Fat gets a lot of the attention for many good reasons. Fat can raise cholesterol levels in the blood, increasing a person's risk for heart disease.
In addition, some fatty foods (such as bacon, sausage, and potato chips) often have fewer vitamins and minerals than low-fat foods.
Moreover as mentioned, fat has about twice as many calories per gram as carbohydrates and proteins. A gram of fat has 9 calories, while a gram of carbohydrate or protein has 4 calories. In other words, you could eat twice as much carbohydrates or proteins as fat for the same amount of calories.