Christian fasting isn't some kind of a "work" that's commanded by Christ or required by Scripture. However, that doesn't mean that fasting isn't recommended as a part of our spiritual growth. The Book of Acts records believers fasting before they made important decisions (Acts 13:4; 14:23). Fasting and prayer are often linked together (Luke 2:37; 5:33).
Too often, the focus of fasting is on the lack of food. However, the purpose of fasting is to take our eyes off the things of this world and instead focus on God. Fasting is a way to demonstrate to God and to ourselves that we are serious about our relationship with Him. Although fasting in Scripture almost always refers to fasting from food, there are other ways we can fast. Anything you can temporarily give up in order to better focus on God can be considered a fast (1 Corinthians 7:1-5).
Fasting is recommended to be limited to a set time, especially when fasting from food. Extended periods of fasting without food can be harmful to the body. If unsure about fasting from food, seek medical advice.
Fasting is not intended to be a form of physical punishment any more than it is intended to be a dieting method, but a doorway that leads us to experience a deeper relationship with God.
Yes, anyone can fast.
Some may not be able to fast from food (diabetics, for example), but everyone can temporarily give up something in order to focus on God. Even unplugging the television for a period of time can be an effective way to fast.