Any diet can work in the short run. But what your best choice if you want to keep the weight off? Here are the pros and cons of different types of diets.

Fixed-menu program:
A fixed-menu diet provides a list of all the foods you will eat. This kind of diet can be easy to follow because the foods are selected for you. But, you get very few different food choices, which may make the diet boring and hard to follow away from home. In addition, fixed-menu diets do not teach the food selection skills necessary for keeping weight off. If you start with a fixed-menu diet, you should switch eventually to a plan that helps you learn to make meal choices on your own, such as an exchange-type diet.

Exchange-type program: 
An exchange-type diet is a meal plan with a set number of servings from each of several food groups. Within each group, foods are about equal in calories and can be interchanged as you wish. For example, the “starch” category could include one slice of bread or 1/2 cup of oatmeal; each is about equal in nutritional value and calories. If your meal plan calls for two starch choices at breakfast, you could choose to eat two slices of bread, or one slice of bread and 1/2 cup of oatmeal. 

With the exchange-type diet plans, you have more day-to-day variety and you can easily follow the diet away from home. The most important advantage is that exchange-type diet plans teach the food selection skills you need to keep your weight off.

Prepackaged-meal program:
These diets require you to buy prepackaged meals. Such meals may help you learn appropriate portion sizes. However, they can be costly. Before beginning this type of program, find out whether you will need to buy the meals and how much the meals cost. You should also find out whether the program will teach you how to select and prepare food, skills that are needed to sustain weight loss.

Formula program:
Formula diets are weight-loss plans that replace one or more meals with a liquid formula. Most formula diets are balanced diets containing a mix of protein, carbohydrate, and usually a small amount of fat. Formula diets are usually sold as liquid or a powder to be mixed with liquid.

Although formula diets are easy to use and do promote short-term weight loss, most people regain the weight as soon as they stop using the formula. In addition, formula diets do not teach you how to make healthy food choices, a necessary skill for keeping your weight off.

Very-low-calorie diets:
Very-low-calorie diets (VLCDs) are commercially prepared formulas of 800 calories or less that replace all usual food intakes. VLCDs are not the same as over-the-counter meal replacements, which are meant to be substituted for one or two meals a day. When used under proper medical supervision, a VLCD may allow a severely to moderately obese patient to lose about three to five pounds per week, for an average total weight loss of 44 pounds over 12 weeks. Such a weight loss can improve obesity-related medical conditions, including diabetes and high blood pressure. VLCDs are generally safe when used under proper medical supervision in patients with a body mass index (BMI) greater than 30. Use of VLCDs in patients with a BMI of 27 to 30 should be reserved for those who have medical complications resulting from their obesity. VLCDs are not recommended for pregnant or breastfeeding women. VLCDs are not appropriate for children or adolescents, except in specialized treatment programs. Physicians must evaluate, on a case-by-case basis, the increased risks and potential benefits of drastic weight loss in people older than 50, and for those with significant medical problems or who are on medications.
Many patients on a VLCD for four to 16 weeks report minor side effects such as fatigue, constipation, nausea, and diarrhea, but these conditions usually improve within a few weeks and rarely prevent patients from completing the program. The most common serious side effect seen with VLCDs is gallstone formation, though it’s unclear whether VLCDs directly cause gallstones or whether the amount of weight loss is responsible for the formation of gallstones.
Although VLCDs are efficient for short-term weight loss, they are no more effective than other dietary treatments in the long-term maintenance of reduced weight.

Questionable diets:
You should avoid any diet that suggests you eat a certain nutrient, food, or combination of foods to promote easy weight loss. Some of these diets may work in the short term because they are low in calories. However, they are often not well balanced and may cause nutrient deficiencies. In addition, they do not teach eating habits that are important for long-term weight management.

Flexible diets:
Some programs or books suggest monitoring fat only, calories only, or a combination of the two, with the individual making the choice of both the type and amount of food eaten. This flexible type of approach works well for many people, and teaches them how to control what they eat.

One drawback of flexible diets is that some don’t consider the total diet. For example, programs that monitor fat only often allow people to take in unlimited amounts of excess calories from sugars, and therefore don’t lead to weight loss. It is important to choose an eating plan that you can live with. The plan should also teach you how to select and prepare healthy foods, as well as how to maintain your new weight. Remember that many people tend to regain lost weight. Eating a healthful and nutritious diet to maintain your new weight, combined with regular physical activity, helps to prevent weight regain.