Anecdotally I found my performance to - both in the gym and in the office - increase not decrease. From athletes and academics I follow on social media, they also say the same. I've read a few hypothesis as to why this may happen. In an evolutionary sense, when in a fasting state we would require more energy to go out and hunt/gather food to take us back out of that state. IIRC, metabolism increases while fasting. It wouldn't make sense for our body to reduce performance because that just makes starvation an even more likely possibility, as it suddenly becomes much harder to go out find a food source due to said >"major performance decrease".
There are a few studies knocking around about regarding it, but I've only got a minute so this is the best I could do for the moment-
"Findings indicated that pre-exercise feeding enhanced prolonged (P = .012), but not shorter duration aerobic exercise performance (P = .687). Fasted exercise increased post-exercise circulating FFAs (P = .023) compared to fed exercise."[1]
I experimented at the start of the year and didn't experience any drop in performance - office or gym - with water fasts less than 24 hours.
Fasting between 24-72 hours, though, really affected my sleep and made me feel weaker during workouts (though it didn't really affect me mentally). Curious to see if others experienced the same.
Can't comment on longer fasts as I didn't exceed 72 hours (though I did read many reports of it actually getting easier after that point in time).
Currently doing IF (very rough 20/4) which is working pretty well.
Honestly it varies massively - I play it by ear, as it's normally interrupted by going out to dinner with friends or dates.
I fast once every 10 days minimum (arbitrary number, but it keeps me disciplined). If I've had a few weeks of excess (lots of drinking and greasy takeaways) I might do 3-4 days. At least 2-3 times a year I like to do a 6-8 day fast. I've done this for the past 4 years and I've felt remarkably better for it, with the most noticeable thing being reduction in scar tissue (from surgery) and inflammation symptoms.
In terms of how it makes me feel while fasting, it depends on the day. A one day fasts tends to make me just feel hungry around meal times, assumedly because I'm still largely running on the glycogen in my muscles. I used to find day 2 pretty rough, as I'm guessing that's how long it would take for the process of ketosis to start in me. As your body adapts to frequent fasting though it becomes plain sailing though. I'll often arrange my fast to coincide with a large stint of work, as I feel my mental clarity is much higher - akin to taking Modafinil if you've ever tried it. Hunger isn't an issue for me at all once I'm in a state of ketosis.
I highly recommend doing an extended fast at some point. If anything it allows you to become much more satiated by smaller portions, and it eliminated any sugar cravings I used to have.
Very interesting. I remember reading that traffic accident rates go up significantly in Muslim majority countries during the first few days of Ramadan (daylight fasting), so there appears to be an adaptation period with decreased performance before the benefits kick in.
"Except major performance decrease. Some people cannot afford that."
This was my first reservation about fasting and while everybody is different and you'll need to see how your own body responds, I am happy to report that the following activities:
- mid to long distance runs (4-8 miles)
- 60-90 minute power movement weightlifting session
- routine crossfit workout and/or plyometrics
- BJJ class with 5 minute sparring rounds
... are not only not impacted, but are in many cases enhanced by being in a fasted state. The most positive impact is in my weightlifting workout[1] which, ironically, is the activity I thought would be most negatively impacted.
I can't speak to 50 mile ultra runs and I know I can't do all of the above in a fasted state - but I never attempted to do all of the above on the same day anyway.
Just try it.
[1] Power movements, relatively heavy weights and relatively low reps. Just the kind of workout you'd think would be difficult while in a fasted state.
When following an intermittent fasting protocol (eating within the same 8 hour window, for example), productivity tends to increase in the fasted state. Maybe there's some initial adjustment period.
