Question

We store the bulk of our energy as fat. Suppose that on another planet, animals stored all their energy as carbohydrate. In that case, to store the same amount of energy, an alien would have to weigh more than twice as much as an animal on earth. If a human weighed 120 pounds, an alien equivalent storing just as much energy would weigh about 270 pounds. Why?

Answer 1

Because when while  oxidizing molecules we are able to obtain more anergy that from  fats, far more that from carbohydrates as fats store more potential energy due to the fact they reduce  carbohydrates. I hope it is clear. Regards!