Good fats are essential in the diet. Though I believe it essential on both sides of the energy equation, I think it especially true when deficite dieting. Good fats I mean from: Walnuts, Almonds, Nat. PB, Flax seed, oily fish (salmon). I ate these throughout my dieting. I have done alot of text book reading on fats and alot of research on this nutrient, and if effectively eaten within a deficit diet, it can do more help having it in the diet, and wreak havoc if its not. (this is another topic though).
I am not minimizing the importance of Protein and carbs here (most know how I feel), of course these are important too. But, in general, fats get a bad name, and this should not be the case.
Main thing to worry about is the laws of energy balance. If trying to lose weight, ensure you have a healthy deficit calorie diet, and a good ratio of Carbs, Fats, and Protein.
Good fats do NOT make one fat. In its basic form, eating more than you need (excess calories) can lead to weight gain and/or unwanted fat tissue gain.
Another important concept to keep in mind is homeostasis. Homeostasis describes the tendency for your body to maintain a steady state.
Generally, it likes things just the way they are. Your body does not want to gain or lose weight and there are certain biological mechanisms for maintaining this steady state. At any given point, your body will be in either of two states: an anabolic (breakdown) state or a catabolic (buildup) state.
When you gain weight, you will gain muscle and fat: Anabolic
When you lose weight, you will lose muscle and fat: Catabolic
This coupling of fat and muscle tissue is inevitable and it is just how the body operates; accept it. This means that you can't build muscle and lose fat at the same time (perhaps with the exception of "newbie gains").
There is an endless pursuit of imore muscle and less fat, but you can't do both at once! Think of this concept like friction, because it always works against you. Because of this, when you are building muscle (anabolic) you aim to minimize the fat gained. Complimentary to this, when you are losing fat (catabolic) you aim to minimize the muscle lost. These are opposites. Some try to manipulate these states though changing up the calories and dietary cycle (I do, and many others have), and this works, but up to a point and has its draw backs as compared to a full and careful bulk cycle.
Im not ramballing off topic now..........LOL