In Proverbs Solomon also speaks of "riotous eaters of flesh". Eating lots of meat has always been a sign of gluttony.
I'm admittedly skeptical of the idea that meat affects one's emotional state: I've never found this to be true in my own case, and I haven't been able to find solid scientific studies showing this. Nevertheless, some people do report that meat-eating affects them in this way, and it seems to have been a prevalent notion in ancient medicine, whence the Fathers, who offered as a reason for fasting that meat affects the passions. Personally, I interpret this in the same way I interpret other cases where the Fathers have been scientifically inaccurate: they were simply using the best available secular wisdom of their time, and even if they happen to be wrong in this instance, this does not negate the value of fasting overall.
Eating meat is enjoyable, and part of the purpose of fasting is to abstain from legitimate pleasures. Also, it is undeniable even in modern medicine that excessive meat consumption is harmful. This fits well with what is said in Proverbs, and by St Paul. Excessive consumption of meat or wine is harmful and inconsistent with Christian moderation.