Fasting was originally a religious practice, as adherents went without food for various periods to purify the spirit and atone for sins. It may sound like punishment, and it may feel like it, too -- your body needs food to produce energy, and it has a number of survival mechanisms that kick in when it notices prolonged starvation. Some people practice fasting for weight loss purposes, but they are doomed to repeat the practice. Any weight lost during a fast will return because simply depriving yourself of food does not teach you healthier eating habits, and it can be unpleasant while it lasts.
Fasting causes your blood sugar to remain at low levels instead of being periodically boosted throughout the day after meals. You may feel dizzy, lightheaded, and nauseous, and headaches are common. You may develop an unusual body odor, similar to the smell of rotting fruit, as your body begins producing ketones as it burns fat for energy after the carbohydrate stores have been exhausted. Your muscles may begin to ache because there is no protein available to repair the tissue that is damaged through normal use, and you'll feel colder as your body slows down your circulation. These symptoms are all your body's way of telling you that you need to conserve fuel.
Your most immediate danger during a fast is hypoglycemia, or low blood sugar. When you allow your blood sugar to remain low for long periods of time, you may experience confusion, anxiety, tremors, and even seizures and coma in extreme cases. You're also at risk for dehydration, despite the tea -- tea contains caffeine, which is a diuretic, and will flush fluids from your body. Losing weight at the rate produced by a week-long fast can lead to gallstones, and your bowels may stop functioning because there is no food to create waste. All of these dangers are compounded if you have a medical condition or are taking any medication, so consult your doctor before fasting. Naturopath Leon Chaitow recommends that any fast longer than four days be medically supervised.
The weight loss achieved with fasting is primarily water, especially if you drink tea. The diuretic action flushes excess fluid from your body, and you may weigh a couple of pounds less. These couple of pounds will come right back after the conclusion of the fast, when your body is allowed to store water again. Of course, starving yourself for a week will produce some weight loss, because although you're not putting calories in, your body is expending calories just to keep basic body function going. You may lose some fat, but you'll lose primarily muscle. Every time you use a muscle, you cause damage that gets repaired by protein. No protein, no repair, so your muscles degrade.
A weeklong unsupervised fast isn't safe for anyone, but it is especially unsafe if you are already very thin, because you may suffer from malnutrition or dangerously low blood sugar levels. If you drink alcohol or use narcotics, fasting can cause the release of toxins into your blood stream. Pregnant women and infants should not fast, nor should diabetics, anemics, and those with kidney or liver disease. Fasting takes an enormous toll on these organs because they must filter out the heavier waste that comes from burning fat for energy.