But some diets have endured. Does this mean they are tried-and-true and must really work? Are they good for you? How can you decide which new diets are effective, yet safe?

It may seem like you need a degree in nutrition to make sense of all the information that bombards you from TV, magazines, the internet, and your best friend who swears that her low-hydrogenated fat, high-fiber all-grapefruit, tofu, and sawdust diet is the answer to all of your weight loss woes.

But luckily, there are a few rules of thumb you can use to evaluate a diet plan.

First of all, beware of diets that eliminate entire food groups. The body needs a variety of foods carry out all of its functions. This includes the fats and carbohydrates that several popular diets severely restrict or forbid.

It is true that excess fats and carbohydrates (or excess calories from any food) make you gain weight. But fats are essential in providing the body with energy and certain vitamins. Carbohydrates are the other main source of the body's energy. Going without fats and carbs is a quick way to run your body down and get sick.

A healthful diet will not restrict daily calories to dangerously low levels. The minimum number of calories you need to stay healthy varies from person to person and can best be determined by your health practitioner or a nutritionist. But, in general, any diet that has you eating less than 1,000 calories per day is going to make you ill as your body goes into "starvation mode" and starts to shut down. Besides making you sick, it can prevent you from losing weight as your body tries to hold onto stored body fat.

Another sure sign that a diet is not a healthful one is when it is short in duration. A six day all-cabbage diet, for instance, may cause you to lose water weight, but is certainly not the way to lose body fat sensibly or to keep it off long-term.

So, those are the bad ways to diet. What are the good ways?

A sensible diet will not only be all of the things the bad diets are not -it will include all of the food groups and a sensible calorie count - it will, ideally, teach you how to eat healthfully for life.

It will either provide you with a daily menu of what you should eat, or prepackaged meals that are perfectly portioned. It is unlikely that you will follow a menu or eat frozen dinners for the rest of your life, so it is crucial that a diet teach you how to choose the proper foods, prepare them, and eat them in appropriate portions.

If you are looking to lose weight, don't just follow the crowd and go on a diet just because you hear a lot about it. Take the time to do some research and apply the basic rules above. Learning how to eat healthfully for life will reward you not only with permanent weight loss, but with a life of energy and vitality.