Why command `cat test.log |while read line; do echo $line ; done` would compress whitespace?

I have a file named "test.log" with contents： 2 root 20 0 0 0 0 S 0.0 0.0 0:00.01 [kthreadd] Then I use while-read command to process it: cat test.log |while read line; do echo $line ; done and It returns 2 root 20 0 0 0 0 S 0.0 0.0 0:00.01 a Wired,something was truncated.What happend?