Calahonda1984 wrote: »

... On my non fast days I'm also being good and eating healthy meals (mainly) and not going over my TDEE. I'm also exercising - doing a fair bit of walking and aerobics sessions. ...

Sounds like your fast days are fine (the rules are simple)...but you may want to examine your regular days more closely. These days are actually more complicated...here are a few things you should look for:

Logging: it has to be done...at least at the beginning until you are confident in your estimations. Be truthful and accurate.

TDEE: is it accurate? Do you have your activity level correct? Is your BMR right? These values can vary (sometimes wildly) from person to person and depending on the methodology used. Again, be honest and accurate (as possible)...if you are using a "moderate" activity setting, but that's really just on 1 or 2 days a week, then choose "sedentary" and log any and all activity/exercise you do above that. In my own scenario I use sedentary but actually am less than that (I work from home), so MFP's standard calculation is high on my TDEE by about 15%. To get an idea on what all goes in to calculating an accurate TDEE (and why this value is so speculative) you can take a look at a calculator I wrote a couple of months ago (http://www.sailrabbit.com/bmr/). Be sure to click on the help icons around the page, they explain each of the values in detail.

Activity/Exercise: Have you done an accurate assessment of this...logged and detailed everything you are doing? Let's say your "true" TDEE is 2000 cal and you are doing ~1000 each day in exercise/activities...if you are eating just 2000 cal a day then your body is slowly moving into starvation mode (if it isn't already there). The idea is to keep your metabolism cranking...this is hard for people to grasp at first because they are so used to eating less they don't realize that it can actually work against them. If your body detects that it has plenty of fuel (feast mode) then it will burn calories normally, then when you fast the body actually kicks it up a notch and starts to burn up the fuel reserves (fat) at a higher rate (increases metabolism). It's not until the body gets into famine mode (don't worry it would take 90+ hours of fasting to even get close to this) that it starts burning up muscle and slowing down your metabolism. The problem arises when you reduce calories daily over a period of weeks...this can also result in your body detecting "famine", resulting in a reduced metabolism.

My suggestion is to go with your gut...if you feel you are starving then try finding a more accurate TDEE and be sure to eat back your calories burned from exercise/activity on non-fasting days. If you're feeling stuffed/sated then start reducing your daily caloric intake (by ~100 a day...a week at a time) on non-fasting days until you start seeing changes, but remember you still need to eat back those burned calories.

I always say this (others in the group have heard it many times), but I still consider myself new to fasting. I'm much better informed than when I started but still expect I have much to learn, plus I'm very large (started at over 500 lbs) which means my MFP TDEE is probably about double yours...so their's that grain of salt (our body types/lives couldn't be much different).

This may all seem a bit daunting now, but you're going to be surprised at how "in-tune" you'll get with your body (if you aren't already)...the more fasts you get under your belt the easier it will be to detect/understand how certain choices/actions affect you.

Good Luck

Seems like stalling if very common with 5:2 and these are some great answers to that issue. @Orlcam & @Melaniecheeks - seems to me this would be a great post to add to the announcements or turn into a FAQ?

@Calahonda1984 - I am wondering if it has to do also how much one has to lose. I think the more you have to lose the faster the scale drops. For me I am trying to lose 20 lbs. A great week for me is 1/2 pound. So pretty much a turtle and one week I gained a pound for no particular reason.

@flumi_f - I have been wondering if as you have been doing 5:2, have you found your weekly weight loss become more stable as time went on or has it been erratic the whole 18 months?

Here you go Jknight. My weekly losses and gains since May 2013 ;-) A bit of a bumpy ride. When I had more to lose, one good weekly loss was often followed by two slower weeks. In the beginning I was losing an average of 1-2lb/week, then 1lb, then 0.5lb, etc. Losses got slower as my TDEE sank due to my lower weight. I've been maintaining on about 1800-2000 netcals per day on non fast days and 2 fasts per week. Which is actually alot of cals for a 5'1 and 57-58kg woman. If I were more strict on the input side on non fast days, I would probably be able to lose those last 3kg

And this is with my daily weighins.....Fluctuations are normal

Here, this is pretty crucial to understand, IMO. Your weight can stay the same while your BF% is dropping, which is actually ideal:
http://en.wikipedia.org/wiki/Body_fat_percentage

Assuming your calories are where they should be, then yes, something is happening in your body when you fast for a day.