Can fasting be good for you?
Just for the heck of it, because there are already a number of great answers here (that I would not be able to add additional information to FOR fasting), and because I've done a great deal of research to support both sides, I'm going to play devil's advocate. Mwah ha ha ha! I'll will take the side of why fasting isn't good for health. First of all, other than fasting before blood work, pre-surgical restrictions, and some other medical procedures, fasting is typically a religious purpose, and I've heard of very few religions that don't come with the specific instruction that pregnant women, children under "x" age, or people over "x" age are not required to fast. While we can understand that children, who are a lot less capable of understanding the religious purpose for fasting, pregnant women and older persons are. Meaning that there must be some reason to think that they need to eat rather than fast. Therefore, I don't think it would be entirely without reason to assume that this was done with the persons health in mind. So, if there are people who are excluded from religious fasting because it is an issue of health...then it wouldn't be entirely out in left field to say...fasting isn't really good for the health, yes? Although, if there are any other reasons they shouldn't fast, I would love to hear them. I'm completely open minded and I ADORE learning!! Again, I'm merely playing devil's advocate...I don't have "a horse in this race" so to speak.
The length of time between meals has actually always been a very "hot button" topic with doctors. It has long been suggested that people need to eat smaller meals frequently through the day rather than 3 large meals per day. The reason for this is that the body's systems are overly taxed upon the first meal that is consumed after any portion of "rest" (as in not eating). There are many arguments, from the side of those who champion eating all day long, that any benefit that has been gained from fasting is actually completely undone by the first consumption of food. The blood sugar/insulin spikes, the digestive system is overloaded, the kidneys are put upon and so on and so forth. Again, though, this is the argument of one side. My grandpa was actually a diabetic. He had a very extreme adult onset case and quite literally he pretty much had to eat little bites all day long, sitting down to a large meal would almost kill him. Again, though, he had a lot of medical problems that were really out there. However, my vet has me now feeding one of my dogs three times daily - he has medical issues, he's on prednisone and we are trying to get weight off of him, and feeding him throughout the day instead of one or two meals helps him considerably. His system is always active, his metabolism stays active and he doesn't have periods of complete inactivity, which is what fasting produces.
And for my last "point" I will go a little extreme. Please hear me out, as I do have a very logical point, although my original example may upset you, it is not where I'm ending. I don't know how everyone else fasts, I don't know what is required to each religion or health program, but one thing I learnt from having a sister with an eating disorder is that the body spends it's time trying to protect itself. When you continually deny your body food, our bodies try to protect themselves by hoarding everything that it can possibly use. Bulimics won't "lose" weight despite that they are constantly ridding themselves of food unnaturally - their bodies are hoarding fat to survive. This protective instinct is why anorexics grow a peach fuzz on their skin - to keep warm, to protect against heat loss. The body is going to protect itself from anything that isn't it's normal behavior. Now, I'm absolutely not stupid, and I'm not at all suggesting that anorexia (nervosa) is ANYTHING like fasting, it isn't...I am merely stating that the body, itself, does not accept the idea of being denied proper nutrition. It is how people stranded in the desert or in freezing temperatures manage to be found days later - their bodies began compensating for the environment, protecting them from the elements. Whether you are fasting, or dieting, or suffering from a mental illness - your body will change it's normal patterns of behavior to compensate for what you are doing to it. I just can't say that fasting is good for your health, because your body is going to react to the fast negatively. As soon as it realizes that you aren't doing what it expects, it will begin to store up it's reserves to protect you against harm. A fast that lasted over a matter of hours could result in more negative factors than positive ones.
Myself, I'm not into fasting. I do observe the Catholic days of fasting - that's my faith, that's my belief - so I do it. For all other days, though, fasting has never been shown to me to be beneficial - from research I've read and from my own observations of my own health. I've seen more evidence that I'm healthier, I feel better, look better, when I eat healthier small snacks or small meals throughout the day. I think it comes down to the person themselves. It's also going to depend on what a person chooses to eat as well. I love eating vegetables - and no one has yet been harmed eating fruits and vegetables all day long - however, if someone was eating potato chips or junk food all day long...then they probably could use a fast.
That's the other side of the argument...for whatever it's worth. My opinion...money back guarantee! LOL