A smoothie diet can be useful in losing weight so it can be a good idea. But just because you are drinking "smoothies" doesn't automatically mean you will lose weight; you must consider the ingredients you put in them.
Drinking fresh green smoothies that are well balanced and nutrient full can help with weightloss but smoothies with dairy, sugar, fats and lost of carbohydrates may not be so helpful. Keep in mind that while what you eat is very important for losing weight, other factors such as how much you eat, exercise and rest are very important as well.
