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

Question

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?