It seems America has managed to make an industry out of eating nothing.

Amazon.com is full of books about how a diet of only lemonade or only juice can help you lose weight and feel better.

You can spend $70 on a "Master Cleanse" kit, which gives you enough maple syrup, sea salt and cayenne pepper to mix into a concoction of water and lemon juice to sustain yourself for a 10-day fast.

A few years ago, Beyonce Knowles gushed to Oprah Winfrey about how she used the Master Cleanse to lose weight for her role in the movie, "Dreamgirls."

The concept of fasting is as old as time. Just about every major religion has a tradition of fasting as a way to purify, denounce worldly desires and get closer to God.

This month, Muslims observing Ramadan are fasting from sunup to sundown each day, a tradition that's combined with a call to read scripture, pray and perform acts of charity.

But religious fasting is different from the fasting regimes that are marketed for weight-loss and detoxification purposes.

The idea of forgoing food for five, 10 or more days to cleanse the body is popping up more and more in popular health magazines and on Web sites, but it hasn't gotten the seal of approval from most dietitians. No peer-reviewed research or governmental regulatory agency has certified the value of such fasting programs.

Joanne Larsen, a registered dietitian who runs the Web site, Dietitian.com, has fielded several questions about whether fasting is advisable for health purposes. Larsen said she hears from folks who are interested in the detoxification benefits many fasting regimes tout.

She tries to lay out the truth: Fasting is starvation.

"There are products that claim to 'cleanse' your body of toxins to remove 20 pounds of waste that is sitting in your intestines," she wrote in an e-mail. "Take a look at 20 pounds of sausage and ask yourself if you think you have that much waste sitting in your intestines."

METABOLIC MELTDOWN

The body is constantly cleansing itself of toxins through the digestive and respiratory systems, and also through the skin.

Fasting literature often claims that fasting is beneficial because it allows the digestive system to rest, and gives the body a chance to reset itself.