Tomatoes are considered to be diuretics because of the fact that they are 90% water. This particular vegetable is highly recommended by certain mainstream diets as well as Weight Watchers because of the fact that it is such an effective diuretic. Because they are made up almost entirely of water, they serve this explicit purpose rather well.
Besides being a great diuretic, tomatoes also have a lot of other things to offer, such as riboflavin, potassium, vitamin A, and niacin which is especially good for those who are trying to lose weight. Overall tomatoes are very healthy and nutritious so you should add them to diet your daily quite liberally.