for i in $EX_LIST ; do ...

 #!/bin/sh

EX_LIST=' '
TXT_FILE=./my_file.txt

get_first()
{
        cat $TXT_FILE |while read line
        do
                first_word=`echo $line | awk '{print $1}'`
                echo This is first word: $first_word
                tmp_list=$EX_LIST
                echo This is temp list: $tmp_list
                EX_LIST=$tmp_list" "$first_word
                echo update new list: $EX_LIST
                echo ======***======
        done
        echo $EX_LIST
}

get_first

echo Printing out the result:
for nn in $EX_LIST ; do
        echo item: $nn
done
echo done!

This is first word: john
This is temp list:
update new list: john
======***======
This is first word: jack
This is temp list: john
update new list: john jack
======***======
This is first word: kelvin
This is temp list: john jack
update new list: john jack kelvin
======***======
This is first word: mary
This is temp list: john jack kelvin
update new list: john jack kelvin mary
======***======

Printing out the result:
done!