According to MayoClinic.com, a healthy rate of weight loss is 1 to 2 lbs. a week. It's possible to lose weight faster than that during the first couple of weeks in a diet plan, but your body should eventually stabilize, and you should be losing no more than 2 lbs. per week after that. Rapid weight loss is not only dangerous, it is usually ineffective. MayoClinic.com points out that when you lose weight fast, you're more likely to put it back on soon after going back to your normal eating habits.
Your body has a limited capacity to burn fat. According to MayoClinic.com, people who lose more than 2 lbs. per week are likely losing water or lean tissue rather than fat. Losing muscle is a bad idea for several reasons. Muscle keeps your body looking lean and fit. If you lose muscle quickly but retain the fat, you'll probably look "soft" and have no definition. Also, muscle keeps your metabolism working at optimal speed. When you cut down your calorie intake drastically, you lose muscle and your metabolism slows down.
Gallstones occur more commonly in obese people, according to the Weight-control Information Network, or WIN. While losing weight helps to lower the risk of developing gallstones, losing weight too fast may increase the risk. Rapid weight loss may also lead to the formation of silent gallstones, which produce no obvious symptoms but may be equally serious and damaging to your body. To avoid gallstones, WIN recommends losing no more than 3 lbs. per week.
Lack of Energy
To lose weight rapidly, chances are you'll need to "crash diet" by cutting down your calorie intake drastically. This may lead to feeling tired, weak and sluggish -- both physically and mentally. According to medical site Epigee, crash diets may also take a toll on your mental health and may lead to depression or even the development of an eating disorder.