Exercise — increase calories on Fast Day??

Welcome to The Fast Diet The official Fast forums Fast Exercise Combining Fast Diet and Exercise
Exercise — increase calories on Fast Day??

This topic contains 16 replies, has 15 voices, and was last updated by  sleepmilkywaymirmars 1 year ago.

Viewing 17 posts - 1 through 17 (of 17 total)

  • I apologize if this questions has already been beat to death. However, on a FAST day if you exercise can you increase the calories by a reasonable estimate of what you burned? I often try to do a HIIT workout on the fasting days simply to keep myself occupied doing something other than eating. I can tolerate staying at the 500 calories but that extra 100 would be nice.
    Thanks in advance.

    The short answer…NO! fast day is 500 calories (600 for men) or 25% of your TDEE whichever is the lower. It’s not a good idea to ‘eat back’ exercise calories on a fast day as the idea is to make your body get rid of stored fat. It won’t do this successfully if you increase the calories you eat.

    Doing exercise will not only burn your calories but will also boost your immune system resulting to reaching your height to the maximum level.

    Reaching my height to the maximum level? Wait whut? If you mean to say exercise has many other benefits besides calorie burning, I completely agree 😉

    Hi Cat, While I totally agree with everything that Sylvestra said and that is absolutely the way it’s supposed to work I do want to add something for those new to the 5:2 and exercising combo.

    Once you get used to this lifestyle (in my experience) it is no problem at all to do any amount/intensity of exercise that you would usually do on a non-fastday. I do most of my exercise on fastdays and on a totally empty stomach towards the end of the 36 hours – it’s no biggie and often I’m not even hungry afterwards.

    However, from my own experience and others’ I know that when you’re just starting out it can be really, really hard to stick to 500 calories on an intense exercise day and some people say they litterally conk out during exercise due to lack of energy, so it’s not quite as cut & dried as ‘Don’t do it’ when you’re new to this.

    I would recommend that if you’re the sort of person who was always capable of going all day without food and not noticing any loss of energy – you do what I do and exercise on an empty stomach as close to the end of your fast as you can manage, then have all 500 calories after your workout, preferably as late in the day as you can manage, so you’re not starving hungry when you go to bed. This will get easier as you get into the lifestyle.

    If you’re someone who is likely to conk out due to lack of energy then I don’t know the best solution for you but I’d experiment with giving yourself some kind of lowish calorie/high energy boost just before your exercise and saving as much of your calorie allowance as you can for later on after the exercise and I’d also say that if you really, really need it don’t beat yourself up if you go over your 500 on a high intensity fastday, especially not at the beginning and especially not if you’re being very careful not to exceed your TDEE on non-fastdays.

    Hi All,
    I’m no expert here, but I was listening to a cycling podcast about 18 months ago, and they were talking about the paleo diet for cyclists. The expert (Joe Friel) talked about how the body adapts to burning fat instead of carbohydrates when living on a low (or no) carb diet. He also tried to dispel the tradition of carbo loading leading up to an event with the fact that fat is energy dense, and you don’t really need much in the way of fat stores in your body to be able to exercise for a very long time.
    This previously was always a concern of mind, when thinking about paleo, or sugar free, or whatever other regime friends or family talked about. But with theories about how much energy dense fat stores I’m walking around with, and that I could train my body to not require lots of carbs before and during exercise, I thought I’d give the 5:2 diet a go. You see, I cycle to work twice a week, and being a fair weather rider, I change the days I ride quite often. It’s 32km each way, and I treat it like a training ride, not a sunday ride. We’re talking trying to keep the pulse above 140-150 (75% max HR) for the entire 75 minute ride. I’ve found that fasting has seemed to make zero impact on my performance. I really thought it would on fast days, where I have no breakfast, a coffee at 10, no lunch, a coffee at 15:00, and only eat at dinner time.
    I would’ve thought the morning ride would use anything I had stored, and with no solid food all day, the 75 minute ride home I would bonk (cycling term for zero energy).
    Well, it hasn’t proven to be the case so far, I’m really surprised, and impressed at the ability that the human body has to be able to perform with what ever resources it has to use…


    Thanks for your reply. I have found that I can do a moderate (120 BPM heart rate) exercise on a fast day with relatively little problem. Often I will do moderate exercise on a fast day simply to have something to do that doesn’t involve eating.

    I have found however that attempting HIIT is a total no-go. Which physiologically makes sense. If the liver/muscle glycogen stores have been depleted then going into anaerobic zone just won’t work since fat cannot be burned anaerobically. It’s OK, I’m happy to keep HIIT to the other 5 days – particularly since you really aren’t supposed to do it more than 3-4x a week anyway.

    I’ve been on the 5:2 for just over 18 months now and I started introducing hard exercise in to fasting days after about 3 months. I’m a cyclist and as long as I keep the work out to under 2 hours (ideally 1.5 hours or less) I actually find I have better performance on fasting days. Around 10%.

    I normally save all my calories for the evening meal and just eat maybe 50-100 with milk in coffee and tea during the day. However on an exercise day I will eat just a little before a serious work out. Typically a small piece of fruit, just to keep me going.

    I tend to find exercise kills my hunger any way. The only thing I would say with High intensity training is to adjust your zones to take account of your lower HR on a fasting day. Typical HR for me on a fasting day is 35-38bpm and 43-48 on a normal day. I set my Max at 178 on eat days and 170 on fasting days to take account of this. Otherwise the world starts to look a bit pink when flat out. 😉

    If you find it hard doing fasting and exercise stick to what I call the safe foods Soups and salad, where you can really eat rather a lot and fill up without taking on lots of cals.

    I was (up till August) doing the 5:2 and also excercising between 4-6 days a week – two runs of maybe 6 miles plus a longer 10 – 12 miler at the weekend, and then would go to the gym and do bodypump or circuits on top.

    absolutely no issues with feeling fatigued on fasting days – in fact I’d agree with Sue as I also found exercise helped in taking my mind off feeling hungry.

    I’m going to look at the HIT stuff for this year but need to be careful as I had an unplanned wee heart attack last year which means that I’m starting from a stupidly low fitness base now and don’t want to push my ticker too much.

    I’m more likely to be running keeping my heart rate in a particular zone and doing it the old fashioned way.

    Reading this is really interesting. It was only my second fast day today, so I’m a newbie. I’ve been running twice today (I usually run 3-4 times a week, generally with a rest day between), and found it no problem at all. In fact, I got a PB on my second run of the day! I had some fruit for ‘lunch’ after my first run, and am now about to have my main meal. I’m just starting to feel a touch hungry, but have been fine all day. I almost feel as though running on empty has been easier.

    Hi all,

    I do a lot of weight training not to bodybuilding levels but three times a week every body part.. My question is do I still need to add good carbs an protien after a weight workout and will it be detrimental to my muscle building gains / recovery if I don’t put the nutrients back in my body whilst on a fast day?

    Hope you can help I did send the same question to the website but not had a response.

    Regards Leigh

    Hi leigh and welcome:

    The question is ‘What is your goal?’

    Do you want to lose weight or build muscle?

    5:2 is simple – 500/600 calories or less on your two diet days each week.

    Many people successfully exercise on their diet days. If you want to exercise on yours, just eat 500/600 calories of carbs and protein. But you get no ‘extra’ calories for exercising, as exercise is included in your TDEE.

    If that does not work for you, exercise on non diet days and eat what you want.

    This might help: http://thefastdiet.co.uk/forums/topic/the-basics-for-newbies-your-questions-answered/

    Good Luck!

    Do NOT increase your calorie intake on fast days even if you exercise. I exercise a lot and on fast days I often do a double exercise session (2.5km swim in the morning and then a 45 minute cycle or spinning session later). I also find that this distracts you so you are not thinking about food. I keep to my 600 calorie limit and have lost 7kgs in 7 weeks. The more you exercise the quicker the weight will come off. As far as the non-fast days are concerned I do watch my intake and try not go over 2400. One day a week I let myself eat what I want.

    Just re-iterating for newbies, in case they haven’t read this whole discussion. Although, long-term there should be no problem doing whatever exercise you want for however long you want on a fastday and suffering no energy lag (you might actually find, like me and many others, you actually perform better on ’empty’), if you can’t face it as a newbie then don’t beat yourself up about it.

    Get used to the fasting first, then look at introducing additional exercise on fastdays. If you can’t do that without upping your calories on your fastday (very slightly) to begin with then don’t beat yourself up about doing that either. Just be sure to reduce back down once you are accustomed to it.

    And for those who cannot/ will not be doing any additional exercise alongside 5:2 – don’t feel like you’re a second class 5:2er or you’re somehow doing it wrong. You DO NOT necessarily need to do any additional exercise (beyond what you’ve always done/ not done) with 5:2 in order to gain health benefits or lose weight.

    Without exercise we can’t fit our body…Its possible to increase calories on fast day…

    Many moons later… I spoke to my Dr about this and he said yes, absolutely. It’s 25% of calories, so if by exercising you’ve burned 600 calories, you can increase caloric intake the that day by 25% of calories burned exercising. It’s also helpful to know your basal metabolic rate to know what 25% of your base metabolism is to know with more accuracy what 25% of your daily calories burned are to set your fasting goal. I’ve been consuming up to 750 on the days I fast where I burn 600 calories in a workout. I count every single calorie though – tracked through an app. I also know my BMR is 2200-2300 cals daily. So that, plus 500-600 cals burned in an hour of HIIT, X 25% puts me safely at a max of 750 cals.

    To answer your question, if you’re doing a HIIT workout on your fasting days, it’s reasonable to estimate the number of calories you’ve burned and increase your intake accordingly. However, keep in mind that the goal of intermittent fasting is to give your body a break from constant digestion, so you may want to focus on light exercise instead of intense workouts on your fasting days.

Viewing 17 posts - 1 through 17 (of 17 total)

You must be logged in to reply.