Low-calorie diets: It is harmful to reduce your daily calorie intake lower than 1400 calories per day, because your body adjusts to a semi-starvation state and looks for alternative sources of energy. In addition to burning fat, your body will eventually burn muscle tissue. Because your heart is a muscle, prolonged starvation will weaken it and interfere with its normal rhythms. Low-calorie diets don't meet the body's nutrition needs, and without nutrients your body cannot function normally.
"When going out for fast food, I used to get the large-size value meal. Now, I satisfy a craving by ordering just one item: a small order of fries or a six-piece box of chicken nuggets. So far, I've shaved off 16 pounds in seven weeks, and I'm on track to being thinner than my high school self for my 10-year reunion later this year." —Miranda Jarrell, Birmingham, AL