Definition. The urine creatinine test measures the amount of creatinine in urine. Creatinine is a breakdown product of creatine, which is an important part of muscle. Creatinine is removed from the body entirely by the kidneys. Creatinine can also be measured by a blood test.
Ketones are the byproduct of breaking fatty acids down to be burned. Okay, it's a water fast, but we can assume that after 3 days, ketosis is acheived. About 250 grams of fat is about the maximum amount of fat that will be burned daily. I say around 250-300 grams per day.
If you take in 500 calories per day less than you burn, that creates a 500 calorie deficit or deficiency and you will burn 500 calories of fat. And, if you do that every day for a week, you will burn 7 x 500 = 3500 calories or one pound of fat in a week.