If only there was a simple answer to that question, we would all be perfectly fit, but the fact is that it isn’t just carbs that make you fat, and it isn’t just fats that make you fat.
Rather it is the quality of carbs and fats, and the amount of carbs and fats that you consume which will determine how you put on or lose weight.
The body needs fats to function, but it is the good quality fats that you should be consuming which are rich in nutrients.
The fats to be avoided are the saturated fats and the hydrogenated or trans fats. It is these that will pack on the pound and have no nutritional benefit.
Like bad fats, there are bad carbs. The refined or simple carbs are the ones not good for you.
Complex carbs that take time to get absorbed are more beneficial. The Glycemic index of the carbs that you consume will also determine how good they are for you.
And finally it is the amount that you eat. Even if it is best quality of fats that you eat, it is most certainly not good for you to eat a pound of walnuts, even if they contain the best kind of fat. Even if it is bananas that you eat you are not going to lose weight if you eat a dozen of them!