I often hear folks talk about getting rid of toxins or the "chemicals" in their bodies. It's ridiculous. Not only are we a bag of chemicals held up by bones, those chemicals are not harmful to us. Nevertheless, folks continue to espouse the wisdom of "fasting" to "detoxify (or purify) the body" or "cleanse the gastrointestinal track" and "eliminate toxins and parasites" from the body. Some years back a popular diet book was based on the notion that when certain foods are eaten together they "rot," poison the system and make us fat. The authors encouraged a strategy of eating fats, carbohydrates and proteins at separate meals to prevent "clogging" the body.

All these ideas are utter nonsense. Our bodies are naturally detoxifying every day. It's a normal body process that's accomplished with a healthy colon, liver, kidneys, lungs, lymph glands and skin.

There is, admittedly, a powerful psychological effect that comes from fasting-especially in the framework of the contemplative life that is part of many long standing spiritual traditions including Lent, Ramadan and Yom Kippur, for example. But physiologically, fasting produces ketosis-a physiological state when the body calls on stored tissue when it isn't getting enough calories-especially carbohydrate calories.

I'm the first to admit that a one day fast is likely to be harmless-especially if you are going to spend it in contemplation and if you are in good health. But if you want to argue that fasting will make a sick person better or that it will cleanse me of toxins-especially if your argument includes that it will work better than a good workout and a healthy diet, you'll have a hard sell without the scientific data to back it up.