Voluntary fasting is practiced by many humans in an attempt to lose body weight. In a study, fasting increased serum Total Cholesterol, LDL Cholesterol and Apolipoprotein B in healthy, nonobese humans.
Under normal circumstances, your body derives most of its energy from carbohydrate metabolism, according to the McKinley Health Center. When you fast for an extended period of time, you deprive your body of its normal source of fuel, and it eventually starts to break down its fat reserves for energy. Your liver begins to secrete more cholesterol into the bile it produces. In addition, bile may stay in your gallbladder longer because it may not empty normally,
The consequences of fasting and fat metabolism may lead to the formation of gallstones. They may not cause you any problems unless they get bigger or get stuck in the bile duct and prevent the normal flow of bile from the gallbladder to the small intestine. The classic symptom of gallstones is pain in your upper abdomen, which may become very severe and last for up to several hours, according to Johns Hopkins University.
"Fasting is not a weight loss tool. Fasting slows your metabolic rate down so your diet from before the fast is even more fattening after you fast," says Joel Fuhrman MD, author of Eat to Live: The Revolutionary Plan for Fast and Sustained Weight Loss and Fasting and Eating for Health.
Rather than pursue acute and dramatic weight loss by fasting—even if it is just ‘intermittent’—it is better to take the long-term view and avoid doing things that can compromise lean tissue and function.
Health is defined by where you will be 1 year or 1 decade from now, not where you will be in 1 week or 1 month.