I did SW a very long time ago, and I lost two stone on that too (seems to b my magic number!) I started following IIFYM after i lost 4 stone last year. This is when I began weight training and my body composition completely changed. My arms and legs toned out, my butt lifted and my stomach flattened, even though there was not much weight change, I have kind of stuck to the principles of watching my macro nutrient count because I want to make sure whilst losing weight on 5:2, I tone up at the same time and doing IIFYM has been the only thing to help me with that.
IIFYM - if it fits your macros - allowing you to eat whatever you like as long as you stick within your macro nutrient goal. For me that's around 120g protein, 60g fat and 160g carbs.. in essence its just a balanced diet really!
I've kind of split my calories up so my TDEE is around 2100, I stick to 500 on fast days and around 1700 on mon, wed, fri.. allowing me around 2400 on the weekend! Allows me to indulge a little more, because im pretty good at being strict with my diet on a weekday!
If you are enjoying 30DS you will enjoy 3rd phase. Defo the phase I saw the most change! I also did Banish Fat Boost Metabolism (i think thats what it was called) which was great for a high cal burn, but its a longer programme.