The stories of Catholic monks subsisting on beer during difficult Lenten fasts may seem fanciful, but a homebrewer who tried a water and beer-only diet for 46 days touted its many benefits, most of which stemmed less from the beer and more from the practice of self-denial. Despite the regular alcohol consumption and the calorie-rich beer, he lost weight and gained clarity of mind.
Having fasted myself in a variety of ways, I can personally attest that there is a significant improvement in the clarity of mind when we fast from those things that normally cloud our minds with seeking the next pleasure or worrying about the next pain.
There are other benefits to the beer as well, one of which is that for those who do not have ready access to clean water, the process of brewing cleans the water and provides a beverage that is safe to drink. This came in handy when the plague came around and many lives were saved (under the direction of St. Arnold of Soissons), as clean water always does.
Along with St. Amand and St. Arnulf of Metz, St. Arnold is the patron saint of brewers. I did not develop a strong enthusiasm for beer until fairly recently, perhaps because of a general reticence about alcohol from a Protestant upbringing and a very sober family. But now, I am very willing to drink the beer of fasts and deny myself many other things which I realize are more profoundly separating me from God.
By Mpolo - http://en.wikipedia.org/wiki/Image:St.Arnoldus.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3092846
Note: The picture above is a depiction of Arnold of Soissons, patron saint of brewers, in stained glass.