Anorexia nervosa is a mental health condition characterized by a relentless drive for thinness, leading to extreme weight loss from excessive dieting and exercising, says the National Institute of Mental Health. Because anorexics become so underweight, they can develop serious health problems.

If you've diligently tracked your diet and exercise and concluded that you're burning 1,000 calories a day, congratulations! You're on track to lose 2 pounds per week. That's just at the upper end of the Centers for Disease Control and Prevention's recommendations for a healthy, sustainable rate of weight loss.

Men over age 50 have special nutritional concerns to attend to when dieting. At this age, you have a lower metabolism and a greater risk of cardiovascular disease, gout and prostate cancer than your younger counterparts, according to Eat Right Ontario.

The high-protein, low-sugar diet is a diet that includes a variety of vegetables, proteins and complex carbohydrates to meet the nutritional needs of healthy, active adults. Before starting this diet, get medical clearance from your primary care doctor.

Genetics, aging or hormones are just some of the factors that can trigger fat to accumulate at the sides of a woman's waistline.

A 15-pound weight loss in two months is ambitious, but possible, if you have a focused dietary plan and if you engage in regular exercise. You'll need to lose about two pounds a week, consistently -- a rate at the high end of the safe, sustainable range, according to the Centers for Disease Control and Prevention.

If you are frustrated by lack of results from dieting and exercising, you may be tempted to try a weight loss pill like Hydroxycut to help you shed the pounds.

When you're trying to gain weight -- whether it's to avoid the health risks of being underweight or for aesthetic reasons -- your eating habits can make or break your results.

Although there are an abundance of weight loss books, products, supplements and foods on the market, one thing holds true of all successful weight loss approaches: The dieter consumes fewer calories than he burns.

"Overweight" is a term that refers to an excess amount of body weight that typically comes from muscles, bone, fat and water; however, "obesity" means an excess amount of body fat. Body mass index, BMI, is a weight-for-height measure commonly used to classify overweight and obesity in adults.

Fat around the waist is not only dangerous to your health, but it's also often the most responsive to traditional weight-loss methods. This type of fat, called visceral fat, is biologically active and releases compounds into your body that increase the risk you'll develop type 2 diabetes and cardiovascular disease.

Making long-term changes in your eating habits and physical activity remains the proven way to slim down. However, because shedding pounds is neither fast nor easy, some dieters try diet pills in efforts to get quicker results.