Many factors go into determining which weight loss plan will work for you. Age, sex, genetics, general health, how much you exercise, what types of food you'll eat, and your psychological status all influence your ability to lose weight. What works for one person may be inspiring, but may not produce the same results in every person.

Just about everyone has tried the "do-it-yourself" diet, whether it was from reading a diet book and adopting the guidelines there or just by using a common sense approach of cutting back. Perhaps you've heard that "95% of all diets fail." I think it would be impossible to know the exact percentage of Americans who go on diets and do not lose weight, but researchers have found that unless certain factors are put into place, the majority of people attempting a short-term diet plan will not be successful.

Research conducted through the Department of Psychology at UCLA doesn't question calorie reduction diets as an effective method for weight loss. However, they do find that for the majority of people, it is short-term. Among people who were followed up for two or more years after an initial weight loss of 5-10% of excess body weight, 83% eventually gained back all they lost, plus more.

So, are commercial weight loss programs more successful in producing a lasting weight loss? Some research says yes, and that the larger the program, the more successfully a person loses weight. Dr. Arne Astrup of the University of Copenhagan in Denmark researched information from 22 weight-loss centers across five countries gathered from a previous large clinical trial. For every additional 10 people who signed up to a center, the average person loses half a percent more weight over the course of two months (the length of the study).

OK — so this doesn't seem like much, but for the average 200-pound woman, this means an additional pound of weight loss for every two months in the program over participants in smaller programs. Over the course of a year, that's six extra pounds gone! Remember that even small improvements can lead to significant clinical health benefits.

For any weight loss program to be successful, they must include three basics: a healthy diet that reduces the amount of daily calories ingested, an exercise component that increases metabolism to burn calories, and behavior modification so that you don't go back to the same old habits. This explains why many weight loss efforts fail — because they attack food intake, but not habits; or they fail to add exercise, thinking severely cutting calories for a short period of time will give them the results they desire.

WebMD offers this advice for choosing a commercial weight loss program:

• Choose a program that has counseling available from a qualified professional to help with the behavioral aspect of weight management. Look for registered dietitians, exercise physiologists, physical therapists, doctors and nurses, particularly if you have a chronic condition such as diabetes or heart disease.
   
• Look for programs with flexible and suitable food choices, including the appropriate number of calories for a safe weight loss. A program that dictates the food you eat is not likely to be satisfying, leading to feelings of deprivation and eventual relapse into old habits.
   
• Make sure the program encourages exercise. A program such as Weight Watchers that offers rewards for extra physical activity is more likely to have long-term success than one such as MediFast, where the focus is only on a very low calorie diet.
   
• Find programs that offer support systems so that in moments of weakness, there is an empathetic friend to encourage and motivate you. Family and friends mean well, but may offer conflicting advice to the plan you are following.