Well yes, but the trials were of alternate day fasting so that creates a much bigger calorie reduction in that the subjects would have to eaten 175% of their normal daily calorie requirement on feed days in order to compensate for the fast days. Because we are only fasting twice a week, it is much easier to end up compensating for the fast days. If you do the maths assuming you are an average woman and your daily calorie requirement is 2000 cals (i.e., 14000 per week), then the reduction in calories over the week on 5:2 is 3000 cals, so if you were to eat 2600 cals on feed days instead of 2000 you will cancel the fast day reduction out and not lose weight. So, you
can eat what you like but not necessarily as much as you like!
Most people find that the appetite reduction they get from fasting means that they don't overeat at least on the first feed day after a fast anyway. It can take a while for this appetite reduction to kick in though. It took me a long while to work out that the stomach discomfort I was feeling on the first feed day was due to overeating
. The problem was that my brain was used to seeing a certain portion size for breakfast and so I was putting the same amount as before into my breakfast bowl and then wondering why my stomach hurt! Now I reduce my breakfast by about a third and all is comfortable.
However, having said all that, the natural day to day variation in weight that you can get anyway is pretty big so that you could
appear not to have lost any weight over the 3 weeks when in fact there is an underlying fat loss that is not showing on the scales. Remember the average loss per week is only 1lb so even if you have lost 3lb, your scale weight can vary by more than this daily anyway.
So here are some things you can do:
1) measure your waist (and other bits too if you like) and see if there is any change there
2) work out your TDEE (links in the FAQ) to find out what your feed day cals should probably look like
3) make a rough calculation of your feed day cals and see if there is a big difference from the TDEE calculation and if so try to cut down a bit on feed days
4) wait another 3 weeks and see where you are then.