Portion control diets, such as Weight Watchers, don't necessarily restrict the types of food you eat, but restrict the amount you eat in a day.  This can be measured as calories, "points," or even "bites."  Of the three main categories of diets, I would say this category gives the best long term results.  These diets can be less radical than other diets, which makes it easier to stay on long term.

 

Carbohydrate restriction diets have been gaining greater attention lately.  These raise HDL (good cholesterol) and lower triglycerides better than  fat restriction diets.  They may be the preferred diet when someone already has a low HDL and high triglycerides, when they have fat distributed more around their stomach rather than hips and buttocks (apple shaped body), or if they have a tendency toward diabetes.  A bit more muscle mass may be lost with these diets, as the anabolic action of insulin on muscles is decreased to a greater extent.  Of the diets in this category, I prefer the South Beach Diet.

 

Fat restriction diets are viewed as traditional diets that, when followed and maintained, are effective in weight loss and reducing cardiovascular risk.  Some people have a hard time maintaining this diet because the low fat content of the food has a tendency to leave the feeling of an empty stomach.  These diets are superior to the carb restriction diets for lowering LDL ("bad") cholesterol, and may perform better for those who keep more fat on their hips and buttocks (pear shaped body).