Thanks Amazon, but doesn’t the glycogen in your liver and muscles become depleted when you are fasting so that it’s insufficient to fuel a workout? Endurance athletes take a lot of care to ensure that they have sufficient stores of glycogen (pasta parties before the marathon for example) and consume a lot of glucose before and even during their events to prevent muscle breakdown (drinking lucozade for example) but if you are fasting wont you be effectively running on empty even before your workout?

Oh, Monty28 – I think that’s the point of 5:2 though isn’t it? It gets you to deplete your glycogen so that when you workout you don’t have that available and you switch to burning your fat reserves instead. You don’t want your muscles to suffer, so you don’t take the ‘deprivation’ to extremes (undereating your BMR more than 2-3 times a week) but as long as you’re not ACTUALLY starving, your body is going to go for your nice juicy fat stores before it starts eating muscle tissue. Plus you can always have a protein rich 500Kcal to help repair & build your muscles after your FD workout.

I guess runners do carbs before a long run because they always have and their bodies would go into ‘shock’ if they ran out of their ‘normal’ fuel mid-run for no obvious reason. However, I don’t see why you wouldn’t be able to train your body to cope on fat reserves instead?? Maybe a resident nutritionist can educate me but I’m a fairly long-distance swimmer and I’ve never conked out in the middle of a 5K swim on a fastday.

Hi Tracy 🙂 it would be great if you were right about the body using fat before muscle but I don’t think that is how it works. The first time I tried this diet I loved working out on my FDs because I actually felt more energetic than on eating days (weirdly) but the main reason I stopped the diet was because of this issue with training and fasting not being compatible. This time round I’m only going to train on eating days (I used to train everyday regardless). I’m really interested to hear yours and other people’s views on this subject because I love the 5:2 lifestyle and it definitely works for me but I don’t want to ruin my body composition doing it.

This is fascinating!

Tracyj, your comments make sense, but why are you starving if you eat below BMR more than two or three times a week?

On 4:3 and ADF or you not doing exactly that? Surely athletes with very low or zero body fat have a problem with the body ‘eating’ muscle, but someone with 30%+ won’t have. Wouldn’t the body burn off all the fat before muscle?

I work to TDEE at a target weight, not my ultimate target, an interim weight, but it means that I am working around my BMR calories for 4 or 5 days, doing a quarter of those calories on one or two days, and a full fast at least once a week.

I thought starvation mode came in after weeks of continuous full fasts.

Monty you make an interesting point regarding your concern for your body composition. I am sure that you are aware that building muscle involves working it to the point of causing small tears, and that when the healing process is complete it will be bigger and stronger. Glycogen stored in muscle is only used by muscle when other glucose is not available, and the rest of the body uses that which is stored in the liver.
If using up its store of glycogen is what is meant by the term muscle breakdown, then there is no reason for concern as it is not in fact destroying or damaging muscle tissue, and will be replaced as soon as excess glucose becomes available. Any excess will be stored as fat, something we all know about. When doing IF and depleting glycogen stores the fat will be used until we refuel our bodies with food, which as Tracy so aptly put it, is the point of doing 5:2
I hope that makes sense 🙂

Proper fasting means a greater calorie deficit and therefore a slightly faster rate of weight loss, which is a good thing.
My previous post regarding glycogen depletion on 5:2 was inaccurate as I was a little confused and should have checked the facts before posting.

Oh dear, Sorry my post threw up some confusion, just popped back in now – glad it all got resolved. All the best everyone 😉

hi all, just wanted to share my experience. I started 5:2 about 10 months ago, had some success and then stopped when I went travelling in Europe for 10 weeks.

I started 5.2 again in January this year and by that stage had been back at the gym for 3 months and was working out 4-5 times a week for 45-60 mins but had only shifted 1kg. I didn’t want to restart 5:2 earlier because I was worried I couldn’t fit it into the gym schedule. I am not an extreme gym goer by any means, a big session for me would be body attack followed by body pump and I only do that occasionally. But like a lot in this discussion I was worried I wouldn’t be able to perform at my best.

Anyway, eventually I felt like I was used to exercising again and so re-started 5:2 in January. At the start I only exercised on non-fast days but after a while it became easier to just exercise when I could fit it in and so gym days ended up on fast days sometimes. At the start I really struggled and felt like I wasn’t putting in 100% by the end of the class, but I think it was more in my head than my body.

Just this week I got to the end of a workout and didn’t even think about the fast day until I was on my way home and started thinking about what I needed to do to cook tea. I don’t think I perform ‘better/worse’ on fast/non-fast days as other people have said but I do find the gym distracts from the fasting because I don’t eat anything until the evening.

Good luck everyone xoxo

I’ve just came across this thread and was seeking reassurance ,
I’m now back on the 5:2 but intend to do it on the 4:3 basis for a few months.
When I last entertained the 5:2 diet I always made sure I didn’t attend the gym on a fast day . However today and my previous fast day I’ve been to the gym and completed a full body workout , I find it take your mind away from feeling the hunger but what I want to know how do you feel a month down the line on a gym session which was also a fast day ?