Intermittent fasting and exercise

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Intermittent fasting and exercise

This topic contains 74 replies, has 61 voices, and was last updated by  Billgardiner 6 years, 9 months ago.

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  • I’ve fasted on exercise days for a few months and found the only thing was that I felt much more hungry than if fasting on rest days.

    On the basis that an hour of hard cardio should help the body better process food over the following hours (BBC Horizon – The truth about exercise) I intuitively think it should be better to fast on rest days when less active. something like this…

    M: Gym + eat normally
    T: Fast + HIT
    W: Gym + eat normally
    T: Fast + HIT
    F: Gym + eat normally
    S: Run + eat normally
    S: Slob out

    I’ve been fasting for about six months now – zero calories, or as near as possible, (I sometimes forget to drink my coffee/tea black at work & have the odd splash of milk) from 7pm to 7pm. I’m a keen runner, typically running around 80km per week, and cycling about 50km. Initially, running was difficult on fast days when I felt very sluggish, but has improved. I ran an ultra marathon (31 miles) at New Year and felt great, although shuffled my fast days around that week to have a normal day the day before. My weight has not moved at all since starting the 5:2, which has surprised me, but I was at a healthy BMI to start with, and embarked on the plan for the additional health benefits, not to lose weight. I do feel a little leaner around the waist and middle. I have a couple of marathons and 50 and 100 mile races coming up over the next few months, and am hoping to be able to keep up the fasting without any loss in performance.

    I just bought this book and am excited by the program. I’ve been on the HCG diet for a month or so and have lost 14 lbs. HCG diet is only 500 calories EVERY DAY so this looks like heaven. I’m wondering if the long term 500 cals per day with effect weight loss on your diet. I will be eating so much more (thank god).

    I am starting the plan, however I am not sure of a few points for example on the fast days can I munch on fresh raw carrots during the day or does this defeat the object. I would include them in my overall calorie count

    I complete my 14th fast day tomorrow. I am 64 yr old male and excercise at the gym 3 – 4 days a week. I excercise quite easily on a fast day and at the moment focus on cardiovascular workouts. I normally do between 30 – 45 min workouts burning between 450 and 650 cals. I mentally add the total weekly calorie to my “banked 3800 cals saved on my two fast days. This means in a good week I can “bank” a total of at least 6000 cals, not bad on a 2 day a week diet. I have found no negative effects while working out on my fast days but I believe it is a personal issue for each individual.

    Hi all.

    I have been following the diet since January since i discovered the book on bought it for my kindle and have lost 4 kilos so far so have been pleased.
    Can anyone tell me if I can have a glass of wine on a fast day as part of my 500 calories? On my fast days i only eat at dinner and wondered if I could have a 350 Calorie meal with a 150 calorie glass of wine? Thanks all.

    Im getting into training to cycle Lands End to John o’ Groats in July. I want to work up to 90miles a day. Yesterday started out being a fast day, I did a hilly 34mile ride (1350cals used?), having had a 300cal breakfast. But I was struggling towards the end and dived into a cafe for a bowl of soup and a coffee to get me the last 5 or 6 miles home. I cant see how I could do up to 90miles on a fast day in future, I’m sure I would end up with the dreaded “cyclist’s bonk”. Any thoughts?

    I should say Im male, 66 and have been cycling regularly for getting on for 25yrs.

    My wifeI started the diet about a month ago and so far has only lost a pound in weight. Her main concern is that the day after diet day she always get diarrhea and wonders what she can do within the constraints of the 5:2 diet to alleviate this problem. She is hypo thyroidic and also has glucose intolerance. Can you give us any advice. Keith Nicholls

    @phild, Sounds like an impressive challenge to cycle to John O’Groats! Given the amount of energy you are likely to burn during long and hilly cycle rides I would strongly suggest you abandon the fasts on those days and possibly during the recovery day(s)too. Good luck and let us know how you get on. BTW – what is cyclist’s bonk??

    @keith Nicholls – A few people have commented that they get a change in their bowels with fasting. I wonder whether your wife’s diarrhoea may be related to more roughage on the fast day if she is not used to a higher fibre diet?

    Can you provide the names of scientists doing research into fasting and exercise? I’m a 51-year old woman, therefore probably menopausal, trying to get back into triathlon after having my children (they are 9, 7 and 2). Fasting before and after going to the gym seems to be no problem whatsoever – I often skip breakfast anyway – but the other day I was going for a run late on (8pmish) and had got very hot and headachey during the day, and ended up finishing my fast after about 23 hours as I really felt the need for a bit of food before I ran (I’d been drinking all day: and ate home-made guacamole with pitta bread before running). I’d also be interested in offering myself up as a guinea pig – I’m training for two half marathons in June/July at the moment.

    this is my 3rd week fasting. i typically do a hard cardio workout 6 days a week burning 500-600 cal depending on how hard i can go at 5am. the am after my first fast day was so awesome i will now make a point of doing my workout before i break my fast. i cant remember a better workout! and breakfast tastes awesome after!

    Today was my first time fasting, so I decided to skip my run tonight as I was exhausted all afternoon and I didn’t know how my body was going to react.  I’m new to running (6 weeks in) and it’s still a struggle for me, so I’m concerned about trying it on so few calories.

    I’ve been limiting my exercise on the CR days to two, sometimes three, twenty-minute walks at a good pace around the lot I work on.

    One of my trainers has urged me to work out on the CR days, suggesting that I would use up available glycogen stores and that this would then promote fat burning. I worry that I’ll crash at the end because the workouts are pretty vigorous:  90 minutes and up to 1200 calories burned (if the calorie meter on the heart rate monitor is at all accurate). I’ve experienced such a crash before and it is not pleasant, and needs to be alleviated by a cup of apple or orange juice — which would defeat the calorie restriction.

    So for now, I’m doing the CR days on Monday Wednesday and training Tuesday Thursday Saturday Sunday.

    It also depends on the type of exercise. When I went into this diet for the first time, there was some days when, if I was feeling really hungry, I found some poses really uncomfortable to do in my Bikram yoga practice – I’m referring in particular to the spine strengthening floor series.

    You’re lying in prone position (face down) for those 4 poses and backbending, and I found them much harder to do on a completely empty stomach. Your abs have to become like an inflated tyre in those poses, and while fasting you can’t help but feeling deflated in your midsection, no matter how strong your abs are.

    But I’m fine with other kinds of physical exertion like strength training while fasting. I think I’ll stick to using my dumbbells and my Swill ball at home on fast days this second time I’m going into the intermittent fasting diet.

    Having read all of the posts, I am not sure what to do.  I completed my first half marathon very slowly in March and now have another one booked for mid September. Winter training was dire in such cold weather, and I would really like to improve my time by half an hour(which may be a bonkers idea). I need to get back into running after a cold that would not go and start again. My new ambition is to run the same half marathon in March 14 but actually be the right weight for my height! I should be faster at 2 stone lighter, surely?

    I thought that I would try and combine running magazine advice and 5:2 advice together. So ate a banana and then did a slow  4 mile run, ate salmon and salad within half an hour of my return, followed by a LF mousse. Feel fine.

    You do actually need some glucose available to burn fat. Your body can usually find some glycogen lying around to make glucose to start the fat-burning, but I wouldn’t (and don’t) beat myself up if I find I need a few grams of carbs to get started exercising.

    I’ve been doing 5:2 for almost exactly a year now and although the weight loss (3 stone) hasn’t made me go all floppy or anything I am now trying to build a bit more savvy exercising into my routine. I was put off by trying to do my normal swim on a fast day early on (maybe 2 months in) and hadn’t really tried it since (I did do 1 swim on a fast days but only when I could go to an early session). However, now I have basically trained my body to fast every single day until tea time (about 6ish, after work) and then just have either a normal amount of calories 1,600-2,000 or 500 depending on if it’s a feast or a fast day. So for the first time, last night, I have done my regular weekly swim (2.6K in 1 hour or less) on a totally empty stomach and it was absolutely fine. I wasn’t even particularly hungry when I got home but I did polish off my 1,600 calories, as today is a fast day so I was pretty sure I’d need the fuel to get through it. This is definitely something I will do regularly from now on and I intend to build some kind of weights work into each day to combat the bingo wings too 😉


    Intermittent fasting and exercise

    7 Jan 13
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    Intermittent fasting and exercise
    This is one of those questions that I get asked a lot and the short answer is, “yes, it seems to be fine to combine the two and may indeed be beneficial”. The long answer is a lot more complicated. I am just working my way through the academic literature on this, some of which is in the book, but the headlines are:

    Make sure you are well hydrated. We get a lot of fluid from food (some of it added during the manufacturing process to add weight, bulk and therefore value), so if you cut your calories to a ¼ during your fasting day you will be consuming less water. I recommend drinking lots of calorie free fluid during the day, whether you are exercising or not. This can be black tea, black coffee (the idea that coffee makes you dehydrate is a myth), water from the tap, herbal teas, whatever. I am not a fan of diet drinks for reasons i will write about later.

    I have had tweets saying things like, “i have a dry mouth” or “my mouth sometimes tastes funny on a fasting day” and this is almost certainly a sign of dehydration.
    Men seem to not only tolerate but respond better to exercise on fasting days. For women the picture is more complicated. I welcome feedback on this

    One of the key benefits of exercise and fasting is they both increase insulin sensitivity, and insulin sensitivity is an independent predictor of future mortality. But they work in different, complementary ways. Exercise for example, particularly short burst of HIT (High intensity training) depletes the glycogen stores in the muscles, while Intermittent Fasting (IF) depletes the glycogen stores in the liver.
    On a more general note I had a look at the government guidelines for the BBC R4 series, You and Yours, on exercise, 5 a day and alcohol. I attach links to features I wrote about them for the


    “The Truth About Exercise” 28 February 2012

    Michael Mosley investigates recent scientific research that could change the way people exercise, including a study that suggests many could benefit from just three minutes of high-intensity activity a week. He also discovers the health benefits of seemingly innocuous actions, such as walking and fidgeting, and learns why some people do not respond to exercise at all.


    I had been going to spinning classes 3 days a week for a few weeks when I started 5:2. I decided to try to have my fast days on spinning days. This was partly because I go at lunch time and therefore it is much easier to have a very light lunch 😉
    These spinning classes are very demanding. We wear activio heart rate monitors and are instructed to stay in different zones, going over 90% 8-12 times in each class (often using the tabata method). So this is by no means an easy class and I was a bit nervous how I would handle it on fastdays. I have always had some fruit an hour before class, so I always have a few carbs to burn. Maybe one day I will try it on an empty stomach but I am not ready for that experiment yet. But I must admit I love doing this class on fast days. I have to be extra careful to drink PLENTY of water but I don’t have any problems doing the work and I find it easier to fast after the class. Maybe it is psychological or maybe I am just too tired to eat 🙂 . I find it easier to cope with the lack of calories by staying busy (and believe me, during spinning class I am plenty busy 🙂 )

    Hello. Just a feedback on female performance on intermittent fasting. I´m a 30y old female, height 5ft 8in, weight around 122lbs. My Usual routine: I do a 36h fast once a week to maintain my weight, but if i want to loose weight I do it twice or three times a week. It works great when I´m not exercising or exercising very mildly (15min runs twice a week). But now that I´m training for my police physical test, I feel very sick if I fast more the 12 hours. Although I´m not hungry, I can´t function, can´t think straight, feel like fainting all the time, it takes a lot of effort to do simple things, very scary. I know the fasting is causing this cause I instantly feel better as soon as I eat something. After a couple of fasting days of feeling miserable, I am changing strategy for a while so I can improve my performance for my test (which is my priority right now). It´s with a lot of regret that I´m thinking of going back to eating every 3-4 hours for a couple of months, at least until my body gets used to the training :/ Has anyone experienced something similar?

    Do you have any update on biking on fast days?
    I am just starting the 5:2 fast and worried about riding 30 miles three times a week? On plat diets I had to eat 3 to 4 oz. of protein (Chicken) before the ride to survive without being dizzy.

    Any. Suggestions for what to eat for my 250 cal. Breakfast when I plan to ride 30 miles on my bicycle?
    Protein and/or fat? Carbs are too quickly depleated by intense exercise?
    Your thoughts?

    Phil D: any response? I have similar issues.

    How is it working? I plan to start similar routine but I cycle and can’t “bonk” hall for way through a 30 mile ride?

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