Insulin causes our body to retain water. In the first 3 days or so of a long fast like that you pee water like a firehose as your insulin levels plummet to near

Insulin causes our body to retain water. In the first 3 days or so of a long fast like that you pee water like a firehose as your insulin levels plummet to nearly zero. Also fat burning becomes less efficient in the absence of glycogen stores due to ketone creation. In addition human growth hormone levels will increase. 10kg in 9 days is likely about 3-4kg fat/protein and 6-7kg water roughly speaking.