Good Friday is tomorrow, so I thought this would be a good time to share some thoughts on fasting. I'm not actually very good at this, but I've learned a few things from past mistakes, so maybe this will be of some help to you.
Rule number 1: Don't skimp.
Okay, the Church is pretty lenient when it comes to fasting. Catholics are allowed a full meal and "some food" two other times a day. (The whole "two smaller meals that don't add up to be greater than the full meal" thing is spurious, at least here in the U.S.) Heck, that's not much less than I eat some days anyway.
And there's more: There's no limit on beverages, nor is there apparently a distinction between a beverage and a drinky-foody-kinda-thing like a Slim-Fast. Similarly, on days of abstinence (which include both the mandatory fast days), "soups made with meat" are no longer expressly prohibited, which—if Jimmy Akin is right—would technically let you eat all the meat you want as long as it's in a soup. (I'm not sure I buy it, but Jimmy makes a reasonable case.)
But come on, you can do better. The point of the lenient laws isn't that you shouldn't do any more. It's to set the point at which you can't do any less. (Doing less anyway is a grave sin, which may be why they make it so easy.) You and I need every ounce of grace we can get, and we can't afford to slack off.
By the way, Jimmy has a guest post by SDG saying more or less the same thing.
Rule number 2: Don't get distracted by technicalities.
Remember, fasting is a spiritual thing. It's not about the mere act of giving something up. It's about uniting yourself to Jesus via suffering.
That means you don't need to agonize over whether you're fasting "enough" (so long as you're following the rules), whether you could/should have gotten by with even less food, how you're doing compared to last year, or any such nonsense. That doesn't give you an excuse to slack off, of course; see the first rule. I'm just saying, don't focus on the technicalities of your food intake.
Instead, focus on how your penance is going to bring you closer to Jesus. Denying your own desires and accepting suffering are ways of imitating Him. So focus on being Christlike, not just in the fact that you're fasting, but in the way you respond to your hunger. For that matter, you should focus on being Christlike in everything you do. Fasting is good practice for that.
This all applies to your voluntary penances, too, by the way.
Rule number 3: Don't overdo it.
This may sound like a repeat of the last rule, but this time I'm looking at the physical side. Overdoing fasting can be a big problem.
First, low blood sugar is not exactly the friend of a healthy spiritual life. I know. I've been there. The last time I fasted, I ate next to nothing all day. I also did next to nothing all day because I had a headache and no energy. I would have been much better off eating an egg or a small bowl of cereal and having the energy to say some extra prayers or perform some extra works of mercy. As it was, I couldn't even accomplish the scant few things I needed to do that day.
Second, fasting too much is not healthy. Penance is one thing, but starving yourself is not a good idea. Your body is a temple of the Holy Spirit, remember? You're obligated to take good care of it. You wouldn't put a brick through a church window and call it penance, would you? Then don't make yourself sick as a penance.
If you really want to go the extra mile, eat a grilled cheese sandwich and say an extra Rosary. Or better yet, make two sandwiches: One for you and one for the guy with the cardboard sign. (And still say the extra Rosary.) Or instead of starving yourself two days a year, do some sensible fasting more than two days a year.
Again, I'm not giving you permission to slack off. If you can manage 24 hours without a bite of food, great. If not, you should still aim as close to that mark as you reasonably can. But if you can't, don't push yourself to the point of being unhealthy.
Of course, you don't have to follow these rules. They're just my opinions. (Jimmy Akin has the actual rules covered.) However, I'm hopeful that my "rules" will be helpful to someone out there. Have a good Triduum and a blessed Easter, everyone!