I started the 5:2 about 4.5 weeks ago and generally have coped well. No real difficulty dealing with the fasting and in fact looked forward to them. Furthermore I never went to bed hungry on fast days nor did I wake up hungry the morning after. To date I have lost 10lbs and my BMI has dropped below 25 – Great so far!

However over the same period that I started the diet plan I noticed that my sleeping pattern had changed. I was getting off to sleep ok but I started waking up for no apparent reason usually between 2 and 4am. I use to wake up at between 6 and 7am. At first I thought it may have been because I might have a prostrate issue or UTI as when I woke up I needed to go to the loo and that it was my bladder that as waking me but I have eliminated this as a cause after getting this checked out. I now think the causation is the opposite direction (ie Am waking up dor some other reason and then find that I need to pee!)

I have done a bit of research and have come across articles that has identified a possible relation between the 5:2 and disturbance of the circadian rhythm. The theory is that the constant switching between fasting and non fasting over the weekly cycle might confuse the brain and affect the body internal body clock.

I have read threads on this site ( I think? I have done so much research I cant remember where I saw it now) which has identified some sleeping problems people have encountered doing this diet but this has been limited only to problems on fast days where people go to bed maybe still feeling hungry and have difficulty getting off to sleep. But for me it affects every night of sleep regardless of whether I fasted that day or not. I do feel tired each night I go to sleep but I just wake up really early and obviously this is unsustainable. I can not think of what other reason could contribute to my poor sleeping. I do not feel stressed; I am quite active during the day (including exercise and walking the dog) so I do expend energy; and practice good sleep hygiene (ie no distractions in the bedroom, no caffeine and alcohol in the evening etc)

I have decided to take a 2 week break from the diet to see if my normal sleeping pattern returns to normal. However I would be really interested to here if any other faster has noticed similar experience.