If a diet says it focuses on removing fat from your stomach, arms, hips or anywhere specific then it is being misleading. If that were the case you would see many overweight people with flat stomachs. You lose fat in the reverse order that you gained it. If you build muscles in a specific area such as your arms, they will look more toned but you will not have lost any additional fat from them.

Here’s the FDA’s review of weight loss options.
http://www.cfsan.fda.gov/~dms/wgtloss.html

Some diets claims you can lose 10 pounds in a week. Realistically, the 10 pounds are possible, but you will not be losing 10 lbs of fat. It would be a combination of mostly, muscle and water loss, with fat being a small percentage.

In order to lose 10 lbs of fat in a week, you would need to burn about 35,000 calories. If your body needs 2000 calories a day, you will only be burning 14,000 in a week. That means if you consume zero calories and jog 6 hours each day, you could burn the remaining 21,000 calories in a week. Or, you could actually eat (consuming an average of 2,000 calories a day) and you would need to jog 10 hours a day to burn the 35,000 calories. Granted, doing this would also cause muscle loss and is not physically possible, but it shows that fat loss cannot really happen that quickly.

Follow this link to read the Federal Trade Commissions reviews on common diet trickery. http://www.ftc.gov/bcp/conline/pubs/health/evidence.htm

To see why crash dieting fails we will start with someone that needs 2,000 calories a day to maintain their current weight. They go on a crash diet and lose 10 lbs of fat and lose 4 lbs of muscle. Every pound of muscle burns 50 calories per day. The 4 lbs of muscle loss reduces their total calories burned per day by 200. Because of the loss, the calories they need per day will have dropped to just under 1,800. If they go back to eating 2,000 calories a day after the diet, they will gain back all the fat they lost within 6 months. Just going on a crash diet for a week can result in muscle loss that can take over a month to rebuild if you are exercising.

Many crash diets limit the types of food you can eat. Excessively depriving yourself of certain foods increase your to cravings for food and can be a big distraction in everyday life. Diets that increase cravings can lead to overeating. By causing yourself to crave and overeat too often you can get stuck in a cycle of overeating which can then lead to depriving yourself to lose the weight gained.

Also, eating only a limited variety of food will not provide complete nutrition to maintain the rest of your body. The lack of nutrition from crash diets can leave you feeling tired and/or dizzy. Even multi-vitamins will not always provide all the nutrition healthy food would have given.