Make sure you drink lots and lots of water!
And don't you need to 'prepare' your body for a fast by gradually decreasing the amount of stuff you eat?

And plenty of juice :)
I've never done the 'prepare' thing... seems to be working fine so far. This is my fourth time.

I found a website with health guidelines for fasting from an Islamic medical association. Considering they've been practicing Ramadan for what, centuries now..? They must have figured a couple of things out.

http://www.submission.org/ramadan/health.html

I also found this page, which seems to do a relatively decent job of explaining the proposed benefits to health of fasting.

http://serendip.brynmawr.edu/biology/b103/f02/web1/wcarroll.html

It does, however, rely entirely on anecdotal evidence. I'd hold out for an organized and scientifically rigorous study before I put any faith in the idea. However, I do find interesting his explanation for why appetite is often lost during illness. I remain open, but skeptical.

Also found these words of caution, which seem to be deliberately printed on the site in an ant-sized font, so I'll just copy them here:

http://www.mothernature.com/Library/Ency/Index.cfm/Id/1066008

During a fast, a person purposely abstains from food for a specific period of time. Fasting has been practiced throughout the ages for both religious and therapeutic purposes. A one-day fast is unlikely to cause any harm to a healthy body. Slightly longer fasts (two to three days) are also well-tolerated by most healthy people.

No matter how short the duration, fasting is unwise and potentially dangerous for some people, including pregnant and lactating women, people with cancer, diabetes, gout, hypoglycemia, stomach ulcers, liver, kidney, or lung disease, or anyone with a compromised immune system. Some health experts caution against fasts lasting more than two to three days, even for healthy individuals-if longer fasts are practiced, they should be medically supervised.

During the first 24 hours of a fast, the body is able to utilize its stored carbohydrates-in the form of glycogen-to fuel essential body processes. When glycogen reserves are depleted, fat becomes the preferred energy source, so that protein (e.g., as found in muscle tissue) is partially spared.

However, some muscle tissue is often lost, even during short fasts. Weakness, nausea, headaches, and depression can also develop during a fast, because ammonia and nitrogen are released into the blood during the breakdown of muscle tissue. Ketones, byproducts of fat metabolism, are produced once the body switches from burning carbohydrates to burning fat. Elimination of ketones is accomplished by the kidneys. In extreme cases, extended fasts can lead to disturbances of heart rhythm and death.

"Modified" fasts, in which fruit or vegetable juices and herbal teas are consumed, are probably easier on the body than all-water fasts. Even so, a modified fast should be limited in duration; modified fasts lasting more than a week should be supervised by a healthcare professional.

Why do people follow this diet?
Proponents claim that environmental toxins build up in our bodies over time and need to be removed periodically through fasting to maintain optimum health. Cleansing fasts are an important part of a detoxification program and may be part of a weight-loss program.

What do the advocates say?
Advocates believe that fasting periodically gives the body a break from digestion and allows it to eliminate the toxins that cause disease, while promoting healing and reversing the aging process. Studies indicate that fasting helps health conditions such as rheumatoid arthritis, migraine headache, and skin diseases. Acute illnesses such as colds and flu, colon disorders, allergies, obesity, and respiratory diseases may also respond to fasting. Proponents claim a one-day fast creates a clearer mental state and increased energy. They believe a three-day fast rids the body of toxins and purifies the blood, and that a long-term fast promotes healing, alleviates food allergies, sheds pounds, and rebuilds the immune system.

What do the critics say?
Critics believe that fasting depletes the body of important nutrients, essential minerals and energy, may be unsafe, and is an ineffective weight loss aid. The few pounds that are lost in the beginning of a fast are from water, and this weight will return as soon as the fast is over. Few scientific studies have been done to back up health claims and demonstrate that fasting works by releasing toxins stored in fat.

Are there any groups or books associated with this diet?
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