for loop over input lines

Do it this way instead:

while IFS= read -r fecha; do
    echo $fecha
done < <(xml2 < podcast | egrep "pubDate" | grep -Po "(?<=\=).*")

Bash will separate "words" to loop through by characters in the Internal Field Separator ($IFS). You can temporarily disable this behavior by setting IFS to nothing for the duration of the read command. The pattern above will always loop line-by-line.

<(command) makes the output of a command look like a real file, which we then redirect into our read loop.

$ while IFS= read -r line; do echo $line; done < <(cat ./test.input)
Fri, 22 Jan 2016 17:56:29 +0100
Sun, 13 Dec 2015 18:33:02 +0100
Wed, 18 Nov 2015 15:27:43 +0100

xml2 < date_list | egrep "pubDate" | grep -Po "(?<=\=).*" \
| while read L
    echo $L

read breaks on lines, and doesn't split words unless asked. :-)

However, tackling XML with regular expressions is bringing a knife to a gunfight. It's very easy to construct valid XML that the above pipeline will either miss, or capture incorrectly.

If you deal with much XML, you really want to get comfortable with a SAX parser.