A study in the New England Journal of Medicine looked at three popular diet plans to find out which is most effective. They studied a low fat diet that cuts the fat and cuts the calories, a Mediterranean diet that cuts calories while eating fruits, vegetables, and vegetable fat, and an Atkins like diet that does not worry about calories but replaces carbohydrates with protein and fat from fish, chicken, and vegetable sources.
The Atkins type diet brought the most weight loss, the Mediterranean came in second, and the low fat diet came in third.
For what it's worth, the study was partly funded by the Atkins people. However, the Journal study says this at least shows that simply cutting out fat is not the best way to lose weight, because some fats are healthy fats, like fish oil.