Umm wrong. Your body is far more efficient than you give it credit for. Fat can get stored as fat whenever it's in excess, as can protein or carbs. Insulin can assist fat storage when there are carbs, fats (and to a certain extent protein) present. Fat has other methods of getting stored when insulin is low. Basically the biggest advantage of a keto diet is that your appetite is supressed from all the fat so it is harder to accidentally eat too many calories, and even when you're counting calories you generally feel more satisfied on fewer keto calories. Another way to look at is is to ask yourself "how do traditional Eskimos manage to grow on a mainly ketogenic diet?" Answer is because they get plenty of calories and just enough carbs.