Fat is the most misunderstood macronutrient of all. People never seem to know whether fat is universally evil or a good thing to have in their diet. The answer is that all fats are not created equal. There are good fats, and there are bad fats. Proteins and carbohydrates deliver 4 calories per gram, while fats deliver 9 calories per gram. This is true whether the fat is good or bad. So, since fats deliver more calories than proteins or carbohydrates, you need to watch your fat intake because either one can quickly bring you to your desired calorie limit.
Fat matters in other ways besides calories, though. Different kinds of fat often promote entirely opposite physiologic consequences in your body. In short, there are two kinds of good fat and two kinds of bad fat. The good fats are unsaturated-either polyunsaturated or monounsaturated. The bad fats are saturated- either naturally or through a chemical alteration that creates trans fats. Recent research suggests that saturated fats may not be quite as bad as we had previously thought (although trans fats are harmful); however, a healthy diet is still considered one that minimizes both saturated and trans fats.