As long as you are hydrated before you exercise and properley hydrate afterwards you will be fine. Yes you retain water, but only for a few hours, you wake up the next morning with it having fell off again (if you hydrated properley afterwards). In my first week I had a couple of games of golf, sounds easy but it takes about 4 hours to walk all the way round a golf course. I also done a 15 hour shift in work the day before weigh in, which was energetic, I lost 14lbs in the first week (although it was day 9 when I was weighed)
I have started exercising in my second week, so my body had properley adjusted into Ketosis. It is a simple fact that if you exercise you will burn more calories, being in Ketosis and on a very low calorie diet, it is also a fact that the energy will come straight from your fat stores of your body, as the shakes only have 550 calories (approx) anyway. You are already burning the extra calories needed by the body from your fat storage, which is why you lose so much weight. It is estimated that you have to create a 1000 calorie deficit from what you consume to what you burn in order to lose 1lb of fat. That means technically if you are doing 100% TFR then you should burn on average 1.5lbs a day. Now I know this isn't exact and all people are different but exercising can only be a positive thing, as it burns more calories which come straight from the waist line. I have done 2 long runs this week and feel great, but the proof is in the pudding and I get weighed today so I will update later with my results. Due to my weigh in being day 9 on the first week, It has only been 6 days since last weigh in, so i'm expecting a bit of a disappointment but really hoping for 7lbs.
fingers crossed xx