Many. Low calorie diets are usually between 1000 and 1200 calories females, allow for some fats (mostly the "good" fats). They should be balanced with complex carbs (not refined) and good quality protein. The "low fat diets" only work if you don't substitute sugar and simple carb calories for the fat you don't eat. Low fat diets did not work in the 1980's because sugar/carbs were consumed instead of fat.
See below. Calories are the measure of energy in any food or drink. Our body then uses this energy to keep us alive, but an excess of calories leads to an excess of energy which we store as fat. A low fat diet reduces the amount of fats, such as animal fats or oils in the diet. Since fats and oils have lots of calories, they are often low calorie. A low-cal die has less calories from any source.