Losing 3-4lbs a day pre-op... not a HumbleBrag, legit concern.
My guess it that if you kept this up the loss would slow dramatically. The first bit is "water weight" and it comes off much faster and easier.
It does seem a bit weird to me though that a pre-op diet is under 400 calories. Are you sure you're adding that up right? I recommend MyFitnessPal to log food if you aren't already using some other method. A 70 calorie shake doesn't seem like it would have much protein in it.
Good luck to you on your surgery - it'll be here before you know it!
There have been times in this process, especially in the beginning where I was concerned with how fast weight was coming off. But, it does slow down and then sometimes even stall and you'll forget those times that you were concerned about the fast loss even happening! Congrats on the success so far!
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The first two days I think I lost something like 10 pounds and then it was a pound or two a day for the next month. After the surgery it was a pound a day for a long time. It is fun for sure.
Doesn't seem like your shakes are all that good. I know surgeons like to sell stuff to make money or to make it easier on you to find it, but I recommend going to GNC and get the Total Lean 25. The chocolate/peanut butter tastes like a reece's cup and the banana is just wonderful. And you get 25 grams of protein in 8 oz using water as a mixer. Your calories shouldn't drop below 600 although it doesn't really matter for a couple of months. Starting at 430 means you have lots of reserve so go for it. Good luck. It will be the best thing you have ever done for yourself that is legal....
800 calories and less than 20 net carbs is the shizzle