Exercising the day after a fast day

This topic contains 2 replies, has 5 voices, and was last updated by  Tobias Karlsson 1 year, 10 months ago.

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  • I’ve been doing the fast diet for a while now and quite often run on a fast day, which I’ve discovered has no detrimental effect on my energy levels, in fact seems to be an appetite suppressant.

    However, I have been surprised at how much energy I have when I run the morning after a fast day. I thought that as I didn’t have any reserves I would find it hard going, but I feel so energetic and my muscles feel so light. Is this a known effect or is it all in my head?

    I’ve just started the 5:2 diet myself so my experience is still limited. However, I must admit that the day after fasting I, too, find myself with so much energy & have my more productive cardio sessions. On the flip side I also did one of my fast days the day of my cardio (spin class) & found that I struggled more with hunger that whole day than any of other days. Lesson learned, I now try to keep my fasting days to the non-cardio days. At least for now, until I become more experienced with this process.


    If you are doing 5:2 in order to lose weight you will have reserves ie your fat cells. If you are doing it for health benefits it’ll take more than one day of 500 calories to deplete your glycogen reserves so in theory you shouldn’t notice any difference in energy levels and I actually think that some of those who say they feel tired and lacking energy after fasting are actually experiencing sugar/carb withdrawal.

    I exercise several times a week and haven’t noticed any difference at all regardless of whether it is a fast day or not.

    I do find that if I do consecutive day fasts and I go to the gym on the second day I am very hungry but my energy level is always good.

    Some people find it easier to draw energy friom fat reserves than others we are all different. However if you stick with exercise on or after a FD you can train your body to switch energy systems more efficiently. If you find it hard now it will get easier.


    I have a 36h regime where I have one meal at around 700kcal or so after 24h. Then I go to bed and the next morning I have quite a tough workout (I burn off around 700kcal during intense cardio training). Then I have breakfast. I tried this out of curiosity as I normally really feel like eating the next morning (no wonder) after those 36h. I realised I have no problem to do tough running after that regime. I think it was only the first time I tried that it felt a bit weird, but now it is second nature. I do make sure though to have a larger and very healthy breakfast right after my workout; I think that is critical. But exercising during a fasting period – although my case is by no means extreme – I think is just a question of getting used to it. Just pay attention to your body and stop if you are lightheaded etc!

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