restricted eating (TRE) every day (which, according to a lot of data, gives the best fasting blood sugar levels).

You could also improve the TRE days by shifting to 20:4 (i.e., 20 hours fasting and 4 hours eating), this giving your organs a longer break on those days.

Want to learn more?

For a much more comprehensive discussion of the strengths and weaknesses of different approaches to intermitted fasting, check out:

Complete Guide To Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting – By Dr. Jason Fung

Enjoy!