In the world of nutrition, fats have received a bad wrap, though sometimes justifiably. Trans fats and saturated fats are linked to an increased risk for heart disease and can lead to an increase in total medical costs and a decrease in overall health; however, one of the often ignored facts about nutrition is that there are two major types of fats that are actually healthy! Poly-unsaturated and mono-unsaturated fats have been proven time and time again to actually improve the overall heart health of an individual consuming them (in moderation of course).
So what's the difference? Saturated fats are solid at room temperature (think of the bacon grease that you drain into a can and allow to cool). This is a major warning sign. We usually consume fatty foods at a temperature that is warmer than room temperature, meaning that as we consume these fats, they cool and become thicker. This is what leads to the negative health effects related to saturated fats, such as arterial clogging and heart disease. Conversely, unsaturated fats (both mono and poly) are liquid at room temperature, which means that even after they are consumed and cool, they easily move throughout the body without clogging arteries or other critical anatomical structures (think olive oil).
Not only do unsaturated fats remain liquid at room temperature, they are also shown to improve overall heart health, increasing total HDL (good cholesterol) levels and decreasing total LDL (bad cholesterol) levels.
Finally, fats are more dense nutrients than protein or carbohydrates, at 9 calories per gram versus 4 calories per gram respectively. Many people view this negatively, arguing that they can consume twice as many carbohydrates or protein for the same amount of total calories. This is a true statement. One major point that offsets this factor, however, is that fats leave an individual's appetite satisfied for a longer period of time. Although carbohydrates have less total calories per gram, an individual will not feel as full after eating carbohydrates as they will after eating fats.
Some excellent sources of "healthy" fats are avocados, nuts, and olive oil. Some examples of foods which are high in saturated fats and should be avoided are bacon and butter.
This being said, fats should still not become the "go to" nutrient in our daily lives. A healthy balance of the three major nutrients (fats, carbohydrates, and protein) is essential for total well-being. Therefore, a maximum of 30% of your daily calories should come from fats, with less than 10% of this amount coming from saturated fats. Consume as few trans fats as possible, as they are extremely unhealthy and provide zero nutritional benefit. Try your best to be conscious of what you're eating, and above all, stay active!