I have a good one for this that more people need to hear. 1lb of fat can spit out about 25kcal per day. If you are 200 lbs at 10% body fat you have around 20lbs of fat. That means your fat can give up around 500kcal per day. If you restrict more than that over time, you will lose something other than fat. This is the magic pill to figuring out a top end limit you shouldnt try to exceed for loss rate. Its too bad guessing body fat is such a crap shoot. Either way its a good way to guess if you can loose .5lb per week or 3lb per week.
Thing is, dont think of it as a daily thing. Its more like a battery with a big slow battery charger. Your liver can convert all sorts of crap into usable substrate, but it takes time. Its the same reason v02max stuff is really aerobic. You use up a bunch of fast energy but it still has to be recharged over the sub ftp times via the big system wide generator (aerobic engine).
Fwiw, you didnt lose 12 lbs of fat (or muscle) in a week. You lost 12 lbs of water and glycogen. I do it way too often, and it used to be worse when i was low carb.
Step 1, Eat a normal american diet, lots of carbs lots of fat, LOTS of salt. Do some training in the heat or just generally be outside in the summer to drive up your plasma volume. Drink when thirsty.
Step 2, decide to clean up your diet, maybe even go low carb. Carbs in your body hold 3 units of water (I think, maybe 2? I dont recall. lots.) per unit of carb. Your 700 grams of liver carbs alone can be 2 or 3 kg of ‘weight’ swing when you make this change suddenly until you body adapts.
Step 3, drink way too much beer. Blow off all the rest of the water in your body, all the extra salt will go away and lots of water with it. You will now be down another 6+ lbs. You have now lost 10-12lbs in 5 days. You feel like death. You are less healthy. 0/5 stars, do not recommend.
At 5 10, 217 dont eat 1200 cal. You are not helping yourself. Eat 2200 and eat back your calories from training. Get 140 grams of protein per day and all the quality carbs you can with whats left over. Eat stuff with colors.
Website with article
relevant quote:
A 2005 study found that body fat stores can liberate, at most, about 31kcal/day to be burned. In a subsequent interview (which, unfortunately, I can’t find the link to anymore), the lead researcher admitted he botched a couple of calculations, and the limit was closer to 22kcal/day from each pound of body fat. With this information, we can use a nifty little formula that can tell you how fast you can shoot to lose fat without unnecessarily increasing your risk of losing much (or any) lean mass in the process. I’m using 25kcal/day per pound of fat because those 3kcal/day aren’t going to make a meaningful difference, and they’ll simplify the calculation a lot, as you’ll see in a second. Body weight x bodyfat percentage = total body fat x 25kcal/day per pound of fat = daily caloric deficit x 7 = weekly caloric deficit ÷ 3500 (since there are roughly 3500kcal per pound of fat tissue) = pounds of fat you can lose per week