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.
Based on these guidelines, limit your saturated fat intake to 18 grams or less when consuming 1,600 calories per day, 22 grams if you eat 2,000 calories per day, and 29 grams or less when consuming 2,600 calories per day.